Welding same grade material with different CE value 1

[engrom]

Is it allowed to weld a X70 line pipe(6" WT 7.9mm)to F70 flange with different CE values? The WPS is qualified for CE 0.31max, but the flange has CE 0.38 as opposed to line pipe CE 0.26. Does it require a re-qualification? My thoughts are, for dia upto 500mm, WT below 10mm and CE value less than 0.4%, there is no major concern. What are the other options than getting the WPS/PQR re-qualified? All required NDT tests / hydro will be carried out to prove the weld.

 

[BigInch]

Unfortunately that WPS still won't work no matter how many hydros you do.

**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

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[SJones]

The only other option is to get a deviation signed off by the responsible party. The restriction has been made to limit the effects of steel composition on weld hardness when moving from the qualification test weld which, at a guess, was made with material having a CE value of 0.28.

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

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

 

[rneill]

I agree with BigInch and SJones. A change in CE value can change the properties of production welds from that intended. If I were the customer, I would likely want to see a new PQR with material that was "close" to the CE of the materials to be used in production welding to verify that my required properties could be met.

 

[bmtbne]

jotting these notes by memory, you will need to refer to your relevant piping standards (ASME B31.3, AS4041, BS etc for sections & clause numbers)

I'd expect the original WPS would nominate a material grade rather than a range of CE.

Weld procedures can be used across similar metals. A weld procedure can swap metals within a material group (ie p group) as defined within the piping standards.

The customer may insist on the weld procedure being requalified due to the criticality of the service, number of welds to be conducted or the regulatory/operational/environmental situation he finds himself in.

HTH.

 

[engrom]

Thanks friends for all your response. Agreed that the main issue is the weld hardness with such difference in CE value. Just thinking whether it is feasible to test the production weld with mobile hardness tester in the field to evaluate strength of the weld. Is this a good option?

 

[rneill]

Portable hardness testing is usually quite unreliable and can only be used to test the weld cap (not the through thickness of the weld as required by NACE MR0175/ISO 15156). It would not be an acceptable substitute to weld procedure qualification with materials of CE close to that used in Production welding.

If you refer to NACE SP0472 para 2.3.5.6.2, the CE difference of 0.03 that SJones mentioned is cited here ..

"The WPS shall state that the maximum CE of the production base metal shall not exceed the CE of the procedure qualification specimen by more than 0.03%".

 

[engrom]

rneill, thanks...
Would like to know which mobile hardness tester you've used and what method? We've recently analysed with Krautkramer's tool and found the results very close.

I do understand the importance of WPS/PQR, but I'm looking for an alternative option. Practically I think the CE value below 0.4% is not going to matter significantly as long as Carbon content is almost same and there is no Boron in the material.

Can someone educate me about the microstructure and the weld hardness in this particular case influence the quality of weld?

 

[rneill]

engrom, I'm not sure what you are asking ... it is clear that the higher the CE, the higher can be the hardness in the weld. That is well accepted but it is impossible to tell you how hard you will be in this particular case and whether or not the actual results obtained will meet acceptance criteria or not - there is simply not sufficient information. For a start, we would need to see the full chemistry of all affected materials and the actual WPS.

Regardless, no one that I know accepts a theoretical analysis of expected hardness as a substitute for a properly performed PQR. In the case of sour service, the PQR must meet the hardness testing requirements of NACE MR0175/ISO 15156.

As I pointed out earlier, having completed your PQR and achieved satisfactory results, NACE SP0472 then says that the WPS is qualified for use with materials that have a CE that is no more than 0.03% greater than the CE of the materials used to perform the PQR.

I know that it is very common to accept CE values of up to 0.4 for low strength carbon steel materials in sour service without being particularly worried about it (0.43 is the NACE recommended limit) but that is for normal low strength materials; typically to a maximum of X52 (359 MPa). In this case you have high strength pipe (X70, 483 MPa) and it is extremely difficult to achieve NACE specified hardness values with X70 material and so a CE value well below 0.4 is likely required to have acceptable welds. In fact, the end users I work with would simply not accept this material in sour service at all.

This is not the answer you are looking for but I think it is the only answer you're going to get. I would be advising the end user to refuse to accept the material in the absence of a PQR meeting the full hardness requirements of NACE MR0175/ISO 15156.

Assuming sour service, hydrotesting is completely unable to provide reassurance for this issue since the problems would only develop once the pipe was put into service. You could pass hydrotest one day and the crack and fail two weeks later.

 

[BigInch]

Carbon about the same?? That reasoning only applies to low alloy steel, but the CE difference indicates one is not low alloy. Why do you think they went to the trouble to include elements other than carbon in the CE.


**********************
"The problem isn't working out the equation,
its finding the answer to the real question." BigInch

http://virtualpipeline.spaces.live.com/