How to determine pipe need to stress

<...a pipeline that need to be stress...> Eh?

Er, "pre-stressing" is a technique used to make concrete that will withstand tension. It is also used on continuously-welded railway lines while being laid to make sure that thermal expansion forces are contained without the track buckling. So need is not what this post is about.

The stress in an empty pipe lying on its side is practically negligible. The stress in a pipeline is a function of the pressure difference between the fluid inside it and the fluid without. It responds nicely to a bit of basic mechanical calculation using the wall thickness and the strength of the materials-of-construction. Traditional analysis involves taking a theoretical slice lengthways along the pipe across the diameter and doing a force balance between the pressure forces and the tensile forces in the pipe walls at the edge of the slice.

Does that help?

Hello Chem, There are a number of us out here in Engineering CyberSpace who are salivating and chomping at the proverbial bit, trying to lend some assitance to you. Alas, our intentions are severely frustrated because we have absolutely no clue as to what you are asking! If you'd like our help, could you please re-phrase your question?

hi,

Sorry that my question can't be understand. Actually what i'm asking is exactly like PennPiper wrote;

What is the criteria for sending piping lines or systems to a stress engineer for stress analysis?

Which lines need stress analysis and which lines do not?

Thanks.

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.

1. "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

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 stress analysis.

3. 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.

Here is my answer to a related question.

Pipe Stress Criteria #2 (Revision #20)

The question:

What is the minimum recommended temperature or temperature range for which flexibility analysis should be done per ASME B31.3?

My answer:

I do not have a copy ASME B31.3 (Old or current 2009) so I can't cite any specifics therein. However I would be surprised if B31.3 would give a minimum temperature for the requirement of flexibility analysis. There are just too many variables.

Flexibility Analysis might come in a number of forms and should consider many 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)

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 Lead and the assigned Pipe Stress Engineer are responsible for the proper engineering and design of the project.