Valve seat and disc hardfacing 1

[osuamp]

I have crack problem at seat and disc hardfacing of parallel gate valve size 26 inch .It use F91 and Stellite #6 .I think many valve have the same problem.So I want to change a new valve.What material could we use? Operation temperature is 565 C and pressure is 25 bar.Fluid is steam.

 

[RXH]

Are you saying that one face is F91 and the other is Stellite 6? Which one has cracked? What is F91 anyway ? - sorry, I'm not familiar with this designation.

RXH

 

[Celebur]

Do you mean ASTM A336 F91, which is a forged alloy steel for HP/HT service? Is it a Stellite #6 overlay on the F91? More details required...

 

[stanier]

Severe service valve manufacturers such as CCI or Valtek may be able to help with a better selection of valve.

You can share knowledge but you cant share wisdom. Using knowledge wisely separates engineers from the enthusiastic amateurs that burden our society

 

[Hush]

What you see as cracks is probably ferrite. You may have better luck for this service overlaying a low alloy such as 4130.

 

[unsy]

osuamp

I would guess the problem you have here is not due to materials but the valve design itself. With the advent of changing plant operating philosophies, valves are now heated up and cooled down far more frequently and quickly than previously. This leads to a significant thermal gradient across the crotch area of a Parallel slide valve,(or Wedge gate) often resulting in cracking across the seating area. F91 was meant to overcome this problem as it allowed much thinner sections in this area due to its improved mechanical properties at elevated temperature. Unfortunately many valve companies have copied designs over the years and have not understood the differences between say a WC9 design and an F91 design. They just simply change materials and end up with the same problem.
I believe this is where your problem lies. Try speaking to a UK manufacturer who have modified their designs to suit, Hopkinsons or Dewrance would be a good bet.

 

[Weldingoverlay]

To make a new valve for high temparatures application we are used basic material 304H with a stellite 6 overlay it works good whitout cracks, preheat the 304H up to 200 degrees celcius before cladding stellite 6 for more information and questions keeshendriks3msn.com

 

[Weldingoverlay]

Sorry my e-mail adres above is wrong this is the right
e-mail keeshendriks3@msn.com

 

[dave2109]

I've heard of this problem occurring with a number of other F91 valves. I believe the problem lies in the procedure originally used to apply the Stellite 6 overlay on the F91 material. These failures prompted valve manufacturers to change the overlay procedure and perform additional NDE and I believe the problem has been corrected on more recent F91 valves. You may want to contact the valve manufacturer and determine if they have an updated overlay procedure. You could possibly then repair the existing valve rather than replace it.

If you still want a new valve, I'd suggest a WC9/F22 material. This will handle the conditions you mentioned however the valve pressure class could go up and you may end up with a wall mismatch with your existing piping.

Good Luck