RT Film Interpretation usng ASME B31.3

Date 08-10-2009 06:29

NDTIII,
It is noted to be evaluated by RT only in the 2002 edition however the 2008 edition has both Visual and RT.
Regards,
Shane

By BryonLewis (****)

Date 08-10-2009 11:04

I ran into that the other day. I thought it was a typo, undercut not being on the VT list.

By 3.2 Inspector (***)

Date 08-10-2009 11:24

Most RT codes I have worked with has undercut, depth of penetration and other depth/height acceptance levels even though it can't be determined with accuracy.
I think it is a good idea to write in the "comments" section of the RT report that undercut has been detected, but can't be evaluated.

I see it as a little bit problematic that the RT technician actually sign that a given weld is acceptable according to a certain standard, when he can't evaluate several kinds of defects.

3.2

By NDTIII

Date 08-10-2009 12:15 Edited 08-10-2009 12:18

I agree somewhat however, making comments like that on a report can cause concern for the proponent and problems when it comes time to commisssion the plant.
My concern is these welds are being rejected by RT alone. That I have a problem with. We are being made to repair welds without any basis and possible for no erason which can lead to mucho backcharges later on.

It is not a large problem here but I have a problem when interpreters that work with various codes have difficulty staying with the code they are working to and applying the acceptance criteria correctly.

The code interpretation I saw before said you can ignore undercut by RT. Basically they didn't care about the length. Only the depth. Any deep undercut was rejectable but you could have shallow undercut 360 degrees.

My problem is the interperters are rejecting undercut without any basis. They are carrying their pipeline acceptance over to the plants and that is wrong!

The code needs to be more specific. I guess I will have to generate an inquiry to the committee.

Will someone please tell me on what basis do you reject undercut by RT alone when the acceptance criteria in the code you are working to AND the NDT procedure both state "depth of undercut" and do not mention length.

By 3.2 Inspector (***)

Date 08-10-2009 12:33

It is not often that you and I have agreed in the past :O
This time we can both agree and disagree....

I agree that the interpreters must stick to code when accepting/rejecting welds.

Not to long ago I worked on a project where the client had specified the depth of penetration on the root only to be 1mm.
During my review of the the RT films I discovered areas whith very light density, I asked the interpreters why it was so light and why it had not been rejected.

They rightly answered that they can't evaluate the depth on the RT film.
To make a long story short, I requested some welds to be cut out (on my expense if the welds where good) and some manuel VT of the root to be done.

It turned out that the penetration in some cases where 3-4mm and as a consequence were rejectetable. The client now requested UT to be done on all the welds with the 1mm requirement.....The result: More than 250 welds had to be cut out, and not only that, a big part of the boiler had to be removed in order to repair the welds.

My point is, if only the RT crew had written that they could see excessive penetration, but not evaluate the actual depth, the client could have acted much sooner and repairs could have been done without having to strip the boiler apart.

3.2

By CWI555

Date 08-10-2009 18:21

I.D. undercut is also listed in 341.3.2.
I seem to recall what your refering to. As I recall it was saying you can ignore the indication of an O.D. undercut on the radiograph as it's required to be visually examined.
Something that could be seen and measured as acceptable could turn around and reject the weld under RT. I believe that was the driving force behind it.
It is my opinion that the potential for root undercut is why RT still remains on the list.
Measuring depth is bogus without a composite shot and triangulation, even then it's error factor leaves something to be desired.

My 2 cents worth,
Gerald

By Shane Feder (****)

Date 08-10-2009 23:14

Morning guys,
I agree with both Gerald and 3.2, I also have a couple of questions / comments to make.

1 NDTIII, if the welds were rejected by RT for undercut why were they not visually examined / re-examined to determine acceptability / rejectability based on the visual acceptance criteria ?
If I was in your position I would have taken the repair tracing, gone and measured the depth of the undercut and if it was acceptable demanded they get their ass.s out and show me why it was rejected !
If it was indeed visually rejectable I would be asking serious questions of the person who had accepted it originally.
2 I have always been taught to report all discontinuities on the RT report, not just rejectable defects. I cannot find anywhere in ASME V this requirement. Is it noted anywhere else (or is it overkill) ? I am not talking about every tiny thing but things such as undercut, excess pen, root concavity etc that are not classed as rejectable defects but which may require further investigation.
3 There is an interpretaion in B31.3 dealing with the use of a densitometer to measure root concavity and the reply was the code does not address that issue. If density can't be used how can they possibly gauge the depth of undercut ?
4 I don't think the B31.3 committee have made a mistake by nominating undercut for RT (as Gerald noted it is the only way to identify internal undercut) because ASME V Table A110 has it noted as well - Undercut - RT - All or most standard techniques will detect this imperfection under all or most conditions.???

Regards,
Shane

By Shane Feder (****)

Date 08-11-2009 00:50

Hi Guys,
Did a search of the interpretations and I am not sure if these two are relevant. (more to the point I can't understand them)
It does say in interpretation 6-04 that consideration will be given to clarification of this subject but it doesn't seem to have happened.

Interpretation: 2•8
831.3 Interpretations No. 2
Subject:
Date Issued:
File:
Table 327.4.IA
May II, 1983
1663 (B31 83-016)

Question (2): Does the Code describe evaluation of undercutting, revealed on a radiograph, by use
of the film density differential?
Reply (2): No.

Interpretation: 6-04
Subject:
Date Issued:
File:
ANSI/ASME B31.3-1984 Edition With Addenda Through ANSI/ASME
B31.3c-1986, Tables 341.3.2A and B; Acceptance Criteria
December 14, 1987
B31-87-023

Question (3): In accordance with ANSI/ASME B31.3, Table 341.3.2B, weld undercutting imper.
fections can be evaluated by visual examination. Table 341.3.2A indicates undercutting imperfections
to be evaluated by visual or radiographic examination. In this case, are the radiographic examination
acceptance criteria stated for use as a supplementary examination?
Reply (3): No.
Note: Consideration will be given to clarify Tables 341.3.2A and 341.3.2B.
65

Regards,
Shane

By NDTIII

Date 08-11-2009 04:55

Thanks gys. Shane that is exactly what I was looking for. You see. the comittee will not comimit. They are saying yes you can see it on a radiograph but we will not tell you what to do with it. It's up to you.

The undercut is on the ID so a visual is not possible. The densities are not high enough in my opinion to warrant a repair. and the indications are not wide enough to get an accurate density reading.

I guess the committee is leaving this answer up to each owner's Engineering Department. I think it's high time the code committee do something about this and give us a clear answer. The same thing can be said for Exess Penetration. but I'm not going to get into that right now.

By Shane Feder (****)

Date 08-11-2009 08:34

NDTIII,
How about bringing in a UT tech ?
I am not that knowledgeable about UT, maybe Gerald can answer, but the tech should be able to give you the exact thickness of your pipe and the exact depth of your undercut.
If it is less than 1 mm you give the bill for the UT to the RT company.
If it is more than 1 mm you cut out and repair and apologise to the RT guys.
Regards,
Shane

By CWI555

Date 08-11-2009 10:55

UT would be a good idea in this case, but it needs to be someone with a high level of skill.

By NDTIII

Date 08-12-2009 12:42

Thanks for your help guys but I have been doing this for a very long time. When TOFD and Phased Array were new technologies. You cannot accuratley size undercut. I don't care what anyone says,.
The bottom line is this; There is NO length acceptance criteria in B31.3 for undercut. Therefore you CANNOT reject it by RT alone. If I were the contractor, I would be hitting you with a big backcharge.
Granted if the undercut looks dark on the film. Real dark then it might be acceotable to assume it is deep. Otherwise you have NO basis for rejection.

By Shane Feder (****)

Date 08-12-2009 13:11

NDTIII,
Not sure where you are coming from.
One minute you are saying "we" are being made to repair welds and then you are saying if I was the contractor I would be hitting you with a big backcharge.

"My concern is these welds are being rejected by RT alone. That I have a problem with. We are being made to repair welds without any basis and possible for no erason which can lead to mucho backcharges later on."

"If I were the contractor, I would be hitting you with a big backcharge."

I have a huge amount of respect for Geralds knowledge when it comes to UT and if he says that undercut can be measured by a skilled technician then I believe it.

I strongly suggest you spend less time arguing with the radiographers and more time finding out why your welders are getting internal undercut in the first place, no matter what the depth. If you can see it on the graph then it has some depth (1/32" or 1 mm is miniscule).
If it is showing on the graph there is a strong possibility it is at least 1/32" or 1 mm deep,
Regards,
Shane

By CWI555

Date 08-12-2009 22:21

We will have to differ on that. I've seen it done, and I've done.

By Jim Hughes (***)

Date 08-19-2009 23:28

A also agree with Gerald and 3.2.

I have one comment concerning this. I have had NDE companies reject B31.3 welds for external undercut. What we have done is show the tech our VT inspection report that showed that we measured the undercut and it was found to be acceptable. That usally satisfies them. The probplem is they can't tell the depth of undercut by the film. I agree with some ones post about B31.3 code committee evaluating this and either taking it or putting a note that says if it can be dertermined by VT that the external undercut is in code then it is acceptable.

Thanks
Jim Hughes