ASME Sec Viii Div 1 UCS-56 calls for PWHT at min. 650 deg C for P No 4, Class 1/2, if thickness
is above 16mm (refer Note 2).
As reported by you, PQR mention PWHT of 300 Deg C which is not code complaint of base metal
thickness is above 16mm.
PWHT requirements are generally 1,150 to 1,400 F (621 to 760 C) for one hour. PWHT helps rid
the weld of hydrogen that may have been picked up from the filler metal, the base metal, or the
atmosphere and can help minimize the chances of cracking. Most low-alloy filler metals designed
for chrome-moly applications also come with recommended stress-relieving temperatures and
durations, either on the package label or on the included specification sheet.
Does your application require Impact testing? if yes then I suggest plates must be ordered with
Quench and Temper Heat Treatment, Extended time at PWHT has detrimental effect on impact values
therefore Plates must be ordered with expected PWHT cycles (min 2, accounting PWHT repair),
Usually client specification would entail these requirements.
Please refer ASME Sec ix QW-407 for P no. 4, if you qualify PQR with PWHT @300 Deg C, then
production welding must not exceed lower transformation temperature and also QW-407.2 for PWHT repairs.
ASTM A387 implies that Tempering temperature shall be min.620 deg C, whatever it is but make
sure "Tempering Temperature is 30 deg C above PWHT Temperature".
Please notify if above does not make sense to you.
Regards
Manpreet Singh
On Tue, 07 Feb 2012 07:09:08 +0530 wrote
>Dear All,
Regarding post heat treatment(DHT) for SA 387 GR 12 CL2 Low alloy steel material,
I have PQR'S with post heating a temperature of 300 Degree C for 2 Hrs,
My question are,
1) Is it possible to make WPS (production weld) without post heating(DHT)?
2) Is it any code(ASME SEC VIII or IX) call for DHT after welding?
3) Why we have to do DHT, if it is required?
4) Is it any where mentioned that the SA 387 GR 12 CL2 material is required post heating(DHT)?
we are doing DHT because avoid cold cracking(Hydrogen cracking) in weld and HAZ . any other
major reason to carry out DHT for low alloy steel.
Kindly provide your valuable guidance/ advice/ experiance on this subject.
Regards
Vijay Katkar
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