We are facing one serious concern regarding PWHT of weld joints of A335 Grade P11 & P22 piping in very high pressure superheated steam and syn gas service. Due to some unforeseen circumstances at our site, PWHT of some weld joints was not done effectively and resulted in higher hardness of weld joints although HAZ area hardness values are OK. The hardness number of weld joints is in the range of 260 - 320 HB which is unacceptable as per code requirements.
I want to seek your expert opinion on the following:
1. Can we take these weld joints is operation and defer PWHT for planned Outage after one and a half year from now?
2. Is there any relaxation which can be taken in hardness readings, for example, welds with hardness up to 260 may be accepted and above this number must be PWHT again?
3. What effects can it cause after taking these weld joints in service? Weld failure can occur immediately or would take some time?
4. As HAZ area hardness number is standing in the range of 115 - 150, would repeating PWHT effect this number and further reduce the hardness of HAZ which may not be acceptable?
Your inputs would definitely help me in making a correct decision.
Regards,
Ashfaq
I believe this problem justifies retaining the services of a welding expert that is experienced with the alloys you are dealing with.
While there are several members of this forum that have the type of knowledge you seek, this problems deserves more attention and research than a couple of lines of text. A quick, terse response will not do your problem justice.
Best regards - Al
Wow, I think I would have to check my insurance policy before answering anything other than "Consult the EOR"
But just for the fun of it:
1) Can you hear it blow up from your house?
2) I dont know
3) If you know that weld failure is inevitable, why would you even consider putting it into service?
4) Yes repeating PWHT would effect this number.
What code are you referring to?
And in that code where are the requirements for hardness testing after PWHT located?
The other thing is, for those alloys the curve of PWHT response should allow a greater weld metal hardness reduction than the HAZ.
If a requirement has to be met, I'd cook it again.
As you have already read this is an Engineering issue but for the sake of conversation a few things to consider.
In some cases stress relief happens in service---high operating temp for extended periods will relieve welding stress.
Operating temp. The base material and weld in the as welded condition is most likely not at issue. As you expressed the HAZ that would be a concern.
The biggest concern for the HAZ most likely is Stress Corrosion Cracking due to hardness but as you say they are in range.
How long has these welds been in service? Super heated steam is real close to a 1000'F, what PWHT temp was used?
Like you have said that in some cases, stress relief will also take place when exposed to high temperature for certain time. I just want to confirm whether steam blowing cycles would also improve the conditions of residual stress within the weld joint? Steam blowing temperature would be
The weld joints have not been taken in service yet and as we are at the verge of plant commissioning, we want to take a careful decision as one single day delay would be causing a million dollars hit.
Yes the temperature would be like 900 deg F plus when in service and the PWHT temperature was about 1300 deg F.
Regards,
Ashfaq
Were the PWHT's skipped all together? If not, what was the problem with them?
I think the only one that could make a judgment call of this magnitude would be the owners people.
The problem is that if you cannot show that the (code) procedure was followed to the letter you have no sound Engineering premise to stand on should one fail.
If it were my hind end on the line, I’d re-do the PWHT and make sure I had charts to show as well as hardness surveys as a CYOB.
As to your earlier question about the HAZ being effected by a 2nd PWHT. Not likely, if you do not exceed the original soak temperature.
They were heat treated but not effectively like thermocouple attachment were not proper, soaking time was not given the way it is prescribed in design code.
We are the owners and all this has been done by Construction Contractor and right now we are in a fix as plant commissioning is just some 5-7 days ago and 900 suspected weld joints have still to be checked for hardness.
We could not practice an effective control on Contractor's PWHT works.
What's the way forward? Delaying the plant commissioning and go for re-PWHT? It would be hitting us for million dollars for ever single day.
The reason for PWHT is to get rid of residual stress both in the weld metal and the HAZ.
You're talking about very high pressure superheated steam, and I'd guess that this piping falls under B31.1 (power piping). You also mention syn gas, and I'd guess that this piping falls under B31.3 (chemical plant and refinery piping).
Let's begin with your very high pressure superheated steam piping. In this piping, very little or negligible corrosion is expected. So, the purpose of PWHT and subsequent elimination of residual stress is to prevent that the pipe internal pressure plus the residual stress are higher than the metal tensile stress, and the weld will collapse.
Now let's take a look at your syn gas piping. In chemicals carrying piping, the purpose of PWHT and elimination of residual stress is to increase the metal resistance to corrosion. It's a well known fact that metal subject to stress is less resistant to corrosion. Any corrosion book will tell you that.
So, our first deduction is that PWHT of your pipings is necessary, either to prevent collapse or to prevent corrosion.
For many years residual stress could not be measured in place, i.e., where the weld is actually located. Nowadays it's possible using portable Xray difractometers, but when the standards were first written it wasn't.
So, how could one know that the PWHT was successful in removing the residual stress? It's a well known fact that hardness and stress the metal is subjected to are related. Although there's neither mathematical equation nor conversion table that relates both variables with each other, it's well known that the higher the stress the higher the hardness.
Experience demonstrated, and many years of piping design and operation confirmed, that if after PWHT the metal hardness was below a certain figure, it was safe to assume that the residual stress had fallen below the maximum acceptable. That's why standards state a maximum hardness value to be achieved after PWHT.
So, our second deduction is that the hardness values MUST be met.
And our third deduction is that if they weren't, PWHT MUST be repeated.
Giovanni S. Crisi
Sao Paulo - Brazil
Thanks for your valuable reply.
Design piping code for both services is ASME B31.3.
Giovanni,
I agree about the high pressure superheated steam piping falling under B31.1. If that is the case then you have a couple of issues that I don't think have been addressed yet.
1. B31.1 does not give any hardness requirements for P11 or P22 material. This code is silent about this. I have spoken with B31.1 code committee memebers to convince them that the boiler industry needs some help here. We get so many clients that have there own hardness requirements that are all over the map. The B31.1 committee is reviewing this but at a snales pace.
2. B31.1 table 132 gives you some relief on P11 and P22 material in the general notes, some of which are based on material thickness, carbon content, and other considerations.
3. If the person that made the original post could tell us what hardness testing equipment is being used it could shed some light on this issue alittle. If they are using a electronic devise such as a Kroutkramer MIC 10, or 20 then I would check the following, calabration, technique, procedure, and battery life. I have witnessed these devises lie to techs on a number of occasions. At a min I would use a mechanical tester such as a Pin brineller, or aTelebrineller to make sure the electronic unit is functioning correctly or use a mechanical unit instead of a electronic unit.
4. It would be helpful to know what welding process is being used. FCAW will net higher hardness readings on Chrome material, at least that has been my exp. Because of this when the FCAW process is used on our projects it is manditory to perform PWHT even if B31.1 gives us relief.
Thanks
Jim
3) You mean..... No calibration on a known block before taking the readings????
If the OP want reliable readings every time he should use an "Ernst hammer"
The Pin brineller is not stable on thinner materials!
3.2
The Ernst Hammer is a Pin-Brineller.
thanks
Jim
My bad, I thought you meant something else :(
3.2
Jim,
The main reason why the code committees are moving so slow on this is that it is a tougher thing to resolve than you would think at first blush.
First of all there is considerable scatter in the technologies available for field application (even lab testing has considerable scatter) and they are hesitant to carve into stone something that could cause a rejection of a perfectly acceptable part.
Secondly there is considerable disagreement as to exactly where the standard should be.
Thirdly, hardness testing is a surface testing procedure and even if the surface does not comply it does not necessarily mean hardness is non compliant through the thickness. There is surface hardening phenomena that can occur through oxidation that can render a surface hardness unacceptable when the PWHT was perfectly acceptable. This requires griandingdown into the part, perhaps even to the point of violating min wall which then requires a repair.
Fourth, hardness is room temp test when many of the materials of concern are high temp application materials (P11, P22, P91) in which case, how relevent is the hardness test?
The committees are very sensitive to the fact that the industry is looking for some guidance here but IMO guidance is not what the committees should be concerning themselves with and IMO I believe the caution here is very warranted.
Good points Jeff. In the end, the creep-rupture properties that need to be confirmed before a decision could be made to place the welds in service. Creep-rupture performance data for similar heat treatment results would be needed to perform a thorough evaluation. Boat samples to check the metallurgical condition would be helpful also, to provide knowledge of the resultant grain structure and presence of carbides as an indicator of tempering. Perhaps the original poster needs to contract a metallurgical consultant to review all of the data and provide a sound recommendation. Opinions from the internet are only worth what you pay for them.
" Opinions from the internet are only worth what you pay for them."
Thats funny. No truer words were ever spoken.
I'm sure your in the know better than I am, and I agree with what your saying. The person I spoke with did mention that there is a back and forth going on between ASME Sec. II and B31.1 committee's on who is going to make the final decision on this. I think I'm just worn out with dealing with clients in the boiler industry that every time they go to an EPRI conference they come back with a new set of guidlines. :) I would like to know your thoughts on my comments on hardness testing and on the FCAW process giving you higher hardness readings than other processes.
Thanks for your post
Jim
Jim,
I feel your pain. Being a fabricator I am in the same boat. The primary discussion is taking place with the Creep Strength Enhanced Ferritic Steels Task group of ASME. There are B31.1 guys on it (though its a Boiler Code task group), and participating fully with it. Whatever comes out of this task group will most likely carry, with some revision of course, through to other Codes. I am not convinced we will see anything soon. The consensus seems to be opposed to any sort of imposition until further data is received, which may take some time.
If there are independent discussions being carried on in B31.1 moving toward a consensus to impose something I am not aware of it. I can't seem to find the time to do B31.1.
Jim,
One other thing I'd like to add.
The CSEF guys are sincerely concerned about this issue and some of them are experiencing the same difficulties you are. But if there is a consensus it is not to do something unless there is confidence they are doing the right thing, and with real technical justification.
Again,,,,,,what code? Somebody tell me where the hardness requirements are for the superheated steam.
And keep in mind, the hardness of the HAZ is going to be considerably less than the weld metal because the base metals MSTS is 60ksi whereas the fillers are 80ksi and 90ksi for B2 and B3 respectively.
Your most likely form of failure is going to be HAZ Type IV cracking.
Design code for piping in both services is ASME B31.3.
Would you please elaborate HAZ Type IV cracking?
Regards,
Ashfaq
ashfaqanwer,
Your post seems to imply that you or your company have missed an important part of the fabrication process and you are looking on this forum for assistance in how to convince your client that your piping is actually acceptable.
Basically, if your piping is designed/fabricated to ASME B31.3 and PWHT is required per that code then you must perform PWHT, failure to do this means your piping does not comply with B31.3.
It is between you and your client as to whether the piping is acceptable,
Regards,
Shane
Shane,
Interestingly, we are the client ourselves and just wanted to share if there can be any relaxation.
Anyhow, got very clear... there should be any relaxation given to the Construction Contractor.
Regards,
Ashfaq
Type IV cracking is indicative of the types of alloys you are talking about (bainitic/martensitic low alloys) wherein a soft region of the HAZ surrounded by stronger harder regions is susceptible to cracking under stressful service conditions. There is no way to avoid the phenomena other than solution annealing which nobody is going to do for those alloys.
There is actually quite a bit of info available on the net for Type IV. Just google it and you should get plenty of info.
ashfaq,
let me be a little sarcastic and don't get upset for that.
Suppose shortly after the plant is in operation a weld explodes and you are at 2 meters distance of it. Wouldn't you think that it would had been a good idea to perform PWHT again on all welds?
Giovanni S. Crisi
Yes, considering safety aspects, risks, life span I agree that it's better to perform PWHT again.
Thanks.
Regards,
Ashfaq
Ashfaq,
The same query was posted in the other forums also. For P11 and P22 welds , 260 - 320 HB hardness readings are high while for HAZ, 115 - 150 HB is quite low. If you're talking about high temp superheater steam line the operating temepratures (easily over 100 deg C) and pressure would be very high,any mishap could be serious , both to human and plant life.
Hence accepting a weld without proper heat treatment will be highly unacceptable. B-31.1 does not have any hardeness requirement, but B-31.3 . have typically 225HB(P11) and 24HB(P22) requirements after PWHT. Welds with hardness above this shall be re PWHT.
Many a times hardness values could have scatters,that's why re-verification of PWHT charts, hardness readings and re-measuring hardness values(if required) may be your starting points. Welds not properly heat treated as per the PWHT chart shall be re PWHT. PWHT is a serious issue and should not be deferred till the next outage.
Thanks.
P.Goswami,P.Eng.
24 or 240 HB? I think there's a typographical mistake on your answer.
Giovanni S. Crisi
Hi Giovanni,
It's 240 HB. Thanks for pointing out the mistake.
Regards
Pradip Goswami
Welding Engineer/Specialist
Ontario Power Generation Inc.
pradip.goswami@opg.com
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