Pipe Stress Analysis Steps 5

[aprincezk]

I am a mechanical engineer and have been put on a project in which I am acting as a piping engineer. I am to design the piping and layout (including supports) and complete a stress analysis on the layout for a high pressure, high temperature compressor testing facility as per B31.3.
I am currently using TRIFlex software for my stress analysis; however, I am worried that I am skipping a few imperative steps in the stress analysis process.
A) Can anyone suggest a good text material that outlines piping stress analysis process?
B) What are some key "rules-of-thumb" to follow when performing a piping stress analysis? I am thinking along the lines of % allowable expansion stress to shoot for, maximum allowable deflection/rotation of pipe compared to Nominal Diameter, typical forces and moments.
Thanks!

 

[Zapster]

What are some key "rules-of-thumb" to follow when performing a piping stress analysis?

The number one rule of thumb for a B31.3 piping job is to realize that the code is not a design guide and that the code is not a substitute for experience. If this piping system is to be designed to code the following is required of the designer:

(a) Completion of an engineering degree, requiring four or more years of full-time study, plus a minimum of 5 years experience in the design of related pressure piping.
(b) Professional Engineering registration, recognized by the local jurisdiction, and experience in the design of related pressure piping.
(c) Completion of an engineering associate’s degree, requiring at least 2 years of full-time study, plus a minimum of 10 years experience in the design of related pressure piping.
(d) Fifteen years experience in the design of related pressure piping. Experience in the design of related pressure piping is satisfied by piping design experience that includes design calculations for pressure, sustained and occasional loads, and piping flexibility.

By the nature of your question I doubt that you have the above education/experience. If you have a mentor that meets the requirements above, you should be asking him/her these questions. If you lack experience and don’t have an experienced mentor with the above experience and your employer is requesting that you proceed with this design, by B31.3 definition, the design will not be B31.3 compliant unless you specifically get authorization from the owner to continue with the design without the minimum qualifications as stated in B31.3. With the litigious environment that we live in, I doubt that the owner of the project would accept a designer that did not meet the minimum B31.3 requirements.

 

[BigInch]

Totally. Get all the above.

In the meantime you can take an introductory free pipe stress course here,

http://www.sstusa.com

BigInch-born in the trenches.

http://virtualpipeline.spaces.msn.com

 

[Zapster]

Oops. I meant one of following: a, b ,c, or d in my previous post.

 

[pennpiper]

aprincezk,
You wrote:
I am a mechanical engineer and have been put on a project in which I am acting as a piping engineer. I am to design the piping and layout (including supports) and complete a stress analysis on the layout for a high pressure, high temperature compressor testing facility as per B31.3.

In my piping history, includung over 45 years of training and experiance:
The Piping Designer designed the complete piping system including the flexibility and all supports.
The Stress Engineer acted as a consultant to the designer as required as the system was being designed and then checked the complete system.
If you design the system then you cannot check your own work.
Something to consider.

 

[aprincezk]

Thank you for the replies. Obviously, my point was missed. Following appropriate practice, I will not be checking my own work -- a registered PE will be checking and verifying soundness of engineering and design. I plan to take a pipe stres course ASAP, however in the mean time there is still work to be done. I have turned to the experienced professionals on this site in hopes of receiving valuable mentoring, not to tell me I am not experienced enough. We all must gain experience somewhere and thanks to my company and current projects, i am doing just that.
Can anyone suggest any books that are good for process piping analysis? Perhaps share some key things to watch for that you have learned through your experience?
THANKS!

 

[Zapster]

I am acting as a piping engineer… I am worried that I am skipping a few imperative steps in the stress analysis process.

aprincezk, I do not believe that there was a misunderstanding of your statement. Quoted directly from B31.3, “The Designer is the person(s) in charge of the engineering design of a piping system and shall be experienced in the use of this Code.” Then B31.3 goes on to specifically state what qualifications need to be met in order to make a B31.3 design. Those qualifications are in my first post as (a), (b), (c), and (d).

I will not be checking my own work -- a registered PE will be checking and verifying soundness of engineering and design.

Is the registered PE in charge of the engineering design or will he be just checking your design? The red flag that was of concern is, “I am worried.” If it is the registered PE that is the person that is in charge of the engineering design, why isn’t he/she the first person you would ask about the “imperative steps?” And if you asked the PE, why are you still worried that you skipped a few imperative steps?

Best reference would be:

Process Piping, The complete Guide to ASME B31.3, by Charles Becht IV

Another helpful reference:

CASTI Guidebook to ASME B31.3, Process Piping, by Glynn E. Woods & Roy B. Baguley

 

[ApC2Kp]

aprincezk,
The specification of piping components and the design of a piping system geometry with its supports can be accomplished and confirmed to be Code compliant, which is a basic requirement. Your task of providing a piping system to test high pressure, high temperature compressors is a couple of levels above basic analysis. The compressors are probably reciprocating units. There are usually very limited allowable loads on such compressor units. Inlet and outlet pulsation bottles are designed with the compressor and piping to deal with the flow dynamics. It is a design problem in which you need to take advantage of experience of designers and also study previous installations of similar compressors. Be careful of what sounds like an easy answer, or 'rules of thumb", like suggestions to put a flexible expansion joint at equipment connection to isolate piping loads from compressor.
One suggestion for routing the piping and locating the piping retraints : The compressor would have 2 neutral axis for thermal growth that usually are 1) shaft centerline, and 2)anchored end. The piping thermal expansion loads can be minimized by routing the piping to cross over each of the neutral axis lines, and place a piping restraint at each nuetral axis line (axial line stop restraint). The compressor thermal growth is then matched by corresponding piping thermal growth. Spring hanger supports would be used to compensate for vertical thermal growth of the compressor unit. The placement of the spring hangers would be best if the centroid of the spring hangers is close to the location of the piping connection to equipment.

 

[JohnBreen]

Hi aprincezk,

I would urge you to get a copy of the ASME published book by Dr. Charles Becht IV. Dr. Becht includes checklists of the sort that you are trying to find. However, just reading the books will not substitute for years of experience and formal engineering in piping engineering.

Piping engineering is a specialty field within mechanical engineering and as such there is much to learn before the required level of competence is attained. You may find my posting on the COADE Caesar II board of some use:

http://www.coade.com/ubbthreads/ubb...Words=John+Breen&topic=0&Search=true#Post5702

Regards, John.

 

[aprincezk]

Thank you for the helpful responses and reference book suggestions.
Any other tips, experiences or references would be greatly appreciated!
Thanks!