Leak ball valve issue

[ceasar20]

Dear mates ,

After first leak test with helium we was found leakage in valve 24 inch (from 20 bars ) between nut and stud (pos 21& pos 22) see attachment .

we changed the lip seal (pos 24 ) and the graphite gasket (POS23) but the leakage persist .

service pressure of valve : 80 bars

Please Advise how to repair this issue

BR

 

[Danlap]

Hi,

Assuming the drawing is scaled and true, it is a bit odd to install lip seal (pos 24) as the first barrier. The size, the pressure and lip seal is not placed within some sort of groove. Yet, it has been proven to work from new until today (when you attempt refurbishment) up to 20 bars.
Also cmiiw, when you tighten bolt pos 22, it does not really increase the seating stress of graphite pos 23. It seems like all the seals are subject to seal by means of pressure energized
Just thinking out loud over the possible root causes:
improper installation - as lip seal is very sensitive, a not so good workmanship might have damage the seal.
concentricity issue between the bonnet and the body.
some scratches on the sealing area.
Insufficient seating stress applied.

Is it possible to change the lip seal to another seal such as spiral wound gasket or kamprofile?? I see there is some some space in front of the lip seal

Suggest to again dismantle the bonnet and check the lip seal:
- Were the previous the leakage occurs on the same bolts?
- Dismantle bonnet, check the compression or sealing / contact area between the lip seal vs bonnet and/or body. And also the graphite. If you see its not "really deformed or sealing" on the leakage area, you might need to check that particular area condition such as dimension, scratches, area.
But if most lip seal are not "deformed", would recommend to alter the sealing design or component.

Good luck, it seems to be a very delicate valve.

Regards,
MR

https://nosuchvalve.com

All valves will last for years, except the ones that were poorly manufactured; are still wrongly operated and or were wrongly selected

http://www.eng-tips.com/faqs.cfm?&rat1=2&fid=376

 

[bcd]

So below 20 bar it seals ok? I think that is what you mean by leaking from 20 bar. If it holds to a certain pressure and then starts to leak indicates a gasket or seal compression issue. Is there something in the body joint (like paint or rust) that is preventing full compression on the graphite gasket? Are the body bolts properly tightened to the required amount?

The lip seal is not working. But even if it does not seal, the graphite gasket should stop the leak.

So graphite seal is also not working. What density graphite should it be and what do you have.

To seal Helium, the lip seal requires pretty high pre-compression. Would be very difficult to assemble without damage.

Was valve shell tested at 1.5 times the rated pressure? Should of found this leak then unless the body joint is capable of sealing water at least long enough that the leak did not appear or the paint prevented it.

Best seal you have right now is the paint.

Lots of potential reasons for the leak. A little more homework is needed to get tot he root cause.

 

[gerhardl]

Both comments above gives a very sensible way looking at things. According to the video the leakage occurs at one bolt nut. One bolt/nut only? With or without any grease/ locking paste?

Suggestion:

Change bolt/nut, use locking paste. (Bolt accurately fitting or wore down threads bolt /bolthole? Bolthead flush against valve body?)

Change the sealings to precision sealings, micrometer accurate to be compressed accurately, with proper material.

If this does not work you will probably have material damage difficult to locate, even hairsize scratches will of course give helium leakage at this pressure.


Good luck!

 

[ceasar20]

hi,

Thanks mates ,

i will try to change again the gasket and lips , i will add locking past ( loctite ).

If it does not work , some damage occurred and i hope to get provisional solution before replace it .

BR