Development of a Reinforced Bend with Shear Control Ring for District Heating

As a fitting to changing the direction of district heating pipes, bends are subjected to a transverse loading by the soil reaction. Generally the foam cushion are buried together to absorb the expansions. However foam cushions are often squeezed by the repetitive thermal axial forces and the soil reactions, it loses its function to secure the expansion space of pipes. It can be a cause of pipe fracture and decreasing the lifetime. In this study, the new reinforced bend was developed without foam cushion but satisfying the structural safety level of current bends with foam cushion. Shear control ring (SCR) was suggested and determined to deconcentrate the shear stresses in the polyurethane insulation based on the finite element analysis [1]. The Taguchi method which is one of design of experiment (DOE) method was introduced to optimize the specification of the SCR [2]. In situ test was also performed to validate the performance of SCR bend without foam cushion by comparing to current bend with foam cushion. Shear stresses of two bends were measured and analysed under the same burying and operating conditions. As a result, it was confirmed that the SCR band without foam cushion has a similar safety level itself with the current bend with foam cushion.