There are several types of materials approved for gas work. The codes for the local jurisdiction should always be checked but in general
may be used.
Steel pipes can be used above ground as long as corrosion due to the environment and the conveying gas is of no problem. Steel pipes and copper pipes are the most common materials used inside buildings.
Copper pipes used in gas systems should be of type L or K and approved for gas.
Yellow brass pipes may be approved for inside installations.
Aluminum pipes should not be used in the ground. Aluminum is not approved in all jurisdictions.
Ductile iron pipes may be approved in some jurisdiction for underground work.
PVC - Polyvinyl Chloride - pipes may be used in pipelines buried outside a building.
PE - Polyethylene - pipes may be used in pipelines buried outside a building.
Flexible connectors are used to connect appliances to gas sources. Flexible connectors must be approved.