What is the criteria for PWHT as per ASME B31.3?

[swapnil gorantiwar]

Hello all,

What is the criteria for PWHT as per ASME B31.3?

 

One is thickness criteria i.e. Carbon steel to be PWHT for thk 20mm and higher or alloy steel 13mm and higher

 

What are the other criterias?

 

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Best Regards,

Swapnil Gorantiwar

 

[Ramin Kondori]

Dear swapnil:

In ASME B31.3 the requirement for PWHT is mainly to reduce welding residual stress and prevent cracking (even before service).

PWHT may be enforced for other reasons.

• In sour service piping, some specifications require PWHT for all welds. The reason is with reducing the weld residual stress, you will reduce the risk of corrosion especially where SCC is involved.
• Sometimes you need to reduce the hardness level and this will be achieved by PWHT (carbon steels etc.).
• It may be a part of low temperature requirements. LTCS piping welds shall be post-weld heat treated regardless of thickness otherwise HAZ toughness will not meet the minimum requirements.
• Sometimes you need to apply PWHT to complete production process for precipitation hardening materials which need some kind of tempering or aging to reach their full potentials.

The list can be a long list but above mentioned examples will cover many applications.

Regards

Ramin Kondori

Sr. QA/QC Engineer

SINOPEC

r.ko...@petroyada.com
+98-2123592322
+98-9132150320

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[Octane Mac]

ASME B31.3 has the following major factors to recommend PWHT:

- Thickness

- Alloy chemistry yielding in higher carbon equivalent (hardenability)

- Tensile strength

Octane