Nace mr0175 hardness survey 1

[jimmy23]

In regards to NACE MR0175 (sour service) does clause 7.3.3.4 apply in all cases? In other words must I ALWAYS hardness test production welds or "sample coupons" when sour service is applicable? I have reviewed a few posts on this subject on this site which give bewildering replies. If I am using SA-106B (which is pre-qualified) and using a wps proven to give adequate hardness (following the essential variables) why do I need production hardness? It has been said on this site that the pqr by no means guarantees a production weldment of the same hardness if the same heat of steel wasn't used. Doesn't this seem ridiculous for P1 materials approved for NACE (according to MTR) when the only thing needed to lower hardness values is very moderate preheat?

The below is an excerpt of NACE MR0175 Sec. 7:


"SSC-resistant carbon and low alloy steels may be selected from the pre-qualified materials identified in NACE MR0175/ISO 15156-2".

"Generally, no additional laboratory testing of pre-qualified materials selected in these ways is required. The materials listed have given acceptable performance under the stated metallurgical, environmental and mechanical conditions based either on field experience and/or laboratory testing."

If these materials have demonstrated "acceptable performance", as stated above, and my pqr shows that SA-106B welded by the specified parameters produces acceptable weldments (hardness below 250HV)....why necessitate further testing?

The bottom line is that NACE MR0175 explicitly states:

NACE MR0175 Sec 7.3.3.1:
"The qualification of welding procedures for sour service shall include hardness testing in accordance with 7.3.3.2, 7.3.3.3 and 7.3.3.4".

While 7.3.3.4 states:
"Weld hardness acceptance criteria for steels qualified and/or selected using option 2 (see 7.2) MAY be established from successful SSC testing of welded samples. SSC testing shall be in accordance with Annex B."

Where does the above turn into mandatory hardness testing of completed production welds or sample coupons?

If that is indeed what is intended by NACE then they are worse than ASME for lack of clarification.

I have also seen "as welded" quoted on this site in regards to A.2.1.4 as found in the technical circular....how is this applicable to pipe welds where the root is inaccessible? Both cannot be satisfied.

Am I crazy thinking these measures are absurd in regards to P1 materials?

 

[SJones]

Hmmm - seems like you have a lot of issues with MR0175; join the club. First of all, bear in mind that it would appear that nobody with great welding expertise took charge of the welding section. It looks like a typical corrosion engineer's attempt.

Why do you need production hardness? Well, as per MR0175, it is not a requirement - there is nothing under sub-subclause 7.3.3 that demands production hardness testing. As to heat to heat variation of hardness, simply classing a material as P1 doesn't guarantee chemical composition control and 'moderate preheat' may not be enough to keep the hardness down if the carbon equivalent is five plus points higher. Also, don't forget that ASME IX allows a 55 degree drop in preheat without requalification, and, undoubtedly, people will attempt to take advantage of that without realising the implications for sour service because ASME IX simply is not produced to deal with the vagaries of such an application.

So, given all that, would it be wise to forego production hardness testing? The answer, as they say, is: the risk is all yours. 7.3.3.4 applies in all cases, but 7.3.3.1, 7.3.3.2 and 7.3.3.3 only deal with 'procedure qualification,' so one can conclude that only qualification welds are required to be hardness tested for Option 1.

What gives you the impression that production hardness testing is a requirement?





Steve Jones
Corrosion Management Consultant

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

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

 

[wegm]

please have a look at this link:

http://www.weldinguide.com/gdanastasiadis/viewtopic.php?f=5&t=244