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Re: [MW:12259] Hairline cracks in stellite 6 coating (HF) - A216 WCB

By Materials & Welding
Sir
With proper preheating & very slow cooling the surface hairline cracks can be definately avaoided in stellite 6 coating
We have done very successfully very large casting that to CA6NM (Very difficult to weld) stellite 6 coating on surface approx dia 36 Inches ,(Pump impeller casing)
with no cracks visible on DP 
Whole casting Pre heated to 260 0C  post weld covered with asbestos flakes with lime power & covered with glass wool & asbestoss cloth , alloed to cool to room temp after 36 Hours the bundle was opened  
Regards
Suneel Gore  

On Fri, Aug 12, 2011 at 1:30 PM, Materials & Welding <materials-welding@googlegroups.com> wrote:
Is it true that stellite 6 HF will leave hairline cracks on the
surfece?, one of the reputed valve vendor is quoitng that

"Seat overlay made of Stellite 6 is possible but not recommended by
us. We clearly mention that it is not possible to perform a Stellite 6
completely free of hair cracks. Probably after final machining the
surface will show hair cracks which is normal in case of using
Stellite 6 and this do not affect the sealing function. We normally do
not use Stellite 6 because of this fine cracks and because of much
better experience with Stellite 21. If you insist on Stellite 6
seating surface showing hair cracks will not be a reason not to accept
the valves if seat tightness test is ok"




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