ok, so in my cases practically i used to get often distortions and in many cases i found to be either partial repairs or axial loads, but when partially repaired with axial loads then definitely there will be a distortion, observing distortion with your naked eyes is an art of your experience, even how minor it maybe, might be in your case partial repairs and axial loads has played before PWHT and after PWHT minor distortion becomes bulging?
Static or dynamic strain aging / PLC effect / (Plastic deformation).
Sometimes Luders band transition into the Portevin–Le Chatelier effect while changing temperature or strain rate, this implies these are related phenomena.
See below TWI implications on existing welds and some samples just for info.
What are the implications of welding over existing welds?
It should be remembered that welding over weld metal is actually a very common occurrence. Multi-pass welds after all are manufactured by welding over weld metal! There are also many accepted procedures in which welds overlap. Pipeline circumferential welds cross the longitudinal seam welds, and pressure vessel nozzles cannot always be added in regions free from fabrication butt welds. Split tee connections will also require welds impinging on the original pipeline fabrication welds.
Even though welds on welds are common, there are nevertheless some potential concerns. Of particular importance are any differences between the welding procedures of the two overlapping welds. If the heat inputs are different, such as when a multi-pass girth weld overlaps a single-pass seam weld, the cooling rate of the weld metal in the two cases will be different. Thus the weld metal, which was designed to give satisfactory properties (in this case) with a slow cooling rate, may not perform so well in the HAZ of the faster cooling girth weld. Another factor to consider is compositional variation between the two welds. For example, alloying which may be required to obtain satisfactory properties in a high heat input weld, may result in poor microstructure and/or excessive hardness when incorporated into a low heat input weld by dilution.
Another issue to be careful of is hydrogen control. A high strength weld metal may not be able to tolerate hydrogen introduced by welding over it with a high hydrogen consumable.
In addition to metallurgical factors, it is worth bearing in mind that an existing weld is more likely than parent material to contain defects, such as fabrication flaws or cracking from service. Defects which are welded over, and not melted out, can suffer locally intensified strain age embrittlement by static or dynamic strain ageing at the region of concentrated strain at the flaw tip, leaving a planar defect with its tip in a region of low toughness (Dawes M G). It is therefore important to inspect the region to be repaired in advance (as well as afterwards), using appropriate non-destructive testing methods (see Further Information below).This is particularly important for repairs; however, in many cases new construction welds are also routinely inspected prior to over-welding.
https://www.twi-global.com/technical-knowledge/faqs/faq-what-are-the-implications-of-welding-over-existing-welds/
From: José LuÃs FerreiraDate: 2018-11-10 06:00Subject: Re: [MW:28608] Deformation during PWHT - P92--Yes, there is a heavy piping above.
On Thursday, November 8, 2018 at 11:34:05 PM UTC-3, kannayeram gnanapandithan wrote:this is due to heavy welding for 15mm thick, heavy axial load while doing PWHT??THANKS & BEST REGARDS,KG.PANDITHAN, BE, IWE, CSWIP 3.1,ASNT-Level II in PT,MT,RT & UT.International Welding Engineer.CONSULTANT-WELDING & QUALITYMobile no: +919940739349From: José LuÃs FerreiraDate: 2018-11-10 05:55Subject: Re: [MW:28608] Deformation during PWHT - P92This is bulging?A: Yesany welded valves adjacent which is 1500 or 2500 ratings?A: No, but there is a heavy piping above and restriction below.Did you carriedout postheating after welding?A: Yes, 2 hours @760°CDid you had bolt torquing either side fixed strongly?A: It doesn't have any flanges.Is there any distortion after welding and carriedout PWHT without any rectifications?A: No, distortion appeared after PWHT.Or Modifcations done for repairs (Cutout or partial repairs) before PWHT?A: Yes, it was done partial repair before PWHT.--https://materials-welding.blogspot.com/https://www.linkedin.com/groups/122787---You received this message because you are subscribed to the Google Groups "Materials & Welding" group.To unsubscribe from this group and stop receiving emails from it, send an email to materials-welding+unsubscribe@googlegroups.com.Visit this group at https://groups.google.com/group/materials-welding.--This is bulging?any welded valves adjacent which is 1500 or 2500 ratings?Did you carriedout postheating after welding?Did you had bolt torquing either side fixed strongly?Is there any distortion after welding and carriedout PWHT without any rectifications?Or Modifcations done for repairs (Cutout or partial repairs) before PWHT?Basically, distortion or deformation will not come under NDE and even your Hardness gets accepted, for this you need do Metallographic Examination as special case for root causes, anyhow this cases shall be rejected visually regardsless of NDE and to know the root cause welder or welding inspector fully assigned can give you the real scenario, catch the welder or ground level workers to scrutinize the root cause.Regards,Muneeb.--After the PWHT it was observed that along the side of the weld a deformation appeared as a collapsed pipe (see figure). After the PWHT were performed hardness test (ICU) and PAUT. All tests were accepted.The main hypothesis about the causes of the occurrence is related to the thermal expansion constraint (due to heavy equipment and fixation devices).PWHT Parameters:Temp. 760 ° CTime: 2hThickness: 15.1mmMaterial: A335 Gr.P92Position: vertical (tube)Has anyone seen this? What can happen to the mechanical properties of this material? Some bibliographical references that follow. indicate to follow for an opinion?
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