The outside diameter of the gasket should be sized to locate inside the flange bolts to align the inside diameter with the bore. The bolt circle diameter and bolts size vary with pressure class and hence the gasket OD will differ.
Max
Try the following:
British Standards Institution. They may still publish a handbook under their Technical Help to Exporters service that summarised international requirements for pressure vessels.
Lloyd's Register may be able to carry out design appraisal under Indian Boiler Regs.
The...
