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Technical Discussions
JoshuaWilliams
NDT Inspector,
USA, Joined Jan 2014, 8

JoshuaWilliams

NDT Inspector,
USA,
Joined Jan 2014
8
13:02 Jan-10-2014
Passing UT but failing RT

I am trying to gather some information regarding UT vs RT. I am currently running a job that requires 100% UT per API 5L and 20% spot RT per UW-52. The pipe itself is .750 wall, 98.00" diameter spiral welded. My confusion lies in the fact that I can scan the weld per API 5L and not find any rejectable defects, but when I have the weld examined via RT I am getting rejects. Is there a method in which I could adjust the sensitivity of both the in-line UT machine and the handheld units to locate the defects that are causing the RT rejects?

 
 Reply 
 
John
John
19:12 Jan-10-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 13:02 Jan-10-2014 (Opening).

Apple and oranges. Hard to compare. Example under sec viii:
Possible to have slag line the length of the weld yet not break DAC - acceptable
Would be be completely reject able per RT Criteria

 
 Reply 
 
anjafo
NDT Inspector
Norway, Joined Aug 2009, 204

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
21:39 Jan-10-2014
Re: Passing UT but failing RT
In Reply to John at 19:12 Jan-10-2014 .

Beside the apples and oranges and the fact that some defects will just be missed by one method (hence why sometime both requested) you could try some simple hand scans with different probes and settings. First thing I would do would be to up the db and see if you can see anything at all where defect should be. If so I would consider calibrating on smaller artificial defect than currently used or switching probe. But then you might get too many rejects within accept limits.

I think a better answer can be given if you advise more parameters such as probe used and calibration sample used as well as defect type missed, material and whatever info you have.

At the end of the day you want to stop the defect in production not just make sure you find it before a costly RT or for whatever reason you want to find it by both methods.



 
 Reply 
 
John
John
03:41 Jan-11-2014
Re: Passing UT but failing RT
In Reply to anjafo at 21:39 Jan-10-2014 .

My point is that you cannot compare the acceptance criteria from two different methods from two different codes. Just do the ut followed by the rt as required. Simple as that. No need to tweak the cal to make rt & ut fall in line with each other, use them to compliment each other. That is my best guess to why you are required to do both

 
 Reply 
 
anjafo
NDT Inspector
Norway, Joined Aug 2009, 204

anjafo

NDT Inspector
Norway,
Joined Aug 2009
204
10:59 Jan-11-2014
Re: Passing UT but failing RT
In Reply to John at 03:41 Jan-11-2014 .

Its actually a good point that John. You want to perform testing according to specs but I can also understand if josh is trying to save himself effort by finding RT defects earlier by UT :)

If he can spot potential RT fails that are within UT limits when scanning with UT then it might be worth a little tinkering. Possibly an extra gate if possible.

Im just presuming here now though.

 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 221

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
221
12:30 Jan-11-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 13:02 Jan-10-2014 (Opening).

This may be a naive question, but have you tried UT to investigate the sites where RT shows defects?

Are the defects detected by RT ones that you would expect to be detected by UT?

 
 Reply 
 
JoshuaWilliams
NDT Inspector,
USA, Joined Jan 2014, 8

JoshuaWilliams

NDT Inspector,
USA,
Joined Jan 2014
8
13:12 Jan-11-2014
Re: Passing UT but failing RT
In Reply to Frank Lund at 12:30 Jan-11-2014 .

I have checked a few spots that have failed RT but managed to pass the in-line UT inspection. When performing the UT, I found the defects that were be detected by RT but again, those areas were only located after making an adjustment to the sensitivity level on the UT unit. I scanned the area 15 dbs over my reference in order to pick up the indication that was causing the RT failure. The bulk of my defects have been slag, porosity, and/or root aligned porosity. I fear that the porosity is small enough to pass UT yet the accumulation is what is causing the RT failure.

 
 Reply 
 
JoshuaWilliams
NDT Inspector,
USA, Joined Jan 2014, 8

JoshuaWilliams

NDT Inspector,
USA,
Joined Jan 2014
8
14:34 Jan-11-2014
Re: Passing UT but failing RT
In Reply to anjafo at 21:39 Jan-10-2014 .

In regards to the request for more info, on the hand held units we are using a USN-58L, 70 degree shoe, 2.25 mhz transducer. As for the material, the sample used for calibration is A139 Gr C, while the material being used in production is ASTM A1018, SS, Gr 36, Type 1.

 
 Reply 
 
whitevanman
whitevanman
05:03 Jan-12-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 14:34 Jan-11-2014 .

Radiography is more suited to volumetric indications, slag & porosity. You'e applying two inspection methods to the same part, . You have to sentence each methods results according to the specified acceptance criteria.

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
21:31 Jan-12-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 14:34 Jan-11-2014 .

Josh

Unless its coarse-grained material or stipulated by the controlling Code, for 19mm thick material I would prefer the European norm of a 4 MHz probe to a 2.25MHz. Better sensitivity and resolution definitely. Maybe try the higher frequency with the range of angles and the responses from volumetric defects will probably be of higher amplitude than the 2,25MHz. But you'll need to use the range of angles, 45, 60 and 70, not just the 70 degree you write you are currently using.

 
 Reply 
 
Joe Buckley
Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT, United Kingdom, Joined Oct 1999, 526

Joe Buckley

Consultant, ASNT L-III, Honorary Secretary of BINDT
Level X NDT, BINDT,
United Kingdom,
Joined Oct 1999
526
23:44 Jan-12-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 14:34 Jan-11-2014 .

Key thing to look at is when you say you are getting 'No rejectable defects' are you getting indications that are a bit below threshold or seeing nothing at all, and are the RT indications a bit above reject level or huge?

If you are seeing defects with both methods and in one they just pass and one they just fail then there's not much to say except 'welcome to the NDT business' its not an exact science, however much people might like to pretend it is.

All NDT methods are (or should) designed to reject defects at a level comfortably below where you expect them to reduce the safety of the part being tested.

If the UT is passing 'major' defects then you have a concern (and that's why they want RT as well) otherwise you shouldn't worry too much.

 
 Reply 
 
JoshuaWilliams
NDT Inspector,
USA, Joined Jan 2014, 8

JoshuaWilliams

NDT Inspector,
USA,
Joined Jan 2014
8
16:05 Jan-13-2014
Re: Passing UT but failing RT
In Reply to Joe Buckley at 23:44 Jan-12-2014 .

Based on the film that I have seen, the rejects per RT are just above reject level, but of course with the accumulation of said defect is causing the failures. As for the UT, when I scan said defects at reference level with the handheld unit, I am seeing nothing close to being rejectable, but when I increase my Db level by 15-20Dbs, I can then see the indications break the gate or come very close to breaking the gate. After further investigation via gouging and welding, I have found that there are multiple layers of porosity, some just beneath the surface and some that is root aligned porosity.

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
17:59 Jan-13-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 16:05 Jan-13-2014 .

Thanks for the update Joshu.

15 - 20dB over sensitive and still not breaking your curve.

I realize your choice of 2,25MHz probe may be constrained by the Code, but have you tried higher frequencies and different angles? Their narrower beamspread should pick up better and discriminate better near-surface defects.

P. S. Is there an equivalent to ndt.net from the States? There are over 800 USA members of this forum, but only a small percentage post here.

 
 Reply 
 
JoshuaWilliams
NDT Inspector,
USA, Joined Jan 2014, 8

JoshuaWilliams

NDT Inspector,
USA,
Joined Jan 2014
8
18:54 Jan-13-2014
Re: Passing UT but failing RT
In Reply to Nigel Armstrong at 17:59 Jan-13-2014 .

For the most part, when I scan 15-20Dbs over, everything that is there breaks the gate. Occasionally I find a few defects that come close to breaking the gate, mostly very small porosity. As for an equivalent site such as this here in the states, I'm not aware of one that exists such as this one.

 
 Reply 
 
john
john
20:38 Jan-13-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 18:54 Jan-13-2014 .

In your own response, you have just given the reason for multiple inspection methods. Porosity usually is very hard to reject with UT unless in a cluster. the methods you are using compliment each other. they are not the same

 
 Reply 
 
Nigel Armstrong
Engineering, - Specialist services
United Kingdom, Joined Oct 2000, 1096

Nigel Armstrong

Engineering, - Specialist services
United Kingdom,
Joined Oct 2000
1096
10:10 Jan-14-2014
Re: Passing UT but failing RT
In Reply to john at 20:38 Jan-13-2014 .

John

You know it, I know it, the whole of ndt.net knows it but the money men couldn't give a fig and certainly wont splash the cash to run two volumetric ndt methods!

On pipeline AUT weld inspection, mapping channels use 7,5MHz probes to detect porosity backed up with TOFD.

 
 Reply 
 
Ed Ginzel
R & D, -
Materials Research Institute, Canada, Joined Nov 1998, 1286

Ed Ginzel

R & D, -
Materials Research Institute,
Canada,
Joined Nov 1998
1286
14:11 Jan-14-2014
Re: Passing UT but failing RT
In Reply to JoshuaWilliams at 18:54 Jan-13-2014 .

Joshua, you are not the first to identify this situation. As John posted, you are comparing apples and oranges. UT has an amplitude threshold, RT has no threshold and is based on whatever the radiographer can discern on the film. The acceptance criteria you are working to is called Workmanship. The process is intended to simply "check whether an acceptable workmanship level is met or not". There is a Nordtest document (TR 427) that was prepared to allow NDT users to rationalise changing from one NDT method to another. Although mostly intended for fitness-for-purpose applications, there is a section dealing with Workmanship. This document provides a great explanation of the process. If the NDT method identifies that the quality requirement has not been achieved it leads to corrective actions. This is often done as a punishment by forcing manufacturers and their personnel (welders, etc.) to do corrective actions by repair or replacement. More seldom the violation of the workmanship standards leads to a fitness-for-purpose assessment of the findings made, which could avoid damaging repairs to be done.
In the late 1980s and into the 1990s I worked for a company in Canada where 100% RT and 100% UT was done on every pipeline joint. There were flaws found by both and there were flaws found only by UT and those only found by RT. Tens of thousands of welds were tested. As fitness-for-purpose become the preferred acceptance criteria RT was dropped because it was seen to be missing more of what was considered a serious flaw (side-wall nonfusion) whereas the less critical porosity that RT was calling was the flaw more often not identified by UT.

 
 Reply 
 

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