Governor valve stems made of Inconel-718 material will expand more than the original 410 stainless steel stems for the same temperature rise.
Valve assemblies exhibit binding at operating temperatures even when they stroke freely on assembly.
This condition results in loss of governor control. Any Inconel stem with a diameter greater than 0.4988 inch is susceptible to interference with the carbon washers at temperatures above 500 degrees F and could result in turbine control problems. In 1995, the Terry Turbine Users Group recommended using stem material that is not susceptible to corrosion, such as gas-nitrided steel or Inconel. The staff has been working with the Terry Turbine Users Group to develop data for this information notice.