Exemptions to Mandatory PWHT ASME B31.3 ed 2014

[ASL92]

Hi all, I've just get the latest edition of ASME B31.3 2014 edition.

Referring to PWHT scope, I found a big difference from previous edition (2012 edition) which said an exact number of temperature for thicker material (over 20 mm).

Instead at latest edition, there're an exemptions to mandatory of PWHT (table 331.1.3) which in my opinion is we can prevent to use PWHT if some additional requirements is fulfilled (ex. for P-1 all groups, we can apply high preheat and do multiple layers for exemption from PWHT)

My question is, if we work with thicker goods let say 22 mm or above. Can we substitute the use of PWHT with only high preheat temp? I think these two treatment is for different use. How can we get a stress relief with only using a high preheat temp?

Thanks in advance.

 

[metengr]

The changes to Table 331.3 in B31.3 (2014 Edition) were similar to changes in ASME B31.1 (2014 Edition) to sync up both preheat and post weld heat treatment requirements and exemptions for an eventual new ASME B31 Standard on Preheat and Post Weld Heat Treatment.

The exemptions for PWHT for P-No 1 base materials are now specifically listed and must be followed if no PWHT is performed. For example, a preheat of 200 deg F (95 deg C) is required for base material with a control thickness greater than 1 in (25mm) is necessary to exempt PWHT.

PWHT is not required for all thicknesses and weld types for P-No 1 base material, provided all applicable Notes are followed in the Table.