In Service Inspection of Control Valves

[James01]

Does anybody know of an effective technique for in service inspection of Globe Control Valves.

I have a problem with solids erosion on the outlet side of the valves that I need to keep an eye on whislt remaining on-stream. Radiography is effective on diameters up to and including 3", UT has proved ineffective due to the internal variations in thickness, internal and external surfaces not parallel to one another (cast bodies).

 

[NDTLevel3]

You might try leak testing if you just trying to determine if they are leaking by or not. The equipment is cheap enough and simple to use. See these sites

http://www.amgas.com/sonpage.htm

http://www.leakzone.com/fa/industrial.htm

Bill

William E. Blum
Manager
NDT Consulting Group Inc.

http://www.ndt-cgi.com

wblum@ndt-cgi.com
USA 1-877-638-2441
Fax/Voice Mail 1-214-853-5131
Sweden 46-42-14 39 99

 

[James01]

Bill

Thanks for the reply. Unfortunately I need to get early indications of erosion damage, long before it leaks. We do use leak testing for the seals around the valve stem on a regular basis.

Thanks
Jim

 

[pvcguy]

James

I have seen valves up to 6" easily x-rayed using a cobalt source. Not every NDT contractor has a cobalt source it's worth a try.

 

[James01]

pvcguy

Never thought of Cobalt purely because there is no way it would be allowed offshore to the platform.

Thanks anyway
Jim

 

[quadswift]

If you mark up the valve end with a grid system and take regular U/T wall thickness readings at exactly the same grid references, then they would be relative and provide a base-line reference.

You could then identify any loss of wall thickness, from the starting measurement, at any reference point. If you need lots of readings, you just use a smaller grid.

This is the principle used on many in-service inspection regimes. They take the readings at installation and compare them at intervals pre-determined by the written schemes of examination.

Regards,
Quadswift

 

[ElderX]

James01,

I used to use cobalt offshore and it was never a problem, with proper collimation and shielding it is do-able the biggest hurdle is handling as the exposure device is rather heavy and 2 find an NDT contractor with a cobalt source ` 50 ci or so.

Also Mr. Blums suggestion re leak detection I think or at least I interpreted it as using an ultrasonic leak detector to listen to the sound from the valve for changes . Take a new valve and compare it's signature to one that is known to have corrosion. There should be a marked difference in the sound signature. The valve does not need to be leaking to the atmoshere only internally past the ball or seat.

Hope this clarifies.

 

[James01]

Thats folks, thats given me some food for thought.