PWHT of carbon steels greater than 3/4" thick is not always a requirement. MOST of the Boiler & Pressure Vessel Codes I deal with provide an exemption from PWHT provided a 200 degree F preheat is applied. As for structures, PWHT is non-mandatory for AWS work as far as I know, if I'm in error someone please slap some sense into me! Most often, PWHT for structures is a specification requirement rather than a Code requirement, at least in my experience. This may vary, of course depending on Code, one may find that ASME III, Sub. NF to be the exception. Ok, all from me!
Dear sir
You suppose that we want weld a pump casing with thickness over 3/4"
and c/s material.Is it nessesary PWHT or not?
please tell me your reference standard code.
best regards
Ali Sharif
In my experience, PWHT of low carbon steel for structural purposes is very seldom used. The only exceptions would be if the steel is to be machined after welding, or in rare cases to inprove the fatigue life.
I do not believe PWHT would be required per AWS D1.1
By -
Date 07-18-2003 04:44
PWHT is not required by AWS D1.1. The first sentence of paragraph 5.8 (2002 edition) states, "where required by the contract drawings or specifications, welded assemblies shall be stress relieved by heat treating".
Therefore for a structure built in accordance with D1.1, PWHT will be required only if stated in contract documents.
Mankenberg
Should PWHT be required by specs then Para. 3.14 states that it is prequalified provided it is approved by the Engineer and the conditions listed in 3.14 are met. Para. 5.8 gives guidance as to how to go about it and it also lists a number of types of steel that should NOT be PWHT.
All this is of course is Structural Code D1.1 and would apply to the structural steel itself, not the piping, valve bodies or pump casings.
John Wright
