China national standard seamless steel pipes, such as:
Seamless steel pipe use in high boiler: GB5310-1995
Low/medium boiler seamless steel pipe: GB3087-1999
Fluid seamless steel pipe: GB/T8163-1999
Structure seamless steel pipe: GB/T8162-1999

These pipes are carbon seamless steel pipes mainly, also involves some alloy seamless steel pipes.

The specification mainly as follows:

OD: From 21mm to 508mm
Wall thickness: From 3mm to 45mm