Improving the design of multilayer pipes

Production of multilayer steel pipe for gas pipelines up to 1420 mm in diameter, designed for pressures of 10 to 12 MPa, is discussed. The multilayer wall structure, when properly designed, assures high reliability of pipes, primarily due to the reduced danger of sudden failure. However, multiple layers give these pipes certain special properties which under certain conditions may have a negative influence on their performance. Special design decisions are required to limit these negative influences. The possibility of a leak in the inner layer must be considered. In this case the gas penetrates into the gap between the first and second (counting from the inside) layers of the shell. The pressure in the gap becomes as great as the pressure in the pipe and the first layer is no longer functional, resulting in an overload on all subsequent layers. This process is accompanied by gradual elevation in stress. To prevent these problems, several perforations must be made in each shell, passing through all layers except the innermost layer.