what is the difference between ASME S stamp and BS 12952?
Offhand, probably one's American and one's British. BS is usually British Standard
one big cert is Boiler Welding. Boiler steel is much thicker than other steels and also is different in composition.
ASME is the American Dociety of Mechanical Engineers and BS is a British Standard. Both are usually acceptable for boiler manufacturing. Without going into the details thay are quite possibly equivalent. The difference is on the jurisdiction licensing or approving the boilers. Strangely enough boiler certification comes from the insurance companies insuring the boilers. So that is where any differences will be manifest.
