Intermediate heat treatment in B31.1 2014

Date 02-10-2015 16:47

The first question that comes to mind is whether you are welding P5B or P5E base metal or not. If you are not, the requirement does not apply.

Best regards - Al

By Jovi Zhu (**)

Date 02-12-2015 14:20 Edited 02-13-2015 00:44

Toey,

What base metal(s) are you dealing with? I agree with Al that this requirement applies only to P5B and P15E.

If you are dealing with Gr.91 (P15E), one of the most widely used Creep Strength Enhanced Ferritic Steel (CSEF), I happen to have a hint to share here.

The following is quoted from a guideline for welding of CSEF;s:

Post Weld “Bake-Out”
A post weld “bake-out” may be of critical importance, especially for heavy sections or where
flux-type processes are used. This involves maintaining the preheat/interpass window for an
extended period of time subsequent to interruption or completion of the weld in order to facilitate
hydrogen diffusion from the weldment. Of the many variables involved when attempting to
establish the length of time necessary, are the thickness of the material, length of time the
weldment has been exposed to the heat regime and the extent of “low hydrogen” practices. If the
fabrication schedule requires the weldment to cool to room temperature prior to PWHT, a 4 hour
bake-out at the preheating temperature is a good starting point. Shorter times at higher
temperatures are also common; e.g. 15 minutes at 316C (600F). Where proper preheat,
consumables and storage/handling are implemented, bake-outs can be minimized or even
eliminated. However, maintaining preheat or use of a post bake can minimize the potential for
inadvertent contamination and reduce the risk of stress corrosion cracking (SCC).

With this clue I am inclined to believe that the B31.1 intermediate heat treatment = post weld "bake out".
B31.1 does not use the "bake out" or "post heat" probably because they are nonstandard terms. Let me know your thoughts.

Have a great day.

Jovi

By Toey TNDT (**)

Date 02-12-2015 22:48 Edited 02-12-2015 22:55

Thank for comment Joey & AI

Before i read B31.1 . I have read API 934 A Materials and Fabrication of
2 1/4Cr-1Mo .

API have Intermediate stress relief (ISR 593 ํC) & dehydrogenation heat treatment (DHT 300 ํ C) that in B31.3 doesn't state same API 934 A

B31.1 2014 title 131.6 Interruption of Welding , i assume that before complete welding may be same Intermediate stress relief (ISR 593 ํC)

and Then Post weld heat tretment 690 °C again

Thanks for advance comment

Regards ,

By Jovi Zhu (**)

Date 02-13-2015 05:28 Edited 02-13-2015 05:59

Toey,

Thanks for sharing the API RP. Good info. However, the API RP does not cover any P5B or P15E materials.

By Toey TNDT (**)

Date 02-13-2015 09:27

Yes , I checked Api 938-b about P91
Does't state about Intermediate Heat tretment .It just say Pre heat , Dehydroyen and Post weld Heat treatment and Interrupt welding not show intermediate heat tretment

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By js55

Date 02-13-2015 14:55

Not sure if the original question has been adequately addressed.
The intermediate heat treatment in the pressure piping codes does indeed pertain to post weld 'bake outs' with the intent of hydrogen evolution.
These requirements have a long history.

By 803056

Date 02-13-2015 15:22 Edited 02-13-2015 15:28

Be cautious about mixing apples and oranges. Terminology differs from one code to another and the philosophy differs as well. An attempt to use a different welding standards than that specified to justify a practice or deviation from a code requirement can create more problems than it solves.

Decisions about the need for PWHT, the method, and the specific procedures should be referred to the Engineer/design professional. Inspection personnel are responsible to ensure the design requirements, procedures, etc. are adhered to and followed as specified. When question arise, inspectors should defer to the engineer/design professional.

Best regards - Al