Piping Stress Analysis
Piping Stress Analysis
(OP)
Hello, first time poster with a query regarding piping stress analysis.
At the moment I work in plant design Process Engineer. Before issuing drawings we send selected lines out for Stress Analysis (our somewhat simplified criteria for Stress Analysis is D>2", dT>100 Deg C). It is now desired to do this analysis in-house.
I've taken it upon myself to research this.
I've assembled numerous guides (including the CASTI guidebook to ASME B31.3 & Process Piping the Complete Guide by Charles Becht).
I know that Caesar, Autopipe and others are used, but for various reasons they don't want to go this route. Instead they want to establish either a guideline or program that will cover the stress analysis.
We can characterise out piping networks quite easily, in terms of fittings, equipments dimensions, operating conditions etc. via our database system and 3d model.
So what I'm really looking for is somebody that works at this day to day, to give some pointers. I've spoken to my former mechanical engineering lecturer who thinks developing it from the ground up is a bad idea (i.e. go the Caesar route). I would like to get some other opinions on this. If it really is a bad idea, its best to find out at this early stage.
From reading the guides, a lot of it seems pretty vague, or at least up to the designers dicretion.
I would like to know how those working at it proceed and if to develop our own properitary procedures/software is feasible.
I'm assuming for all this that ASME B31.3 is the main guideline to consider regarding Stress Analysis for Process Piping.
Thanks for getting this far!
At the moment I work in plant design Process Engineer. Before issuing drawings we send selected lines out for Stress Analysis (our somewhat simplified criteria for Stress Analysis is D>2", dT>100 Deg C). It is now desired to do this analysis in-house.
I've taken it upon myself to research this.
I've assembled numerous guides (including the CASTI guidebook to ASME B31.3 & Process Piping the Complete Guide by Charles Becht).
I know that Caesar, Autopipe and others are used, but for various reasons they don't want to go this route. Instead they want to establish either a guideline or program that will cover the stress analysis.
We can characterise out piping networks quite easily, in terms of fittings, equipments dimensions, operating conditions etc. via our database system and 3d model.
So what I'm really looking for is somebody that works at this day to day, to give some pointers. I've spoken to my former mechanical engineering lecturer who thinks developing it from the ground up is a bad idea (i.e. go the Caesar route). I would like to get some other opinions on this. If it really is a bad idea, its best to find out at this early stage.
From reading the guides, a lot of it seems pretty vague, or at least up to the designers dicretion.
I would like to know how those working at it proceed and if to develop our own properitary procedures/software is feasible.
I'm assuming for all this that ASME B31.3 is the main guideline to consider regarding Stress Analysis for Process Piping.
Thanks for getting this far!





RE: Piping Stress Analysis
I wonder if the employer is happy to spend on design research from scratch (unless this is a educational project), which is already available in the market at competitive prices!!
Good luck.
Siddharth
These are my personal views/opinions and not of my employer's.
RE: Piping Stress Analysis
I'm thinking you could be right.
What it really boils down to though is that noone here has dealt with stress analysis before. I asked why not go with Caesar and was told the cost was prohibitive. I don't know how much it is, I'm guessing around the €5000 mark (Please, if anyone knows, correct me).
What I'm looking for is a way for us to do Stress Analysis. The method isn't too important, only the end result.
What's involved in using the software and in Stress Analysis overall.
I don't mind getting stuck into the deep and dark calculations in the guides but if it can be avoided then all the better.
I'll be delighted to hear all suggestions, but please provide pros & cons for each.
Many Thanks.
RE: Piping Stress Analysis
Well, this should be interesting. I think that you will get many replies as this board is frequented by many of us who are primarily pressure technology (including piping) engineers. You will also get some replies from folks who are members of various Piping and Pressure Vessel Code Committees. ALSO, you have apparently done some research via looking up previous applicable threads - THANK YOU!!!
I do not think the Guide Books by Glynn Woods and Chuck Becht are very vague - I think they are really rather explicit. However, the Piping Codes do not give you much in the way of design direction - that is intentional as it is not the job of the Codes to guide design. The B31.3 Code assigns most of the responsibility for design (including analysis) to the owner. I assume that you have looked at the scope paragraphs in the Piping Codes and you have decided that B31.3 is the appropriate Code for your company's systems. There can be some variations on that; some companies specify the B31.1 Code be used for the piping in the steam-water loops of boilerhouses. If you have been charged by your company to develop a sort of corporate piping design (and fabrication, erection, examination, testing and repair (fitness for continued service would be included) standard it would not be unreasonable to ask to be sent to a professional seminar on the B31.3 Code (Mr. Woods and Dr. Becht both teach such seminars). Even if you do not intend to do pipe stress analysis in-house, it would be VERY helpful to go to a Caesar II seminar just so that you would be competent in reviewing the formal analyses that are done by outside consultants.
So, when should you do structural analysis (piping flexibility and stress analysis) of any particular piping system? Are you familiar with the B31.3 concept of various fluid services? The fluid service (see B31.3, Appendix M and paragraph 300.2) of the piping system would be one of the variables (the "except for"s that you would want to address in your general dimension-temperature related guideline. It would also be useful to weigh the implications of the consequence of failure against the likelihood of failure in making these decisions (see B31.3, Appendices F and G). Inservices temperature and pressure cycling would also be a factor.
Most larger CPI and HPI corporations have in-house Standards that guide the design of piping systems and in many cases those standards include some guidelines for when a piping system must have a "formal" analysis. Note that the ASME Piping Codes do not require an analysis of every piping system - so in this regard hey are vague. Your D>2", dT>100 Deg C) criteria is not bad for a start but there should be exceptions "allowed". You will of course have to address those exceptions in "your" standard.
If I did not have much experience, I would not want to develop a set of corporate piping design Standards from scratch. Rather I would want to build on the Standards that were developed by others. I am not saying that I would suggest taking another Company's Standards and adopt them by simply changing the company name on the cover. However it would be wise to read through a few of these standards and at least get some idea of what the structure should be (look at the table of contents). You will get a lot of good ideas that you might want in your standards. Also, pay attention to the application of various piping system materials to the specific pressure-temperature services.
Have a look at this:
http:
So, when should you do structural analysis (piping flexibility and stress analysis) of any particular piping system? As I say, this will be an interesting thread. Thank you for posting.
Regards, John.
RE: Piping Stress Analysis
Look at paragraph 319.4.1 of B31.3 (your company really needs to HAVE a copy in their technical library) "319.4.1 Formal Analysis Not Required"
Well, I am not one for "rules of thumb" but you will find some. The books by Rip Weaver (Process Piping Design, Volume one and Volume two) come to mind.
Regards, John
RE: Piping Stress Analysis
Please go to http://www.coade.com/support_discussion.asp and check your personal messages
RE: Piping Stress Analysis
Thanks for that great response, plenty of things to think about in that.
My saying I found the guides vague is down more to my inexperience than anything else.
I am not a piping designer, so much of the guides content is new to me. The mechanical calculation work falls back to the process department since the pipe designers aren't engineers (The Process Engineers are the closest thing to Mechanical Engineers in the company). So even though we aren't laying out the design we need to figure out how to stress analyze it.....not an ideal situation, I think.
Regarding the ASME B31.3 seminars, I will keep my eyes open, however I'm based in Ireland where these kind of things don't come around too often. Still where theres a will theres a way.
At present, as long as they see "Approved" by the external contractor then they are happy. I guess I'm really driven by this whole thing because a)I don't know enough about it, and b)think things should be done a bit better. At the moment it seems like some dark mystery to everyone.
The LANL manual was one of the first things I came across, and perhaps I should concentrate more on practical applications like this.
I really hope this will be an interesting thread. I'd like to get a discussion going among those that work with Stress Analysis day to day, since I think these are the people with that can give the best direction.
Please keep the opinions coming, and if anyone can give me a rough price for Caesar also that would be great. Thanks.
RE: Piping Stress Analysis
1. Being able to run the software and being able to do the analysis are not always the same thing.
2. If you have any equipment (vessels, tanks, pumps) or interesting in anyway pipe, rules of thumb may not work.
SLH
PS, cost for Ceasar II should be pretty easy to find...
http://www.coade.com/dealer.asp
RE: Piping Stress Analysis
Since you are in the UK, are you using one of the BS codes, eg BS5500?
Since you asked for rules of thumb, here are a few. A formal stress analysis is required for:
- Liquid lines above 650 F
- All lines above 750 F
- Lines 16" and larger in diameter (e.g. to check for local loads and stresses on pipe wall at supports)
- Lines having substantial concentrated loads such as heavy valves, fittings, unsupported vertical risers and branches
- Lines having local reduction in strength due to the installation of special fittings
- Lines connected to vessels or tanks having appreciable settlement or where there are long vertical runs greater than 30 feet
- Lines with less than standard weight wall thickness
- Lines using non-standard supports and/or having pipe attachments
- All lines connecting to rotating equipment regardless of size
- All lines attached to API 12B bolted tanks larger than 4" NPS
- Lines where corrosion allowance is greater than 1/16" for lines through 4", or greater than 1/8" for all line sizes
- All process, regenerating, and decoking lines to and from fired heaters and steam generators (vibration should be considered for these as well)
- All air-cooled heat exchanger piping (because fin-fans are structurally flimsy)
- All lines with maximum short-term temperature below minus 50 F
- All lines having very long straight runs either horizontally or vertically (definition of 'very long' is in the eys of the beholder)
- All blowdown and flare header systems (forces due to fluid dynamics)
- All multi-phase flow lines (dynamic loads)
- All lines with relief valve with set pressure above 50 psig (thrust load)
- Others: Cast iron lines, FRP, copper, etc.
Of course there are plenty of exceptions to this.
Does this help?
There are manual stress analysis methods out there. One is listed in the book "Piper's Pocket Handbook" by Rip Weaver, available from Gulf Publishing.
Hope this helps! Pete
RE: Piping Stress Analysis
Even though I'm in ireland we still would use the ASME guidelines primarily.
I guess what I'm really looking for, more so than rules of thumb, is a work flow process. What procedure does one follow to perform stress analysis. (e.g. acquire isometrics, define process conditions then build computer model)
I'd like to hear from people in this field as to how they approach it and the process by which they perform stress analysis.
And also in response to doberdorks comment
"1. Being able to run the software and being able to do the analysis are not always the same thing."
I'd like to know what would allow me to use the software to full and proper effect. I'm assuming the software vendor would offer training in the use of the program, but even still a lot of the parameters etc. would be down to the user. What guides/books/areas of study would most benefit correct use of the program?
Thanks.
RE: Piping Stress Analysis
Basics of pipe stress analysis
thread378-189629: Basics of pipe stress analysis
RE: Piping Stress Analysis
Your costs for CAESAR are only half the picture. Someone needs to be trained to use the program, maintain the program, and interpret the results. That is really the major cost.
My understanding is that you can get a corporate license for CAESAR relatively cheaply and then buy "packets" of run licenses that are something like $10 per run. Once you have some experience the number of runs per system is pretty low. Compared to the labor costs, it is still not the major expense.
I used AutoPipe for years and compared to the CAESAR of the same era, it was a joy to use. Its graphical interface was especially nice. We had an outright license, no per-run cost, but it cost about $15k/year for 6 concurrent users back in the late '90's, including their tech support which pretty much was useless but included free upgrades. It was easy to play with supports on a system to gauge the effects. It is now integrated with their other products and while I have not used it, it would appear you could bury some of the cost of analysis by using AutoPlant for your system designs.
RE: Piping Stress Analysis
We actually use Autoplant 3D for our pipe modelling, however for various reasons, they don't really want to deal with Bentley (primarily the annual licenses issue and the poor support in the past). I'm thinking Caesar II will be the choice if we go that route.
I've taken a look at John Breens previous thread and there is a lot of great info in there which I'll assimilate over the coming days. In the meantime if anyone has any further thoughts/opinions I'd like to hear them.
Thanks.
RE: Piping Stress Analysis
I would suggest you to provide more details on your application. The more specifics you will provide, I am sure you will get more detailed response on your query by the most senior and respected members in the industry.
regards,
Siddharth
These are my personal views/opinions and not of my employer's.
RE: Piping Stress Analysis
Our application would be pharmaceutical piping. Primarily utilities and process fluids. These would include steam, cooling oils, nitrogen, solvents etc. Line sizes would generally range from 1/2" up to 6" (with occasional larger lines). We would also be responsible for specifying and designing various equipment layouts (reactors, pumps, heat exchangers etc.) and the piping to and from these.
What we would like is to perform out own stress analysis rather than contract it out.
I apologise if my initial query was vague, but this is down to my inexperience and lack of knowledge on the subject. Essentially we are starting from scratch, trying to find the best approach for performing our own stress analysis. What I am looking for here is suggestions and direction. I'm happy to say that I've received some very helpful responses so far.
RE: Piping Stress Analysis
As you are in Ireland and intend or are using ASME how do you ensure the requirements of the PED are met since ASME does not implicitly cover all requiremnts of the PED?
Also why do you want to use Caesar? I know Caesar is used widely but there is a UK based software (PSA5) which is used also in the UK and has excellent user support. Also it covers most Piping Codes and can handle up to 100 load cases. It also automatically calculates the highest stress levels around a bend whereas Caesar only calculates stresses at particular specified points around a bend.
I am not "hammering" Caesar here but want to point out that it's not the "be all and end all" of pipe stress packages and does have limits.
What you need to remember is the Stress analysis software should be considered as a "clever" calculator and should be used as such and in order to achieve a safe and Code compliant system other aspects come into consideration.
I would like to ask if the Process Engineers also have other "hats" such as Instrument Engineer, Electrical Engineer, Civil Engineer etc or is it they feel that Mechanical Engineering is so close to chemical engineering that they can undertake that function without formal training? Remember "horses for courses". I would doubt if a piping stress engineer would consider performing Process engineering tasks!!
RE: Piping Stress Analysis
The process engineers generally wear process engineer hats, with occasional costume changes. They don't masquerade as civil engineers or electrical etc. This is a piping issue and it's the lack of dedicated piping & stress engineers (in-house) that has caused the overlap.
I assume this overlap is due to the similarities between process and mechanical engineering (to an extent). Some of the process department are actualy mechanical engineers.
The piping designers have trained in buidling services so wouldn't have the same kind of mechanical background as the process department.
Nobody is assuming that the process department can take the place of trained stress engineers. I'm researching ways to proceed and so I can hopefully offer an infromed opinion on possible directions for the company to take.
RE: Piping Stress Analysis
I kind of fell into the same position you are in at your company when I started here except that the decision to perform stress analysis in house was already made. The reason it was made was the cost for the program and training was FAR LESS than having a consultant perform the analysis. In other words the pay back was huge.
Since I started, the original engineer that first did stress here has left and I have taken over the reigns. I started out using DOS Triflex. We then upgraded to AutoPIPE for Windows. We recently built a huge stock washing plant with SS piping all running at 140-160F and did stress analysis on almost every pipe on the job - due to SS expansion. One thing that I learned when we started to bring in contract engineers (hired guns for help) is that every engineer has their own program preference and we ended up with a version of Triflex, Caesar and AutoPIPE. The contractor I most admired and felt was the expert of the group liked AutoPipe as well, so I felt better that we were trying to standardize on AutoPipe.
Starting from scratch sure sounds like nothing but problems because the calculations can be complex.
One of the things that I would recommend is that because your employer is shying away from program cost is to use a consultant for stress design for a job or two and have them track costs for JUST THE ANALYSIS separately. You'll find there is a payback there to doing it yourself. That was the path our company took when we were trying to make that decision.
One of the other experiences I've noticed is that if I don't do an analysis job for a while I have to relearn the tips/tricks/requirements (the right way to model supports, anchors, friction, etc). I've also noticed that if you do end up doing an analysis, it is a full time job. You need to do a lot of coordination with the piping designer and structural engineer and it can be an iterative process. The designer puts support locations on the line you're analyzing, you tell them if they are sufficient, you give the loads to the structural engineer and they need to make sure the structure can take what you're dishing out especially when you restrain the pipe. Designing and ordering spring cans takes some iterations as well.
It all takes time and there is no silver bullet. Managers want a program that reads and sucks in the info and drops out a repeatable, canned solution that's easy to implement with no interaction from an engineer. Each job and situation could require a different approach depending on steel design, available space, piping materials/thickness, criticality of systems, etc. You can develop some standards to deal with things, but you can't cover everything.
THE FINAL HURDLE: Getting construction managers and engineering managers and anyone concerned with project cost not to have a heart attack due to the extra money a properly supported and analyzed line costs AND getting them to install the line correctly.
An example: The big job I referenced earlier... The construction manager purposefully tried to keep engineers off site so that we couldn't tell that they weren't installing the supports as designed. The problem was it was a "unit rate" contract and the contractors units didn't include the increased number of specialty supports we called for. The best part was that when they started the systems up, you could tell the systems that weren't restrained or supported correctly. Pipes were running into pipes, there was so much stress on pump suctions that the pumps came out of alignment, lines that we knew were going to be dynamic were hopping around in the rack. We were then called in to diagnose the problem and found all the issues with missing supports (there was a pile of spring cans and guides sitting out in the job lay down yard). It cost 10 times more to fix the job after the fact.
Another example: I did stress analysis on some large bore piping that came down into some large fan pumps (1000 hp). These were important process pumps, alignment was critical and the piping into them could not be designed flexible enough. I ran the analysis made my supporting recommendations and the project manager flipped out due to cost. He then took the piping to a consultant, paid the consultant $75K to reanalyze the lines and the consultant recommended bigger, beefier supports than I did.
Bottom line: Doing the analysis in house can eliminate safety factors that a consultant may use. Maybe a better way to say it is: YOU HAVE CONTROL OVER THE ANALYSIS. If you have enough time to learn and do the analysis, it's cheaper than a consultant. Buy a program. Don't ask which one because 20 different engineers will give you 20 different answers. All of the companies will give you trial versions to try (Caesar, Triflex and AutoPIPE). Make the decision you feel is best and then go to a training class by that software company. Also try to hit a B31.1 or B31.3 class.
Sorry the post was so long, hope it was worth reading...
UtilityLouie
RE: Piping Stress Analysis
One must know the Code being employed, one must understand the generalized 3D state of stress that exists in pipe under various loadings, one must understand the fundamentals behind combined loadings on a beam (bending + torsion + axial), one must understand the fundamentals behind Mohr's Circle and/or the stress transformation equations, one must understand something about failure criteria, e.g. Tresca or von Mises. These are the basics of pipe stress and are crucial whether the stress work is done by computer or by manual methods, and are the skills that set apart the stress engineer from the 'casual user' of TriFlex. This can't be overemphasized. The person that does not know these things is not able to accurately interpret the results from TriFlex/C2/AutoPipe/Whatever.
Maybe there's a reason why the engineering firms have guys who do this full-time?!?!?
We have heavy designers who run stress. They are not degreed engineers. They are -mostly- capable. I am the guy does QA/QC on their work. They get it right about 65% of the time. The rest of the time? Errors caused by misunderstandings of how loads are combined, about how forces and moments can combine to offset each other, how the reactions manifest themselves against restraints or vessel/tank/rotating equipment nozzles, misuse of friction, incorrect modeling of branch connections, misunderstanding of how the Code calculates stresses and stress ranges, etc.
You probably wouldn't want me designing a reactor. Sure, I can read about Kij's, read the Campbell texts, and use software or the vendor to size trays. Why would I expect a proces engineer to be able to run stress right off the starting line??? If I was going to size columns and reactors I would damn sure work under the tutelage of some much more experienced.
If you want to do this, go ahead and buy the stress software. Then read your Code book, read up on Mohr's Circle and Tresca, take a course from the publisher of the softare, and get your first few models checked by an EXPERIENCED stress engineer.
RE: Piping Stress Analysis
I've secured money today to purchase the B31.3 guideline, so thats a start.
The overall impression I'm getting is to go with the software route.
I think the annual license renewal with Bentley is a contentious issue, hence the reluctance to consider AutoPipe.
Considering the software option, I have a number of questions:
Can anyone offer ballpark figures for single user licenses for Caesar II, ,AutoPipe and and any others?
If we were to concentrate on correct use of the programs, then. What should we consider? I assume you need to be able to fully characterize your system in terms of fittings & equipment and operating conditions - is it a case of feeding our 3d model into the system and defining operating conditions?
We use AutoPlant for our 3d modelling which exports to the .pcf format for isometrics generation (using the ISOGEN program).
Can any stress analysis programs accept this file format, or will it be necessary to rebuild our piping model each time within the program?
Once one is proficient in use of these programs, what kind of man hours are generally involved in carrying out the analysis? (obviously this will depend on the job size....lets assume 10 lines to be analysed)
The big driver for this project is cost. Or more precisely cost savings.The cost to contract the analysis out needs to be contrasted with the cost of implementation, so the above questions are geared towards that,
Also, I realize I'm a bit rapid fire with the questions at the moment but I'm finding some useful pointers on this forum, all of which are very much appreciated.
RE: Piping Stress Analysis
The overall impression I'm getting is that software is not the catch all solution.
When we get the returned stress reports from the Contractor, done using Caesar II, we get a list of stresses, moments and strains. These are then compared against values which the report says are defined by ASME B31.3.
If we were to consider the job of stress analyst and piping designer as 2 seperate roles (is this a dangerous assumption?). Can the stress analyst not input the designed model and operating conditions and have the program workout the various forces etc.
I am assuming that when Caesar says it has various codes built in, it is referring to acceptable limits and such as defined by the codes.
I assumed perhaps that it would then state if the system stresses were within these acceptable limits.
If anyone could post a sample Caesatr output i'd be very interested to see what kind of things need to be considered.
I don't have the stress report to hand, but I can post the details from it next monday if anybody is interested.
RE: Piping Stress Analysis
http://
Some of the problem in deciding who does what is caused by the more recent "titles" that are in use (as opposed to "job descriptions"). What is a "designer"?
The people who do the piping layout work and figure out where the supports will be placed (based on where the supporting structure will be) and do the material take-offs etc. are NOW called "designers". Not many years ago they were called "draftsmen" and then (unisex) "drafters". These same people were charged with doing table look-ups for sizing hanger rod thicknesses and since hangers are "load rated" that lead to determining all the rest of the hanger assembly component "sizing". The graduate engineer was charged with picking the spring hanger units (cans) based upon weight and thermal expansion movements and for doing any required calculations. Of course these lines were blurred when very experienced "draftsmen" were involved.
It MUST be recognized that the design of piping is based upon the Codes and Standards required by the jurisdiction in which the piping system will be installed. The ASME B31.3 Code has been mentioned here. The ASME B31.3 Code is largely based upon beam theory and the person responsible for the "design" of piping (the person responsible for the calculations be they done by hand or by computer) MUST TRULY UNDERSTAND the Codes and must equally understand the associated beam theory calculations. Without that background, the "design engineer" cannot truly be responsible and it would not be prudent to assign such responsibility to a person who did not have the appropriate background. Of course the Code allows the responsible engineer to apply more rigorous methodologies (more rigorous that beam theory, which in some cases, for some components will not predict the highest stresses due to loadings) when it is appropriate. I personally believe that if it is beam theory software (typical for piping analysis) or if it is more general finite element analysis software there MUST be a mechanical engineer in the line of responsibility. I have seen some excellent "designers" who are very capable of developing computer drawings and are equally capable of developing accurate beam element computer piping models. The software will routinely run through the calculations but then there must be an engineer to interpret the calculated results and to back-check the model and the loadings. This engineer SHOULD be charged with the responsibility of REVIEWING every aspect of the design calculations and signing off on its credibility. Anything less than that would be cheating the client.
Over at the client's office, there SHOULD be someone who is charged with the responsibility of REVIEWING every aspect of the design calculations and signing off on the credibility of the resulting design.
Some of the "more routine" decisions regarding when must a piping system undergo "formal" analysis then made by the simplistic "rules of thumb" that were written into company standards. These standards cannot be blindly applied and the limits of these "rules of thumb" should also be part of the company standards.
Regards, John
RE: Piping Stress Analysis
http://www.coade.com/PricingPages/CAESARII_2008_PriceList.pdf
Richard Ay
COADE, Inc.
RE: Piping Stress Analysis
I know PED and ASME B31.3 have different implications BUT if the PED is applicable then the analysis must be consistent with the requirements of the PED. ASME B31.3 does not implicitly address the PED requirements.
Also you say that the lines you intend to analyse will be installed on site and are exempt from the PED. I think you need to confirm this with your appointed NoBo. Generally the entire plant needs to be given a certificate of conformity by the NoBo. Individual Vendor packages are/or should be supplied with a Certificate of Conformity from the Vendor stating that the unit meets the PED. However the pipework between individual vendor equipment (even if installed on site)needs to meet the requirements of the PED unless the pipework is Designed/procured/fabricated and installed by the user. If the user sub-contracts the fabrication then the fabrication is not supervised by the user and the PED applies. I have argued with a NoBo over this point and stated that the PSSR regulations apply but their stance was that if the "user" does not "supervise" then the PED applies to on-site installation of pipework.
RE: Piping Stress Analysis
Thanks for that pointer about the PED. To be honest, i didn't even consider PED for stress analysis. We always considered it a vendor responsibility. But, as you say, if we are in effect the Vendor for the piping, then we may be responsible. I'll have a look over this point.
I'm guessing it's a grey area - if you were arguing with your NoBo about it.
RE: Piping Stress Analysis
Yes it is a grey area but for piece of mind I would talk to your designated NoBo. Also the materials must be PED compliant so if you are intending to use ASME materials then you need to get PMA's prepared and approved by the NoBo. Risk assessments for the systems will be required to show how the piping system meets the PED. If you are doing the piping design and getting a sub-Contractor to install then you need to get a Module B Cerificate for the design and give that to the Sub-Contractor so he can show the NoBo. Also the Sub-Contractor should be certified under the PED by a Nobo to perform the work.
I have gone through all this for what should have been user installed pipework on a large industrial site. The NoBo came in to review the Stress Analysis and the design documents including pipe specs etc and we had to show how we had addressed all parts of the PED. When he was comfortable with the design we received a Module B Certificate to give to the Fabricator who was also certified to Module H for the construction.
RE: Piping Stress Analysis
May I ask you to do all of us North American piping engineers a favor?
Would you, for our edification, explain the PED requirements that you guys work with. It would be very useful for us to understand Module B and Module H and NoBo and some of the rest of the terminologythat you used above. We thank you very much for the education.
Best regards, John.
RE: Piping Stress Analysis
I'm looking over the PED implications for Stress Analysis this morning. When you say that the user "Supervises" the installation, what would be your definition of this? Are recorded inspections etc. required as part of this?
RE: Piping Stress Analysis
RE: Piping Stress Analysis
Click on the grey rectangular picture left of:
"Klik op de afbeelding hiernaast om het programma te downloaden."
When You run the program, You can choose the english version
RE: Piping Stress Analysis
What our NoBo said that for a "User" installation (therefore exempt for PED) it must be seen that the "User" supervises all activities Design, Fabrication,Installation, Testing and NDT and must ensure these activities are in accordance with the relevant Codes.
RE: Piping Stress Analysis
We would be operating on behalf of the user. In essence we would taking the place of the user for this supervision. All those items you mentioned would be covered by our piping team during the installation. I assume then that the Client Project manager would have final sign off on all documents generated.
Essentially we carry out all the work and the client ("User") approves it. I would assume that this would exempt the Site Installed piping from PED.
It's an interesting point though, and one that can probably be interpreted a few ways.
RE: Piping Stress Analysis
RE: Piping Stress Analysis
We've tried it and it has never worked really well. It is not a seamless transition to say the least. We found that we needed to at least cross check our iso's with the model that was imported. This too can be time consuming. If there are any strange fittings, they can throw off the import.
HOWEVER, we do not use AutoPLANT and thus have never tried an AutoPLANT to AutoPIPE transfer. When you speak with Bentley, they are pretty confident that it is pretty easy to do. I wouldn't swallow that one whole, but it may be partially true.
Some of the issues that I've seen throw of the import process is any customization that you've done to your piping database in your model program. The coversion process doesn't seem to hold up well with customization.
Getting an engineering estimate time to enter/analyze pipe models is a tough nut to crack. My thoughts are that it depends on engineering experience with stress analysis. On a large job --- 100,000' of pipe --- we spent an average of .1 hours per ft of pipe, but a lot of this pipe was rack pipe with similar supporting techniques. I wouldn't even use this .1 hours per foot as a starting number. There were complex pipe arrangements that required well over an hour per foot of pipe. I'd guess .5 hours per foot as a starting point.
The biggest thing for management to realize --- because they hear the "sales pitch" of perfect importing of lines into any program --- is that it is not perfect. We tried importing pcf files into Caesar II, Triflex AND AutoPIPE. None of the imports were satisfactory and we decided to hand enter all iso's to make sure they were correct. The way we lessened cost was to have a pipe designer enter the pipe into the program and the engineer would analyze the pipe. This way we felt we were getting our designers started on the "road" to learning stress analysis. This also helped because then the designers would take the hand marked iso's and make the changes designated by the engineer. The designer was on the front and back end of the stress analysis.
RE: Piping Stress Analysis
The .pcf import did sound too good to be true, I imagine hand checking the model is the only way to be certain.
I finally got the B31.3 guide today, so I'll be absorbing that over the next few weeks. In the meantime if anyone has anymore thoughts/suggestions please let me know. Thanks.
RE: Piping Stress Analysis
It certainly imported whatever was in the file quickly and accurately, but that just means you can get garbage into your analysis model that much more quickly. When an incorrect analysis puts my career and reputation on the line, there is no way I'm trusting an analysis model built off of an import file generated from the designer's 3D model.
The designer has to model in a specific way to be able to trust that correct and complete information will be imported into the file, and he just may not know how to do that or be set in his ways and refuse to do it. The databases on both ends that first generate the pcf/pxf file from the main model and then translate the pcf/pxf file into an analysis model might be flawed and errors in translation may occur.
There are just too many things between there and here that can go wrong, and I'd end up hand checking the models against the isos (which are controlled documents here). Building the model from the isos was quicker and easier and gave me an extra layer of sanity checking as I could often spot mistakes on the isos that would have gone unnoticed had I just imported the model.
If a foul-up in analysis means a steam line ruptures and kills someone, I'll be darned if that foul-up is because I blindly trusted a multi-stage process to work correctly. Your process might be set up differently, but the moment you can't trust the input to the analysis, you've lost any benefit the import process has gotten you.
That's my two cents.
RE: Piping Stress Analysis
RE: Piping Stress Analysis
"Essentially we carry out all the work and the client ("User") approves it. I would assume that this would exempt the Site Installed piping from PED".
From this response you are acting as a Contractor not the "User". Therefore PED applies to the site installed piping.
We had the situation that the "User" was another branch of the Company I worked for but still the NoBo said we were acting similar to a Contractor as we were not the "user" in the sense of the PED. Therefore we had to furnish a CE mark to the actual "user" for the plant. (Ie global CE mark for the site installed piping)
RE: Piping Stress Analysis
It's an interesting one alright.
I assumed that we are checking the mechanical contractor's(not us) work, on behalf of the User. The user would then approve and sign off our documentation (i.e. approving our supervision of the contractor). I would have thought that this may constitute "User Supervision".
I'll be interested to see the responses I get when I bring that point up here, I must read up the PED guides first though.
RE: Piping Stress Analysis
Also remember that plant modifications(unless under the supervision of the "user") could fall under the PED if they are "significant". However to get a NoBo to agree on what a "significant" modification constitutes is difficult. Best thing is to discuss with the NoBo before you assume that it is an insignificant modification and then find out you needed NoBo involvement. Difficult to do this retrospectively (especially fabication requirements)
RE: Piping Stress Analysis
RE: Piping Stress Analysis
Could you please supply the Internet address for the CAEPIPE users discussion forum?
Thanks, JB
RE: Piping Stress Analysis
CAEPIPE internet address is:
http://www.sstusa.com/
The product seems well presented and the website reads well, but there seems little mention of it outside of it's own website. I do not know about the product myself, though I have downloaded the evaluation version and played around with it. From that limited perspective it seemed good. I wonder if there are any CAEPIPE advocates out there that could tell us something about it, useability, validity, strengths, shortcomings.
REGARDS
Barry
RE: Piping Stress Analysis
I've been using CAEPIPE from 1998 (dos version) to 2003 (windows version) and then switched to C2, because I entered another company.
For my usage (oil and gas, power piping, mostly B31.3 and french CODETI codes) it took almost no time to change from one to the other.
And I still go to SST USA - CAEPIPE site to look for their tips!
If I had not changed company I may still use CAEPIPE.
yours truly.
RE: Piping Stress Analysis
Trying to set up to handle stress work in house essentially starting from nothing is certainly a daunting task.
In truth, if your company is serious about this (though, their balking at the cost of a Caesar license suggest otherwise), I would recommend that your company find a senior, experienced stress engineer to come and and effectively give you a brain dump and create a stress design basis for your company.
As for the long term, my boss, one of the finest stress guys I've ever known, has said that it takes five good years of development to build a stress engineer. Most of us that do this for a living stand on the shoulders of the giants who came before us.
Edward L. Klein
Pipe Stress Engineer
Houston, Texas
"All the world is a Spring"
All opinions expressed here are my own and not my company's.
RE: Piping Stress Analysis
If your company doesn't normally do business with a good Engineering Design firm, spend a little money and get Caesar II with a limited run license (probably $1000 or less), model the sytem and run it. After you do it for quite a while, you'll be able to look at a system and determine what level of analysis is needed--detailed with spring supports, or just a visual review.
RE: Piping Stress Analysis
But remember the cost of the software is but a minor cost compared to learning how to use it effectively and far less than if an inexperienced engineer makes a mistake that translates into a catastrophe.
If an engineer were to join the Institution of Mechanical Engineers he/she would have access to over 1000 books including those on pipe stress analysis. Refer www.imeche.org.
RE: Piping Stress Analysis
Well pointed out - it's not just a case of getting some software and using it as you so well indicate. The previous post seems to suggest that by buying C2 with a $1000 limited run license is all you need to become a proficient Pipe Stress Analyst. We have too many of these at the moment without any more. I do have to venture out on Plants and do not like the thought of working around pipework which has been "designed" by a "two week experienced" Stress Engineer.
RE: Piping Stress Analysis
Please bear with me as I do a little "nit-picking".
A little history. Strictly speaking, NONE of these new software products have anything in Common with the Navy Mare Island Mec-21 (and its derivatives like Mel-40) pipe stress analysis program (except that they use Castigliano's second theorem for the basic structural solution). I began using Mec-21 in 1963 and I had the responsibility to maintain and update it for 12 years (we made the conversion from IBM 7094 dependent Fortran II to Fortran IV). MEC-21 was written by Bob Creamer based upon the chapter of “The Piping Handbook”, Fifth Edition, (S. Crocker and R. King) by John Brock (If anyone has a fifth edition, this chapter is historic and you should read it again). Mec-21 used the flexibility method in its solution engine (I still have the original manual – yes, I know, “get a life”). This (flexibility method) greatly limited what we could do with Mec-21 as far as adapting it to perform dynamic analyses was concerned. All these new products use the stiffness method.
The first "break-through" came when the SAP IV software became available in the public domain. The Sap series of structural analyses programs came out of U-Cal Berkley and they used the stiffness method and beautifully written "top-down" Fortran IV in writing the program. Due to the "clean-ness" of the SAP analytical engine, it was adapted by several proprietary software products in 1970's and 1980's. The SAP software included a TRUE curved beam element and this was something else that Mec-21 lacked (Mec-21 created many lengths of slightly angled straight pipe to approximate the bend). If you did side by side comparisons of an analysis of the same structure there would be differences. If you analyzed a close coupled piping system with a dominant large radius bend in it the SAP software would give you an accurate solution but MEC-21 would "go wrong". One of the dominant software products at that time, TRILFEX (by Reid McNally), was originally based upon the MEC-21 analytical engine and then they (Dan Yongue at TRIFLEX – a great guy) created another version based upon the SAP analytical engine. TRIFLEX offered both versions ("Flexibility and "Stiffness") for a while. Tony Paulin’s approach, when he originally wrote Caesar II, was completely different and all his code was original – an entirely new analytical engine.
ASME published at least two books for the purpose of piping software verification. These books has many "benchmark" sample piping systems with solutions from several software products (including ANSYS) and the solutions were all within about 7 percent of each other. What we learned from these "benchmarks" was that if you used commercial software to model a piping system for analysis and your "answers" were more than about 7 percent "off" you better go look at YOUR model to find the errors. I think that is also the case today – there are so many ways you can model a piping system in various programs that it is really easy to “create” differences. Conversely, it is too easy to in advertently describe the same system differently. This is usually the reason for “different” answers.
Folding his collapsible “soap box”, the old guy now toddles off to take his afternoon nap
Regards, John.
RE: Piping Stress Analysis
What a valuable lesson you have given me. I used Triflex back in the 1970's , punched cards and all. I made the mistake of repeating what my mentor had told me in those days without keeping up to date. You have certainly put me straight.
I have a copy of Crocker & King 5th Edition. I will certainly re read it now. It has been a while since I did read it.
Perhaps I am hoarder but I have Piping Design Manual Kellogg's , Piping Engineering by Tube Turns, Piping Design and Engineering by ITT Grinnell and Process Equipment Design Brownell & Young. They do me no good sitting on the shelf I have to re read them. I used to study them on the train but now have a home office so do not get the chance.
Be assured we readers appreciate your insights into the history of the tools we use. I hope I can pass on such useful information when it is time for me to get the collapsible soapbox, still using an upturned milk crate at the moment.
RE: Piping Stress Analysis
Add to the above Reference
DAVID BURGEEN
1 DESING OF POWER PLANTS STRUCTURES
2 PRESSURE VESSEL ANALYSIS
3 PIPING ANALYSIS
4 ELEMENTS OF THERMAL STREESS ANALYSIS
Leonard Thill, Jakarta
RE: Piping Stress Analysis
Sincere thanks for your kind words.
Leonard Thill mentions the Burgreen books. David originally published them himself when he was a professor at Brooklyn Polytech. The "publisher" was C-P Press, Jamaica, NY. David became a good friend and he allowed me (in writing) to use excerpts from his books in my ASME piping analysis seminars. David's "Piping Analysis" book provides a rigorous treatment of the math involved in this science - don't look for much "nut and bolts" stuff there. However, it is still one of the books (as are the other three) that I pull down off my (many) shelves and read periodically.
The title of David's book "Design Methods for Power Plant Structures" (again, C-P Press, 1975, 446 pages) is a little deceiving as it is a wonderful treatment of the development of the equations and methodologies found in the ASME B&PV Code. David carefully explains the importance of each of the shell stresses (primary and secondary) in the context in which the Code uses them. This is far and away the most lucid treatment of this subject matter that I have ever seen. The complete description of the various theories of failure that David presents is worth the price of the book. The bad news is that it is out of print (albeit it can be found on the used book market at a price). In my view, the novelty of these books is that they were written by a teacher and they were intended for university students so they assume the reader brings very little background knowledge to his/her first reading.
After David's passing, These books were again printed by Arcturus Publishing and offered for sale for a while (Arcturus Publishing, 1971-06-01, list price: $48.00, ISBN: 0916877027). Regrettably, even these have been out of print for a while. The Arcturus published books can also be found on the used book market.
Ooops, sorry, I seem to have gotten out the collapsible “soap box” again.
Regards, John.
RE: Piping Stress Analysis
To register for any or all of these webinars, please go to Webinar Registration.
Thursday March 13, 2008 9:00 AM CST:
"Part 2 Fatigue Design – Fatigue Evaluation with ASME Section VIII Div 2, 2007"
Tuesday March 18, 2008 9:00 AM CST:
"Beams (CAESAR, AutoPIPE, Triflex, etc), vs. Shells (WRC?) vs. Bricks (FEA) - Who's Right"
Thursday March 20, 2008 9:00 AM CST:
"Part 3 Fatigue Design - Comparison of Fatigue Design Lives Using ASME, BS, and EN Design Codes"
Tuesday March 25, 2008 9:00 AM CST:
"Rules of Thumb for Expert Analysis of Piping Systems"
Thursday March 27, 2008 9:00 AM CST:
"External Loads on Nozzles (Comparisons of WRC107, B31, EN13445, VIII Div2 and.Mean-Life-to-Failure)" (web042)
Tuesday, April 1, 2008 9:00 AM CST:
"What is 100% of the Allowable Stress for Pipes and Pressure Vessels".
Houston 9:00 AM Start Time
New York - Tue 10:00 AM
London - Tue 3:00 PM
Berlin - Tue 4:00 PM
Moscow - Tue 6:00 PM
Dubai - Tue 7:00 PM
New Delhi - Tue 8:30 PM
Beijing - Tue 11:00 PM
Sydney - Wed 2:00 AM *
Auckland - Wed 4:00 AM *
TRAINING:
Second Qtr 08 Training: Two Days – Beginning and Intermediate Content. Two Days – Advanced Content.
Course Description: PRG FEPipe and NozzlePRO Course Outline
Course Registration: PRG FEPipe and NozzlePRO Course Registration.
NEW WEBSITE:
Topics include WRC107 experimental validation, Stress Intensification Factor explanations, Accurate SIFs, Pipe stress errors, Freeware downloads and more. Paulin Research Group Website
Software Bundling – PRG FEA Technology is included in each copy of Compress sold by Codeware Inc. Compress - PRG Bundling
TEMA Thick Walled Expansion Joints – PRG FEA Technology is used in the new TEMA Flanged and Flued Stiffness and Stress Analyzer.
www.tema.org/software.html
ASME ST-LLC – PRG Research Projects include alignment of stress intensification factors and external load design rules. See for more information.
Paulin Research Group Website
FOR MORE INFORMATION:
For more information call 1-281-920-9775 ext. 808, or email information@paulin.com
L S THILL
RE: Piping Stress Analysis
I've been away for a while and just got to catch up with this thread again.
Well, as I said this was originally intended as a research exercise. The overwhelming response is that it's not a straightforward operation.
To do things properly it seems more economically viable to continue contracting out the work (at least for the number & size of jobs we deal with).
Thanks for the suggestions & pointers - the experienced views were both appreciated & helpful. I'll keep everyone updated if things go any further.
RE: Piping Stress Analysis
Question??
continue contracting out the work neet the verification and validation (DOE STANDARD REQUIREMENT)??
Reference ASME B31.3 PIPING CHECKLIST by PRG www.paulin.com
SYSTEM SPECIFIC B31.3 CODE REFERENCES - Short
300.2 Normal Fluid Service: a fluid service pertaining t omost piping covered by [B31.3].
i.e., not subject to the rules for Category D, Category M, or High Pressure Fluid Service.
Normal Fluid Service applies to piping that can be designed in accordance with the first
chapters of the Code and the fluid service is not Category D Fluid Service, nor is the piping
in severe cyclic conditions.
304.3.5(b) Branch pipe connections made by welding the branch pipe directly to the run pipe should be avoided
under the following circumstances:
1) when the branch size approachs the run size, particularly if the run pipe is formed by more than 15%
cold expansion, or expanded, or of a material subject to work hardening.
2) where repetitive stresses may be imposed on the connection by vibration, pulsating pressure, temperature
cycling, etc. In such cases, it is recommended that the design be conservative and that consideration
be given to the use of tee fittings or complete encirclement types of reinforcement.
304.3.5(e) Where branch connections do not meet the following requirements, integral reinforcement,
complete encirclement reinforcement, or other means should be considered:
1) D/T < 100 and d/D<1
2) If D/T>=100, d/D < 0.5
3) The angle between the run and the branch is greater than or equal to 45 deg.
4) The axis of the branch intersects the axis of the run.
306.5.1 Fabricated branch connections can be used in Normal Fluid Service if designed according to the
[B31.3 pressure design rules for intersections - 304.3] and [welded with the standard B31.3 acceptance
and examination criteria (311.1)]
Note 1 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (1) Stress intensification
and flexibility factor data are for use in the absence of more directly applicable data. Their validity has
been demonstrated for D/T ratios less than or equal to 100.
Note 6 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (6) The designer is cautioned
that cast buttwelded fittings may have considerably heavier walls than that of the pipe with which they are
used. Large errors may be introduced unless the effect of these greater thicknesses is considered.
Note 12 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (12) The out-of-plane
stress intensification factor (SIF) when > 0.5 d/D < 1.0 may be nonconservative. A smooth concave weld
contour has been shown to reduce the SIF. Selection of the appropriate SIF is the designer's responsibility.
Note 13 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (13) Stress
intensification factors for branch connections are based on tests with at least two diameters of straight
pipe on each side of the branch centerline. More closely loaded branches may require special consideration.
GENERAL B31.3 CODE REFERENCES - Short
300(c)(3) Engineering requirements of this Code, while considered necessary and adequate
for safe design, generally employ a simplified approach to the subject. A designer capable
of applying a more rigorous analysis shall have the latitude to do so; however, the
approach must be documented in the engineering design and its validity accepted by the
owner. The approach used shall provide details of design, construction , ... with calculations
consistent with the design criteria of this Code.
300(c)(5) The engineering design shall specify any unusual requirements for a
particular service. This may include, but not be limted to, two-phase flow,
hydraulic shock, mechanical/flow induced vibration, and unusual operating, relief,
or clean-out procedures,
300.1 The Designer is the person(s) in responsible charge of the engineering design of a piping
system and shall be experienced in the use of [B31.3]. The qualifications and experience
required of the Designer will depend on the complexity and criticality of the system
and the nature of the individual's experience. The owner's approval is required if the
[individual performing the engineering design] does not meet at least one of the following
criteria: (a) ... Engineering degree requiring 4+ years of full-time study, plus a minimum
of 5 years experience in the design of related pressure piping. (b) a [professional engineer]
experienced in the design of related pressure piping. (c) Associates Degree: 2+ years of
full time training + 10 years of experience, or (d) 15 years of experience in the design
of related pressure piping including design calculations and pipe flexibility...
301.3 ... The maximum design temperature ... may be established by test or calculation, and
may be the fluid temperature, but for uninsulated components shall not be less than: 95% of
the fluid temperature for valves, pipe, lapped ends, welding fittings ..., and 90% of the
fluid temperature for flanges (except lap joints), including those on fittings and valves,
and 85% of the fluid temperature for lap joint flanges, and ... 80% of the fluid temperature
for bolting. Per 301.3.3, for externally insulated piping, the design temperature shall be
the fluid temperature unless calculations, test or experience , ... show otherwise.
301.5.1 Hydraulic shock, liquid or solid slugging, flashing and geysering shall be taken
account in the design of the piping system.
301.5.4 Piping shall be designed, arranged and supported so as to eliminate excessive
and harmful effects of vibration which may arise from such sources as impact, pressure
pulsation, turbulent flow vortices, resonance in compressors, and wind.
301.7.2 [Piping shall be designed to accomodate or eliminate an unequal temperature
distribution at any cross section that may result in thermal bowing. This often occurs due
to thermal stratification, partial filling, or during startup or shutdown. See F301.7.
301.10 Fatigue due to pressure cycling, thermal cycling and other cyclic loadings shall be
considered, including the surface effects due to mixing flows at intersections, [and the
surface evaporation effects downstream of desuperheater valves.]
302.2.4 [A VARIATIONAL temperature and pressure does NOT need to be included as a design condition for
wall thickness calculations providing all the following are true (LIST IS SUMMARIZED):
a) All metals are ductile for variational temperature range
b) The hoop stress: (PD/2t) < Material Yield Stress at variational temperature.
c) SL + Occasional (Variant) Stresses < 1.33 Sh
d) Number of variations above design conditions occurs less than 1000 times in the piping system life.
e) Increased variation in pressure does not exceed test pressure.
f)(a) Variation does not exceed 33% for more 10 hr. at any one time, or more than 100 hr/yr, or
(b) Variation does not exceed 20% for more than 10 hr. at any one time, or more than 500 hr/yr, and
(c) Designer determines effects are safe and owner accepts, (See Appendix V).
g) Combined effects of sustained and cyclic variations on serviceability of all components is evaluated.
h) Temperatures below the minimum allowed temperature are not permitted unless per 323.2.2.
i) Sealability or operation of any valve or other component are not jeopardized by the variation.
302.3.5(c) The thickness of pipe used in calculated (SL) (the sustained stress) shall be the
nominal thickness minus mechanical, corrosion, and erosion allowance for the location under
consideration. (Mill tolerance must be removed from the nominal wall.) The loads due to weight
should be based on the nominal thickness of all system components unless otherwise justified in
a more rigorous analysis. [Many piping product specifications, for example SA-106 allow the
minimum provided thickness to be 12.5% under the nominal wall thickness. More stringent
requirements may optionally be provided by contractual agreement permitted by the piping product
specification.]
302.3.5(d) Footnote 3) B31.3 fatigue rules apply to essentially noncorroded piping. Corrosion can sharply
decrease cycle life; therefore, corrosion resistant materials should be considered where a large number
of major stress cycles is anticipated.
302.3.5(d) Footnote 4) The minimum value for f is 0.15, which results in an allowable displacement stress
range, SA, for an indefinitely large number of cycles. [For SL=0, and Sc=Sh=20,000 psi, the endurance
limit for an infinite number of cycles is (0.15)[(1.25)(20,000+20,000)] = 7,500 psi.
302.3.5(d) Footnote 5) The designer is cautioned that the fatigue life of materials operating at elevated
temperature may be reduced. [See NH reports in NozzlePRO or FE/Pipe to evaluate this reduction.]
302.3.6 (a) The sum of longitudinal stresses (SL), due to sustained loads (pressure and weight), and
of the stresses produced by occasional loads, such as wind or earthquake, may be as much as 1.33 times the
basic allowable stress given in Tables A-1 and A-2.
302.3.6 (b) It is not necessary to consider occasional loads such as wind and earthquake as acting
concurrently with test loads.
304.3.1(b) The [B31.3 pressure design equations] are minimum requirements valid only for the following
branch connections.
1) D/T < 100 and d/D<1
2) If D/T>=100, d/D < 0.5
3) The angle between the run and the branch is greater than or equal to 45 deg.
4) The axis of the branch intersects the axis of the run.
When these requirements are not satisfied, the pressure design shall be quaified by successful prior
experience, tests, finite element analysis or other calculations per 304.7.2.
304.3.5(a) [B31.3 pressure design requirements] do not include considerations for external forces and moments,
or movement at terminal points.] Special consideration shall be given to the design of of a branch connection
to withstand these forces and movements.
304.3.5(b) Branch pipe connections made by welding the branch pipe directly to the run pipe should be avoided
under the following circumstances:
1) when the branch size approachs the run size, particularly if the run pipe is formed by more than 15%
cold expansion, or expanded, or of a material subject to work hardening.
2) where repetitive stresses may be imposed on the connection by vibration, pulsating pressure, temperature
cycling, etc. In such cases, it is recommended that the design be conservative and that consideration
be given to the use of tee fittings or complete encirclement types of reinforcement.
304.3.5(c) Adequate flexibility shall be provided for small pipe at small d/D intersections to accomodate
thermal expansion and other movements of the larger line.]
319.1.1 Piping systems shall have sufficient flexibility to prevent thermal expansion or contraction or
movements of piping supports and terminal points from causing failure of piping or supports from overstress
or fatigue, leakage at joints, or detrimental stresses or distortion in piping and valves or in connected
equipment such as pumps and turbines....
319.2.1(c) Movement due to earth settlement, since it is a single cycle effect, will not significantly
influence fatigue life. [A displacement stress range greater than that permitted by f[1.25(Sc+Sh)] in
302.3.5(d) may be allowable if it can be shown that excessive localized strain and end reactions do not
occur. Some type of plastic analysis including full material plasticity or plastic hinges can be used
to demonstrate that localized strains do not occur. Similar systems subject to the same settlement
magnitudes may be qualified per 304.7.2]
319.2.1(d) Thermal displacments, reaction displacements, and externally imposed displacements all have
equivalent effects on the piping system, and shall be considered together in determining the total
displacement strains in various parts of the piping system.
319.2.3(a) In contrast with sustained stresses, displacement (thermal) stresses may be permitted to attain
sufficient magnitude to cause local yielding in various portions of a piping system. [These displacement
(thermal) stresses diminish with time due to yielding or creep, but the algebraic difference between
strains remains substantially constant during any one cycle, which is used as the criterion in the
design of piping for flexibility...]
319.2.3(c) Average axial stresses over the pipe cross section due to longitudinal forces caused by
displacement (thermal) strains are not normally considered as part of the displacement or thermal solution
since large axial loads are not present in typical piping layouts. In special cases consideration of
average axial displacement (thermal) stress is necessary. Examples include buried lines containing hot
fluids, double wall pipes, and parallel lines with different operating temperatures connected at more
than one point.
319.2.4 When cold spring is properly applied there is less likelihood of overstrain during initial
operation, hence cold spring is recommened especially for piping materials of limited ductility. There
is also less deviation from as installed dimensions during initial operation, so that hangers will not
be displaced as far from their original settings. [Cold spring can also reduce the hot operating stress
and as such may significantly improve creep life of a piping system.]
319.3.1 The temperature range for thermal displacement analysis is from the minimum to maximum
operating temperature for piping operating above the installed temperature, and from the maximum
to minimum operating temperature for piping operating below the installed temperature.
319.3.4 The allowable displacement stress range: [ f[(1.25)(Sc+Sh)-SL] ] shall be for systems primarily
stressed in bending and/or torsion.
319.3.6 In the absence of more directly applicable data, the flexibility factor k and the stress intensification
factor i shown in Appendix D shall be used for flexibility calculations ... [FESIF provides calculated
stiffnesses and stress intensification factors using the exact branch geometry for the user to compare with
values from Appendix D. This comparison with Appendix D values is done automatically by FESIF.]
319.4.3 ... the restraint introduced by support friction shall be recognized [in the evaluation of the piping
system as a whole.]
319.7 Where the piping lacks built-in changes of direction, or where it is unbalanced, large reactions or
detrimental overstrain may be encountered. The designer should consider adding flexibility by one or more
of the following means: bends, loops, offsets, swivel joints, corrugated pipe, expansion joints or other
devices permitting angular, rotational or axial movement. Suitable anchors, ties or other devices shall be
provided as necessary to resist end forces produced by fluid pressure, frictional resistance to movement,
and other causes. When expansion joints or other similar devices are provided, the stiffness of the joint
or device should be considered in any flexibility analysis of the piping.
321.1.1 The layout and design of piping and its supporting elements shall be directed toward preventing
the following: (a) excessive pipe stresses, (b) leakage at joints, (c) excessive thrusts and moments on
connected equipment, (d) excessive stresses in supporting elements, (e) resonance with imposed or fluid
induced vibrations, (f) excessive interference, (g) unintentional disengagement of piping from its
supports, (h) excessive pipe sag in piping requiring drainage slope, (i) excessive distortion or sag of
piping subject to creep under conditions of repeated thermal cycling, or (j) excessive heat flow,
exposing supporting elements to temperature extremes outside their design limits.
321.2.2(c) Sliding supports or shoes and brackets shall be designed to resist the forces due to
friction in addition to th eloads imposed by bearing. The dimensions of the support shall provide for
the expected movement of the supported piping.
321.3.1 If the weight of a vertical pipe is supported by a clamp, [or other nonintegral attachment],
it is recommended to prevent slippage that the clamp be located below a flange, fitting, or that support
lugs be welded to the pipe.
345.9.2 A flexibility analysis of the piping system to be leak tested using an alternative
(sensitive) shall be made in accordance with the requirements of 319.4.2(b) if applicable,
or 319.4.2(c) and 319.4.2(d).
M300(d) Consideration [shall be given to the possible need for additional containment, personnel
protection, shutdown, startup, or failure scenarios that might be damaging to personnel. See
Safeguards Appendix G.]
Note 1 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (1) Stress intensification
and flexibility factor data are for use in the absence of more directly applicable data. Their validity has
been demonstrated for D/T ratios less than or equal to 100.
Note 6 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (6) The designer is cautioned
that cast buttwelded fittings may have considerably heavier walls than that of the pipe with which they are
used. Large errors may be introduced unless the effect of these greater thicknesses is considered.
Note 12 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (12) The out-of-plane
stress intensification factor (SIF) when > 0.5 d/D < 1.0 may be nonconservative. A smooth concave weld
contour has been shown to reduce the SIF. Selection of the appropriate SIF is the designer's responsibility.
Note 13 to the B31.3 Flexibility, and Stress Intensification Factor Table D300 states, (13) Stress
intensification factors for branch connections are based on tests with at least two diameters of straight
pipe on each side of the branch centerline. More closely loaded branches may require special consideration.
Precautionary Appendix F301.7 warns about bowing during cooldown, an effect that can occur usually in
horizontal piping on introduction of a fluid at or near its boiling temperature and at a flow rate that
allows stratified two-phase flow causing large circumferential temperature gradients and possibly
unacceptable stresses at anchors, supports and within pipe walls. Two-phase flow can also generate
excessive pressure oscillations and surges that may damage the piping.
Precautionary Appendix F301.10 warns about the potential for thermal fatigue on surfaces exposed to the
fluid when mixing fluids of different temperatures occur, e.g. cold droplets impinging on the pipe
wall of a hot gas stream as often occurs downstream of desuperheater valves.
Precautionary Appendix F301.11 warns about the possibility of condensation occurring inside
gaseous fluid piping. Means shoudl be considered to provide or trap drainage from low areas to avoid
damage from water hammer, corrosion or erosion.
Precautionary Appendix F309.1 recommends the use of controlled bolting procedures for high, low, and
cycling temperature services, and under conditions involving vibration or fatigue to reduce the potential
for joint leakage due to differential thermal expansion, or the possibility of stress relaxation and loss
of bolt tension.
Precautionary Appendix F323.1 provides the following design points for considerations:
(a) exposure of the piping to fire and the melting point, or point of significant loss of strength.
(b) susceptibility to brittle or other failure from thermal shock when exposed to fire protection measures.
(c) ability of thermal insulation to protect piping against failure during fire exposure
(d) possibility of crevice corrosion under backing rings, in threaded joints or in socket weld joints.
(e) eletrolytic effects in dissimilar metal welds
(f) compatibility of lubricants or seals used on threads with a particular fluid service.
(g) compatibility of seals, packing and o-rings with the fluid service.
(i) chilling effect of sudden loss of pressure on highly volatile fluids in determining lowest temperature.
(j) possibility of pipe support failure due to low or high temperature embrittlement
(k) compatibility of materials in strong oxidizer fluid service, i.e. oxygen or fluorine.
Precautionary Appendix F335.4.1 recommends that consideration be given to the susceptibility of
microbiologically influenced corrosion (MIC). This condition is especially prevalent in no flow,
high moisture environments. Internal MIC may also depend on the characteristics of the treated or
untreated test fluid. Intenral MIC may be lesssened or possibly eliminated by properly draining and
drying systems and/or by proper selection or treatment of the test fluid.
G300(a) Safeguarding is the provision of protective measures to minimize the risk of accidental damage
to the piping or to minimize the harmful consequences of possible piping failure. (b) In most instances
the safeguarding inherent in the facility is sufficient... (c) ... where safeguarding is required by
B31.3 it is necessary to consider only the safeguarding that will be suitable and effective for the
purposes and functions stated in B31.3 or evident from the designer's analysis of the applications.
G300.1 The following items should be reviewed when determining any added degree of safey or precaution
needed with the piping system being designed:
(a) the hazardous properties of the fluid
(b) the quantity of fluid that could be released by piping failure
(c) expected environmental conditions and how it effects a piping failure
(d) the probable extent of operating, maintenance, personnel exposure, and possible damage
(e) the probable need for grounding of static charges to prevent ignition of flammable vapors.
(f) the safety inherent in the piping by virtue of material of construction, method of joining and
history of service reliability.
G300.2 Adding extra safety to an installation (safeguarding) might include:
(a) plant layout, spacing, slopes, buffer areas, etc.
(b) protective installations such as fire protection systems, barricades or shields, instruments for monitoring
(c) containment and/or recovery or facilities for emergency disposal of hazardous materials.
(d) operating practices, such as restricted access, work permit systems or special training.
(e) means for safe discharge of fluids released during a pressure relief, operating, blowdown, cleanout, etc.
(f) procedures for startup, shutdown, and operations management, such as gradual changings of temperature, etc.
G300.3(a) Engineered added safety may be added to systems that includes: (a) thermal insulation, shields or
process controls, (2) armor, guards, barricades, or other protection from mechanical abuse, (3) damping
or stabilization of process or fluid flow dynamics to minimize destructive loads, e.g. severe vibration
pulsations or cyclic operating conditions.
G300.3(b) Engineered added safety may be added to systems to protect people and property against possible
piping failures such as confining and safely disposing of escaped fluid by shields for flange joints, valve
bonnets, gages, or sight glasses, by automatic shutoff or excess flow valves, flow limiting orifices, or
automatic shutdown of the pressure source limiting the quantity of fluid in the process at any one time.
P300(a) Appendix P provides alternate, more comprehensive rules for computing the stress range
and includes an operating stress allowable and recommendations for axial stress intensification
factors. Axial stress intensification factors can be found in FESIF and NozzlePRO for use in
P319.4.4 calculations.
V300(a) B31.3 Appendix V covers applications of the Linear Life Fraction Rule, which provides a method
for evaluating variations at elevated temperatures above design conditions where material creep
properties control the allowable stress at the temperature of variation. Appendix V is a Code requirement
only when specified by the owner in accordance with the last sentence of para 302.2.4(f)(1) for variations
in operating pressure and temperature.
X300 ... The detailed design of all elements of the expansion joint is the responsibility of the manufacturer.
X301.1 The piping designer shall specify all necessary design conditions including:
(.1) The design conditions including any possible variations of pressure or temperature.
(.2) The cyclic conditions including operating, startup, shutdown and abnormal operation.
(.3) All other loads that should be considered including dynamic effects, snow, ice, etc.
(.4) The properties of the flowing medium, its velocity and direction
(.5) Any other conditions that might effect design such as the use of shrouds, external or internal
insulation, limit stops, constraints, and additional attachments such as drains or bleeds.
X302.2.1(c) A full fillet weld may be used as a primary weld to attach a bellows element to an adjoining
piping component.
ANALYSIS NOTES and COMMENTS
1.0 General
Have cyclic system, but good layout should minimize thermal stresses.
The minimum required pipe thickness = 0.0285 in
The nominal pipe thickness = 0.25 in
The pipe minimum thickness is below 20% of the required minimum thickness. Pressure stresses
will likely be low providing good external sustained load carrying capacity.
Per 319.4.1 this system may NOT need a formal analysis.
When Dy/[(K1)(L-U)^2] is less than 1.0 a formal analysis is not required. Max and min
estimated values for Dy/[(K1)(L-U)^2] are given below:
Dy / [(K1)(L-U)^2] = 0.004365 to 0.2420748
2.0 SIFs and Flexibilities
Including intersection flexibilities at full sized branch connections may reduce loads
on the intersections by up to 22.074 %
Thermal Fatigue Safety Factor (Normal)= 3.387
Thermal Fatigue Safety Factor (+Corrosion) = 3.387
Thermal Fatigue Safety Factor (+Corrosion + Sif Anomalies) = 3.387
Thermal Fatigue Safety Factor (+Corrosion + Load Redistribution) = 3.222
Estimated Actual Thermal Fatigue Safety Factor (with Flexibilities) = 3.837 This value reflects
the fact that the general trend is for loads and stresses to be reduced in a more flexible system although this
is a function of geometry and interacting changes in line size.
4.0 Rain Effects
Restrained Stress on Uninsulated Pipe due to Rain = 9519. psi
Top of Pipe Temperature on Uninsulated Pipe in Rain = 95.29 degree F
Free End Liftoff in 100 ft. (30 m.) Due to Bowing = 35.66 in
5.0 Probability of Failure
The calculated probability of failure of this piping system in any one year will
be a function of the line routing, types of intersections, etc. An estimate of
the possible ranges of these probabilities (%) is 0.0001809 % to 0.000216866 %
The calculated probability of injury due to a failure of this piping system in any one
year will be a function of the line routing, types of intersections, etc. This probability
can be compared to the probability of being in an auto accident in any one year. An
estimate of the range of this probability ratio is 0.0302 % to 0.0361 %
In a worst case scenario, it is safer to work near this pipe system than it is to ride
in an automobile.
The calculated risk of operating this piping system in dollars per year is a function of the
line routing, types of intersections, etc. An estimate of the possible ranges of this risk
per year is between $2.71 to $3.25 By comparison, the approximate risk for
operating a car per year is $2.00.
 
RE: Piping Stress Analysis
RE: Piping Stress Analysis
Gator (Industrial): Mr. LEONARD STEPHEN THILL, Independent Contractoris not with PRG.
Tony gave me the ASME B31.3 Piping Check List on March 31, 2008. in Houston.
Additional work is beeing done on the ASME B31.3 Piping Checkand will be update for Design Verification / Design Validation
Team Member are working on the ASFME SECTION VIII Div 1 and Div 2 Check List.
Best Regards
Leonard Stepehn Thill
L S THILL
RE: Piping Stress Analysis
Did you get the 'plug-in-the-variables' software version or just the text you posted?
The software version I saw a month earlier is pretty neat, I hope it gets released soon. Maybe we're not talking about the same thing.
Paul
RE: Piping Stress Analysis
Paul contact Tony Paulin for additional Technical Information in regards to ASME B31.3 Piping Checklist build Date March 15th 2008.
Regards
Leonard Stephen Thill, Bombay India
RE: Piping Stress Analysis
no offense but its no more Bombay, it is Mumbai.
regards
Siddharth
These are my personal views/opinions and not of my employer's.
RE: Piping Stress Analysis
I'm having some trouble designing the steam pipe from the boiler to the turbine, on my college the subject about stress analysis of piping systems doesn't exist.
So i have read this and other posts looking for answers but so far no results.
I have the kellog book and the bentley autopipe software. I have some questions about them.
When i use the guided cantilever method on a simple L, i get some numbers different to those that the autopipe finds. I'm not using an elbow on the guided cantilever, but the results are somewhat 10 times as bigger than of autopipe.
Can some one tell me why?
Thanks to all.
José M. Roca
RE: Piping Stress Analysis
It sounds like you have some data wrong somewhere. Also it sounds like you are in-experienced in performing pipe stress analysis. I would suggest you contact a competent pipe stress engineer to analyse your line between the boiler and turbine so you do not end up damaging the turbine or boiler. These lines need to be analysed/designed correctly - not by a newcomer to the pipe stress field.
RE: Piping Stress Analysis
I'm totally in-experienced in this subject but i teach strenght of materialsat the state university, so i think that with some good reading i will be getting the basics pretty soon.
The other thing is that in my country (Uruguay) i don't recognize any specialized company or engineer on the subject.
Thank you very much.
RE: Piping Stress Analysis
I would suspect just as dsb, that there is an input or calculation error. You should not be getting answers with an order of magnitude difference. Autopipe has developed a pretty good reputation in accuracy of its results, so based on the evidence provided and without further details, we would have to conclude the possibility of an error in your calculations is, shall we say, slightly higher.
I would suggest you start a new thread and post a diagram of your piping configuration and both your hand calculations and computer analysis input data and results. And be sure to state the design code you are using. Than somebody might take the time to review them and suggest a meaningful answer to your question.
"If everything seems under control, you're just not moving fast enough."
- Mario Andretti- When asked about transient hydraulics
http://virtualpipeline.spaces.msn.com
RE: Piping Stress Analysis
I worked for Sargent & Lundy Engineers and Bechtel Corp., performing Nuclear and Fossil Power Plant Pipe Stress Analysis for 8+ years.
I switched my career to automotive component design/analysis in 1985. I am currently working for one of the Big 3 in Detroit. I plan to take an early retirement. I would like to get back in the Pipe Stress Analysis field.
While at Sargent & Lundy Engineers and Bechtel Corp., I used PIPSYS and ME101 programs to analyze Piping and determine support loads for thermal, deadweight, seismic and fluid dynamics conditions.
My questions are as follows.
Have the codes changed a lot in the last 24 years?
How do you combine stresses/loads from different static and dynamic events for piping qualification?
What else can I do to transition back into Power Plant field? Appreciate any help!
RE: Piping Stress Analysis
Have the codes changed a lot in the last 24 years?
Since 1984, I hope so.
The ASME B31 Piping Codes still incorporate a lot of what you remember but ASME B31.3, Process Piping has really taken the lead in changing things. Quite a lot of the piping being done now is Process Piping so if you can get into an ASME B31.3 seminar preferably one that has Glynn Woods or Ron Haupt as an instructor, you will pick that up quickly. Also read the books by Glynn Wood and Dr. Charles Becht IV.
How do you combine stresses/loads from different static and dynamic events for piping qualification?
Pretty much the way it was done in 1984. Stresses are still combined in accordance with Tresca failure theory with the exception of a minimum wall calculation that we put into the B31.3 High Pressure Chapter. The ASME Codes have you look at the primary stresses (stresses due to sustained pressure and weight) and compare them to the allowable stresses (as shown at temperature in Appendix A). You will find that we have now included an equation for calculating sustained stresses that we did not have in 1984. The secondary stress ranges (due to the displacement of thermal expansion/contraction and other cyclic loadings) are compared to a calculated allowable stress range in accordance with B31.3 - however NOW we consider values for "f" in that equation that are greater than 1.0 (low cycles in the life of the system).
Have a look at this:
h
What else can I do to transition back into Power Plant field?
Learn the software. You will find that the software has greatly improved and the Internet had provides a lot of discussion forums where you can go to learn the "tricks of the trade". The Internet is REALLY great for sharing the knowledge. Then of course you will have to know the ASME Codes for Pressure Piping and what changes have been incorporated since 1984. Not too bad as the basics still apply - Pi is still approximately 3.2415926 (give or take).
Appreciate any help!
You are welcome.
Regards, John
RE: Piping Stress Analysis
Pi has not change THAT much - it is approximately 3.1415927... and some change. Sorry 'bout the dyslexic fingers.
John