text: Double-walled pipe system may use plastic pressure pipe systems materials of high-density polyethylene (HDPE), polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), polypropylene (PP), polyvinylidene fluoride (PVDF), and ethylene chlorotrifluoroethylene copolymer (ECTFE).  Dual-wall stainless steel tubing is most commonly used in semiconductor plants for the containment of highly toxic gases.
  A leak detection system in the containment pipe indicates if the carrier pipe is leaking.  Double wall pipes are usually hydrostatically tested, or tested to hold and maintain a target gas pressure before the first use.
  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.