Plastic collapse pressures of boiler-tube-bends - effects of variation in wall-thickness

摘要

Tube-bends are extensively used in boilers of power plants. While the design of a straight section of a boiler-tube is well established, this is not so for bend-tubes. The behaviour of internally pressurized bend-tubes is complex due to the fact that the cross-section of a bend-tube becomes oval during its manufacture resulting in its thickness varying around its circumference. The first author and his research team have previously studied the effects of the ovality of the cross-section of a bend tube on its plastic collapse pressure. This paper studies the effects of variation in thickness that exists around the wall of a boiler-tube-bend on its plastic collapse pressure. To the authors' knowledge no such study has been carried out before. It has been found that the plastic collapse pressures for bends manufactured by heating (hot-bends) are higher than those bends manufactured without heating (cold-bends). Also, there are linear relationships between the normalized plastic collapse pressures (i.e., plastic collapse pressure/yield strength) and some normalized geometrical dimensions for both cold and hot-bends. Simple equations have also been presented to aid the design of a boiler-tube-bend.