ansi 9standards0 code issues - ansi b16.5 rating specifi

huangyhg

ansi ansi  b16.5 rating specifi
hi all ,
i have a question regarding the rating for class 150
according to b16.5 1977
the pressure for @200deg is 195 psi
according to asme sectiii addendum s or w74
(which refer to b16.5)
the pressure for @200deg is 240 psi
it seems to had change after 1974 and before 1977
anyone can tell me when this change has occur ?
is it possible to have more details for this change ?
regards