Hi,

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

Regards,
Waqas

I do not have a copy ASME B31.3 (Old or current) 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 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.

The code does offer guidance on when formal analysis is required. In ASME B31.3 article 319.4.1 they list when formal analysis is not required such as when the piping system duplicates or replaces without significant change, a system operating with a successful record or can be readily be judged by comparison with a previously analyzed system. A third way gives a formula for a two anchor system which I rarely used in my 40 years experience.
I have worked on projects where complicated charts are used to determine if formal analysis is required. They are typically based on multiple factors such as pipe diameter, temperature, pressure, material or critical equipment attached to the pipe. But in the end the engineer and owner still hold primary responsibility for designing safe piping systems. (ASME B31.3 300 (3), the "Owner" has overall responsibility for compliance with the "Code")

I agree with Bob that B31.3 does provide guidance on Formal Stress Analysis criteria but it stops short of specifying what should be the temperature or size where a formal analysis is required. So the minimum temperature as covered by B31.3 is as per Table A-1 which is the minimum temperature for the material. However for analysis below 29 deg C the analysis is in cryogenic zone that requires special considerations. Normally the allowable stress range is reduced to 50% of that calculated in B31.3 to ensure that there is no chance of brittle fracture in the welds on the first cool down to the sub-zero temperature.
So in short the answer is no.