A182 F6a Class 4 allowable stress

[reverman]

Looking at ASME Section II Table 1A it only has allowable stresses for A182 F6a for Class 1 and 2. Can anybody point me to an allowable stress vs Temperature table for the Class 4 condition?

I need the allowable stress at 1070°F

 

[metengr]

The higher strength Class 410 stainless steel (classes 3 and 4) looses strength more rapidly and significantly in comparison to lower strength Classes 1 and 2. If this is for a pressure vessel application, Classes 3 and 4 are not endorsed by the ASME B&PV Code, Section II Subcommittee.

Why do you need ASME B&PV Code allowable stress values? What is your application?

 

[reverman]

Need it for a valve stem. Customer has an application at 1070°F and wants to use F6a. I'm trying to convince them to use 316H but they wanted me to look into using a higher class of F6a

 

[metengr]

For 1070 deg F valve stem service, I would not recommend F6a. I would use 422 stainless as an alternative to F6a. The 422 stainless behaves similar to 410 except it has higher creep strength.

Keep in mind, that a change in material from an austenitic stainless steel (specified by the customer) to a martensitic stainless steel requires very careful consideration for valve service because of the differences in linear coefficient of expansion (clearance issues) and creep deformation differences between the two grades of stainless. In lieu of 316H, I would use 321H to take advantage of higher allowable stress values in comparison to 316H.