Corrosion Testing to ASTM G48 using Method A

[Syedabbas]

Dear experts,

The subjected testing was performed on Duplex steel for welding procedure qualification at testing temperature of 22C for suggested time period of 72 hours as per ASTM G48 using Method A. The testing medium was acidified FeCl solution. The sample was pickled and prepared but still could not meet the client requirements (no pitting or crevice corrosion in either weld metal or HAZ is permitted) and failed in testing twice. Could any one explain the potential reasons for the failure and moreover what countermeasures shall be considered to avoid repeated failure ?

 

[EdStainless]

First of all, if you were using scidified ferric chloride it was method C.
Secondly, have you done an A923 test? Where you cut a sample and grind the surfaces, no pickle or passivation allowed, and test in ferric chloride? This should indicate if you have any intermetallic phases present.
Or at least do micros.

Which duplex? Are you sure that the temp is correct for the alloy?

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Plymouth Tube

 

[jwhit]

Are you working with a cast duplex product? G48 Method A is commonly called out for cast superduplex stainless with a 24 hour test period at 50C and 24hrs./22C for the lower duplex alloys. Otherwise, for wrought it normally would revert to A923 for testing. If testing protocol isn't the problem I would look at composition and solution treatment for answers.

 

[Syedabbas]

The material is normal duplex (ASTM A790 UNS 31803, smls pipe) not the super duplex. The product is wrought duplex but testing to G48 using Method A is client specification requirement for welding procedure qualification at 22C for suggested 72 hours. The specimen size is 1" X 2" cut at 180 gegree and prepared only using 120-grit abrasive paper and was not passivated or pickled. The acceptance criteria, no pitting or crevice corrosion either at weld metal or HAZ is permitted, is mentioned only in client specification.

 

[EdStainless]

1. You did not add HCl to the test solution did you? Practice A does not use acid.
2. Is the pipe pickled? Then after cutting you should pickle the sample.
3. You should ignore any edge corrosion

If samples fail then they were not annealed correctly.
Perhaps not at temp long enough or not cooled quickly enough.

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Plymouth Tube

 

[Syedabbas]

Yes, we did not add HCL to the test solution. We hired an independant 3rd party to perform corrosion testing (to G48 Method A) as per client requirements but by mistake 3rd party booked the specimen to A923 and testing was done also to A923 and result is OK. Client is not accepting the results and require to perform the testing to G48 Method A for 72 hours. Please advise, is it acceptable if we may submit TQ to client to lower the testing time to 24 hours instead of 72 hours for normal duplex wrought specimen because G48 is flexible on timings and suggests 72 hours although variations may also be used.

 

[pradipgoswami]

Hi Syed,


Passing G48A test is always a challenge to welding engineers.The variables causing failures could be anything, welding parameters/Metallurgy, surface finish,duration of the test, test temperatures.120 grit finish is deemed to be resonable by ASTM, however many specifications allow finish up to 600 grit or more.

Many Upstream Oil gas specifications allow 24 hrs of testing duration for such test( see extrats as below):-

Corrosion testing shall be performed for each welding procedure qualification in accordance with the following:
1.ASTM G 48 Method A.
2. Exposure time shall be 24 hours.
3. Full thickness specimen.
4. All surfaces shall be exposed. The sides (only) may be ground to a 600 grit finish and the edges may be rounded.
5.Samples shall not be pickled or passivated prior to test.
6. Test temperature for UNS S31803 or S32205 weld samples (22% chromium duplex) shall be 20°C.
7. Test temperature for UNS S32550, S32750, UNS S32760, S39274 weld samples (25% chromium "super" duplex) shall be 40°C.
Acceptance criteria: -No pitting at 20X and maximum weight loss shall be less than 1.5 g/m2.

Should the clients' insistence is for 72 hrs duration then:-
--Advise would be to get the base metal tested @ the same duration and temperature.
-Get the same for welding consumables.

If the results for BM and consumables are satisfactory then only pursue 72 hrs test for weld coupons.

If you're forced to pursue the wrost case scenario, then the other option is to use super duplex 25-9-4 welding consumables for the weld coupon.

Regards.


Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

P.S:-You may read this article for further information on the pros and cons of this test-

http://www.twi.co.uk/technical-know...ification-of-duplex-stainless-steel-weldments

 

[EdStainless]

Pradip, and All
Don't confuse G48 and A923. They use similar test solutions but they are done for very different reasons. There is not one single test that will accomplish both. Don't play mix and match with test conditions and procedures.

The purpose of A923 is to detect intermetallic phases. All sample surfaces must be freshly ground with no further treatment.

G48 is looking to determine the resistance to the initiation of chloride pitting. You may polish the edges, if the finished product is pickled then you can pickle, the times and temps are general guidance. If someone has a specific procedure that they want reproduced then that is the way it is to be done.

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Plymouth Tube

 

[pradipgoswami]

Ed,

The issue is not confused.The intent of ASTM A 923 is not same as G 48A test. The cautionary note from ASTM A-923 on this is:-

-Although this test method(A-923) uses some equipment and procedures similar to those of Test Methods G 48, this test method should not be confused with Test Methods G 48. This test method does not determine the critical pitting temperature or test for the suitability for use in a particular environment. This test method is designed solely for detection of the precipitation of detrimental intermetallic phases in duplex stainless steels.

G48 A method is designed to determine the relative pitting resistance of stainless steels and nickel-base, chromium bearing alloys. In reality it assesses a Go/No Go scenario for various Duplex alloys at 22 +/- 2°C range and with a testing duration of 72 hrs max.

If 31803 alloy consistently fails at the above specified testing regime, assuming that metallurgical factors are not contributors then the ways to get around it on G-48A test would be :-
- either reduce the duration of the test to 24 hrs
-or reduce the temperature (within ASTM specified range). A reduction from 24 Deg C to 20 Deg C could be helpful.

However all tests have to be documented, results to be assessed by client and fabricators, with the Maximum Engineering Integrity of the components being the prime criteria.

Thanks.

Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist
Ontario, Canada.
ca.linkedin.com/pub/pradip-goswami/5/985/299

 

[SJones]

The oil and gas industry has spent a great deal of time and effort since the 80s in arriving at a standardised G48 test for duplex. This time and effort is enshrined in standards such as NORSOK M-601, or methodologies such as the TWI Recommended Practice

http://www.twi.co.uk/technical-know...e-use-of-ferric-chloride-solution/?locale=en.

Unfortunately, if the client wants a 72 hour test, that is their prerogative.

Steve Jones
Materials & Corrosion Engineer

http://www.linkedin.com/pub/8/83b/b04

All answers are personal opinions only and are in no way connected with any employer.

 

[NickClark]

I don't know any end users who test for 72 hours. If you have a generally sound wps. Low heat input. Overmatched filler etc and you have good micros and impacts then the test is probably just too severe. A good suggestion earlier is to test the base metal this will demonstrate if you have any chance of passing.

 

[MBosatra]

Dear Syedabbas, I think that CPT in wrought 22Cr DSS should be slighty higher than 22°C, so if the samples have failed G48 or A923 Met. C tests at that temperature is clear that the microstructure have been affected. I would try to cut the tested specimen through the cross section (BM-HAZ-WM) and investigate on the microstructure (you could polish and etch first with Oxalic acid and then with NaOH or KOH, electrolytic) in order to understand if some intermetallics (sigma) or carbides/nitrides are present. Furthermore did you notice the presence of pits scattered on the entire surface of specimens or they are localized for example in the HAZ region? Are the specimens with or without PWHT?
BR, Matteo