Can Post weld heat treatment be replaced by Preheating

[Hosseinelahi]

One of our contractors claims that the PWHT could be replaced by preheat; I want to know if this is correct. Is there any standard for confirming this claim.

 

[metengr]

There is a standard to allow for this. However, it is based on certain limitations - carbon steel with a maximum of 0.35% carbon content by mass, preheat must be a minimum of 300 deg F. It is permitted for repair only and not to be used for fabrication.

This information can be found in the National Board Inspection Code (NB-23) which is an international in-service inspection, repair and alteration standard for pressure retaining items.

 

[gtaw]

I guess I would have to ask what is the applicable fabrication standard?

Just because one standard permits a particular practice does not mean it can be applied to a different standard or all standards.

Best regards - Al

 

[metengr]

Repair standards are not fabrication standards.

 

[weldstan]

Hosseinelahi,
It could be used but you need to be more specific. What is construction Code? What is the service (stress corrosion cracking)? What is the material? In addition to the NBIC repair standards, ASME VIII permits the application of a 200F preheat to eliminate PWHT when 1 1/4" < T < or = 1 1/2".