Hardfacing of Valves for Nuclear Applications

Control valves for high pressure and abrasive sen/ice are hard faced with cobalt base alloys like stellite satisfactorily. Hard facing of SS Trims with stellite has been well established and at present no problems as far as quality and productivity are concerned.

However control valves for nuclear applications present a different scenario. Primary requisite is that cobalt base alloy is not advisable being radio active. Only Nickel base alloy like Colmcnoy and Deloro***could be used. Since most of the Nuclear applications demand the use of SS 316 material, depositing nickel base alloy on SS will be difficult proposition considering the poor wettability between them. Stringent quality needs provide the chain of challenge The challenge grows stiffer when facing smaller and inaccessible valve seating areas of hand operated bellows sealed valves which handles the heavy water constitute the major part of any nuclear control valve scheme.

This paper deals with the various techniques in depositing nicke based alloys on SS valve interiors, the problems encountered and the proven solutions to circumvent them to get optimum results in productivity without compromising the stringent quality&reliability requirements.