Impact Testing Welds in Duplex and Super Duplex 1

[stanier]

Is there any benefit in impact testing welder qulafiction procedures in these materials? The process duty doesnt go below 10C or above 45C. The requirement was found in a specification and I dont want to propogate a myth.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[gr2vessels]

G'day Geoff,
I assume that you are concerned by the impact test requirements and also exemptions allowed in the ASME VIII. Try to review the clause(s) UHA-51. Obviously, it's totally different for structural applications.
Cheers,
gr2vessels

 

[stanier]

No this is for piping to ASME B31.3 in a desaliantion plant.

I can understand the ferrite, hardness testing and corrosion testing of the test welds but impact testing was unexpected?


Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[EdStainless]

In duplex grades(at least 2205 and higher alloys) you can check for intermetallic phases by either a corrosion test or an impact test.
If your corrosion test is actually a corrosion test and not a check for intermetallics, then you may want to do an impact. I would do them cold, -40. Look in A923.

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[metengr]

Is there any benefit in impact testing welder qulafiction procedures in these materials? The process duty doesnt go below 10C or above 45C. The requirement was found in a specification and I dont want to propogate a myth.

No. Perform the corrosion test if you have concerns.

 

[EdStainless]

Back to my question, Are you doing the corrosion test to simulate a service, or are you trying to determine if there are detrimental intermetallics?
If it is intermetallics, then a low temp impact can tell you the same thing.

The test in FeCl to detect intermetallics is not a corrosion test per se, it can only be used for microstructure evaluation.

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[stanier]

Corrosion tests to G48 have been specified for the weld, HAZ and parent metal.

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[stanier]

Corrosion testing shall be performed for each welding procedure qualification in accordance with the following:-
• ASTM G48 method A
• Exposure time shall be 24 hours
• Specimens shall be full thickness
• Sample shall include the weld orientated n the transverse direction in the centre of the sample and the sample shall include both heat affected zones and associated unaffected base metal
• All surfaces shall be exposed
• The sides only may be ground to a 600 grit finish and the edges may be rounded
• Samples shall not be pickled and passivated prior to test
• Test temperature for UNSS31803 weld samples (22% chromium duplex) shall be 20ºC
• Test temperature for UNS S32750, UNS S32760 weld samples (25% chromium super duplex) shall be 40ºC.
• Acceptance criteria-No pitting at 20X and maximum weight loss shall be 4.0 g/m2


Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[EdStainless]

This test isn't either G48 or A923, but a bit of both.
At minimum you should move to the G48 practice C for the test solution. It is more stable and repeatable.
Are there exceptions for end grain type of attack?
Has all of the plate been qualified at higher temperatures?
You are exposing the as-welded faces in an attempt to show that the CPT exceeds the test temp.
At the same time you are looking at the edges trying to detect intermetallics.
It isn't that you can't do it this way. It is just like making sure that your impact tests for A923 also meet the requirements for UHA-51 (always use -40 or colder and always measure lateral expansion). It saves testing time and costs
You need to just keep in mind that the test might be severe enough to detect intermetallics, but is it a good CPT verification?
What test was used to qualify the plate? Higher temps than these I hope.

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[stanweld]

stanier,
I have seen these requirements before, but never for a desalination system. They were specified for specific refinery/chemical plant applications and oil/gas gathering/processing systems. There was some early (20-27 years ago) real concern that the welders would not satisfactorily implement the WPS, which was qualified with additional corrosion tests and impact tests before A-923 came into being; also the ferrite number at the root of the pipe welds exposed to the corosive media could not be verified. As a result additional training and qualification testing was mandated to assure that welders would weld to the WPS.

Your specification requirements appear to be hold over from that earlier time period.

 

[stanier]

Gentlemen,

Many thanks for your input.

The specification I suspect is a cut and paste from a previous project and the history before that is unknown. Like many specifications its antecedants are lost in time.

I shall get hold of A923 and read up on the requirements there.

The material is pipe not plate and has been specified as ASTM A 790-S31803. No additional testing has been specified other than required by this standard. Coupons are to be cut from the pipe for testing.

I would like to be able to see a specification for a desalination plant and compare the requirements. I have checked the Norsok site but could find anything there. Is there a website you could recommend?

Geoffrey D Stone FIMechE C.Eng;FIEAust CP Eng

http://www.waterhammer.bigblog.com.au

 

[EdStainless]

I'll make a couple of calls for you.

Your material should be S32205, not S31803. All of the better mills work to the restricted chemistry, but you never know.

A923 should be required on the tube/pipe as well.

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[EdStainless]

I have talked with a couple of people around the industry. The consensus is that every corrosion failure of welds in 2205 that they have seen was related to intermetallics. If there was weld corrosion it was due to improper weld process.

I would suggest that you consider using the A923 test, either FeCl or low temp impacts to qualify the weld procedure (and each welder).
The procedure is a bit different from your spec. I suggest that you get a copy and compare.

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Rust never sleeps
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[SJones]

A nice discourse, but the question relates to WELDER qualification. The philosophical point is: is it required to prove welder performance (as opposed to welding procedure specification suitability) by destructive mechanical testing? The majority of respondents may say not.

The way NORSOK deals with duplex piping materials (not welders) can be found in:

http://www.standard.no/imaker.exe?id=3789

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

If it were my project I would use the same test (A923, either corrosion or impact) to qualify each welder that I used to qualify the procedure.

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Rust never sleeps
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[SJones]

But! Others, particularly those from the fabrication contracting community would say that the corrosion and mechanical performance of the weld is down to the procedure so why should a welder be subjected to the same requirements? If the above approach is adopted then should the welder fail so does the procedure!

Steve Jones
Materials & Corrosion Engineer

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

 

[EdStainless]

I believe that when you are working with critical applications it is reasonable to have every welder qualify.
You are paying for corrosion resistance, you should test to see that you are getting it. If the procedure is robust enough then it should be no problem for every welder to qualify. I don't see that this is any different than weld RT.

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Rust never sleeps
Neither should your protection

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[metengr]

I would like to jump in here regarding welder performance because I deal with these issues frequently, and directly with and Codes/Standards bodies.

Welder qualification is what it is, the ability of a welder to demonstrate that they can produce a weld of acceptable quality/workmanship, and follow directions. The welder qualification does NOTHING beyond this. The WPS provides the necessary technical basis for welds used in service with impact testing or corrosion testing requirements as part of the engineering design specification(s).

Welder RT is what it is, the welder can produce an acceptable quality weld following a qualified welding procedure. Making welders jump thru additional hoops is costly and serves no useful purpose.

 

[EdStainless]

My point was slightly different. I don't see testing the individual welders as making them jump through hoops. I see it as making sure that your process actually generates the results that you are expecting.
Since corrosion in a SS system will almost always be localized (pitting or crevice) and the welds often are the weak link in corrosion resistance, then it stands to reason to be concerned about the specific location of 99% of your corrosion issues.

Certainly different weld characteristics need to be treated differently depending on Code requirements, but in concept I don't see verification of corrosion resistance (in this case actually microstructure) as being any different from verification of size, strength or soundness.

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Rust never sleeps
Neither should your protection

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[metengr]

Interestingly, the ASME Boiler and Pressure Vessel Code (Code) does not deal with corrosion issues because that is more of a design engineering speciality and is left to the Owner/User. The Code deals with assuring adequate stregnth and toughness related to fabrication, and safe operation.

One can always specify above and beyond minimum Code requirements for welder qualification. I am more of the opinion that you have your ducks in a row for the welding procedure specification, and taken into account corrosion issues on the front end.