The gas line that runs between the tank and the structure housing the gas appliances is the service piping, also known as the yard line. The propane yard line generally consists of copper tubing or plastic polyethylene piping. The service piping needs to be installed correctly and legally in conjunction with the propane tank for the entire outside portion of the installation to be safe and serviceable.
The part of the yard line that is visible is where it comes out of the ground next to the tank and at the point it enters the building or where it connects to the point of use, such as a generator or pool heater. Only approved materials and fittings are to be used for any part of a propane gas service line. Materials such as PVC, rubber hose and flex lines are illegal and are not to be used in any part of the gas service line.
Important Note About Underground Piping Materials - Allowable materials used for underground piping/tubing vary from state to state. The photos here depict copper tubing installed underground in a state where copper tubing is approved for underground yard line installations. Copper tubing is not an approved underground piping material in some states. Consult a licensed propane company in your state for more information about approved underground gas piping and yard line requirements.
The yard line is subject to depth requirements for the protection of the line and connections on either end. Depths range from 12 to 18 inches underground, depending on vehicular traffic. The reason for this depth requirement is simple - the earth, dirt, sand or whatever is covering the line needs to adequately protect the underground gas line from damage. A copper line running under a dirt drive that is buried just a few inches underground can be easily crimped or crushed by the weight of a vehicle. Similarly, a line running on the surface of the ground can easily be damaged by accidentally tripping over it. The inadvertent movement of the gas service line can cause leaks to form at the connections on either end of the line. For these simple reasons, the gas line needs to be buried at a safe and required depth. Propane gas lines running along the top of the ground (pictured below) constitute illegal installations.
The materials used for underground piping and tubing are subject to strict limitations. These material requirements are in place because of the unfriendly underground environment the pipe and tubing will be exposed to. Like underground propane tanks, buried piping and tubing must be made of a material that will resist harsh underground conditions. Additional protective measures must be taken in certain cases like placing the gas line in a PVC sleeve or wrapping it with a protective tape. All of these measures are for the protection against loss of propane. If unapproved materials are used for underground piping, propane leaks will form. Also, piping materials such as steel must be protected by sleeving or taping the service line or corrosion will begin to damage the piping (pictured below).