PWHT for API 650 nozzles

[tanaka]

As per API 650 requirements ,it is required to PWHT nozzles as the thickness of shell exceeds 1/2 inch and material group IV,my questions:

1) What is the idea behind prohibiting PWHT on tank after erection on tank?

2) Is it required to perform PWHT only in a furnace or we can perform it with PWHT machine in site before erection?

[M5416]

1. Except tank are small can be perform PWHT whole tank, otherwise local PWHT maybe deform the tank.
2. For API-650 nozzle to shell joint PWHT requirement, Vendor shall pre-fabrication this section, and doing PWHT, then erection at site before erection.
The method of PWHT not limited.