Base Metal Thickness versus Preheat

Date 11-19-2004 07:02

This is the case, I have a thickness range qualified 3/16" to 1-3/4" thick base metal and I have a test coupon 7/8" thick. I implement preheat and PWHT on my 7/8" thick test coupon as my basis so this is within the range of qualified thickness. Does this mean that 3/16" thick base metal qualifies the WPS with preheat and PWHT? I do know a certain limitation with implementing preheat and PWHT considering thickness and chemical composition but 3/16" thick is doubtful to me. Is it ok to apply preheat and PWHT on 3/16" thick base metal? if not then it requires requalification since my WPS has preheat and PWHT which are considered essential variables. Can you me help me clarify this. My test coupon is AISI 4130. Thanks.

By H. Chang (*)

Date 11-26-2004 07:07

Depended on which construction code is applied, if ASME Section IX is the one, then preheat decrease >100F, requalification is required. Changed of type of PWHT or no PWHT will also require new PQR. Our practice is to prepare two coupons, one with no preheat (as far as possible and permit by code) with PWHT; another one with preheat(or no preheat ) but without PWHT(if permit by code).
Kind regards
H.Chang