NACE hardness survey for a WPS 1

[engr2GW]

Good morning all,

I have a company that developed a Welding procedure for joining 4130 weldneck flange to A106 B line pipe, the PQR and resulting WPS is fine, but the number in the NACE hardness survey was not properly converted to vickers hardness, so they used the WPS and welded a new coupon this month and PWHTed it and re-tested the hardness testing and the numbers came out well. The problem is, they did not use the same wall thickness as the that was used in the original WPS in 1999, the original coupon was 4.5"x0.674" and the new coupon is 3"x0.625".
Questions:
1. Can we accept it like that and just limit the thickness range qualified by the NACE to 2 X 0.625?
2. Or can we accept it for the original range of 2 X 0.674"
3. Or Is it even acceptable for the coupon for NACE and PQR to be different provided they were welded with the same WPS (processes, and variables).

I appreciate any input.

Thanks.

 

[metengr]

Can we accept it like that and just limit the thickness range qualified by the NACE to 2 X 0.625?

Yes, this is the correct approach.

 

[engr2GW]

Thanks a lot Metengr!

 

[engr2GW]

so this means
1. for normal service, the WPS is qualified upto 1.340"
2. But for NACE/sour service, the WPS is qualified upto 1.250"
right?

 

[metengr]

Yes.

 

[stanweld]

mysarah,
Yes, provided impact testing was not required per B31.3.

 

[weldtek]

If I understand correctly, the company ran a supplementary test plate with hardness tests only. If that's the case, please provide some insight as to why, from a Code standpoint, the thickness of the supplementary test plate for hardness tests only, has any bearing on the qualified thickness for the WPS.

 

[engr2GW]

@ weldtek,
Why? because the company made a mistake in coverting the hardness reading on the original test and it was a long time ago, since they could find the records to verify the actual hardness scale they used, they used the PQR to weld another coupon and re-tested it for hardness, but the original thickness range qualified still holds for the WPS and the NACE service is qualified only to 2 times the thickness of the new pipe coupon welded...

 

[weldtek]

I guess my question is, why is the qualified thickness range different per Nace?

 

[engr2GW]

that was my original question, because metengr answered and said the NACE qualification should be qualified to the thickness of the coupon upon which the NACE survey was done, and I agreed because I though the thickness for the PQR and NACE has to be the same for the qualified thickness range for the WPS and NACE to be the same.

what do you think?

 

[weldtek]

Which specific NACE standard are you working to?

 

[engr2GW]

I hope this answers your question weldtek:

NACE MR0175, Vickers' hardness test

 

[weldtek]

mysarah,
To my knowledge, while MR0175 provides details as to hardness testing requirements such as those found in par 7.3.3.2 & 7.3.3.3,
I don't see specific comments that would make me think your situation would require limiting qualified thickness to 2x the plate thickness of the test plate that received hardness tests only, especially considering that we're only talking the difference between 0.674" and 0.625".
When I add supplementary hardness tests to an existing PQR I try to reasonably match plate thickness and chemistry, but, I'm more concerned about matching or going over on the CE than I'd be concerned with being within 1/16" of plate thickness.
Of course, this is just my opinion and others may be able to offer some enlightenment.

 

[engr2GW]

I guess what you're saying is that there's no need to limit the thickness qualified for NACE service, in other words, we can have 2 times the orginial coupon thickness all the way right?

Any other thoughs??

 

[weldtek]

That's my take. It may be something you should run by your customer. I recently used a 1" thick supplementary test plate for hardness tests only, to complement an existing procedure which was run on 1.5" thick material. The only customer comment was that the CE on the test plate would govern its applicability. The test plate had a CE of 0.41 so it was judged acceptable for use on materials with a CE up to 0.41.

 

[metengr]

I respectfully disagree with weldtek on this one. The hardness testing was performed using a PQR that had a stated coupon thickness using an existing WPS. I would require enforcement of the WPS to be bounded by the PQR where the specific application for welding requires hardness as part of the qualification for use.

Using the logic above, if I used a WPS that allowed me to go above the thickness bounded by hardness testing, why bother with hardness testing?

 

[SJones]

By the same logic, would it not also require limitations on both heat input and carbon equivalent as well, since they will also drive hardness variations? Just one of the shortcomings that ISO 15156 fails to get across when it deals with welding.

Steve Jones
Materials & Corrosion Engineer

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