Doing Phased Array (PA-UT) on top of RT and asking contractor to fix a defect

[Acidity]

Hi All,

I am working on a Pipeline project in Canada, where our Contractor has developed WPS based on wire-fed processes (GMAW and FCAW) for produced emulsion, gas and steam pipelines and wants to conduct Radiography (RT) to detect imperfections. The owner fears that radiography is not an appropriate technique for detecting imperfections that are inherent to wire-fed processes and proposed to use Phased Array technique (PA-UT)instead. Contractor is adamant on using the radiography as they already developed welding procedures and welders are qualified. Contractor thinks that it is too late for the contract. Now owner is saying that they will do PA-UT on their cost and if there is a defect identified then Contractor will have to repair it. Of course Contractor is not agreeing to that also as they think that it is unfair to use combination of two NDE techniques.
Now I have two questions:

1. based on your experience/understanding do you that RT is not appropriate for these kinds of welding processes? if so, why?
2. Does owner have the right to perform PAUT and ask contractor to fix it, if unacceptable indication is found?

 

[DekDee]

Acidity,
Not enough information.
1 What is the code/standard ?
2 What does the contract say ?
3 What does the project specification say ?

Based on past experience utilising 2 x volumetric inspection processes for the same welds is a recipe for disaster.
Regards,
Shane

 

[DVWE]

based on your experience/understanding do you that RT is not appropriate for these kinds of welding processes? if so, why?

RT is absolutely appropriate for this application. RT is not any less sensitive to wire fed processes, rather, is largely more dependent on the equipment, techniques used, and experience of the RT crew. If I were the owner, that's what I would focus on.

Does owner have the right to perform PAUT and ask contractor to fix it, if unacceptable indication is found?

My opinion, no. If the owners perform secondary NDE and pay for the services, the responsibility also falls on the owner to pay for any repairs that result from the findings.

DekDee is correct. The contract and specifications should spell out the requirements. I also agree that 2x volumetric NDE on the same welds is a recipe for disaster.

The devil is in the details; she also wears prada.

 

[david339933]

I have come across this many times for pressure vessels.....We have put a man on the moon, walk around with powerful computers in our pockets, have self driving cars...but think that no technological advances have been made in wire fed welding processes since the 50's.

 

[weldstan]

The Owner may require PA-UT but it appears that it is a change to the Contract and pricing must be negotiated. My problem with PA-UT is the abilities of the examiners to properly define the linear discontinuity. RT is quite appropriate for the welding described.

 

[brimmer]

I would offer a couple things:

The owner can do whatever they want. They are the owner, it is their kit to operate in the end. The question is more of who will pay for inspection and repairs. The owner has the "right" to do additional inspection, to ask the contractor to fix out of their pocket is another matter. Depends on the contract. If the wording in the contract, or indication found is greater than allowable in the contract or by code, then yes I would say the contractor needs to repair it at their expense.
If the owner is using UT, then the owner needs to have UT procedures developed before they can do UT. They can't just come in with UT behind the RT arbitrarily, they need to follow code still.
UT is generally a more sensitive and better methodology for detecting indications, it depends on which type of indications though. Small linear indications UT will be better, volumetric indications RT is fine. We have been using RT for may years obviously and it has been acceptable, the industry is moving more to UT though. There will be features that UT find that the RT did not, this is why they need a procedure and acceptance criteria developed for the UT. UT will find everything, even very small indications .

 

[Acidity]

DekDee

1. The construction code is CSA Z662.
2. There is nothing in the contract that is specified that says who will pay if defects are detected on secondary NDT.
3. Owner Specifications do not prescribe anything in this regard.

Thanks

 

[EdStainless]

If it wasn't explicitly included in the scope then it isn't in the scope.
As Brimmer said, the owner can do what they want.
But in this case there appears to be no grounds for expecting the contractor to either pay for secondary testing or absorb the cost of rework resulting from the secondary testing.
If the owner wants to do UT then fine, but I hope that they have a well written procedure that covers the test method, procedure, calibration and so on.

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P.E. Metallurgy, Plymouth Tube

 

[Acidity]

Is it not Contractor's responsibility to provide defect free welds regardless of who performs the NDE and whether it's a combination of two or more NDE techniques?

 

[DVWE]

Yes. As long as the contractor knows that requirement up front. Then they can charge the ridiculous astronomical dollar amount to see how bad you really want it.

The devil is in the details; she also wears prada.

 

[KevinNZ]

The contactor will have based their price on the testing requirements in the contract. They would have allowed for repairs based on the amount testing. If you add more testing and therefor, maybe, more repairs the costs go up.

The contractor does not have provide 100% defect free welds. They only need to provide defect free welds that are tested.

10% RT/UT will only pick up 10% of the defects, 90% of the internal defects will still be in the welds.

You can had extra requirements to your contracts, like 100% testing or 100% testing of the welder's first few production welds.

 

[EdStainless]

No, not defect free welds, but rather welds which have no NDE indications which exceed the required limits.
The test method and standards used are critical to knowing what is likely to be rejected, whether it is defective or not.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, Plymouth Tube

 

[brimmer]

As EdStainless points out, "defect free" welds would be welds that don't exceed the limits of the code and whatever criteria you are using. The issue is with two different NDE methods, you will need to describe two different criteria, one for RT and one for UT, this is the issue, agreeing on what is considered acceptable. A weld may pass by one method and fail by another.