Vitrified clay pipe (VCP) is a pipe variant made from clay that has been subjected to a vitrification process. This process involves exposing the dried clay pipe to extremely high temperatures, which causes it to become exceptionally hard and almost totally inert. These clay pipes are commonly used in sewer systems because of their outstanding working qualities. These include excellent chemical resistance, compressive strength, and rigidity, all of which enhance the product's service life and make them ideal for other processes such as trenchless pipe installations. In fact, many modern vitrified clay pipe products have projected service life spans in excess of 100 years.
Vitrification has long been a method of enhancing the excellent inherent characteristics of clay items. The process involves heating the clay article to temperatures in the region of 2,000° Fahrenheit (1,093° Celsius). This serves to fuse the clay particles into a glass-like state, which is extremely hard and inert. In the case of VCP, the pipe sections are first extruded and dried prior to firing. The resultant products are extremely robust and exhibit outstanding longevity in most applications, as well as being among the cheaper types of pipe to manufacture.
These characteristics make the pipes an ideal piping solution for sewer mains, which represent one of the most aggressive pipe system environments. Vitrified clay pipe products used in subterranean applications are less prone to breakage due to compression and more rigid than other traditional pipe types. They also exhibit excellent resistance to chemical attack, particularly the sulfuric acid present in most sewerage systems.
The inherent strengths of VCP also make the products ideal choices for processes such as pipe jacking. In this process, the vitrified clay pipe is installed in a trenchless process that involves jacking the pipe sections together through the soil without any of the disruptive excavation associated with traditional pipe installation methods. The products are also ideal for use in other processes such as slurry microtunneling, static pipe bursting, and pilot tube microtunneling.
The outstanding working properties of vitrified clay pipe products lend them some of the best projected longevity values of all pipe types. Some manufacturers claim projected service cycles of 200 years with the United States Army Corps of Engineers, giving the products a projected reasonable life span of at least 100 years. These figures far exceed those of steel or resin-based pipes used in similar applications.