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B31.3 'Stress Relief' of process piping

B31.3 'Stress Relief' of process piping

B31.3 'Stress Relief' of process piping

Could someone with some experience in stress relieving carbon steel process piping give me some insight on the B31.3 code requirements for this process?  Our customer's PID declares a number of pipe weldments to be stress relieved, but that's the only information they give.  They have not specified any particular temperature, hold times, or processing requirements.  All of the piping is to be done to B31.3.

In the mean time...I'll have my nose in the code.  If I'm not back in 15 minutes, please notify my next of kin...

Fitter, happier, more productive

RE: B31.3 'Stress Relief' of process piping

PWHT is required for P-No1 materials exceeding 3/4 -inch thick. PWHT between 1100F to 1200 F at 1hr/in.. See Table 331.1.1.

RE: B31.3 'Stress Relief' of process piping

stanweld...thanks for the speedy reply...

to amend your reply with what i assume is an appropriate disclosure: 'unless specified by the customer'.

with the criteria spelled out in B31.3, i wonder why this customer is requiring this?  we're talking about 150# class lines with sch 40 wall thickness carrying fluid not in excess of 500°F.  Could this be a CYA thing?  The runs aren't particularly long either...<40ft.

Fitter, happier, more productive

RE: B31.3 'Stress Relief' of process piping

The Owner is responsible for added stress relief for corrosion and cyclic service. It may well be that the line is subject to a stress corrosion cracking environment.   

RE: B31.3 'Stress Relief' of process piping


Although the code of construction (B31.x or VIII-x etc) may not explicitly require PWHT for a given design, most of them do require that the designer/owners engineer consider the situation as a whole, including the service application. It is not at all unusual to specify PWHT for a system which is in caustic, sour, or otherwise in some "metallurgically unfriendly" service based on good engineering judgment and lessons learned (by the process industry as a whole) from experience.

In the case of B31.3, there are at least a couple of references to this:

From the Introduction: The owner is also responsible for imposing requirements supplementary to those of the Code if necessary to assure safe piping for the proposed installation.

From 300(c)(5): The engineering design shall specify any unusual requirements for a particular service. Where service requirements necessitate measures beyond those required by this Code, such measures shall be specified by the engineering design. Where so specified, the Code requires that they be accomplished.


RE: B31.3 'Stress Relief' of process piping

I agree with jte....

But not for the Code references he cites (they are way too damn vague)

Caustic service is an example of a process system where stress relief has been recommended and used for many years.

See Table 1 of this reference:


Also Figure 7 of this fine text:


Hydrofluric acid service (as a recall) might be another candidate (!!??)

Anyone care to repond ?




RE: B31.3 'Stress Relief' of process piping

More stuff........

The Iranians/Shell oil require stress relief on carbon steel pipe bends that fail a paricular hardness limitation.

See section 2.3.2 of this document:


I do not know if this requirement is from ASME B31.3 or it is understood as "good engineering practice"

It has long been my experience that the Shell Oil standards are industry state of the art



RE: B31.3 'Stress Relief' of process piping

See nace rp-472 and Nace rp-403

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