I am surprise to see that no comments from experts.

Krish To answer your question, information on valve throttling, valve control velocity in the system in addition to the metallurgy would help participants to thin and share some of their experiences. To replace a valve stem, you have to consider factors other than corrosion resistance, metllurgical improvement +also the valve design take into account the upstream and down stream flow and valve operational control flow limitations. To my mind, this forum would be better placed to reply suitably than just airing views only on change of metallurgy or valve design. Trust this help you C.V.Srinivasan Nishi Engineers Pvt Ltd India May 30,2006 E-mail: nishi@vsnl.com >We had frequent failure of Visbreaker feed line control >valve stem l.Stem metallurgy is SS321.Feed sulphur >percentage is about 4-4.5% Wt and temperature is around >425-450 deg.C.Is there any alternate material to withstand >the above severity.Whether high carbon material will do the >work?The carbon available for ss321 is max of 0.08%.We are >in the opinion that due to low carbon the stem is not >getting the adequate strength to withstand the load. >regards,