sealing gate valve WC coated problem

[ehsan]

Hi All member
We coated WC on gate and seat for oil industry.During testing valves under 5000 psi pressure of water in closed situation of valve some droplet formed on the surface of the gate it seems water diffuse from outside of the gate to the WC coat and seeped out through the surface of gate.!!!!
It is only my imagine.because i cheked it severally we do not have any another way for seeping out of water through the coating!
Is it possible? and it related to prosity of coating or it is not possible.?
Our coating process is gas hvof.
Attached image should be useful.
Ehsan

[Gordon]

Hi Ehsan

Porosity and or coating cracks. Try sealing coating with an epoxy sealer.

Over what time scale are you observing leak. I assume this is not carry over from closing valve or condensation effects.

[ehsan]

Dear Gordon
When we start the test We can watch small droplet after 1 min and they are growing by time.
I absoulotly believe that droplets seep out from very very small holes on wc coating .
I have same idea with you that we do not have condensation effects but it seems that water carry among the coating from outside of seat to inside section.
I cheked for any cracks with PT but we do not have any cracks.
Regards.
Ehsan

[brazer]

I think it is porosity because when we sprayed ceramic coating (corundum) and after we carried out the impregnation with lake to fill pores we could see this process as bubbles of air were formed in during the impregnation.

[MichiganMan]

Based upon your description and the picture two issues seem to be present.

1) Porosity is allowing water to wick through the coating giving the appearance that the water is "seeping" through the gate

2) There appears to be a higher incidence of leakage around where the gate meets the seat. This suggests that the valve is not seating properly. At 5000 psi there is very little margin for error at the interface of the gate and seat, and it appears from the picture that either the surface finish in the sealing interface is inadequate, or there is not sufficient interference fit to affect sealing. Check both and solve the porosity and I suspect you will find your solution.

[djewell]

There is no sealer available which can withstand 5000 psi. You have to spray with parameters which close the porosity in the coating. Only a few guns can do it. The new M3 gun from UniqueCoat Technologies recently passed this test at 15,000 psi.

[ehsan]

Dear Michiganman
We can solve leak between seat and gate and it is not important,the most problem is that we have leak among of gate!!

---

Dear Gordon
I used one kind of dilute epoxy sealer(poly amin base) but I can not see any diffusion of sealer to the coating .Did you have any experience in sealer for WC coating and it can withstand that pressure?
Ehsan

[Martin]

Hello friends,
my name is martin Iam from Germany and working with HVOF now 8 years.
I do have a problem with the final condition of roughness. The customer like to have a surface roughness after spraying by WC of Ra 13 ... 14 µm ( we spray drums for paper industry )
Used gun DJ 1000 / 4 passes Amperit 526.595 after that 2 passes Woka 3208 = Ra 11 µm
What can I do to increase the roughness. A friend told me to reduce the heat. Is that right ? And how can I do it ?
Parameters are 4 passes with distnace 200 mm / Amperit
2 passes with distance 150 mm / Woka

Thanks for help
Greetings Martin

[derek]

Hi Martin,

I am working on increase Ra now and got some experience. If you choose rougher cut powder and longer nozzle of your HVOF gun, you can get bigger Ra. If it doesn't work, please use APS for the final 2 pass layer.

[ehsan]

(07-16-2010 02:25 PM)Gordon Wrote:  Hi Ehsan

Porosity and or coating cracks. Try sealing coating with an epoxy sealer.

Over what time scale are you observing leak. I assume this is not carry over from closing valve or condensation effects.

Hi Gordon
Recently i found that my customer did not lapping process after grinding is it possible if we had a lapping process we get better result in sealing test some porosity fill in lapping process?
Please offer me your experienced epoxy sealer on wc coating?
Ehsan

[Gordon]

(08-03-2010 04:07 PM)ehsan Wrote:  

(07-16-2010 02:25 PM)Gordon Wrote:  Hi Ehsan

Porosity and or coating cracks. Try sealing coating with an epoxy sealer.

Over what time scale are you observing leak. I assume this is not carry over from closing valve or condensation effects.

Hi Gordon
Recently i found that my customer did not lapping process after grinding is it possible if we had a lapping process we get better result in sealing test some porosity fill in lapping process?
Please offer me your experienced epoxy sealer on wc coating?
Ehsan

Hi Ehsan

Yes, I would have thought surface finish would be critical.

No real experience with sealing ball valves. I know Praxair always epoxy seals their compressor piston rod coatings. I know not the same, but similar very high pressure sealing applications.

Ideally, vacuum seal with low viscosity epoxy resin. Failing that, warm part ~50 C before epoxy application, this partially evacuates coating of some air and lowers viscosity of epoxy resin. Use long cure time epoxies not the rapid cure stuff.

Quote:There is no sealer available which can withstand 5000 psi

I see no reason for epoxy sealers failing. Very high relative strength to coatings and contained/supported by coating. Only problem is getting the stuff in the coating.

[ehsan]

Hi Gordon
What is your mean for Vacuum seal ?I should stuff resin in vacuum condition?
Did you have any experience in post heat treatment of HVOF coating for fusing powders and maybe fill the prosity?
Ehsan

(08-07-2010 06:46 PM)Gordon Wrote:  

(08-03-2010 04:07 PM)ehsan Wrote:  

(07-16-2010 02:25 PM)Gordon Wrote:  Hi Ehsan

Porosity and or coating cracks. Try sealing coating with an epoxy sealer.

Over what time scale are you observing leak. I assume this is not carry over from closing valve or condensation effects.

Hi Gordon
Recently i found that my customer did not lapping process after grinding is it possible if we had a lapping process we get better result in sealing test some porosity fill in lapping process?
Please offer me your experienced epoxy sealer on wc coating?
Ehsan

Hi Ehsan

Yes, I would have thought surface finish would be critical.

No real experience with sealing ball valves. I know Praxair always epoxy seals their compressor piston rod coatings. I know not the same, but similar very high pressure sealing applications.

Ideally, vacuum seal with low viscosity epoxy resin. Failing that, warm part ~50 C before epoxy application, this partially evacuates coating of some air and lowers viscosity of epoxy resin. Use long cure time epoxies not the rapid cure stuff.

Quote:There is no sealer available which can withstand 5000 psi

I see no reason for epoxy sealers failing. Very high relative strength to coatings and contained/supported by coating. Only problem is getting the stuff in the coating.

[Gordon]

Hi ehsan

Quote:What is your mean for Vacuum seal ?I should stuff resin in vacuum condition?

Yes, you need resin and coating at low pressure so that air is pull out of both coating and resin. When pressure is returned to ambient ( possibly pressurized further) there is a driving force to push resin into porosity. Ideally, part and resin should be under vacuum separately before bringing together (helps evacuate coating of air better).

Quote:Did you have any experience in post heat treatment of HVOF coating for fusing powders and maybe fill the prosity?

Only with PTFE onto TSC's. Don't think penetration would be adequate with this though. If you mean fusing with NiCrSiB, then I suggest coating valve with a WC/self fluxing alloy and fusing coating or apply by PTA or other welding process only.

[Asiaf]

Hi,

The conversation is rather old ! Hope the problem is solved , The reason I joined this site is to say that I have experience of exactly the same problem and we solved it before so I,m ready to co-operate in this case !

Overall direction of the history of covnersations is in correct directions but some fundumental steps are incorrect so it needs some changes from the base up to end stage of filling the face with epoxy.

Our main activity was repairing of shear gate valves of Cameron brand which is used in oil drilling facilities. 5000 PSI is rather low pressure for such application while 15000 psi is some how normal pressure.

Regards
Asiaf

[ehsan]

Hi Asiaf
Thanks for your reply and I should say I could not solve that problem completely.
your complete experience will be appreciated .
I used different kind of epoxy but our coating did not has any absorption.
Rgd.
Ehsan



Hi,

The conversation is rather old ! Hope the problem is solved , The reason I joined this site is to say that I have experience of exactly the same problem and we solved it before so I,m ready to co-operate in this case !

Overall direction of the history of covnersations is in correct directions but some fundumental steps are incorrect so it needs some changes from the base up to end stage of filling the face with epoxy.

Our main activity was repairing of shear gate valves of Cameron brand which is used in oil drilling facilities. 5000 PSI is rather low pressure for such application while 15000 psi is some how normal pressure.

Regards
Asiaf
[/quote]

[ehsan]

Hi
Any body has a new solution for this problem or not?
I checked different way but did not get compelete result.
Ehsan



Hi,

The conversation is rather old ! Hope the problem is solved , The reason I joined this site is to say that I have experience of exactly the same problem and we solved it before so I,m ready to co-operate in this case !

Overall direction of the history of covnersations is in correct directions but some fundumental steps are incorrect so it needs some changes from the base up to end stage of filling the face with epoxy.

Our main activity was repairing of shear gate valves of Cameron brand which is used in oil drilling facilities. 5000 PSI is rather low pressure for such application while 15000 psi is some how normal pressure.

Regards
Asiaf
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