100% Xrays 2

[Cuyanausul]

Does any one have experience with a change in NDT for pipe welding in a contract by changing the % x rays from initial 15% to 100% aasked by the client.

In our case due to the diameter of 48" and 36" the hidrostatic tests were not practical and the client decided this change. But... for us, the contractors, I feel this will increase our probability of finding more refused welds, and of course bring more costs?

Would you charge more if you were to do 100% instead of initial 15%, (ASME B31.1). Not by the price of Xrays but because of the probability of more refusals?

 

[SJones]

But you aren't doing hydrotests and, therefore, are saving costs. You have to give something back! And, what sort of quality orientated outfit are you if you worry about the client looking harder and finding 'more defective welds'. Get it right all the time and you won't have to worry about failed welds.

Steve Jones
Materials & Corrosion Engineer

http://www.pdo.co.om/pdo/

 

[ndeguy]

36" and 48" sounds more like transport pipeline than process - however:

Cuyanausul, what stage of fabrication are you at? If completed then this could cost you plenty, not just in increased inspection costs but also in additional repairs that the client contractually was prepared to allow go undetected by stipulating 15% random radiography. If the pipework is still being fabricated, then let all involved know that 100% radiography is going to take place and revise your inspection and test plan to include review of all fit-ups, tacks, and roots. At least you will minimise further repairs.

The client's designer must have known beforehand the pipe diameters and the feasibility (or otherwise) of the hydrotests. If B31.3 para 345.1(c)(1) or (2) is applicable then para 345.9 applies. This clearly states that circumferential, longitudinal and spiral groove welds not subjected to hydrostatic or pneumatic leak tests shall be 100% radiographed or 100% ultrasonically tested. Plus all structural attachment welds shall be either penetrant or magnetic particle tested. The client should have contracted the fabricator for this work prior to fabrication start-up and allowed for the increase in quality costs concomitant with a change from 15% random to 100% radiography and the extra surface NDT.

15% random examination acts as an aid to quality control but it does not pretend to guarantee that all welds will be radiographically acceptable. The owner should realise that there is potential for significant discontinuities to exist in welds that were not radiographed. Also random radiography is intended as a feedback mechanism to allow the fabricator to take corrective action on discovering weld quality is not meeting the acceptance criteria. It is not intended that random radiography be performed after completion of all welding, as no corrective action to improve continuing welding will have taken place. If random radiography at this point shows that repairs are required it can only throw doubt on the quality of the remainder of the welds. In addition each welder is only allowed 2 repairs. On discovery of a 3rd rejectable weld all 100% of his work will have to be radiographed - a costly process compared to pulling a welder off production work on receiving his second repair and not being able to demonstrate his ability to produce sound welds.

I think the answer to your question is "yes". Extra repairs of defective welds will obviously involve extra costs for which the fabricator was not contractually responsible. However if you are fairly confident of your fabrication, welding and inspection procedures with a skilled and committed work force, I would be more worried about the cost of the 6 fold increase in radiographic coverage - especially on the size pipes you are talking about. X-ray film does not come cheap!

 

[Cuyanausul]

We are at 99% completion of all weldings, and for a better picture of the work, this is a geothermal steam system.

I apreciate both replys, I came to this project at 80% completion, and I worry about the quality, the inspector we have is not what I am used to have, I even had to dismiss a 50 years old welder!

One more question, is it that dangerous to do an air pressure test instead of hydro?

Some pictures at:

http://www.geocities.com/simanmecanica

 

[stanweld]

In ASME B31.1, it's either 100% RT or none. The Purchaser required 15% RT in addition to Code requirements. A Change of Contract is warranted; however, it appears that you initially asked for a Change so as to eliminate the hydrotest. I personnaly don't see a problem with hydrotesting large diameter pipe unless water is unavailable; furthermore, B31.1 provides for pneumatic testing in lieu of the hydrotest.

 

[stanweld]

Pneumatic tests are inherently more dangerous due to sudden (explosive) high stored energy release should the pipe burst. The potential for burst can be lessened depending on the stress applied from pressurization as a percentage of the Yield Strength of the pipe and the degree of testing of the longitudinal pipe seams by the manufacturer or others. Safety must be of first priority when testing large volumes but safe tests can readily be achieved.

 

[ndeguy]

Sorry, my mistake, Cuyanausul. I see you did specify the Code was B31.1 and not B31.3 as I wrote for. Stayed up too late the previos night watching World Cup football!

 

[Cuyanausul]

Yeap, and congratulations you guys, US is performing better now in soccer!,
.... hidrotest wasn´t feasible because the pipe was designed for steam, not water so the supports won´t stand more weight,

 

[stanweld]

We hydrotest similarly designed systems regularly. We design and install temporary support systems for the hydrotest and remove them after testing. This is simply part of the cost of construction.

 

[ndeguy]

Thanks for the star, Cuyanausul, even though I did write for the wrong section of B31. I hope you let us know the outcome, because I got one thing right - X-raying 100% of the 36" and 48" will cost a lot more than hydro-test. If you are worried about the quality, then I suppose the pneumatic test is just too risky.

Tough one for US soccer team tonight against a Ghana team revitalised by their last win!

Nigel Armstrong
Karachaganak Petroleum
Kazakhstan

 

[Cuyanausul]

Well guys, first stage Xrayed was 100% satisfatory, and we are still waiting for more, hope it comes same way. You can see some pictures at:

http://www.geocities.com/simanmecanica

.-

 

[IFRs]

In my line of work, whe one uses a lower percentage of x-ray, the design stress is reduced to allow for a lowered quality welds. It is not an insult or an issue.

 

[Cuyanausul]

IFRs: Yes, in this case the client performed 100% because the pipes are 48" and 36" diameter and the supports were not designed for a water filled pipe, they will carry steam.
On other diameters, we are Xraying 1st stage 15% acording to B31.1 ........