The selection of steam piping material depends primarily on the temperature of steam being used.
Carbon steel can sustain temperatures below 427°C. Above this temperature, graphitization of carbon steel occurs thus, rendering it brittle. So, Alloy steel is used as the steam piping material for temperatures above 427°C as it has better material properties at elevated temperatures.
Carbon steel pipes are suitable for steam at a temperature below 427°C. The piping standard used for saturated steam according to IBR is: A106 Grade B Seamless Schedule 40. The schedule of the pipe may change with the pipeline thickness calculations as per IBR.
For superheated steam applications above 427 deg C selection of material depends on Pressure – Temp conditions of the specific application. Some of the piping standards are :
ASTM A 335 Grade P11 or Grade P12 or Grade P22
Upgraded materials are picked up with higher Pressure – Temp conditions.
ASME Sec II has provided material standards for pipes used for process and power applications.
ASME B 31.1 gives guidelines for piping specifications for power piping while ASME B 31.3 gives guidelines for piping specifications for process piping.
These codes give guidelines for constructing the piping and include the following :
- Thickness calculation of the pipe.
- Material of pipe to be used.
- Fabrication of the pipe.
- Inspection of welding defects.
- Testing of pipes.