Use of Pipe Stress Isometrics

[pipesvessels1]

All,

Can someone let me know where and when pipe stress isometrics are used? I can understand the benefit of manufacturing Iso's or even the odd stress iso here and there. However, is there ever a need to produce the stress iso's for a whole package/project?

Cheers,

JohnOD

 

[BigInch]

If you do the stress runs, somebody has to do a diagram. Its virtually impossible to do a correct stress run without a diagram, so its either you or the stress engineer that will do it. Find out who costs more and let the most economical guy do it?

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pennpiper]

JohnOD,
Reguarding your question "is there ever a need to produce the stress iso's for a whole package/project?"
The simple and quick answer would be "No."
However there will always be the exception.

In the book "Piping Engineering Leadership for Process Plant Projects" (by James O. Pennock) there is "Chapter 10, Project Definition -- Scope of Work" This chapter defines the what and why of the process of writing a Project Definition and a definitive Scope of Work.

Each and every Engineering/Design group should prepare there own write-up for the project describing their understanding of what the project is and what it is going to take from their group to make the project a success.

The Scope of Work is made up of two parts. There is Part A which is the Scope of Facilities, and there is Part B which is the Scope of Services.
The Part A (for piping) should describe the number and types of units along with the general type of piping (i.e.: hot, cold, high pressure, low pressure, alloy, etc.). This part should be in as much detail as possible.
The Part B (for piping) should define what services will be provided and what the deliverables will be. The deliverables include both the external deliverables and the internal deliverables. Internal deliverables include stress sketches, normally preparred by the piping designer and then issued (internally) to the Stress Engineer for analysis.

The Stress Engineer is a part of the overall Piping Engineering and Design team on the project and as such did a complete review of the proposed project and has partisapated in the development of the Scope of Work. This review by the Stress Engineer, alone with input from the Client, Project Management, the Piping Department Management and the applicable Codes will identify the level formal stress action recommended for the project.

I could go on and on but thats enough for now.

 

[mizzoueng]

I know that you have to do it for chlorine piping. Even if you are just taking out a part of the line and adding in a regulator or replacing a part.

 

[BigInch]

I'd think that it goes without saying that a line not requiring stress analysis would not require a stress iso, however just might require a fabrication iso.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[pipesvessels1]

Thanks for your replies.

I'm not sure that stress iso's are as frequently used now as they once were. In today's world of interoperability between draughting/design software and pipe stressing software it can be possible to just send the text files.

I appreciate that there may not be a designer/draughter and a stresser within the one company and so it may be necessary to transfer the data in a suitable compact way (to a second or third party).

Cheers,

J O'D

 

[pipesvessels1]

Thanks for your replies.

I'm not sure that stress iso's are as frequently used now as they once were. In today's world of interoperability between draughting/design software and pipe stressing software it can be possible to just send the text files.

I appreciate that there may not be a designer/draughter and a stresser within the one company and so it may be necessary to transfer the data in a suitable compact way (to a second or third party).

Cheers,

JohnOD

 

[BigInch]

Text files are hard to read and convert into a mental graphic. If the text files can be read by the stress program which can plot the iso, there's no problem. I worked with some stress programs where they could not read the text syntax and wound up hand drawing the iso diagram myself. Maybe to be safe, you should verify compatibility.

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[JohnBreen]

Hello all,

I might add that MOST of the fabrication shops in North America would rather work from the isometric drawings than they would with Orthos.

As has already been said, for the stress analysis, isometrics are VERY beneficial. Most power plant piping will require that the isometrics be devaloped and included in the stress package. The iso's are also a very good way of communicating with the pipe support manufacturers the design of the support system. Many consulting companies will have the stress analysis node numbers added to the AutoCAD isometric drawings after the stress/hanger analyses are completed just so there will be no ambiguity regarding where the hangers are to be placed.

As a piping engineer who has been involved in pipe stress analysis since 1960 (when computer graphics were rare and expensive), I can say I would hate to have to work without a verified set of isometric drawings.

Regards, John.

 

[MJCronin]

JohnOD,

As an engineer that has performed stress analysis since the early 1970s, I belive that you should consider the stress isos as part of the calculation package, not as part of the installation package.

Stress Isometrics are absolutely necessary for:

- Establishing and understanding support locations and loads

- Understanding system expansion and vibration

- Understanding system loading of nozzles

- Determining the souce of overstress or high loadings in a system

Of course, an owner/fabricator/installer can accomplish thier function without a stress iso,....but let a support break, or a flange start leaking, and suddenly an urgent hunt will start for the stress calc, the (now ancient)analyst and the stress iso...

My opinion only..

-MJC

 

[RossABQ]

A picture is worth a thousand words (or pages and pages of incomprehenable Fx Fy Fz etc) and their creation is part of the programs I have used for the last 15 yrs. It isn't more work at all to produce and good programs even allow you to import the plant steel to coordinate support locations. They also export the Iso to a dxf that can be inserted in a CAD drawing for issue.

As far as having to "produce" them, for a client or contractor, as stated above it is part of the contract, or not. Certain of my Clients require it as a deliverable, not that they actually review it. They simply want a hard copy to archive.

I have also had projects where it was a deliverable to the Contractor. The iso's need a whole bunch of extra annotation to be useful to them. They expect it to be a support installation drawing, they don't care about loads.

 

[pipingdesigner]

Here is a rule of thumb regarding stress iso's that I picked up along the way ...


1. The 1500 rule (from David Diehl, COADE).
a. If the line size (nominal pipe size) times (x) the temperature (degrees F) is below 1500 then the line "may" not need formal stress analysis.
Example 3' (x) 400 degrees (F) = 1200

b. If the line size (nominal pipe size) times (x) the temperature (degrees F) is above1500 then the line "may" need formal stress analysis.
Example 4" (x) 400 degrees (F) = 1600

2. If the line (regardless of temperature) connects to a pump, a compressor or other alignment sensitive equipment then it should be submitted for formal sterss analysis.

3. The "May" noted above relates to the application of good judgement when considering other factors such as metalurgy and the wall thicknesses above schedule 80.




pipingdesigner

http://www.pipingdesigners.com

 

[MJCronin]

pipingdesigner,

Your "rule of 1500" seems to be very useful and applicable in almost all cases. However, it may ignore thin walled systems, which, in my opinion, can cause much more concern.

For example, I would have detailed analysis performed on a Schedule 5 or 10 - 12 inch NPS line at 300F. (stress intensification factors are very high for thin walled pipe) Whereas, your 4 inch NPS line at 400F probably will not be much of a problem..

By the way, is that some kind of a cult, hex or gang symbol at the end of your post ?

-MJC

 

[pipingdesigner]

MJC,

Note 3 in my post covers the wall thickness issue ... sort of!

3. The "May" noted above relates to the application of good judgement when considering other factors such as metalurgy and the wall thicknesses above schedule 80.

The symbol at the end of the post is the pipingdesigners.com logo ... I suppose it a kind of pipers gang symbol!


pipingdesigner

http://www.pipingdesigners.com