Cracking in H2S Environments 1

[samsarani]

We have applied on forging material (A 105N) the SSC test according to NACE TM177. After the termination time (720 hour) we have noticed the sample is broken (we completely observed the condition of test ex, sampling mechanic, applied force, test media,..) . Forge master has quite confidence to the material because Ceq is under 0.42 and also S Sulfur is under 0.03.
They are going to do metallographic study and get the result and specify the failure reasons.
But my question is: does any other method to assess and evaluation material respect to SSC compatibility? Or we shall do again SCC test in Lab.?
Is there any method to distinguish for this material is rejected without re- testing?
Please send me any information about this matter.
Thanks

 

[SJones]

If you want to get that heat of material accepted it is going to have to pass an SSC test at some stage. Before that, the failure has to be explained in a satisfactory manner. Assuming that it is explained to the end user's satisfaction, the questions then become how many retests and where to test. If it turns into an argument between the manufacturer and the laboratory, material issue versus test procedure issue, walk away from it and reject the material. You will spend more time trying to get the failed material through the test than if the forge master started again. You will then have to also look for another test laboratory.

Steve Jones
Materials & Corrosion Engineer

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

 

[samsarani]

Dear Steve
Thanks for your comment. But you know that this material is belong to a package of valve which manufactured and all of test has been passed except SCC. (ie,HIC, Hydrotest, function test,… have been passed and accepted)
And I want to know we can trust to Metallographic examination or another method for assess SSC test or not. (We reject valve package or we have a way for evaluation?)
thanks

 

[SJones]

No, it was not clear that that the corrosion test had failed after completion of the valves. Moral of the story: complete the corrosion testing before completion of the valves. Apart from that, you need to see a successful SSC test result in the inspection documents. It is good to explain the failure, but that doesn't make it a pass. How many test pieces were tested originally, and how many failed?

Steve Jones
Materials & Corrosion Engineer

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

 

[blacksmith37]

I don't understand what further exam needs be done after failing TM 01-77 ?
Some mills (all in the western hemisphere) asked for their API T-95 broken bars (TM 01-77; 1) to be returned; I expect some did evaluation - the failures were H2S (no suprise).

 

[samsarani]

Dear all
OK thanks, but I am going to find a method (ex: metallographic or something else method) which endorse the failure is regarding to H2S corrosion (SCC) not related to fault of test procedure or apply test condition.
Thanks

 

[blacksmith37]

Stop beating the horse, its dead. Not a suprise for a third (or forth) rate material like A105-welded.

 

[SJones]

I am going to find a method...which endorse the failure is regarding H2S corrosion

The first post asked whether there was another way of assessing susceptibility to SSC amongst other things. And now, it appears to be one of assessing whether the test method was at fault. This is the thing about corrosion testing: fine when it passes, but nobody ever thinks that the material could fail and when it does, what to do about it.

The material was immersed in an H2S containing solution and it failed. Of course the failure will be down to H2S corrosion! Clearly, you are trying to find whether any other factors assisted the H2S. If the test solution didn't go milky, indicating oxygen ingress, the only other procedural faults will be over stressing or poor machining. If all of those are ruled out, what then? Generally, my (bitter) experience is that, when the schedule can't take any more deliberation, somebody makes an executive decision that the test wasn't required anyway and the failure wasn't that bad at all; so everything will be OK carry on!!

I wish you well.

Steve Jones
Materials & Corrosion Engineer

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