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Technical Discussions
Rob
,
Australia, Joined Jun 2019, 12

Rob

,
Australia,
Joined Jun 2019
12
13:01 Dec-06-2019
Eddy current restrictions

Hi Guys. Quick topic regarding eddy current inspection. We are currently doing eddy current on numerous welds offshore. Our techs are putting in Restrictions such as weld profile is irregular, surface is poor, when nodes are being scanned there is limited access inside the knuckle of the node (haz area’s) it just begs the question, is Eddy Current even with it with so many restrictions? Obviously onshore and especially aerospace the conditions are perfect sometimes for eddy current, but offshore???

 
 Reply 
 
Paul Holloway
Consultant,
Holloway NDT & Engineering Inc , Canada, Joined Apr 2010, 253

Paul Holloway

Consultant,
Holloway NDT & Engineering Inc ,
Canada,
Joined Apr 2010
253
14:16 Dec-06-2019
Re: Eddy current restrictions
In Reply to Rob at 13:01 Dec-06-2019 (Opening).

Hi Rob,

I have very limited experience with ET on carbon steel welds, but from what I see it has similar space restrictions as any other NDT method. On the inside of a node there may be limited access for say, an MPI yoke or a UT probe. And irregular/ugly weld cap geometry will trap MPI and LPI (even moreso) solutions and produce false indications.

ET is no different. It's one thing calibrating on a flat, EDM notch carbon steel sample and perhaps the sample that comes with a Weld Test Kit. It's completely different when scanning real welds in the field. Even little spots of spatter that have been painted over will cause the probe to bump and produce a false indication that may move vertically on the screen a little, just like the small crack in the reference piece (I witnessed this yesterday).

ET has many restrictions, just like other NDT methods. Hope that helps!

 
 Reply 
 
Michael Smith
R & D,
Eddyfi Technologies, United Kingdom, Joined Jun 2018, 1

Michael Smith

R & D,
Eddyfi Technologies,
United Kingdom,
Joined Jun 2018
1
17:40 Dec-06-2019
Re: Eddy current restrictions
In Reply to Rob at 13:01 Dec-06-2019 (Opening).

Hi Rob,

Can I suggest that you take a look at Alternating Current Field Measurement (ACFM)? It has been used for years offshore, both above and below water, to inspect welds for surface breaking cracks in place of MT or eddy current testing. The technology is a particular form of testing using induced eddy currents that has been optimized to reduce the effects of permeability, rough weld profile and changes in liftoff (coating variations). The result is a system which can detect and size cracks through coatings and is tolerant to the kinds of conditions encountered on many offshore welds.

ACFM is approved and accepted by the major classification bodies such as Lloyds Register, DNV, ABS and there is an ASTM standard (E2261) which covers the inspection of carbon steel welds.

If you'd like to read a primer on ACFM, I can recommend this link: https://www.qualitymag.com/articles/95086-alternating-current-field-measurement-testing

If you are interested in more information and equipment then you can try here: https://eddyfi.com/en/product/amigo-2

I'm happy to answer any other technical questions on ACFM that you may have.

 
 Reply 
 
Mario Talarico
NDT Inspector,
Italy, Joined May 2010, 423

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
18:42 Dec-06-2019
Re: Eddy current restrictions
In Reply to Rob at 13:01 Dec-06-2019 (Opening).

Rob,
for this type of ET activity, calibration will be performed on notches of various depths on sample pieces having regular surfaces under simulation of variations in thickness of paint.

This may not be enough when difficulties arise due to difficult operating conditions or novice operators. If there are any doubts about the validity of the control over one or both of the above conditions, I think it is best to simulate the control system in use by inserting the reflectors in welded parts such as those under given conditions. I have already seen that nothing is better than this to reassure all or vice versa intervene with motivated corrective measures!

After all we are talking about activities that normally replace applications otherwise followed in much more expensive ways (paint stripping, then MT and / or other) and I imagine this could have a ridiculous impact on the total budget of an activity of this type.

As for the limited access conditions, they should be documented in the report. Only then will the engineers come to our aid.
Greetings
Mario

 
 Reply 
 
Anmol Birring
Consultant,
Birring NDE Center, Inc., USA, Joined Aug 2011, 832

Anmol Birring

Consultant,
Birring NDE Center, Inc.,
USA,
Joined Aug 2011
832
09:13 Dec-07-2019
Re: Eddy current restrictions
In Reply to Rob at 13:01 Dec-06-2019 (Opening).

Please make sure they use ET weld inspection probes. They are special probes for this application.
The CS weld nspection is straight forward if they know what they are doing.

 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 222

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
222
12:53 Dec-09-2019
Re: Eddy current restrictions
In Reply to Michael Smith at 17:40 Dec-06-2019 .

Michael,

I recall attending an ASTM committee meeting on the standard E-2261 at which we addressed the sensitivity of the TSC system to lift-off that could appear as defect indication and/or reduce defect sensitivity. This would happen with no indication of lift-off given to the operator.

We amended the standard to take account of the capability of the NEWT EMA and FGI sensors and software that I designed to assess lift-off and to compensate for its effects.

Regards,
Frank Lund

 
 Reply 
 
Eugene Lo
R & D,
Innerspec Technologies Inc, USA, Joined Jul 2018, 10

Eugene Lo

R & D,
Innerspec Technologies Inc,
USA,
Joined Jul 2018
10
20:42 Dec-09-2019
Re: Eddy current restrictions
In Reply to Frank Lund at 12:53 Dec-09-2019 .

EC has historically and successfully been used (and is still frequently used) for ferromagnetic weld inspection when looking for defects that propogate to and open the crown. In fact, as of several years ago, there was finally even an ASTM standard released specifically standardizing the method. Moreover, there is an ASME standard (somewhere in the process of being finalized) that covers EC in lieu of MT and PT -- sorry that I don't have the document numbers for you but I can find them if you'd like (probably not necessary as at some point, I'm sure someone from Eddyfi will contribute to this conversation as well; Eddyfi is/was the author for both the ASTM and ASME standards).

It is important to differentiate the application though: are you screening welds for potential defects or are you depth (and length) sizing as well? The former is a very common application for EC, and you don't need to do much searching/networking to find inspection vendors using portable systems (such as a Nortec 500 or 600) with specialized weld probes (that can come from various manufacturers). Such inspections occur in both downstream segments (bullet tanks, pressure vessels, etc) as well as off-shore (particularly structural welds) and even non-O&G application such as weld inspection on wind turbine towers.

If your objective is weld characterization, then you will need specialized technology. The predominant (esp. for off-shore) is ACFM, to which someone else referred here. There are also newer, less proven technologies such as Eddyfi's TECA, ONDT's Magnaform ECA, and Echo 3D's EMFI. Off the top of my head, I cannot think of other EM-based methods that provide quantitative data. Purely my opinion, but feel with TECA and other permutations of ECA, that they are a "your mileage may vary" method. Otherwise, I have no personal knowledge of EMFI.

Concerns about lift-off and irregular weld geometry are legitimate but on the other hand, much of the effects on the signals are compensated for by various tools and algorithms in the respective SW, particularly when it comes to sizing. Beyond that, the technicians need a good deal of experience analyzing data.

In short, it's far from unheard of to use EC on ferromagnetic welds.

 
 Reply 
 

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