Most commonly found in the manufacturing, process, and construction industries, a double-walled pipe is essentially a pipe within an outer pipe. A double-walled pipe can act as a containment pipe when transporting harmful materials but also exists as a weight-saving technique in water transportation systems. The inner pipe is known as a primary or carrier pipe, while the outer skin is referred to as the containment or secondary pipe.
The pipes are manufactured most commonly from high-density polyethylene (HDPE) or polyvinyl chloride (PVC). Stainless steel versions also exist, and these are generally used for the transfer of toxic gases. In the case of stainless steel double-walled pipe, a leak detection system can be installed to monitor gas levels between the primary and secondary skins. This system can provide advanced warning of a potential failure in the pipe.
In construction applications relating to ground or wastewater movement, double-walled pipe is commonly used to save weight. In this application, the secondary skin is actually a series of stiffening ribs, which run around the circumference of the smooth primary pipe. These ribs provide core strength to the pipe to prevent crushing underground without the need for thick pipe walls.
The use of double-walled pipe in water transportation can also be required when cross-contamination is a risk. An example of this would be when a wastewater pipe traverses a clean water source. In this case, should the pipe carrying the wastewater fail, the resultant leak could contaminate the clean water source. By using a double-walled pipe, the risk of this occurring can be greatly reduced.
As an alternative, a clean water pipe passing through an area of contaminated land, such as a landfill site, would need to be of a double-wall construction. This prevents external contamination of the carried liquid. The construction characteristics of double-walled pipe mean that the protection can exist for both the liquid in the pipe as well as any sensitive external elements.
A less common application for a double-walled pipe is where temperature control is required for the materials in the primary pipe. These systems are known as jacketed pipes. In this application, the void between the skins of the pipe allows for hot fluid to flow around the primary pipe, elevating the temperature of the carried material. This can be of particular benefit when the primary pipe is being utilized to carry liquids with a high viscosity.