Piping stress

Unless you are working on a Nuclear Power Plant you do not need to do Stress Analysis on all the lines on the project.
1. You need to understand the Clients criteria for the project. What is the Design Code (ASME B31.1, ASME B31.3, etc) for the project and what does that Code say about Stress Analysis.

2. You need to understand your Company's thinking and requirements for Pipe Stress Analysis.

3. You need to understand the Scope of the project as it related to Pipe Stress Analysis. This means the total number of lines and a breakdown of the quantities by Operating Temperature, Operating Pressure, Material and Size grouping.

4. Next you need to document for the project which categories of lines require what type of attention by the Stress Engineer. To help with this I offer the following:

Pipe Stress Criteria
The question:
What are the criteria for which lines need formal stress calculation?”

My answer:
You will get lots of opinions on this one. Here is what I use and teach.

- “The 1500 rule”
(from David Diehl, COADE)
a. If the line size (nominal pipe size) times (x) the temperature (degrees F) are 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) are above1500 then the line "may" need formal stress analysis.
Example 4" (x) 400 degrees (F) = 1600

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

- The "May" noted above relates to the application of good judgment when considering other factors such as metallurgy and the wall thicknesses above schedule 80.




5. You need to clearly understand the different levels of Pipe Stress Analysis that exist. Flexibility Analysis will come in a number of forms and should considered depending on the specific situations.
Forms:
- Visual Review
- Informal Calculations
- Formal Analysis for excessive stress caused by common factors (Temperature induced expansion, Dead/Live Loads)
- Special Analysis (i.e.: Analog studies for reciprocating compressors, seismic studies, Sea-Force studies for Offshore Platforms)

6. Then you need to look at the the pipe line categories for your project and consider all the previous steps along with any possible exceptions. Many engineering companies may set some minimum analysis criteria on a project by project basis but there is always the exception for even "That" project.
Exceptions may include:
- Very large diameter pipe
- Very heavy wall pipe
- Very thin wall pipe
- Exotic Alloy Pipe
- Attachment to strain sensitive equipment (Pumps, Glass lined vessels, etc.)
- Extremely low temperature (Cryogenic) systems
- Any pipe installed in Arctic locations
- All other lines below the stated minimum level on a job installed in a place like Oman or Kuwait

Even if the Code makes a recommendation on this subject each Piping Engineering Lead and the assigned Pipe Stress Engineer are responsible for the proper engineering and design of the project.

7. Now establish a "Pipe Stress Log" (Excel Spread Sheet) listing of all the lines you plan to "Look" at. The spread sheet should have the ability to identify, track and status each line as they travel through the Stress analysis process:

Line Number
Sheet Number
Material
Operating Temp
Operating Pressure
Stress Check Category (Visual, Informal, Formal, Special)
Date submitted
Date Returned
Status (Approved, Revise & Resubmit, Other)
Date resubmitted
Status
Final Sign-Off

8. Now you need to count the number of lines (by the type of handling) on the Pipe Stress Log and look at a realistic number of hours it will take for each type of handling. Then you need to look at the Project Schedule and see when your actual Pipe Stress work will start and when you must be done. How many hours are there? How many people will you have (just yourself or some help?) What other duties (that require hours) will you be involved in? Just for discussion here are some "Other" activities that might eat up your hours.

Attend meetings
Visit the jobsite
Write a Specification (Expansion Joint, Constant Support Spring Hanger, etc>)
Interface with the Structural Group
Interface with the Pump Engineer
Recycle of completed work (Design changes or late Client changes)
Get sick and miss a few days of work

This is just a start and it does not address the actual technical aspects of Pipe Stress Analysis.

Please ask questions and let others here help you.

Ali,
Please E-mail me:
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I have some things that may be of help

Jop