I have a small bore job with numerous welded bonnet gate valves, and they need to heat treated because the material includes P91. In the past I have dealt with bolted bonnet valves, so the valves would be disassembled and sent to a furnace for heat treat.
I would like an opinion or some extra guidance for where to look on weather or not it is safe to send the welded valves as a whole? I do not have access to API 602 to look at specs for valves, if it even states anything about temperature ranges, I don't know? I have tried to contact the manufacturer, but am waiting for a response, so in the meantime; I am turning to my friends in AWS land :o)
My concern is in reguards to getting away from localizing because of time and cost issues.
Thank you in advance for any and all help!!
Safe would be an engineering decision. P91, without exception, to my knowledge, always requires a PWHT, regardless of thickness. So your real problem will be a code violation. Unless engineering is willing to accept responsibility, which they most likely are not, I think you're stuck with a local. Induction, is probably the best way to go.
I'd give a call to your nearest PWHT company and see what they say.
The operations department (where ever the valve is located) should be able to comment on whether or not the required temperature of PWHT will negatively affect the valve....found out about this the hard way.
They should be able to access the manufacturer's tech manual or valve specifications and give you a definite answer.
Since the valve is P5B material, there is a high liklihood that PWHT at 1400F will not negatively affect the valve.
Charles
If you want to send the whole valve for heat treatment you must consider the valve internals and the effect PWHT will have on them. As an example a PWHT suitable for P5B material might cause significant softening of type 410 stainless often used as valve internals. Thus your seats might be in a very different condition that what it was designed for.
Joe
My experience has been that when the elevated temperature of PWHT may be detrimental to valve internals, the manufacturer prominently states it in the valve technical literature.
I'm sure with the liability driven world of today, no one wants to get into the "you didn't say it couldn't be heat treated at that temperature" vs "you should have known the internals couldn't take that temperature" argument.
Charles
A word of warning.
Heat treating a valve, or valve components, most likely (not to say surely) will cause some warping, perhaps very little but unacceptable, because valve components must fit exactly one into the other. So, most probably you'll have to carry out a light machining or some kind of hand adjusting (filing for example) on the affected pieces in order to restore the original condition.
One way to avoid warping is to perform a vibratory stress relief insted of heat treatment.
Giovanni S. Crisi
Sao Paulo - Brazil
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