MULTI-LAYER PIPE Russian patent published in 2001 - IPC

FIELD: plastic pipes. SUBSTANCE: multi-layer plastic pipe consists of at least two layers of different plastic materials. Plastic materials consist of polyolefin plastic. Pipe is resistant of quick propagating of cracks expressed in form of critical temperature of pipe which is below weighted mean value of critical temperature of single-layer pipes made from separate plastic materials included in multi-layer pipe having similar size. Critical temperatures of single-layer pipes made from separate plastic materials differ by at least 5 deg. and critical temperature of pipe is lowest temperature at which crack formed in pipe propagates through distance equal to 4 diameter of pipe at pressure differential between inner and outer sides equal to 0.5 MPa. It is good practice to have critical temperature of pipe below -15 C and composition of material including olefin plastics, for example, polyethylene plastic and polypropylene plastic. EFFECT: enhanced resistance to crank propagation. 8 cl