Counting from the inner lining of the pipeline for the wear layer, insulation, steel wall. Currently lined pipes use of turtle nets double lining, no hexagonal mesh of steel fiber reinforced double lining, no shells steel and fiber-reinforced lining form a monolayer. Since adopting lining, pipe stress, stiffness had a significant impact.Stress state pipeline under complicated loads generated is complex. In piping design usually used in good agreement with the experimental results of the third strength theory (maximum shear stress theory) as the theoretical basis for stress check, and stress checking formulas it is also used in the third strength theory. Once the pipeline is subjected to stress (outside) pressure, weight and stress and other external load generated by a stress can be divided into a membrane state of stress and a bending stress. Pressure from inside the pipe, weight hoop stress and external load generated axial stress (collectively positive stress) and shear stress external force and moment equilibrium conditions should be met. Excessive stress deformation generated will limit increases (ie no self-limited), so that destruction. This stress belong to a membrane state of stress.

Bending stress caused by the weight and external loads is a bending stress. Bending stresses in the pipe section is a straight line distribution. A side cross-sectional tensile stress, compressive stress and the other side, through the center of the neutral axis of stress is zero. When the pipe wall entered the yield, close to the neutral axis is still in elastic state. It may continue to bear the load and stress redistribution. This stress can be applied to analyze the concept of ultimate load, allowing a higher state than the last film of the allowable stress values. General For safety reasons, the provisions of the first pipe stress must not exceed the allowable stress. A stress value of less than or equal to the operating temperature of the material allowable stress, the pipeline can operate safely.