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Up Topic Welding Industry / Metallurgy / Stress Relief
- - By BWolfe Date 10-30-2015 19:14
I have a question.

Our company has fabricated some Trolley Beams that are made out of A572 GR 50 Material, and we are using a AWS Welding Procedure using FCAW to weld these Beams.   During the Course of Welding, we experienced a lot of distortion.    therefore heat was applied and weight  to help to keep them straight.   After the welding was completed, we performed Ultrasonic Testing on all CJP Welds, and had many rejected indications.   After all the weld repairs were completed and found acceptable, it was determined to stress relief these beams.   Problem is our WPS does not call out Stress Relief, and now we are challenged in performing another PQR to qualify the Welding of these beams.    My question is, what is the main factor as to why we must perform another PQR?   What would be the technical answer for me to address why I must redo the current WPS by means of another PQR.    Also where would I find this in the 2010 AWS Structural Code Manuel.  

Please advise
Parent - By In Tension (**) Date 10-31-2015 01:50
From a code-compliance perspective if you opt to PWHT the beams you're required to requalify per AWS D1.1 Table 4.5, Item 37.  If your WPS was qualified by testing to Clause 4 then I assume there was a variable involved that ruled out the use of a prequalified WPS.  This is a shame because A572 Grade 50 is a prequalified base metal that is right on the cusp of allowing PWHT (with Engineering approval) and you may have been able to anticipate this problem with a WPS prequalified with or without PWHT. 
From a technical standpoint, if you perform a thermal stress relief on this material expect a degradation of mechanical properties.  This is the reasoning behind the code requirement to requalify when adding or deleting PWHT... a variable that affects mechanical properties is deemed an essential variable and necessitates a new proofing that the WPS will produce a weldment with the properties assumed in the design calculations.
Retroactively qualifying a WPS is always contentious because it can be difficult to know with certainty exactly how the welds were made, especially if the original WPS had broad ranges built into it.  It's rare that variables are recorded during the production welding operation so how can you genuinely reproduce the actual welding conditions?  At the very least, you'll need approval from the customer.
Do some research and choose your PWHT temperature and soak time wisely.  And also consider that it can be just as difficult to predict how a stress relief will affect the distortion as it is to predict the distortion itself.  The results I've personally seen with PWHT of A572 were inconsistent.  What dimensional tolerances are violated and how far out of tolerance are the parts?  You may want to contemplate other options.  If you give more details maybe some of the structural guys on the forum can offer some advice.  My comments are only my opinion and are given without having done any research so may contain errors.
- - By pradeep4u (*) Date 01-04-2016 07:21
       I have a question which may be very silly but to me it is very important one.  Why alloy steels( SA213 T11,T22)  need stress relieving but carbon steels d not require stress relieving.

Parent - - By js55 (*****) Date 01-04-2016 13:20
The alloys you listed are bainitic in their basic microstructure and are air hardening alloys. However, for those codes in which those alloys are typical, Section I and B31.1, thinner walls do not require PWHT, and ASME is currently liberalizing PWHT requirements based upon some recent research that shows PWHT may do more damage than help, or at the very least makes no difference at all.
Though I will say, since you listed those alloys as T's and not P's that means you are actually asking about tubing materials that generally do not need PWHT due to the fact that they first of all are thin wall small bore materials AND the fact that they are generally applied to ASME Section I applications where the PWHT requirements are even more liberal.
Parent - - By pradeep4u (*) Date 01-05-2016 07:45
The alloys which I referred  are superheater tube materials.  Their thickness is varies from 4.5mm -7.6mm and in my plant these tube weld joints go through stress relieving.
Parent - - By js55 (*****) Date 01-05-2016 13:07
Those thicknesses are common. And though boiler manufacturing is certainly not my area of expertise I would be curious as to the reasoning behind stress relieving tubing that will be placed in the superheater. Seems to me shortly after start up there won't be any stresses anyway. I'm not being sarcastic. Just curious. Is this common?
Parent - By pradeep4u (*) Date 02-10-2016 15:18

Parent - - By Superflux (****) Date 02-10-2016 18:27
It is common to stress relieve the tube to nozzle welds off the drums which are quite thick.
Parent - - By pradeep4u (*) Date 02-12-2016 16:21
why it is done  that is my question
Parent - - By 46.00 (****) Date 02-12-2016 20:36
4u, it is usual to start a new thread when asking a separate question from the OP original post. However as others have responded to your question...T11 (1½ % Chrome steel) and T22 (2¼ % Chrome steel) are typically used for their creep resistant properties. This is especially true in power station environments, where T11 and T22 steels have been used in many applications for years, super heaters, main steam etc.

More recently, T91 and T92 (9% Chrome) grade alloys have been utilised for even greater creep rupture resistance and longer creep life.

The need for ‘Stress Relief’ on these alloys arises because due to the inherent micro structure, when welding is performed on these alloys (which involve temperatures way above operating temperatures.) they become very hard and liable to cracking and/or a shorter creep life amongst other undesirable properties. Stress Relieving/ Post Weld Heat Treatment help’s restore the original materials mechanical properties to what it was before welding took place.

Because basic Carbon steel is a much more forgiving material and much more ductile than chrome steels, less likely to harden after welding unless fairly thick sections are used (12mm+), PWHT is not required. Nor are they really suitable for use where Creep resistant steels are dictated.
Parent - - By pradeep4u (*) Date 02-13-2016 15:16
Yes  u rightly said that I have no common sense.  That's why I asked silly question. I do not have IQ like u.
Parent - By 46.00 (****) Date 02-13-2016 16:55
4u............I never said you didn't have any common sense. In fact the only silly question in my book is the one not asked! I actually have a rather low I.Q. so I have asked many many questions over the years.
- - By Eric Onokpikini Date 11-22-2017 02:24
Good All,

Can anyone kindly guide me through how to determine if Impact test is required using B31.3 as a construction code.
Parent - By fschweighardt (***) Date 11-29-2017 20:46 Edited 11-29-2017 20:50
Put this in the ASME section.  FWIW, its mostly low temp service.
- - By pradeep4u (*) Date 01-11-2018 18:08
Dear all
I have question that during stress relieving of alloy steel tubes like SA 213 T11 and SA 213T22. We soaking time of about 1hour and 30 minutes after heating upto 650 deg temperature. If we give soaking time of 1hr or less then what will happen
Parent - By Maggs47 (**) Date 01-11-2018 20:48
Without knowing anywhere near enough details, like specs, required cycle, material thickness, etc, I'd say you run risk of not bringing the material all the way up to temperature, which could result in not relieving all the stresses expected and possibly ending up with unexpected crystalline structure.
- By Deepu VB Date 02-13-2018 13:09
Since it is about stress releif,

Can I know the PWHT temperature and soaking time of a particular weld can be decided based upon the weld metal PWHT requirements as mentioned in ASME Sec 2 Part C.

For example, I am using a base metal SA335 P11 grade 4" sch 40 pipe weld with E8018-B2 welding rod SMAW process. The PWHT temperature  can be selected according to ASME Sec 2 part C as, SFA 5.5, E8018-B2 PWHT for 690 plus or minus 15 degree celcius for 1 hour soaking.

most obviously the weld metal have similar properties with the base metal. So is it an easy way to find the pwht temperature range as said above.
Up Topic Welding Industry / Metallurgy / Stress Relief

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