Experimental and analytical study of thermal stresses during pipe freezing

Abstract

A review of experimental investigations on stress development during the blockage of a water-filled pipe by freezing was undertaken with the parallel development of an effective finite element thermal stress model. A wide spread of measured stress values was noted as well as a degree of uncertainty in the cases when the gauge output did not return to zero at the end of the freezing cycle. A methodical examination of stress—and temperature—time histories showed that it is possible to divide a freeze into three stages: filling, constant wall temperature and thawing. Since each stage produces quantitatively and qualitatively different stress states, it needs to be examined separately. The filling stage causes stresses through the pipe wall, which vary from tensile on the outside surface to compressive on the inside. These stresses can be significant but are also short lived and their magnitude may be greatly affected in practice by the way that the coolant is applied. During the constant-temperature phase, when the pipe wall temperature is maintained at the coolant temperature, the stresses are mainly compressive, their variation is small within the freezing jacket and they appear to depend on the diameter—thickness ratio. A significant difference between the behaviour within the jacket and at the end of the jacket is sometimes observed. Finally, tensile stresses arise during the reverse process of thawing. Comparison of experimental data with numerical predictions confirmed the above observations regarding the magnitude, distribution and nature of the developing stresses. There are important quantitative and qualitative differences between measured and predicted values, which can be explained by the uncertainty and scarcity of data as well as the simplicity of the adopted material model for ice behaviour.