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- since 1996 -

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Technical Discussions
Mike
Mike
11:36 Oct-26-2017
Angle Beam Reference Block for Solid Round Forging

Hello NDE Experts,

I have a client requirement to have 45° angle beam circumferential scanning of all forgings. The forgings are going to be of different diameters, so unfortunately would not be able to give the specific diameter here. In order to perform this can anyone suggest the reference block type & details to follow depending on the diameter which would be the case. Also suggest the same for hollow forgings which have the OD/ID ratio above 2 and still need a angle beam scanning.

As background info, there will be longitudinal scan in two perpendicular direction which would look for any longitudinal defects in circumferential direction and any volumetric defects within the material depending on the size. The 45° scan recommended is particularly to look for longitudinal defects running parallel to the axis of the forging. We have cases already that longitudinal tight cracks (parallel to the axis of the forging) were found during NDE after final machining of the component which the longitudinal scan would never pick up.

Bit of research into this, from my point of view 100% coverage might not be obtained but still need to cover as much as possible and is what seeking your expert advice on the reference block if to do so.

 
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P V SASTRY
R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D, India, Joined Jan 2003, 195

P V SASTRY

R & D, NDT tecniques metallurgy
TAKEN VRS FROM THE POSITION OF SR. DEPUTY GENERAL MANAGER BHEL CORPORATE R&D,
India,
Joined Jan 2003
195
22:02 Oct-26-2017
Re: Angle Beam Reference Block for Solid Round Forging
In Reply to Mike at 11:36 Oct-26-2017 (Opening).


Dear Sir,

You have mentioned "We have cases already that longitudinal tight cracks (parallel to the axis of the forging) were found during NDE after final machining "

I understand that these cracks were found on the surface of the forging.

Please note that in large diameter forgings there are internal cracks near the center (flakes, fissures etc.). These are very well detected by normal probe scanning done in radial direction.

But there are no longitudinal cracks just below the surface and not opened to the surface. All the longitudinal cracks near the surface are invariably open to the surface (because there are large tangential residual tensile stresses near the surface, just after the forging. After rough machining a thin layer with compressive residual stresses is created near the surface but by this time damage already takes places if it had the right conditions ).

It is true that these defects are well detected by a proper shear wave testing done in radial direction. But this is a very long and tedious process and there are chances of missing if the operator is a little less attentive. This testing is effective only when rough machining is carried out.

Sure way of detecting these defects (with or without rough machining) is to conduct Wet Fluorescent Magnetic particle testing by circular magnetization.

Please post photos of the defects that you have detected.

Best wishes,

P V SASTRY

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

Mario Talarico

NDT Inspector,
Italy,
Joined May 2010
423
23:13 Oct-26-2017
Re: Angle Beam Reference Block for Solid Round Forging
In Reply to Mike at 11:36 Oct-26-2017 (Opening).

zoom image

Scansioni radiali

Mike,
In the state ‘roughed machined’, radial scanning should cover 100% of the surface, otherwise it is not surprising that longitudinal cracks face in the final machining. This is a lot of work!

For the practical purposes of scanning, just a small calculator. The boundary angle of the beam, tangent to the inner surface, is derived from the relation sinus: sin cab = r / R, then angle = sin -1 (r / R). For each lower angle start the rebond of the beam. In a single beam application, the inner diameter must be affected, but also to reach the opposite side of the emission surface to detect external defects.
Greeting
mario
 
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Mike
Mike
08:52 Oct-27-2017
Re: Angle Beam Reference Block for Solid Round Forging
In Reply to P V SASTRY at 22:02 Oct-26-2017 .

Thanks and you were right. The case we had was a hollow forging greater than 2 by OD/ID ratio and tight longitudinal crack in parallel to the axis was identified in the ID of the forging. Visibly seen during final machining like a line drawn with pencil but really a tight crack.

Meantime I've been looking into ASTM E2375 and as per A1.3.2 suggests to use Fig 4 or 5 reference block. Looking into the blocks, Im not convinced that these blocks suite my case, looking into will the DAC constructed using these blocks help the scanning that is going to happen?. Your opinion on this?..

I would like to know your opinion on Fig 3 calibration block is that something helpful here to follow for the area that can be scanned.

Or the only option is have a fluorescent magnetic particle testing with a delay time after rough machining. My thought is to have such cracks identified as early as possible at the forging manufacturer itself. This is not going to end with only this order because even if the client does not specify to have angle beam scanning such cracks identified later is not going to be accepted just because it was not specified. So the approach here is also as a kind of standardization for all upcoming forging.

 
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