Vitrified clay pipe (VCP) is pipe made from a blend of clay and shale that has been subjected to high temperature to achieve vitrification, which results in a hard, inert ceramic.

VCP is commonly used in gravity sewer collection mains because of its long life and resistance to almost all domestic and industrial sewage, particularly the sulfuric acid that is generated by hydrogen sulfide, a common component of sewage. Only hydrofluoric acid and highly concentrated caustic wastes are known to attack VCP. Such wastes would not be permitted to be discharged into a municipal sewage collection system without adequate pretreatment.

There are three main types of VCP produced in the U.S.: Bell & Spigot Pipe (with factory-applied compression joints), Band-Seal pipe (with rubber compression couplings) and NO-DIG(R) Pipe (for trenchless installation with an elastomeric gasket and stainless steel collar for a low-profile compression joint). All VCP manufactured in the U.S. must comply with ASTM C425 to provide a flexible leak-free joint.

Clay pipe has been in-use in sanitary sewer systems for at least 5,000 years