Bolted cover joints [Pressure vessel] to reduce cover od.

Hello friends,

I want your guidance please,

While I am designing a cover joint for pressure vessel with reference to ASME VIII, the bolting area required increase for L7 when compared B7 material, since allowable stress of L7 is less when compared to B7.

Is there any better material which can replace L7, since B7 is not used for low temperature application?

Thank you