Dear Mr.Bazrafshan, There may be two reasons why your weld would have cracked. First it can be weld solidification cracking. what is the orientation of the crack? is it a longitudinal centerline crack, running along the weld or is it transverse? If you find a longitudinal crack running along the weld centre line, then it shoudl be weld solification crackng, Please find attached suutala diagram for predicting weld solidification cracking from weld metal composition, you need to calculate the Cr and Ni equivalents and also P + S content of the weld metal. You also need to check the ferrite content of the weld metal using magnegage or ferrite scope adjacent to the crack, you'll need a flat surface for you probe to sit on it. If cracking is visible on the joint, I think that shoudl be on your SMAW weld.Too low ferrite can do the damage. You stabilizing heat treatment would have opened up the crack making it more visible. Try LPT on one of the as welded joints before heat treatment for screening any cracks. I will recommed you to make a weld pad for both your GTAW and SMAW welding consumables and do the chemical analysis of the undiluted weld metal. You can also check the WRC 1988 or 1992 diagram to understand expected ferrite content and the solidfication mode of your weld metal, if you solification is fully austentic or austenite + ferrite (AF) mode then chances of a solification cracking is very high. if it is FA mode then it cna be ruled out. Second reason may be you would not have maintained cleanliness of the joint and consumables because oil / grease can introduce P & S into your weld metal and give rise to solidification craking. Try depositing a convex weld, which is better than a concave weld in these kind of situations. Hope this helps. Regards, A.Praveen Senior Welding Engineer Muscat
--- On Fri, 1/7/11, pgoswami <pgoswami@quickclic.net> wrote:
From: pgoswami <pgoswami@quickclic.net>
Subject: [MW:9120] MW:9116-PWHT Of 347H
To: materials-welding@googlegroups.com
Date: Friday, January 7, 2011, 9:09 AM
Mr Bazrafshan, The recommended PWHT cycle looks like a stabilizing anneal.You may check the precise requirements of this type of PWHT in NACE RP-170-2004.The PWHT time looks extremely high ( 3 hrs for a thickness of 12.7mm/6.0 mm).Prolonged exposure at this temperature would be detrimental to toughness of the weld. Also Nb:C ratio is very important to prevent hot cracking or stress-relief cracking of 347H. Feel free to exchange information, should you wish. Thanks. Pradip Goswami,P.Eng. Welding & Metallurgical Specialist & Consultant Thanks for support. I am worry about mechanical and chemical properties of material after repeating Heat treatment. You know after new PWHT the material will affected for 6 Hours. also May be we will found new cracks after PWHT, what can we do in order to prevent new cracks. Regards K.Bazrafshan From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Karthik
Sent: Thursday, January 06, 2011 12:24 PM
To: materials-welding@googlegroups.com
Subject: Re: [MW:9115] PWHT Of 347H | Hi,
PWHT can be repeated as per ASME Section VIII,Div.1-UHA-32 (e).Please find below the extraction.Holding time shall be the same as the original/as required by project spec.
UHA-32 (e) Vessels or parts of vessels that have been postweld
heat treated in accordance with the requirements of this
paragraph shall again be postweld heat treated after repairs
have been made. 379,Moo6,Soi8,Nikhomphatana, Phone: 0066 38 897035-8 (Off) Hand Phone: 0066 892512282
--- On Thu, 1/6/11, Bazrafshan,kazem <KBazrafshan@BPC.CO.IR> wrote:
From: Bazrafshan,kazem <KBazrafshan@BPC.CO.IR>
Subject: [MW:9114] PWHT Of 347H
To: materials-welding@googlegroups.com
Date: Thursday, January 6, 2011, 3:28 PM
Base on Project tech Documents we have to do PWHT( in 870°C for 3Hours,Air Cooled) for welding of 2 parts as A312-347H(12.7mm) to A182-347H(6mm,) together((A182 is as a branch to A312). After performing PWHT we found some cracks(dept of crack are from 3 to 8 mm) Just in weld seam. Joint Information: Welding process: GTAM + SMAW. Design Tem: 780°C and Design Pressure is 5.3Barg in convection coils. Welding consumables are :E347H Esab, Wire ER347 esab. Shall we repeat PWHT after repairing or not? If reply is Yes, how much time shall be Holding time ? Please let me know your STD reference As well. Thanks Bazrafshan --
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