A double-walled pipe is essentially a pipe within an outer pipe. The inner pipe is the primary or carrier pipe and the outer pipe is called the secondary or containment pipe. The great majority of double-walled piping is used for the transfer of toxic gases, wastewater, groundwater, and process safety. A different special application of a double-walled pipe is a jacketed pipe, which is used to make high viscosity liquids flow at elevated temperature through the carrier pipe. The outer pipe circulates hot fluids that heat up the interior carrier pipe and its contents in turn. Double walled pipes are manufactured of many different materials eg. steel, stainless steel, duplex, super duplex etc