Ramin,
Thanks for the detailed explanation,
At any case, Residual stress, won't exceed the yield strength of the material.
On Wed, Aug 10, 2011 at 7:47 PM, Ramin Kondori <raminkondori@gmail.com> wrote:
About residual stresses, you shall be very careful...
You mentioned that "it will not affect the Tensile strength"
Welding residual stress is one of the most important elements that makes weldments in thick plates so critical...
Of course in thick plates, there are other parameters like:
- Higher heat sink during weld/HAZ cooling,
- Higher carbon and Mn contents
(higher carbon content to to compensate lower cooling rates and higher Mn to take care of sulfides, comparing to thin gauge plates),- Higher concentration of impurities
- Less strengthening effect of rolling................
etc.
But We are not talking thickness here, right...?!!!
Residual stress is the "hidden" load on any weldment... sometimes the weldments tear apart because of that...!!!
in thick sections (again...!!!), it restrains the weld in Z-direction so that the weld loses its deformation characteristics or in other words it acts like it has become brittle...!!!
Somehow same philosophy is applicable for impact test...
(I do not want to get deep in that...)
one of the reasons that makes PWHT so desirable in carbon steels is that it lowers the residual stress level so the material acts more freely and more ductile so impact will be affected. Metallurgical changes have a whole different mechanism of improving mechanical properties... don't mix them up
They both happen while stress relieving is applied but they are not the same...!!!
About tensile strength,
we are talking about a joint in a system (structure or piping) not a PQR
I mean when you are repairing a weldment, the chances are you have restraint on the joint, it means your weld metal can not shrink like a PQR test coupon (try welding a but joint where other ends are fixed to get what I mean, you will see cracks in the weld center-line unless you do something about it like preheat etc and the hardness is not an issue)
- What happens is that the level of stress on you weld metal will be much more than "1/2 yield point" that is mentioned in welding textbooks and it can easily reach yield point stress, just like that...!!!
- There is a longitudinal residual stress that is already equal to yield stress (and it adds up to transverse residual stress to give you even a higher level of residual stress), even in a PQR coupon.
- If the thickness is high, that will give you a sweet Z-direction stress that is the worst among all...!!!!
That means in many actual cases, your weld is already subjected to stresses near yield stress...!!!
and it will not be that trusted...!!!
You should do something about it...
But for Christ sake, this is an A106 pipe, just cut it out and replace and let's move on...!!!
Regards
Ramin KondoriQC/Welding EngineerIWE AT 0070
On Wed, Aug 10, 2011 at 1:46 PM, K.Babu <kbabupsg@gmail.com> wrote:
Ramin,Measurement of Hardness, depends upon the application & Construction spec.Spec, will not cover all variant conditions existing in practical. I won't say spec. is wrong, rather than it will get refined by people's experience.Since it is CS , we can't ignore.If you consider, all subsea spec., even CS, they will ask us to come up with new WPS by simulating the repair, in that, Hardness is the specific criteria.As per as my exp., Residual stress will not exceed the Yield strength of material, so it will not affect the Tensile strength, but it will affect the YS, which in turn, no yield before failure of the system.Since you say, Brittle fracture, definitely the Hardness impact would be there.Thanks & regards,
On Mon, Aug 8, 2011 at 6:09 PM, Ramin Kondori <raminkondori@gmail.com> wrote:
Mr.Murugesan is right...!!!
A106 is not that critical...in A106, whatever you do, you won't exceed allowable hardness, whatever it is...!!!
BUT
this shall be considered that:
In any weld,
rather A106 or A-whatever, if you had a large volume of weld,
rather it is because of thickness or build up,
it is recommended to carry out PWHT to avoid problems caused by that joint's residual stress.
And it is upon your engineering judgement...!!!
I have an experience on this, it was a steel structure and we had to build up some edges for compensating for large gap (25mm sometimes)
Then our client asked for a PQR and we did it...
Results shocked me...
Material was S275 J0
Thickness 20mm
Residual stress caused all tensile specimens to fail...
Impact was not that promising, brittle fracture was obvious
But it was not hardness issue
we had chemical analysis, hardness, everything...
none of them...!!!
it was residual stress that caused premature failure of tensile specimens...
Yet...
if there are complications, you can cut the pipe and make a new joint with new nipple...
A106 is the cheapest among allso if the repair will be complicated, go ahead and replaceRamin KondoriQC/Welding EngineerIWE AT 0070![]()
On Mon, Aug 8, 2011 at 7:48 AM, murugesan jeyaraman <jmurugesan@gmail.com> wrote:
No need to check Hardness test unless Code or spec ask to do so. Do you mean to say that you will go to do Hardness test after every repair. No need unless spec specifies to do so. I have not come across any specs ask you to do hardness test for low carbon steels. (let aside NACE and Alloy steels).hardness generally do not get affected for low carbon steel for one or two repairs, (unless some sudden cooling or water quenching is done)Yes, if we measure the Hardness and hardness value exceeds the limit, we have to bring within acceptable limit by doing required PWHT.My question is why do you want to go for PWHT and Hardness test when Spec or code specified not to do so.Code is written based on prolonged research by experienced experts and stalwarts in the welding and fabrication field (Much more experienced technologist and engineers than QC personnels like us). So when the code says PWHT not required for thickness below 19mm, why do you want to do the things which code do not requires you to do and pur yourself in unwanted trouble.If you do not agree, please put fourth your views, we will discuss further more technically.ThanksMurugesan
On Sun, Aug 7, 2011 at 8:06 PM, sudhakar kuppuswamy <mechsudhakar@gmail.com> wrote:
Dear Mr.Murugesan,
Let the codes and standards be aside,
I request you to answer my question,
What we can do in such cases if the final hardness value of the joint (particularly at HAZ) is higher than the acceptable limits???
please keep in mind that particular joint after repair ,RT is accepted .But we need to get the hardness value in acceptable limits ....!!!
with regards,
sudhakar.k
On Sun, Aug 7, 2011 at 3:02 PM, murugesan jeyaraman <jmurugesan@gmail.com> wrote:
Dear AllEventhough if this is considered as weld build up or buttering, still PWHT is not required. This is only a small portion of 10 to 15 mm length for repair."Thickness of base metal restored to get the required weld bevel" can be welded by following qualified Butt weld WPS . If no PWHT is required for WPS, no PWHT required for production weld also.Even if you consider, cooling rate would be faster - We can apply pre-heat to 95 C then we can start welding. No martensite formation will happen, here. Doing PWHT will add cost.Since it is a P1 material with thickness 12.7 mm, no PWHT is required,As per ASME sec I and B31.3 - PWHT governing thickness is 19 mm (through thicness direction)As per ASME Sec VIII div 1, UCS-56 - PWHT required only above 38 mm thickness , 32 mm to 38 mm - PWHT not required if Pre-heated at 95 Degree.UW-42 SURFACE WELD METAL BUILDUP (ASME VIII Div 1 - 2010 Edition)
Construction in which deposits of weld metal are applied
to the surface of base metal for the purpose of:
(a) restoring the thickness of the base metal for strength
consideration; or
(b) modifying the configuration of weld joints in order
to provide the tapered transition requirements of UW-9(c)
and UW-33(b) shall be performed in accordance with the
(1) A butt welding procedure qualification in accordance
with provisions of Section IX must be performed for
the thickness of weld metal deposited, prior to production
welding.
(2) All weld metal buildup must be examined over
the full surface of the deposit by either magnetic particle
examination to the requirements of Appendix 6, or by liquid
penetrant examination to the requirements of Appendix 8.
When such surface weld metal buildup is used in welded
joints which require full or spot radiographic examination,
the weld metal buildup shall be included in the examination
Thanks and regards
J. Murugesan
On Sun, Aug 7, 2011 at 1:01 AM, sudhakar kuppuswamy <mechsudhakar@gmail.com> wrote:
Dear all,
Further to Mr Ramin Kondori comments, I like to add some more point to this discussion, I too suggest PWHT for that joint, since repair weld buttering or built up with GTAW, the deposit of weld metal will be in small layer .So cooling rate will so high which may leads to martensite formation (Hard structure), more over HAZ would have been subjected to uncontrolled heating and cooling during initial and repair welding.
So It will be better to carry out a PWHT on that Joint by studying the design temperatures& mechanical properties requirements. If toughness requirement is there it always better to do a PWHT.
--
---------- Forwarded message ----------
From: sami ali <sami_irq@yahoo.com>
Date: Sat, Aug 6, 2011 at 9:10 PM
Subject: Re: [MW:12131] Repair procedure on severely punctured root
To: materials-welding@googlegroups.com
From: Ramin Kondori <raminkondori@gmail.com>
Subject: Re: [MW:12125] Repair procedure on severely punctured root
To: materials-welding@googlegroups.com
Date: Friday, August 5, 2011, 9:58 PM
Wherever you have large amount of welding, you need PWHT...
If you have a standard joint, then 19mm or 25mm criteria roles for PWHT but when the gap is 10-12 mm then the weld volume is high enough to call for a PWHT
You can draw a sketch and calculate the volume of the weld in a 19mm thick pipe, then draw a sketch of you joint with 10-12 mm gap and you will see the weld volume is much more...
Of course it is a matter of engineering judgement. You should consider you fluid, process parameters like temperature, pressure and design requirements.
In my opinion if your specifications requires PWHT for thicknesses above 19mm (for this line) then you should probably carry out PWHT because of your weld metal volume.
Regards
Ramin KondoriQC/Welding EngineerIWE AT 0070![]()
On Fri, Aug 5, 2011 at 9:29 PM, pgoswami <pgoswami@quickclic.net> wrote:
Ramin.Why PWHT? Does a weld thickness of 12.7 mm on SA 106 Gr B base metal require any PWHT as per any commonly referred boiler and pressure vessel code?I would think the suggestion of Prem Nautiyal is the way to go.The technique referred is" common bridging technique" to close in wide-root gaps, which is quite common for manual GTAW. Using 6010 with 10-12 mm root gap would not be safe , as the welder would not be able to control the weld puddle.Hence GTAW would be the preferred technique to bridge the root and proceed further.Thanks.Pradip Goswami,P.Eng.IWEWelding & Metallurgical Specialist & ConsultantOntario,Canada.Email-pgoswami@sympatico.ca,
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Ramin Kondori
Sent: Friday, August 05, 2011 11:10 AM
To: materials-welding@googlegroups.com
Subject: Re: [MW:12121] Repair procedure on severely punctured rootIt's better to apply PWHT after completion of the weld.
Regards
Ramin KondoriQC/Welding EngineerIWE AT 0070![]()
On Fri, Aug 5, 2011 at 12:50 PM, prem nautiyal <prem_nautiyal26@yahoo.com> wrote:
From: limesh M <limesh78@gmail.com>
Subject: [MW:12110] Repair procedure on severely punctured root
To: "Materials & Welding" <materials-welding@googlegroups.com>
Dear All,
Material : ASTM A106 Gr. B
Thickness : 12.70 mm
Welding Process : SMAW
Electrodes used as per approved WPS : SFA 5.1, E6010 (Root)+ SFA 5.1, E7018(Fill&Cap)
During through thickness repair, by mistake root pass has been punctured badly(5-8cm in length after complete removal).Unfortunately,now the root gap is almost 10-12 mm wide and it is difficult to weld root again with E6010.In this case what is the better option other than cut and bevel the joint.Is there any problem to build root with GTAW by using ER 70S2 and fill remaining thickness with 7018?
Regards,
Limesh
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With regards,
Sudhakar.k
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With regards,
Sudhakar.k--
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Thanks & regards,
K.Babu
Singapore
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