Radiography of repair

Date 08-11-2009 06:49

Shane,

I like this requirement, however common sense must also be used here.
The power company I usually work for has it written in their specs as it is not written in any EN standards or PED for that matter.

I like it for 2 reasons,
As you mention yourself: What if the collimator is placed in a different position and a defect is found that wasn't on the first radiograph ?
The weld will obviously be rejected ---> Praise the lord we did the hole circumferental again :)

From time to time the RT tech mark the wrong spot on the weld (turn the meassure tape 180 degrees) and as a consequence the welders is going to repair a perfect sound area, the RT crew (maybe another guy) come back to x-ray it again, their report is in the office.....oh, they have repaired this area, lets shoot this again. I think you get my point.

Lets say a DN 500 weld in a 4 bar cooling water line has been rejected due to a small pore in a stop, IMO that is OK if they just RT that single spot again, however it must be the same guy as did the first exposure and he must have the original report with him when he mark the defected area.

On other more critical lines I think the requirement is justified.

3.2

By Shane Feder (****)

Date 08-11-2009 08:24

I agree with your comments 3.2 apart from the last.
If you have a 4 bar water line and the contract requires it to be fabricated and tested to Normal Fluid Service (when in fact it should have been Category D) and you don't radiograph the whole circ after a minor repair then you are not in compliance with the code.
As you are well aware you can make your specs more stringent than the code but not less, if the code says 100% RT after a minor repair then that is what you must do.
Cheers,
Shane

By 3.2 Inspector (***)

Date 08-11-2009 09:48

I agree.....
My example was not related to any code, which it should as we are discussing a specific code here.....my bad.

I just tried to give an example where I think it is a bit overkill to RT the whole weld again, this is of course not the case if it is written in the code :)

3.2

By Shane Feder (****)

Date 08-11-2009 10:54

3.2,
I think the whole thing is overkill.
My concern is trying to get the contractors to comply, they are not going to be impressed at all. As it is only a draft I will just have to wait until it becomes official.
So, I wonder if this will this be applicable to UT as well ?
Two different UT techs can sometimes give two different interpretations of the same weld. What happens if one tech calls a repair and after the repair is done another tech comes in and finds other defects missed by the first tech.
Seems like a huge can of worms to me !
Regards,
Shane

By CWI555

Date 08-11-2009 11:02

Shane,

The committee's are meeting this week as I recall. Don't look for that one to be approved.
As for finding defects on a second run, That will go to all methods. I don't agree with requiring the whole weld to be re examined, but I do agree with not letting something go if it's found.

Regards,
Gerald

By 3.2 Inspector (***)

Date 08-11-2009 11:20

shane,

It might be overkill, it might not.
By enforcing my clients specs. the RT techs has been "caught" several times, they simply marked the wrong area.
My company has advised our client only to enforce it on the more critical welds, simply because it was very time consuming to argue about some random drain, cooling water or whatever "non-critical" line was being discussed and then loosing focus on things "that really matters" like steam and feed water.

Getting the contrators to comply is almost always a huge fight, which is bound to be won by the client as it is in writting.

If a UT tech miss a defect on his first examination?
Well, IMO it is the same as when you review RT films, which has been approved by the NDT company interpreter, it is not a matter of who can meassure the best.
If for example a pore is maximum allowed to be 2mm diameter, I dont try to get it to be bigger than that, I have to respect the call of the interpreter.
However, if I several times spot pores to be 3-4mm and he has approved it, I start to question him and maybe have him replaced and/or have all his films reviewed by a NoBo.

The same thing goes for UT interpretation, the client has to respect the call of the guy doing the first examination, unless it is proven that he again and again miss critical defects.
If so, he shold also be replaced and/or all his examinations should be re-examined.
The defect is not allowed to be there, even though the tech missed it.

None of this really relate to your first post, I just try to explain why and when I think it is a good idea to either have it in the code or client spec.

3.2

By Shane Feder (****)

Date 08-11-2009 11:50 Edited 08-11-2009 11:53

Gerald / 3.2,
Thank you for both your responses, I agree with your comments.
I had not thought about a second RT crew shooting in a completely different location (mind you I have had first hand experience on a boiler shutdown that turned into a massive lawsuit due to dayshift / nightshift shooting from different directions.)
I would like your opinions on my concern over the placement of the collimator if reshooting the same weld twice, especially as you are both aware RT is an imperfect art.
If one crew shoots with the collimator on the number band side of the weld and a discontinuity (say a large gas pore) is found to be just acceptable.
The second RT crew places the collimator on the opposite side of the weld.
Based on the size, shape and orientation of this pore it may now appear on the film as slightly unacceptable.
How do you possibly tell the contractor and/or the client that the repair is OK but we have now found a new repair in a totally different place ???
Surely this is a major can of worms ! ???
Regards,
Shane

By 3.2 Inspector (***)

Date 08-11-2009 13:53

You will not see the same defect from both sides :)
Maybe I misunderstand what you try to say.

3.2

By CWI555

Date 08-11-2009 15:33 Edited 08-11-2009 16:36

There should not be a reason to reshoot a good weld to begin with. Therefore I am assuming you mean that there is another rejectable indication found elsewhere in the view far enough away that it was not excavated in the repair.
A repair shot takes place, but the tech does not put the source in the same place.

In that situation the RT tech has screwed up. if it was enough to create geometric enlargement of a previously acceptable pore, then it is inversely plausible that the change of incident angle could also change the appearance of the area that was marked up for repair. This brings into question the original shot, especially if it was a small planar that was being repaired. That change of angle could enlarge or shrink the image of the planar.

If you start getting into that kind of business, you might as well reshoot everything three times at three different angles for triangulation of actual size and depth.
That I consider to be a recipe for disaster on a project. The code does not require it, and I've only ever seen one spec that required it.

If that RT tech shifted the source as you suggest, they in effect invalidate the results of the previous shot as your looking at a totally different impingement plane. Since the repair was made based on the original shot, then it's NFG for verifying the original condition that created the repair has been remediated.
The tech makes that mistake more than a few times, it is time for him or her to seek the greener fields of the ROMFO list.

Repeatability is the mark of a functioning NDE program. Anything else is dysfunctional.

My opinion for what it's worth,
Gerald

Edited for spelling

By Arctic 510 (**)

Date 08-11-2009 16:34

"Repeatability is the mark of a functioning NDE program. Anything else is disfunctional."

I like that!

By Shane Feder (****)

Date 08-11-2009 23:17

Hi Gerald,
What I was trying to explain (maybe not too well) was "inadvertent triangulation."
The way I was taught was this:
1 Straddle the pipe facing in the direction you are travelling.
2 Mark your zero on top with arrow facing to the right.
3 Wrap lead number band around pipe on the near side of weld
4 Wrap sliding lead identification plaque around pipe on the far side of weld
5 Place collimator with the front on top of cap with back on base metal so beam is shooting through the HAZ as close as possible to the edge of the cap.

Usually the collimator is clamped, strapped or taped on the far side of the weld but I have seen other techs place it on the near side and even some who shoot straight thru the weld. Who is to say which is right and which is wrong ? Due to the fact that radiation escapes thru the tail of the collimator sometimes it has to be placed facing one way and not the other to lessen exposure to the technicians.

As everyone is aware the direction of the beam and the orientation of the defect are critical in what is actually transposed onto the film.
Let's say for example we have a 12" chromolly pipe weld approx 1" thick. The cap could be anything from 1 1/2 - 2" wide.
The first crew shoot it with the collimator on the near side of the weld and on the film we have an unacceptable gas pore and 8" away we have a gas pore that is acceptable but very dark indicating a bit of depth.
The unacceptable gas pore is repaired and it is re-radiographed.
The second crew reshoot the repair from the same location but with the collimator on the far side of the weld and the gas pore that passed is now unacceptable because from another angle it's true size was revealed.

How many have seen a rejected film where the collimator has slipped or moved during the exposure. Any defects have a shadow and the size and density of the shadow are based on how far it moved and how far into the exposure it was when it moved.

The point I am trying to make is if all the shots are not taken from EXACTLY the same spot the second time round the films (and any discontinuities / defects) will not look the same.
Regards,
Shane