Experimental and analytical study of thermal stresses during pipe freezing

A review of experimental investigations on stress development during the bl ockage of a water-filled pipe by freezing was undertaken with the parallel development of an effective finite element thermal stress model. A wide spr ead 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 h istories showed that it is possible to divide a freeze into three stages: f illing, constant wall temperature and thawing. Since each stage produces qu antitatively and qualitatively different stress states, it needs to be exam ined separately. The filling stage causes stresses through the pipe wall, w hich vary from tensile on the outside surface to compressive on the inside. These stresses can be significant but are also short lived and their magni tude may be greatly affected in practice by the way that the coolant is app lied. During the constant-temperature phase, when the pipe wall temperature is maintained at the coolant temperature, the stresses are mainly compress ive, their variation is small within the freezing jacket and they appear to depend on the diameter-thickness ratio. A significant difference between t he behaviour within the jacket and at the end of the jacket is sometimes ob served. Finally, tensile stresses arise during the reverse process of thawi ng. Comparison of experimental data with numerical predictions confirmed th e above observations regarding the magnitude, distribution and nature of th e developing stresses. There are important quantitative and qualitative dif ferences between measured and predicted values, which can be explained by t he uncertainty and scarcity of data as well as the simplicity of the adopte d material model for ice behaviour.