HVOF Coating Thickness 2

[lylek]

I've been looking into hardface coatings on pipeline Ball Valves and was wondering what the typical coating thickness was for HVOF Tungsten Carbide on balls and seats. Are there specific minimum/maximum coating thickness limits that give the best performance?
Does the thickness put down depend on the properties of the fluid in the line? i.e. thicker coating to reduce effects of erosion?

Thanks

 

[valvit]

400 micron is a good place to start. Any thinner and the erosive resistance isn't what you want...and much thicker and the TCC doesn't have the mechanical strength and ductility to resist shear forces in the seating and can flake or crack.

 

[jaffaotc]

Iylek,

Valvit is correct 400 mic is a good place to start but still its depends upon as you said the fluid in the line?
Mostly we are applying bond arc after the surface preperation of the base material and then final coating, which gives good strenghth.

 

[Nilsoni]

I work in the subsea and the most common thickness is 150 to 200 micron finished grinding and lapping. The TOTAL Oil Company is the only company requireing 400 micron. Thicker coating may crack.
Applied on gate and ball valves all sizes in direct contact with well stream. Base material need to be CRA materials as SuperDuplex or Inconel for hardness. This to avoid denting.

 

[Engtipgb]

400 micron is required only by Total Spec. The std thk. is 150 or 200 micron and, if the adhesion is ok, is enough for any service. Moreover, a bigger thk. is fragile and doesn't add anything to the hardfacing point of view.

 

[PAN]

Nilsoni & Engtipgb,

You may refer to the old revision of TOTAL Spec. In my understanding, TOTAL Spec requires 300 micron coating thickness only...

 

[lylek]

Thanks for all the replies so far. From this and other work I've done I can see that there is quite a varied opinion on coating type, mix and thickness from the powder suppliers, coaters, OEMs right through to end users - all presumably based on experience good, or bad with particular types. Doesn't make selection easy!

A few other things I haven't come across are how much the ball diameter affects the decision - presumably coating thickness will change with ball diameter, or does it stay the same? Are thicknesses on ball valve gates and seats typically the same as on gate valves?