Root Pass Examination 3

[safiamoiz]

We have to butt weld a 2 1/2 NPS Sch 80 pipe with a valve. Our NDE person wants to have radiographic examination after the root pass. He would then allow us to proceed with filler passes and finally with capping passes. After that he will examine by radiographic examination and dye penetrant examination.
Is he following the right path. We believe that radiographic examination after the root pass is not required by ASME Section III. Are we right?

 

[Ron]

vanmorrison...probably wouldn't use Cesium 137. The root pass examination would require detail, and the shot geometry probably wouldn't be amenable to the larger Cesium source needed. A panoramic shot couldn't likely be done, so you'd have to resort to 4 elliptical shots.

A lot of effort that would be better spent with detailed visual/MT.

 

[ndeguy]

Its not usual on plain carbon steels if your QC programme is in control of your fabrication facility. If not, then you have to take special steps to cover for possible defective workmanship and this should include some root pass dry powder MPI inspection combined with borescope of the internal until you are certain your fabricatio proces is back under yuor control. But, as I am certain you are now convinced safiamoiz, volumetric (i.e. RT) inspection when there is hardly any volume of weld to inspect is a waste of time and money.

 

[Mr168]

I would stick to a root pass VT only.

Root pass surface exam on most smallbore is just an additional waste of time and money, and you'll still have a difficult time picking up anything other than a gross discontinuity. A small amount of IP, porosity, etc, isn't going to show with a dry mag, and even if you think you're "good to go", you still risk further defects such as excessive suck back and burn through after the hot pass anyways.

If they're using GTAW, the welder could have probably finished that joint out by the time the NDE tech got there. If using SMAW, he probably could have finished before they even got him over the radio.

I'm a firm believer that if there is such a concern over the adequacy of root pass welds on smallbore pipe, especially if dealing with carbon steel or low alloy, then you've likely got a significant deficiency in either your fit-up inspections, welder testing, or a combination of both.

 

[Kiwi2671]

vanmorrison,
My apologies, I did not explain properly.
I was neither suggesting or condoning safety being compromised in pursuit of speed.
Purely trying to show that the time posted (3 hours) for 1 x 2 1/2" weld was way over the top.
An example -
5 mins to unload truck,
10-15 minutes for one tech to set up shot while the other tech is putting up the barricade / signs.
1-3 minutes per shot dependant on source strength.
2 minutes to change films and reposition source.
Total of 5 minutes max per shot.
3 shots x elliptical or 4 shots x superimposed.
10-15 minutes to pack up gear.
That is 55 minutes maximum or 28 minutes minumum depending on variables.
As stated x-ray will take longer to set-up.
We do that numerous times daily (generally faster, I have been conservative)without ever compromising safety,
Regards,
Kiwi

 

[vanmorrison]

Safiamoiz,

In your original post you reference ASME Section III. So am I correct to assume this valve installation is to be done in accordance to ASME? What does the reviewed and approved I & TP specify for the inspection requirements? Or is the I & TP still in the development and review process?

Kiwi, I am glad to hear that your safety is not being compromised.

 

[racookpe1978]

My experience in X-rays is in multi-level power plants where the exclusion barrier has to be "up" and inspected by the shift leaders for the other work crews, the plant operators, and the plant control room staff before the plant operators can allow the radioactive material to be off-loaded from the truck.

Your times are probably right for a "open site" new construction job with no other crews working, but that's not a refinery or power plant where you've got to wait until after midnight to minimize interferences. (Also, my experience also probably includes multiple shots for the final RT of a larger, higher-pressure pipe, but that's what's normally the case.)

Thanks for the input.

 

[HSIII]

safia,

At the very most I would say perform a PT on the root pass if you or someone else needs additional verification beyond visual. I agree with everyone else that RT on a small (schd. 80 wall thickness) root pass is highly unusual, and also not needed as per code (ASME IX, and poss. B31.1). RT on the full weld, absolutely, but anything beyond PT on the root pass in my opinion is a waste of time.

 

[ndeguy]

I would like to know WHY did the nde guy suggest NDT on the root pass alone before progressing with welding. How was the root quality suspect?

 

[safiamoiz]

The NDE guy says that it is a industry good practice.

 

[HSIII]

No offense, but exactly when is it industry good practice according to your NDE guy? Is it when you don't trust the welder enough to make a small root pass? Or is it when you can't find any requirements anywhere stating need for RT in the first place and try to take advantage of the situation by saying that RT "will catch any flaws that could be inclusive and can't be found by other methods" (I've actually had an RT guy try saying this to me, and when I said "what about UT?", he froze).

Personally, it sounds to me like your NDE guy is trying to drum up more business for himself at the expense of your scheduleand budget.

Unless it is specifically called out in the project specifications or required by ASME, I would not go for it. Follow everyone else's advice on here, stick with VT, or if it's really that important drum it up to either PT or MT. Save the RT until the final weld is completed (if required).

 

[ndeguy]

Hahaha - good practice of his money-making industry! Gone are the days when the nuclear industry had money to burn, I think.

 

[Mr168]

Just because they don't have it doesn't mean they won't still burn it!

 

[ndeguy]

Plus ca change...! I suppose why should they give up their beautiful art of burning other peoples (taxpayers, chiefly) money!