Offer a rule of thumb to estimate the life cycle of steam valves? We are considering substituting A217 WC6 (1-1/4 Cr - 1/2 Mo) for A217 WC9 (2-1/4 Cr - 1/2 Mo) in a high pressure steam line in a combined cycle power plant, as a capital cost savings measure. I'm expecting that the WC6 Water Control  valve will have a shorter life cycle, and I'm wondering how to estimate the reduction in life. I wouldn't even think of trying to throw down a rule of thumb with the info you have given. If it is just clean, dry, steam, either body should last forever. If the valves are on a high pressure drop application and required to shut off for much of the time, the body may be OK for a long time but the trim will probably wire-draw. If the steam has any moisture in it when flowing, The C9 body will probably resist erosion longer the the C6 body, mostly because of the higher chrome content. Even then, if the velocity is less than 1/3 mach, it is not likely to make a noticeable difference. It is at the edges of the performance envelope where one will shine: If you have mach .7 wet steam, put your money on the C9 body.

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