The term hot tapping, or pressure tapping, is used in relation to pipe fitting. It specifically refers to a method of adding a joint to a pressurized pipe or line that is in service. Using a hot tapping machine, the pipe fitter performs the procedure without shutting down the line or draining it. This process is generally used when shutting down a particular pipe might disrupt service for a large area or create outages that could endanger public safety.
In the typical hot tapping procedure, a pipe fitter uses a tap fitting, hot tapping machine, and a gate valve to branch the service. The tap fitting is secured to the main pipe in the proper place, and is tested before attaching the gate valve. When the gate valve is installed and opened, it allows the pilot drill and hot tapping machine cutter to be fed through. The pilot drill makes a small hole to guide the cutter in a straight line through the existing pipe wall. After the cut is made, the hot tapping machine is extracted and the valve is closed until the new lines are connected and ready to be charged.
Hot tapping can safely be used to install valves and branches in a variety of pipeline types. These pipelines are usually made of steel, iron, copper, PVC, or asbestos-cement. The contents of these pipelines may be just as varied as the pipelines themselves, so it is important that a pipe fitter attempting this procedure know how to operate the equipment safely for the particular pipeline type and contents affected. These pressurized lines may be carrying dangerous fluids, including crude oil, sewage, gasoline, natural gas, or steam, so the life of the pipe fitter and others could be endangered if correct methods are not used.
Flow metering devices, temperature sensing equipment, testing or sampling ports, pressure control and relief valves may also utilize hot tapping. This procedure may also be used to inspect the internal condition of a pipeline. Bypassing and draining a section of the pipeline, either temporarily or permanently, can also be completed effectively using this method.
Sometimes, the hot tapping method may be used to create a hole in a pipeline for a line stopping operation in which a plug of the proper size is inserted upon removal of the cutting bit. This plug is called a line plugging head. In these cases, the process of hot tapping and the consequent plugging of the line temporarily stops the flow of fluids to allow workers to perform repairs or permanently shut down service to a section of pipe without requiring the installation of a valve.