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Technical Discussions
Heavy Métal Inspection
Heavy Métal Inspection
03:45 Sep-16-2009
UT shaft inspection

Hi

I have to inspect a 1 1/2" diameter shaft about 6" long for cracks. My only access is by one end. What would you recommend?
-a small diameter with high frequency or
-a large diameter with low frequency

Thank you

 
 Reply 
 
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
13:40 Sep-16-2009
Re: UT shaft inspection
In Reply to Heavy Métal Inspection at 03:45 Sep-16-2009 (Opening).

Hi,

It is essential to know how the shaft has been made and the present service condition/stress direction before deciding the UT technique.

If it is assumed that the shaft is made by forging then it is the convention to direct the ultrasonic beam in the same direction as that of major working. In the case that you mentioned this direction happens to be the cylindrical surface and not the end faces.

Secondly you are looking either for transverse cracks as in the case of fasteners/bolts or longitudinal cracks.

If you are looking for transverse cracks it is always better to use a small dia. high frequency probe.

If you are looking for longitudinal cracks, scanning from one end using conventional techniques is not going give any useful results. Special techniques using pitch and catch configurations (with conventional UT) or sartorial scans with Phased array probes have to be standardized.

The way you have put, it looks that you want to scan a fastener/bolt which is in tightened condition. If it is so the cracks are expected in the transverse direction only but the problem is that they are invariably initiated in the threaded area.

While you can use small dia. (about 10 mm) high frequency about (4 to 6Mhz) probes for this purpose, utmost care is required to discern the incipient cracks from the standard multiple indications emanating from the threads. Careful marking is required with known crack sizes and it is prudent to use a 5mm dia. transducer for marking and scanning for incipient cracks in threaded region.

Wishing well

P V SASTRY

 
 Reply 
 
Manuel Haces
Director, - Wire rope inspection
Haces Inspección del Noreste and Wire Rope Inspection, Mexico, Joined Jun 2002, 125

Manuel Haces

Director, - Wire rope inspection
Haces Inspección del Noreste and Wire Rope Inspection,
Mexico,
Joined Jun 2002
125
02:58 Sep-17-2009
Re: UT shaft inspection
In Reply to Heavy Métal Inspection at 03:45 Sep-16-2009 (Opening).

You can have very good ref. Ultrasonics by Krautkramer & Krautkramer, an old book. It is common to have geometry reflectors, so better to have a croquis and where to expect reflections due to this condition. Regarding the size of the transducer, you should consider the spreading of the beam. I would use 1 or half inch diam and 2 Mhz, at first instance. If you post more information it would be possible to give you a better idea. I mean how this shaft is working, where are the different sections, change in diameter, and so on. Regards

 
 Reply 
 
Michel Couture
NDT Inspector,
consultant, Canada, Joined Sep 2006, 891

Michel Couture

NDT Inspector,
consultant,
Canada,
Joined Sep 2006
891
17:37 Sep-19-2009
Re: UT shaft inspection
In Reply to Heavy Métal Inspection at 03:45 Sep-16-2009 (Opening).

One specification that is used frequently by my customers for this kind of work is ASTM A388. Basically your transducer is 2.25 MHz, a surface area not to exceed 1 square inch and a diameter between 0.75 to 1.125 inch. In your situation, I would chose the smallest diameter allowed to get best contact. The specification allow for Back Wall REflection, DGS or DAC Curve to be used.

This specification is a generic one for forgings and quality level should be determined by the client.

 
 Reply 
 
Heavy Métal Inspection
Heavy Métal Inspection
03:54 Sep-21-2009
Re: UT shaft inspection
In Reply to Michel Couture at 17:37 Sep-19-2009 .

Hi

First thank you for all that help.

In fact, what I have to inspect are shafts used in scisor lift (the ones that make the scisor).
It is made of cold roll steel, probably 1018 or mybay a bit srtonger. It is strait, without any different section, only one hole perpendicular to the lengh.
What I am looking for are fatigue cracks for normal or abusive uses.

Thank you

 
 Reply 
 

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