I referred API-1104-2006 edition for your query. Parallel to API-1104, ASME also has a code on transmission pipelines for hydrocarbons (ASME B-31.4). Both of these codes specifies that preheating, interpass temperature control, PHWT as mandatory requirements for field and shop welds, however the extent of preheating and PWHT (including time and temperature) is left up to the fabricator.
In absence of the same follwing one of the requirements. B-31.1 or ASME –Sec-VIII-DIV-1, as you have listed below would be appropriate to follow. Preheating requirements are same for both the codes however ASME B-31.3(Table-331.1.1) is more specific on PWHT time and temperature and additionally hardness requirements for welds/HAZ are specified, which helps to control environmental assisted cracking, e.g SCC and others.
As regarding PWHT, one has to ensure that PWHT temperature should not be more than the tempering temperature of the pipes., or else the tensile stress will fall after welding and PWHT.
Hope this would help you.
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From: email@example.com [mailto:firstname.lastname@example.org] On Behalf Of ASIF
Sent: Wednesday, January 13, 2010 9:36 AM
Subject: [Norton AntiSpam] [MW:4042] Preheat & PWHT values as per API 1104
how to determine the values of Preheat or PWHT for Cross Country Pipeline Welding (As per API 1104)
Like we refer 330 & 331 tables of ASME B3.3 for process piping
& Non-mandatory Appendix R & UCS-56 of ASME SECVIII div 1 for PV
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