Calculate Stress and Reinforcement of Pipe Flanges? 1

[Bonfouca]

I have been asked to calculate the stress on a pipe flange to determine if any reinforcement is required and if so what it would be. The pipe is 20" OD x .500" wall with the grade to be selected between A-53 gd B or API-5LX-42. The flanges already specified are ANSI Class 300lb slip on flanges. The test pressure of this water line in the mountains is 474 psi.
I am an estimator/project manager in the steel and pipe fabrication industry and the engineer (owner's representative) requests that I submit stress calculations regarding the above for his review. Does anyone out have the formula so I can get this done? This is the first time I have been asked to calculate stress on a flange. I would do this for no other reason than to aquire this knowledge about flanges but I really feel the responsibility for this design aspect should fall on the engineer that design the project. Am I correct? Assistance will be greatly appreciated.

John

 

[JohnBreen]

Hello,

You are being asked act as a mechanical engineer. It may be unlawful for you to take the responsibility for calculating anything having to do with piping design and analysis. You should (depending upon the jurisdiction in which the work is to be installed) ask the state or province authorities (e.g., chief boiler and pressure vessel inspector) about this issue.

To answer your question, find a copy of Bonney Forge Bulletin 502 (search the archive of this board). Also, look in the ASME Boiler and Pressure Vessel Code. The work that you are undertaking should be done only by an engineer experienced with the ASME Code.

Don't sign your name to any calculations and make it clear in the documentation that you are not an engineer.

Failing all of that, tell them "no".

Regards, John.

 

[Bonfouca]

Thank you for your reply. I appreciate your concern for keeping people out of trouble. I often get involved with performing design calculation regarding structures, machinery, crane rigging and some piping.

I always put a disclaimer on my drawings of designs stating that the drawing and or calculations have not been performed by or reviewed by a professional engineer and that I am not an engineer. I even include an area on my drawings for the engineer to approve of my drawings if they are consistent with good enginnering practice. Sometimes I design projects and have my worked reviewed, revised if needed and "stamped" by a P.E. that we hire as a consultant. I did this for some custom spreader bars for a crane. Other times I am asked to submit design details on fabrication projects which are reviewed by the owner's engineer.

Based on the conditions above, I believe it is reasonable to assume that responsiblity for a failure of one of my designs would rest with the professional engineer that reviewed and "stamped" the design. I would feel any law that resticted my actions in these conditions would be "unjust" because my design is only I feel that I am acting in an "engineering assistant" capacity. Would you agree?

I agree that I should tell them no with respect to the flange design. The specifications do not place that responsibility on the fabricator. I'll point that out. I'll probably do the calculations on my own to gain that knowledge and to better understand flanged connections.

 

[JStephen]

You may be contractually liable to furnish design work that you personally can't or shouldn't do. So don't assume that the owner's consultant requiring "you" to furnish these calculations means that you personally should do them. It's quite common for consultants to require that, say, "trench safety" be PE designed, and it is not usually their expectation that the contractor will be that PE. Requirements of this sort should be spelled out in the specifications, rather than an off-the-cuff requirement.

Putting a disclaimer on drawings or calculations saying they were not done by an engineer doesn't really help. The problem is, state laws regulate what work requires licensure for you to do, and a disclaimer won't get you around that. It's like doing surgury and giving a disclaimer that you aren't a doctor. If you're practicing engineering without a license, a disclaimer doesn't change that fact.

State laws vary as to whether "shop drawings" are required to be PE sealed. In some cases, when being submitted to a PE for review, that PE is assumed to be the responsible engineer. Check your state laws on the issue. Of course, that consultant can still require a PE seal on work done by others if so desired.

On the issue of review by a PE, that is a gray area. Many states, perhaps most, specifically prohibit a PE from reviewing and sealing work that was not done under their dirct supervision. I seem to recall that Utah specifically allows work to be reviewed and sealed in this manner, so laws do vary. Anyway, check your state engineering regulations, which should be available online. And as a practical matter, check with the PE in question before you do anything, rather than after it's done.

 

[Bonfouca]

Thanks JStephen for your input. I will look into the state laws. It is interesting that not a single engineer that I have submitted my drawings/designs to has ever brought this up to me! My designs have been submitted in several states.
I have a hypothetical situation and I would appreciate your feedback.
Independent inventor that is not an engineer designs a revolutionary heavy-lift offshore crane that is safe and effective and costs 1/2 to build and operate when compared to current technolgy. He performs a series of calculations and builds a small prototype to test his theories. After successful testing, securing a patent and before any "real world" use of the system he secures the services of an engineering firm to evaluate the crane and revise the design to bring it into conformace with ANSI lifting standards. Would you think the inventor is violating the law in some states by practicing engineering?

 

[JStephen]

Generally not. But once again, the answer is in the engineering laws of the states. In Texas law, I find:

§ 1001.057. Employee of Private Corporation or Business Entity
(a) This chapter shall not be construed to apply to the activities of a private corporation or other business entity, or the activities of the full-time employees or other personnel under the direct supervision and control of the business entity, on or in connection with:
(2) activities related only to the research, development, design, fabrication, production, assembly, integration, or service of products manufactured by the entity.

 

[Cockroach]

Wow, this is absolutely scary!

You are absolutely right, Bonfuca, the responsibility is not yours but that of the designer. Assuming you are in the United States, I would be making a phone call to the State Board.

JStephen provided you an accurate answer that your employer should be given. Perhaps he should be read this!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Bonfouca]

Cockroach, thanks for your words. I am in the States and will look further into the matter. I don't understand why a designer would leave crucial elements out of the construction plans for piping and civil projects and shift that burden to the contractor/fabricator. The designer of these types of projects is always an engineering firm! I have had to do lots of independent research over the years to teach myself about steel properties and stresses just to be able fill in the blanks! Not bad for having an Economics degree! Please keep in mind that I am not discussing design/build projects. Some plans and specs that I see have verbage similiar to "fabricate and reinforce mitered bends and pipe intersections as per ASME code". Heck you nearly have to be a mechanical engineer to know what parts you are bidding on will be! A mechanical engineer should be able to easily specify the required thicknesses and other required information and add this to the plans. I can understand having the contractor "field engineer" minor and non-critical parts of the project to make things fit but leaving pressure and stress calculations relating to the "heart" of the project seems to defy logic.
I feel that this creates more work for the engineering firm in the long run instead of simplifying the design work. Instead of detailing parts that require engineering before the bid, the contractor must submit his own stress calculations and or shop drawings which may be reviewed and rejected a couple of times before the design is finalized. On a few occasions I have been involved with projects that condions changed in the field and I have designed some alternative piping and items that I furnished to the project owner's engineer for approval. I supplied my own drawings and stress calculations that were approved by the project engineer. In this case I think it is fine because no one foresaw the changing the conditions and we were able to keep things on track.

 

[TBP]

I see a LOT of sloppy engineering that involves pressure piping. Some is downright incompetent, like the one "design" that wanted to save money by reducing a steam safety valve discharge line from 6" to 3" so it would go through an existing wall penetration. I have no formal training in piping design - I taught myself after being left in numerous, ongoing situations like yours, Bonfouca. In the Land Of The Blind, the one-eyed man is king.

To a great extent, the root cause are the plant owners who simply don't want to pay for ... anything. Low bid engineering, low bid equipment & material, and low bid contractor. Plus they want it completed yesterday, so the MBA's can start harvesting the "payback". Commissioning? What's that?

 

[moltenmetal]

Who are you kidding, TBP? In the land of the blind, the one-eyed man is put in the insane asylum because he "sees things" that the others don't!

Same goes for engineers sometimes...

 

[TBP]

The squeaky wheel gets...shown the door. Sadly, it's true much more often than a lot of people would like to think.

 

[Bonfouca]

I just squeaked the wheel a little more and am curious to the response that I'll get from the "designer". I put together a package of submittals including welder quals, material specs and wrote a memo that included the following:

"Stress calculations and design of the flange weld joints and reinforcement of the pipe flange weld joints involves the “practice of engineering” which is beyond the scope of the fabricator/supplier."

Maybe I am the blind one...but I am getting tired of doing free "non-professional" engineering just to be able to build a job! Heck, public defenselawyers should get in on that gig...collect the same fees from the state and tell the defendant to research the law for themselves and prepare their own defense and only then will the lawyer look at the facts and arguments of the case and offer any advice!
Isn't this why the division of labor developed?