熱交換器管の応力腐食割れのX線的研究

概要

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By applying X-ray stress measurements some new findings of practical importance have been obtained on stress corrosion cracking phenomena; they connect actual tube leakages of heat-exchangers with studies of stress corrosion cracking and give the procedure of preventing tube-failures. Tensile residual stresses are observed in just the same position as tube leakages on U-bend and it has been confirmed that the crack initiates from the tensile-stressed area. The magnitude of tensile stress on U-bends decreases with the increase of bend radius, and coincides with the possibility of U-bend failures-the statistics of failures in service of each bend radius. Further tests simulating the service environment proved the residual tensile stress strongly affects the life of tubings. Owing to these results unexpected tube leakages can be avoided by reducing tensile residual stress or by attaining compressive residual stress on the surface affected corrosion environment. Again X-ray technique is employed as a means of quality control: to confirm the manufacturing process of tubings and to minimize residual stress including stress-relieving of bends. In the course of experiments, the authors found another detrimental result of tensile-stressed surfaces. They were more severely attacked by general corrosion; many pits and deep pits appeared under pitting corrosion conditions; and sometimes corrosion fatigue occurred.
社団法人日本材料学会の論文
1974-01-15