In Indian Boiler Regulation 350, piping thickness calculation under internal pressure considers 0.5 in place of Y in eq 3a of 304.1.2 of ASME B 31.3 for all types of ferritic,austenitic steels & other ductile metals.

Is IBR-350 formula based on any older thickness calculation formula than ASME thickness calculation chosen among many such formulae available ?

I have a query regarding ASME allowable stress in creep range: when creep & rupture based allowables are for 100,000 hrs, how do we design a power/process plant for 30/40 years (2.5E5 -3.5E5 hrs) continuous operation ?

If we do not meet hoop stress allowables at design temperature in creep range, does it mean that it will remain safe for, say first 5 years of construction, considering higher allowable Sh ?

regards,

sam