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?

 

[cloa]

Better to post in ASME forum but don't double post- click Inappropriate post? or post a link to the new thread. If you have already posted in ASME (mechanical) code please correct this thread.

 

[Eddycurrentguy]

Nothing in Section IX or V that requires RT [or any NDE] examination after completing the root pass. My recommendation would be to perfom an MPI examination of the root pass using dry particles if you are concerned with root cracking. RT is overkill for this application (examination of root)and you have a good chance of missing a smaller crack anyway. Also, unless you re-apply the preheat after RT, your chance of cracking dramatically increases due to root bead contraction.

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.

 

[metengr]

Root pass RT is not required by Code, only final NDT. Do I think your NDT examiner is on the right path? Yes, if they want to ensure weld quality weed out poor welders in production.

 

[stanweld]

On a 2 1/2" pipe butt weld, it is far more cost effective to RT only after weld completion. You should visually examine the root ID surface for full penetration/contour before completeing the root if you have reason to suspect the ability of the welder. If your NDE guy is a subcontractor, he is simply trying to obtain additional money for his service.

 

[racookpe1978]

Your NDE guy is "right" in that you "can" do all that, but he is wrong in requiring it. For a small 2-1/2 inch pipe that thin (only Sch 80) on a simple butt weld, his choice is not only overkill, but he is telling you to shoot it again and cut off its head, then tie the carcass up so it won't run away.

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.

 

[vanmorrison]

Radiography of the root pass may not be required of ASME but a specification or a condition in the contract may dictate this inspection and/or spot radiography. The contract will rule and your NDE guy may not be wrong. Clear expectations must be documented.

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

 

[safiamoiz]

Thank you very much for all the good advice.

 

[unclesyd]

Reasons against RT of root passes,

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.

 

[vanmorrison]

Unclesyd, the above is an excellent summary of reasons against radiography of a root pass.
Regards
Van

 

[Ron]

UncleSyd is right. The density difference alone makes the shot and the interpretation difficult. Could be a waste of time, effort and money.

 

[Duwe6]

UncleSyd hit everything except how fragile just a root-pass is. For shop work, the strength of only a root is adequate. For a fieldweld, it is foolish to stop the welder until he has completed the root and 'hotpass' second layer.

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.

 

[safiamoiz]

Thanks again.

 

[ndeguy]

Calling for RT on a root-welded only 2 1/2 OD 7mm thick weld??? Forget replacing the welders - replace your ndeguy! NB I am aware of the irony!!!

 

[ndeguy]

Should consider the options - access to VT the ID is only possible with a borescope or similar. This should be 1st choice to check for lack of penetration / undercut immediately after welding in the root (lack of fusion will most probably not be detectable by VT) if root welder is "suspect". The OD side of the root can be checked by dry powder MPI for cracking.

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!

 

[vanmorrison]

NDE GUY, I agree with your recommendations on inspection techniques for a root inspection.

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

 

[racookpe1978]

X-ray will require a 75 - 100 foot exclusion zone around the weld point for about 3 hours: 2 hour setup, 1 hour for the shots and checking, plus a little bit for the removal.

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?

 

[Kiwi2671]

racookepe1978,
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

 

[vanmorrison]

My regulations require a exclusion, barricaded, signed roped of zone set up at 10 mr/hr. This needs to be set up prior and during the shot. I am not sure if it is regulation that it is a two man team (it has been awhile since I have been in the regs) however, internal procedures and good practices dictate 2 radiographers minimum in addition to the barricaded exclusion zone.

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!

 

[safiamoiz]

Having read all good advices, my NDE person now wants another advice. Is it good or worth full to do surface examination at root pass. Please comment.