Pipe joint compound--known as threading compound or pipe dope--is applied around the threads of steel gas pipe sections before they are joined together with couplings. The purpose of compound is to seal the coupling to the pipe so that no gas escapes through the joint. If gas does escape, either the coupling is not tightened enough to the pipe thread, or not enough compound has been applied to the thread. The pipe must be removed from the coupling and the thread thoroughly cleaned before more compound is applied.
Mix some soapy water and pour it in a water spray bottle. Spray around each coupling joint in the gas pipeline. Look for bubbles coming from the seams between the couplings and pipe. If any bubbles exist, gas is escaping from the coupling. Mark the leaking coupling with a piece of duct tape, and turn the gas supply off at the gas meter.
Loosen and remove the gas supply hose nut attached to the gas shut-off valve on the end of the gas supply line, using a crescent wrench. The other end of the hose connects to the gas appliance. Place a pipe wrench around the gas valve body, and turn the wrench counter-clockwise to loosen and remove the valve from the end of the gas line.
Place the wrench around the first section of gas line, close to the coupling. Turn the wrench counter-clockwise, to loosen and remove the pipe section from the coupling. Loosen and remove the coupling in the same way. Continue this process removing all pipes and couplings until the marked leaking coupling is reached. Remove the leaking coupling.
Place a rag around the threaded end of one removed section of gas pipe. Holding the rag firmly in place around the thread with one hand, turn the pipe counter-clockwise with the other hand several times to remove the threading compound from the pipe thread. Repeat this process until most or all of the compound has been removed. Brush thoroughly around the pipe thread using a steel brush to remove all remaining remnants of compound from the thread. Follow the same procedure to remove the compound from the threaded ends on all removed gas pipe sections.
Make sure all gas appliances are turned off, or are not required for usage, before turning off the gas at the meter.