Root Pass Examination
Root Pass Examination
(OP)
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?
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?





RE: Root Pass Examination
RE: Root Pass Examination
RT can be performed on the final weld and a wet MPI method, like white contrast can be performed as well if you desire. It is more sensitive that PT and easier to clean.
RE: Root Pass Examination
RE: Root Pass Examination
RE: Root Pass Examination
Agree with the above: If VT on the root, PT (dye penetrant) if you want a check against porosity. Then RT the final pass.
We did 50% RT checks of 4200 psi piping when the pipe walls were over 4 inches thick, and then repeated the RT when the final weld was finished, but never for simple then-walled Sch 80.
RE: Root Pass Examination
Review the requirements/contract with the NDE guy and the customer to understand the rational to RT the root. Maybe he had mistaken a R (RT) for P (PT) because drawings were not clear or smudged.
btw, I like the idea of spot radiography. It keeps everyone at their best performance. The downfall is $.
Regards,
Van
RE: Root Pass Examination
RE: Root Pass Examination
1: RT of a root pass doesn't show very much. Not all RT technicians are able to produce a good picture.
2: The film density has to be low to prevent burning out any relevant indications.
3: On some materials it is best to maintain preheat during welding.
4: On a small weld it is usually cheaper to cutout and reweld if there is any doubt
5: Costs time and money.
RE: Root Pass Examination
Regards
Van
RE: Root Pass Examination
RE: Root Pass Examination
If your welders have such a poor success rate that intermediate RT on fairly thin pipe [less than 3/4" thick] is economically justified, get new welders. Economic justification is easy; compare the cost of RT of 50 or 100% intermediate with your historic cost of repair of RT rejects found at Final RT. Bet your young QC inspector what the outcome will be. Enjoy your winnings.
RE: Root Pass Examination
RE: Root Pass Examination
RE: Root Pass Examination
Now what type RT of the root - X-ray or isotope, quite a significant difference in image quality (especially if your isotope is Iridium which is certainly not suitable for 2mm thick metal(reasonable image quality only for 15mm w.t. and upwards due to "hardness" of the radiation). Also if using an isotope what size is the pill - the root only exposure conditions together with a large isotope will destroy any chance of good quality graphs.
Placing of the film - film ID and single wall X-ray will give the best image of the root and any LOF or LOP but will require multiple exposures due to density differences between middle and outer edges of interpretable graph area. The worst image will be from Double wall superimposed or Double wall double image of root-only (standard for completed welds of this OD) unless the film can be manipulated into close contact with the top of the root (a cut film will help).
So just on the options for producing reasonable quality graphs to justify the expense if the root welder is highly suspect, well this is a non-starter. Ask the NDE person to produce RT technique technique sheets for his proposal for root-only and for completed weld!
RE: Root Pass Examination
X-ray should obtain favourable results. However, I do not know how convienient or possible it would be to use a X-ray unit in the field in a very tight spot and where accessiblity is an issue.
Any experience with Cesium sources on thin material such as a root pass?
Regards,
Van
RE: Root Pass Examination
Now repeat for the second exclusion zone when the welder finishes the cover passes. This thin a pipe wall, probably 3 circles does the whole weld.)
A little bitty weld like the one described takes less than two hours to finish the whole thing (fitting, root and cover pass, final pass.)
Can your NDE guy claim he/she is finding enough flaws in the root weld to justify 3 times the weld time to do (unneeded) NDE not called for by the Code?
RE: Root Pass Examination
I am not sure if you have some outrageous radiation safety laws in the US or if the times you have quoted are a bit exaggerated.
Why would the exclusion zone have to be set up if the x-ray set has not been switched on or the gamma source has not been wound out ?
It is a requirement by law in New Zealand / Australia (and I presume the rest of the world) for gamma radiography to be performed by a two man team.
If I/we were not walking away from a 2 1/2" weld in 30-40 minutes (including set-up / shooting and then dismantling) my boss would be looking for two different technicians.
Total time for x-ray would be slightly longer due to setting up difficulties but still no longer than 1 hour.
Regards,
Kiwi
RE: Root Pass Examination
It concerns me to hear of the production pressures out there especially in far away lands. This leads to errors, fatigue and potential over exposures (including the loss of extremities and loss of life) in the rush to get the job done. Play safe it is your radiography license, your livehood, your safety and the safety of the public. PLEASE PLEASE play safe!
RE: Root Pass Examination
RE: Root Pass Examination
A lot of effort that would be better spent with detailed visual/MT.
RE: Root Pass Examination
RE: Root Pass Examination
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.
RE: Root Pass Examination
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
RE: Root Pass Examination
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.
RE: Root Pass Examination
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.
RE: Root Pass Examination
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.
RE: Root Pass Examination
RE: Root Pass Examination
RE: Root Pass Examination
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).
RE: Root Pass Examination
RE: Root Pass Examination
RE: Root Pass Examination