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Technical Discussions
Dilip
India, Joined Mar 2013, 2

Dilip

India,
Joined Mar 2013
2
07:16 Mar-01-2013
Crack indications seen in MPI but not in UT

Hello,

I was inspecting a round forged bar. I used first MPI method to test the object and it showed a 70-80mm length crack and it is clearly evident. But when I used UT it didn't showed any indication. I've used 10diameter 4Mhz Normal probe.

What could be the reason?

 
 Reply 
 
Malcolm Hill
United Kingdom, Joined Jun 2012, 14

Malcolm Hill

United Kingdom,
Joined Jun 2012
14
08:27 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Orientation- The crack may not lie in a plane suitable for UT detection. If it is running at 90 degrees for example. This would be better for radiography

 
 Reply 
 
Andreas
NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh, Germany, Joined Oct 1999, 131

Andreas

NDT Inspector, Specially in the oilfield
Tuboscope Vetco(Deutschland)Gmbh,
Germany,
Joined Oct 1999
131
09:16 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Hallo Dilip ,
with MPI you find surface and subsurface crack , you can see the length but not the depth.You get MPI indication with a depth less than a millimeter , may this depth will be not enough to be a reflector for UT.

Regards

Andreas

1
 
 Reply 
 
Ed T.
Other, ASNT Level III, UT, RT, MT, PT, VT
NDT Level III, Saudi Arabia, Joined Sep 2011, 169

Ed T.

Other, ASNT Level III, UT, RT, MT, PT, VT
NDT Level III,
Saudi Arabia,
Joined Sep 2011
169
09:27 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Andreas at 09:16 Mar-01-2013 .

Are you absolutely sure it's a crack? I have seen indications like that in forgings. It was clear with MPI but not with UT. Try DPI. If its cracked you will see it. If UT and PT says there is nothing, then it probably came from drastic permeability changes in the forging.

1
 
 Reply 
 
Frank Lund
R & D,
United Kingdom, Joined Apr 2005, 222

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
222
10:22 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Dilip,

It could well be that the defect is very shallow.

Try a technique such as FGI that I developed with NEWT to get the depth

Cheers,
Frank

 
 Reply 
 
James Scalf
NDT Inspector,
Global Integrity, Canada, Joined Oct 2012, 274

James Scalf

NDT Inspector,
Global Integrity,
Canada,
Joined Oct 2012
274
10:45 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Dilip,

For your UT are you using longitudinal or shear wave? if longitudinal the tip of the crack may not have enough surface area through the depth to give an adequate reflection. Try using a 45 degree shearwave instead and orient your transducer so that it is approximately 90 degrees to the side of the possible indication (with the primary beam aimed at the indication) then reattempt the scan. If it is surface breaking locating it should be fairly simple. (remember you will only be working in the first leg of the sound path so set your system accordingly.
I know this works well as we use it on a few diffferent round stock components where I work. One must remember that if your probe diameter is faily large that you may have to contour the wedge face to match the round stock...
Hope this helps...

 
 Reply 
 
Dilip
India, Joined Mar 2013, 2

Dilip

India,
Joined Mar 2013
2
10:46 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Andreas at 09:16 Mar-01-2013 .

@Malcolm : Radiography would over run the cost of inspection so that is not feasible
@Andreas : I too have the same doubt. but let me see if I can check it with DP as Ed. said
@Frank : I'm not aware of such technique can you pls elaborate?

 
 Reply 
 
Harendra Latiyan
Harendra Latiyan
11:43 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Hello Dilip,
I am not sure of dimensions of the bar under test, but I will advise you to have a look at ...
http://www.olympus-ims.com/en/applications/oil-well-down-hole-drilling-tool-inspection/
and search the forum for Phased array inspection of Rail axle.
Hope you will get some idea.

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

Frank Lund

R & D,
United Kingdom,
Joined Apr 2005
222
11:50 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 10:46 Mar-01-2013 .

Dilip,

I happy to help. It's an electromagnetic technique that induces a defined band of current into the surface of the object being tested. The deviations in the current are used to indicate depth and changes in depth. It can do other things, for example, the technique has mapped damage at the wheel-rail interaface.

Here is a typical instrument.

http://www.lizard.co.uk/m8%20nde%20system.html

Cheers,
Frank

 
 Reply 
 
Ed T.
Other, ASNT Level III, UT, RT, MT, PT, VT
NDT Level III, Saudi Arabia, Joined Sep 2011, 169

Ed T.

Other, ASNT Level III, UT, RT, MT, PT, VT
NDT Level III,
Saudi Arabia,
Joined Sep 2011
169
12:41 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Frank Lund at 11:50 Mar-01-2013 .

Try PT and you will know. Let us know what you find out. You have our curiosity now.

 
 Reply 
 
Sachin M
Engineering,
India, Joined Oct 2011, 1

Sachin M

Engineering,
India,
Joined Oct 2011
1
16:09 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

If it is a surface crack...it would be detected by DP... but could not be because of Dead zone of normal probe... but you have good chances to get it in angle probe scanning ....

 
 Reply 
 
Carlo
Carlo
20:50 Mar-01-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Sachin M at 16:09 Mar-01-2013 .

Dear sirs,
I point out that perform PT after MT is not recommended, make sure that the surface and internal area of crack shall be free from any product of MT. Again remember that a crack is not acceptable, so you can grinding up to 3-4 mm depth and perform PT inspection. Remember for ASME BPV you can repair forging until recommended dimension.
Carlo

 
 Reply 
 
Humayun Raza
Humayun Raza
09:26 Oct-18-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

This is because of dead zone formation in UT technique

 
 Reply 
 
Gerald R. Reams
Engineering,
Industry, USA, Joined Aug 2012, 181

Gerald R. Reams

Engineering,
Industry,
USA,
Joined Aug 2012
181
13:56 Oct-18-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Humayun Raza at 09:26 Oct-18-2013 .

All anyone can do is guess without specific information.

What process is used to forge the bar?
Any secondary processing?
What's the material?
What's the surface condition?
What are the dimensions?
What are the parameters of the MT examination?
What are the parameters of the UT examination?
Are you absolutely sure the indication is a crack? It could be one of several types of linear indications.
Have you investigated the indication under magnification?
Etc.

Regards,
Gerald

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

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
16:31 Oct-21-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

Dilip,
in your condition, imagining that the material has not dined the signal, can be a planar radial longitudinal or transversal, or a localized defect in the dead zone - also non-radial - in case you have only used a single beam probe.
Sometimes it pays a heavy price if we hold in the drawer angle beam probes, with which the forge people are a little uncomfortable, because of too much habituation to straight beam probe .
Greetings
mario

 
 Reply 
 
seenukk
Engineering,
Kuwait, Joined Sep 2013, 3

seenukk

Engineering,
Kuwait,
Joined Sep 2013
3
06:45 Oct-22-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 10:46 Mar-01-2013 .

Dear Dilip,

Do you perform DP, and what is the indication after your further investigation?
let us know where it went wrong.

Seenu

 
 Reply 
 
frank ding
Consultant,
TUV SUD, China, Joined Oct 2013, 9

frank ding

Consultant,
TUV SUD,
China,
Joined Oct 2013
9
15:19 Oct-25-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

You may use share wave probe try again.

 
 Reply 
 
CECCON TIZIANO
CECCON TIZIANO
20:55 Oct-29-2013
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

The first step in order to identify the indication is to know the kind of steel grade.
There is a lot of MT metallurgical situations that can cause indication found by MT where PT and UT RT are not able to detect. Mr.J.Scalf Canadian Air Force said right when suggest to know the steel grade and so on.
Probably. there is not a indication as crack, seams ,macro inclusions but high ferromagnetic stringers ( as Ferrite ) or not magnetic Carbides stringers ( as Nb-Carbides ) and Mx Carbides segregation.
If you explained what is the grade of steel and a forging process ( t° , soaking and cooling ) may be it's possible identify the kind of MT indication.

 
 Reply 
 
David Baeley
Engineering,
Australia, Joined Dec 2014, 17

David Baeley

Engineering,
Australia,
Joined Dec 2014
17
11:49 Dec-17-2014
Re: Crack indications seen in MPI but not in UT
In Reply to Dilip at 07:16 Mar-01-2013 (Opening).

I suggest you you can use normal length of machine 50 to 60mm.

 
 Reply 
 
Satish bhadrashetty
Satish bhadrashetty
14:35 Jul-22-2019
Re: Crack indications seen in MPI but not in UT
In Reply to Andreas at 09:16 Mar-01-2013 .

Respected sir,
In our company we r getting a v.very small dia's (0.1 or 0.2mm) crack (6-7mm lenght) in rounded forged bars. So how can we find this in ut.
Iam unable to found this crack by using 10mm 4mh probe. So kindly clear this doubt sir.

 
 Reply 
 

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