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- since 1996 -
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creed
NDT Inspector,
n.n., Joined Jul 2009, 33

creed

NDT Inspector,
n.n.,
Joined Jul 2009
33
12:48 Aug-27-2015
Eddy current testing for Stainless steel weld

Hi everyone,
I have some queries regard to ECT for weld which is stainless steel material.
1. Can we do ECT on weld which is stainless steel material? if Yes can you please show me some instruction for calibration or any required special equipments?
2. Can we do ECT on welds which have galvanised coating on the surface? I experience some weld with galvanised coating on the surface then it changed the lift off signal that is no longer same phase with prior calibration on 1.0mm EDM slot block.
I appreciate for any advices posted up here.
Thanks

 
 Reply 
 
Rakesh Bekkam
NDT Inspector, Executive Engineer in Quality
TATA ADVANCED SYSTEMS LIMITED, India, Joined Jul 2015, 3

Rakesh Bekkam

NDT Inspector, Executive Engineer in Quality
TATA ADVANCED SYSTEMS LIMITED,
India,
Joined Jul 2015
3
13:26 Aug-27-2015
Re: Eddy current testing for Stainless steel weld
In Reply to creed at 12:48 Aug-27-2015 (Opening).

Hi Creed,

How are you ?

May i know which instrument you are using ? Because if you use Olympus, you will not get this problem. Once you calibrate the equipment with appropriate probe , balance the machine when probe place on weld joint. Also there are so many factors effecting on weld joint in Eddy current. Kindly check surface preparation also.

Thank you

 
 Reply 
 
Louis
Other,
Eddyfi, Canada, Joined May 2013, 33

Louis

Other,
Eddyfi,
Canada,
Joined May 2013
33
20:10 Aug-27-2015
Re: Eddy current testing for Stainless steel weld
In Reply to creed at 12:48 Aug-27-2015 (Opening).

Hi!
Generally speaking, ECT is perfectly suited for stainless steel. But it depends if the specific grade is mildly ferromagnetic or not at all. E.g. 316 SS is non ferromagnetic, while 304 SS is a little tricky as it can be ferromagnetic (it can be managed however, not a show stopper at all). Also, it depends on your detection requirements (flaw type, size, etc.).
Here is something about eddy current array (ECA) on stainless steel welds (relevant even if more elaborate compared to ECT): http://www.eddyfi.com/application-notes/inspecting-for-cracks-in-austenitic-stainless-steel-welds/

I would say it is logical that the galvanized coating affects the phase of the signal. Its impact on your detection capabilities will depend on the thickness of this coating, among other things. Comparing the liftoff signal will give you a rough idea of important it affects your signal. A phase difference of a few degrees (e.g. 5) is maybe not so bad, greater than that means it is likely to impact your amplitude a lot too…

I guess your issue is that you do not have a calibration standard comparable to what you inspect… Maybe you won’t like the answer but you could try to find shims of the appropriate thickness and made out of a similar material (galvanized = zinc = about 28% IACS conductivity). I think some aluminum grades are close to 28% IACS so you could maybe try to construct an appropriate cal standard that way… Unless someone has a better idea I think it could help you set an adequate sensitivity and avoid missing critical flaws.

I hope it makes sense. I’ll be away for a little while. All the best!
Louis

By the way, I don’t think this has anything to do with the brand/instrument you are using… it’s physics here.

 
 Reply 
 
Phil Herman
Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards, USA, Joined Oct 1999, 79

Phil Herman

Sales, - Manufacture of NDT Reference Standards/Test Blocks
PH Tool Reference Standards,
USA,
Joined Oct 1999
79
22:13 Aug-27-2015
Re: Eddy current testing for Stainless steel weld
In Reply to Louis at 20:10 Aug-27-2015 .

Hello colleagues,
Louis is correct here; the best solution would be to construct a calibration standard with a galvanized coating. Manufacturers of quality standards do this all the time.

 
 Reply 
 
creed
NDT Inspector,
n.n., Joined Jul 2009, 33

creed

NDT Inspector,
n.n.,
Joined Jul 2009
33
09:49 Aug-28-2015
Re: Eddy current testing for Stainless steel weld
In Reply to creed at 12:48 Aug-27-2015 (Opening).

Thanks everyone,
I agree with the solution use galvanised shim for calibration to get properly phase and gain of crack like signal instead use plastic shim as usual.
But for the stainless steel weld, I am still confusing unfortunately. Usually, I use the Unit Phasec 2D and diff probe with suitable to check C/S steel weld (and this is not Eddy Current Array), I set frequency at 100kHz, phase and gain refer to 1.0mm EDM slot block. My ideal is can i use the same way of setting up with the probe and the unit like that but refer on the stainless steel 1.0mm EDM slot block (of course, phase and gain will difference). I knowledge that the conductivity of stainless steel if totally difference with carbon steel and it stays on the conductivity curve, so the lift off signal and the crack signal is not much difference compare to calibration on carbon steel material.
Anyone have more clarification for this case?

 
 Reply 
 
Muhammad Kashif
Muhammad Kashif
09:32 Aug-31-2015
Re: Eddy current testing for Stainless steel weld
In Reply to creed at 09:49 Aug-28-2015 .

According to my knowledge. Better inspection can be done by Olympus Omniscan Mx with flexible probes that specially designed for weld inspection. I have used Phasec 2d. By using this equipment you cannot perform accurate inspection due to lift off variation/noise signals and limitation of eddy current depth of penetration.

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

Mario talarico

NDT Inspector,
Italy,
Joined May 2010
423
23:06 Aug-31-2015
Re: Eddy current testing for Stainless steel weld
In Reply to creed at 09:49 Aug-28-2015 .

Creed,
adjustment of phases and amplitudes is functional to the type of procedure. Need 3 defects surface breaking at different depths to determine a possible set-up; more so if you have to meet a sam set-up for two materials. If you think too much, considers that to be simulated also the trend of amplitude and phase for the sub-surface defects, at different distances from the surface ( if not explicitly excluded their detection).
Without test-block it may be misleading extend a procedure also for the same material. As always it depends somewhat from the procedure by the requirements to be met.
I'm sorry but I can not add more.
Greetings
mario

 
 Reply 
 

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