07-24-2010, 04:47 AM
We have one order from my client to supply ON/OFF valve from size 4 up to 24 inch. Application is highly sour (H2S and CO2 and water and also a little CL). Material that costumer is ordered is A186 F6a for ball and also request for fully stellited of ball. I asked with some ball valve manufacture for fully stelliting of ball but they didnâ€™t accept and do stelitting only contact area (areas contact between ball and seat ring). They donâ€™t consider high corrosive media that cause SCC on ball. My questions are as follow:
1- What are manufacturerâ€˜s limitation for apply stellite overlay on ball?
2- Is there another method instead of stelliting that cover corrosion and erosion concerns?( customer had bad experience from Tungsten carbide (HVOF) and ENP method in these highly corrosive media)
Please note that fluid is produce in well and these valve are used in wellhead facilities. Also rating of these valve are 1500#
I ask for specialist on this subject to help me to able correct decision.
07-29-2010, 09:19 PM
|RE: stellite coating
Spraying ball valves is rather difficult. The biggest limitations are in the bore. Thermal spray is a line of sight process, and the particles need to hit the substrate at a minimum angle. Below this angle, the particles simply bounce off. In the case of a 4" ball, the bore is very small so it is virtually impossible to coat the ID. Also, where the bore transitions to the OD, there is a high heat and stress concentration during spraying, so it is difficult to spray without cracking the coating. I am not aware of another method to protect the bores of the balls. Perhaps someone else on the forum knows something.
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