Natural gas and propane pipes are normally only installed by professional plumbers. This is because a leak in the home can easily go undetected, and can often be fatal. However, knowing something about these types of pipes are important so you can easily detect any problems and know when it is time for some repairs.
Gas piping comes in two varieties, high pressure and low pressure. High pressure pipes are much smaller than low pressure pipes. However, high pressure pipes require that you have a pressure reduction regulator at the attachment of any appliance. Low pressure pipes may only have a single regulator, located on the meter.
There are three types of pipes that are allowed in residential construction for natural gas and propane. They are flexible stainless steel pipes, black steel, or soft copper pipes that are type k or type l thickness. The thickness of the pipes being used for the natural gas or propane will also depend on whether or not you have a high pressure or low pressure system.
Building codes explicitly rule out hard copper pipes for propane and natural gas, but black steel may also not be allowed by your local building code. Contact your local building office before using black steel to be sure and ask your plumber about other piping options if possible.
Building codes also have several other requirements that are important for the safety of the occupants of your house. Gas shutoff valves must be located within 3 feet of any appliance that uses gas. It is important that you know precisely where your shutoff valves are located in case of an emergency.
A condensation catching drip leg must also be present near any fixed gas appliance like a furnace or water heater. Natural gas or propane pipe joints would always be made with gas compatible pipe joint compound. The only exception is if the plumber is using black steel, in which case gas compatible pipe thread sealing tape would be used.
For movable appliances that might use gas or propane such as dryers and ranges, braided stainless steel connectors are required by most codes. Some codes also require build in safety valves. Even if your code does not require these safety valves, these valves are an excellent thing to consider; if there is a connector break the valve automatically shuts off.
After any propane or natural gas alteration, a plumber will check the joints of the pipes using an electronic gas detector. However, you can check your own joints if you ever suspect a propane leak by using premixed plumbing testing soap, which can be found in most home improvement stores. To use, coat the joint with the soap. If any bubbles appear, shut off the propane and call a plumber to refit the joint.