Dissimilar Welding in Sour Service 2

[strider6]

Dear all

I'd like to have your opinion/experience on Materials for Sour Service.
I've been involved during a recent project in Dissimilar Welding beetwen Carbon Steel and Nickel Alloy (Alloy 625, Alloy 825) in a Sour Service environment.
As per NACE MR 0175 /ISO 15156 there are no particular constrains to apply this solution, but just the usual requiremtns in terms of hardness and so on.
Looking on the internet for technical paper i've found many author stating that a similar solution in Sour Service can be subject to SSC even if all the requirement of NACE /ISO are fully satisfied, due to a hard phase forming during the welding process.
Due the risk associated with a leak/failure of pressure containtment in Sour Service with high H2S conc. i think that even a remote possibility of failure should not be tolerated.
I think that NACE / ISO have a lack beacuse it doesn't metion this possibility of failure.
What are your idea/opinion on this matter?


ref:
- The catastrophic failure of a high pressure hydrogen vessel was the result of a combination of a. dissimilar metal weld that produced a highly susceptible ...

http://www.metallurgical.com/Publications/Publication 24.pdf

- Corrosion of dissimilar steel joints - a cracking tale (Bulletin - September-October 1999) on TWI Website


Thanks

Vict

Corrosion & Materials Engineer

http://xoomer.alice.it/corrosion

 

[GregLamberson]

strider6

You're right, the coupling of dissimilar metals in a corrosive H2S environment may bery well lead to problems of crevice corrosion, hydrogen charging or pitting attack. Howeverm, the coupling of dissimilar metals is only a problem when the more anodic metal, by itself, will corrode in a specific environment.

The codes are guidelines only, they are not meant to be design manuals or exhaustive in their coverage. I trhink you may have a good point though.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[GregLamberson]

Also, wondering if anyone out there is familair wwith Canadian codes, ERCB, ID 87-2 and what they had to say.

I don't have copies of other NACE publications, but have you checked NACE RP0472, NACE TM0177, or NACE TM0284???

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[gr2vessels]

strider,
The Stress Corrosion (induced) Cracking is also linked to the design of the components subjected to the H2S environment;-trivial as it may sound, your problems might be solved with re-design of the components, cladding with Nickel of the "wetted" Carbon Steel parts, etc..As Greg said, the NACE is a guide for the Engineer to work his way around the trouble, not a design manual. Within its limitations, the NACE is still a valuable source of information, updated and revised from time to time.
The subject you brougt up is good and I hope others will join for a healthy discussion.
Cheers,
gr2vessels

 

[GregLamberson]

Did a little more looking into this, B31.8 did include a Chapter on sour service, not sure when, but it is in the 2000 edition.

The B31.3 has, as far as I know, steadfastly refused to consider a Chapter dealing specifically with sour service (at least not in the 2002 edition). They contend that the scope of B31.3 does not include compatibility of materials with service fluids - "F323(a) Selection of materials to resist deterioration in service is not within the scope of this Code".

B31.3 states it is up to the engineering design to specify any unusual requirements for a particular service - "300(c)(4) Where service requirements necessitate measures beyond those required by this Code, such measures shall be specified by the engineering design. Where so specified, the Code requires that they be accomplished."

Anyway, many designers convienently forget this clause and build to base code requirements for "Normal" fluid service with the argument that they have complied with Code. In fact, proper engineering design for sour service requires a number of criteria over and above base Code requirements; as a result, any company dealing with sour gas should develop their own internal sour gas specifications.

But again, it comes back to the fact the codes are not design manuals and are only guidelines.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[strider6]

Thanks for your reply.

I agree with you that NACE / ISO is a guidelines, and also i agree with you that is possible to find alternative choice to avoid this problem.
What i was questioning is the fact that when designin and selecting materials for Sour Service the reference documents is NACE / ISO 15156 and all materials shall fully satisfy his requirements.
Also in my idea when we state that all the requirements of NACE / ISO are satisfied, we are "safe" and we are not expecting a SSC mechanisms.
Since it was the first time i've come across this issue i started looking deeply into the NACE /ISO 'cause i thought that if NACE / ISO doesn't consider the issue i'll not have to worry aobut it.
Looking in internet and books, articles i've found that the normal recomendation is "this kind of solution, dissimilar welding in Sour Service, should not be adopted due to the possibility even if remote of SSC".

At that point i've found myself into some trouble beacuse we have to face two possibilitis;
1) change in the materials selection, it means change P&ID and so on, and we have to justify why.
2) leave as it is and assume the responsibility of a possible failure.

The problem is that is not easy to explain why if all the selection was fully complaint with NACE / ISO , now we was into this kind of problem, and the questio was : are you sure about that? you can imagine that to justify a change of this kind the corrosion engineer shall have a solid base.

This is why i think that there should be some kind of at least "advise", if not requirements,in the NACE / ISO that the user should consider this possibility of failure when designing dissimilar metals welding for Sour Service.

Regards

Vict

Corrosion & Materials Engineer

http://xoomer.alice.it/corrosion

 

[stanweld]

strider6,
Welding of dissimilar metals must always take in to account dissimilar expansion, corrosion compatibilty, etc.
Code PWHT requirements are often inadequate to relieve welding residual stress. The weld between ferritic steels with austenitic (stainless) filler metals has very high tension stress transverse to the weld as a result of the much greater contraction of the austenitic filler during cooling from the PWHT hold temperature. While some tempering of martensitic structures may be acheived by the PWHT, stress relief was not.

 

[EdStainless]

Codes and Standards do not provide guidance or advice. They state minimum criteria that must be met. The active work there is MINIMUM.

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Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[grampi1]

Avoid when possible, always a hard martensitic layer at the diffusion boundary. Often will get away with it particularly if inconel consumables are used. Require 250 HV PQR qualification.

 

[SJones]

Take a look at Welding Journal, Welding Research Supplement, Feb 1999, pp31s-37s

Strider raises a very pertinent question about the perception of being able to 'hide behind' ISO 15156. Unfortunately, a lot of people tend to miss the 'CAUTION' note in clause 1 of Part 1. Essentially, it is an interpretation of the difference between the words 'resistant' and 'immune'.

Regarding the case in question, it would appear that materials selection may have gone awry if you have ended up having to weld carbon steel to 625.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[strider6]

Thanks for the replay,
At this point i'm just a little bit confused betwenn the terms"minimum requirements, advice, criteria, design guidelines" and so on.
Maybe i'm wrong and i'm asking to much from a Standard, but i've supposed that if a standard deals with Sour Service it will cover all the aspect of that particular issue.
Also dissmilar welding can be found when you have an internal partial weld overaly, and is possible to find it in some equipments.
How do i have to face this kind of technical solution? accept it? avoid it? the risk of a SSC is in some way quantifiable? Is it safe to use such a solution?

thanks
regards

Vict

http://xoomer.alice.it/corrosion

http://corrosionist.blogspot.com

 

[GregLamberson]

The answer is to develop internal sepcifications that deal with sour service and bridge the gaps the code does not cover.

Again, B31.3 is pretty clear in section 300(c)(4) and where service requirements do necessitate measures beyond the code, the company must specify those in the design.

I think a good general design & construction spec and a material spec should cover it.

Greg Lamberson, BS, MBA
Consultant - Upstream Energy
Website:

http://www.oil-gas-consulting.com

 

[gr2vessels]

The SSC is still a "work in progress" issue, the "sour service" is still not fully undestood process and I understand your anguish, when the nominated safe code doesn't provide straight answers, just like we tell you that 1+1 might be 2. The NACE standard was already obsolete at the date of publishing, as numerous studies have run with new experiments and new solutions. That's why is a guide only and does not provide foolprof solutions for extravagant design options. I don't believe the NACE MR-0175 was ever intended for the type of design you listed above, like partial cladding and dissimilar welding. It will give you sufficient cover for the basic selection of materials and condition of use as listed in the standard.
However, the engineering was progressed by people like you who who's challenged the obvious and the boring known paths, bringing new solutions.
Try to understand the reply posts you got for your questions, try to make sense of the 250 HV PQR and the high stress built up in the dissimilar weld material and see if it is related to the Stress Corrosion Cracking potential of your application. Don't hesitate to propose the change of inapropriate materials or type of design, you'll get more appreciation for being thoughtful rather than adventurous and without a proper engineering basis.
Sorry for the long tirade,
Cheers,
gr2vessels

 

[strider6]

thanks for your reply, but i'm still a little bit confused..

thanks

regards

Vitt

http://xoomer.alice.it/corrosion

http://corrosionist.blogspot.com