Galling between Stellite 6 and 21 at elevated temperature

[kevlar49]

I have read thread408-91895. I note that there are problems with galling on Stellite 6 on Stellite 21. Can you describe the galling problems? My valve is likely to have Stellite 6 lower stem guides and stellite 21 overlay operating at about 1000°F in the presence of about 75mole% hydrogen and 0.2-0.6mole% H2S. However, the valve is not actuated often. Is the galling problem seen during low frequency actuation or is a high frequency required to start the problem? How bad does it get?