People involved in the valve application, take care before placing order to know the component materials of the valve. The 17-4PH usually used in the stem construction have failed like the below. Tyco valves has observed similar failures in thier inhouse research and has reported the same on using 17-4PH. And are not recommending this material unless specifically asked for.
As all suppliers and buyers do not take much interest in the small components of the valve, it will be the responsibility of the buyer to take note of these before ordering and the complete knowledge of the service involved. Alternatives would be FXM19, F51, F6a Cl4 depending on temp. and service.(17-4PH is 17Cr-4Ni-Pricipatation Hardened)
http://www.hghouston.com/x/25.html
(Photo attached for members not having net access.)
Nomarski intereference contrast photograph of the microstructure of a 17-4PH stainless steel sleeve bearing overlayed with sintered tungsten carbide. A hydrogen embrittlement crack has initiated at the overlay/base metal interface. A mechanical crack in the overlay permitted access of a corrosive downhole environment to the 17-4PH stainless steel base metal. Vilellla's etch. (~65X)
With regards,
Kannan.
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