As you already know the construction codes (e.g. ASME I, ASME VIII) give a minimum PWHT temperature. While these Codes do not specify an upper limit, ASME Section IX, QW-407.1 tells you that a new PQR would be required if the PWHT temperature is above the lower critical temperature (TPWHT > A1 temperature). Thus any sub-critical PWHT qualifies a range from the Code minimum to the lower critical temperature. Some common sense should apply. The engineer must be aware of the change in properties that can occur as TPWHT approaches the lower critical temperature. Obviously, greater softening will occur but at the same time the tensile and yield strength will decrease and the ductile-to-brittle transition temperature (DBTT) will increase. Upper shelf energy also tends to drop.
Generally, this only becomes an issue when a transition joint between Cr-Mo and CS is required. The Cr-Mo side of the joint will drive the necessity for PWHT and the temperature range for PWHT. In my experience, the biggest challenge is selection of the proper filler metal especially if a complex assembly {with CS-CS welds as well as Cr-Mo} is PWHT’ed. Then selection of the carbon steel filler metal or filler metal/flux is crucial to maintaining minimum required properties in the CS-CS welds.
John A. Henning
Welding & Materials
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Tariq Hussain
Sent: Thursday, February 09, 2012 1:18 PM
To: materials-welding@googlegroups.com
Subject: [MW:13648] What is maximum limit for PWHT soaking temperature for P.No.1 Gr.1 & 2?
Dear Friends,
minimum PWHT Soaking temperature is given in ASME Sec VIII Div. 1 UCS-56, My question is What is maximum temperature that we can use for PWHT with reference to some applicable standards or metallurgical point of view point?
OR
Can we do PWHT for P.No.1 Gr.1 & 2 (e.g SA 516 Gr. 60 & 70) maximum up to lower critical temperature i.e. 723 Degree Centigrade?
Thanks in Advance for your valuable share.
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