PWHT ASME B31.1

[fazel1]

Cooling rate in ASME B31.1 shall not exceed 335 centigrae degree per hour divided by 1/2 the maximum thickness of material in inches at the weld , but in no case shall the rate exceed 335 centigrade degree per hr. This means that all the materials which their thickness is less than 2 inches shall have the maximum cooling rate of 335centigrade degree per hr.when we compare this to ASME Sec VIII cooling rate formula, there is a clear difference . why does this difference exist?

 

[VeryPicky]

When you compare PWHT requirements of ASME B31.1 and, on the other hand ASME BPVC Section VIII and even ASME B31.3, you will see a diference in philosophies.
I don't know why such a difference, one could say that what is good for the goose etc.

The trick is to use the proper requirements with a proper code. Don't mix the codes. If you have owner/user experience with one or another set of PWHT requirements, you could impose the prefered ones by including them in the User Spec. Be careful to ensure that they are more stringent than the Code, which is in most legislatures a law.

Putting Human Factor Back in Engineering

 

[metengr]

The reason for the differences is experience and conservatism by the Codes and Standards committees. There is no right or wrong method when dealing with perceived overlap between various Codes and Standards. Most of the PWHT requirements in either ASME B&PV Code or in ASME Piping Codes were developed based on past experience, (no harm to personnel or equipment). Piping is more of a safety concern because it is external to the boiler, as one example of conservatism.