某核电站高温取样冷却器传热管发生开裂，通过宏观观察、化学成分分析、金相检验、硬度测试等方法，对核电站高温取样冷却器传热管的开裂原因进行了分析。结果表明：传热管开裂为磷酸盐引起的碱致应力腐蚀开裂。主要原因为传热管顶部存在局部过热造成水沸腾而发生磷酸盐隐藏。磷酸盐产物浓缩、沉积，沉积产物下局部OH^-富集碱化，Fe₃O₄氧化膜进一步溶解，甚至与新鲜金属基体直接反应，导致表面形成凹凸不平的腐蚀坑，最终导致传热管在残余应力的作用下发生碱致应力腐蚀开裂而泄漏。另外，传热管硬度较高也促进了裂纹的萌生。

The heat transfer tube of high temperature sampling cooler in a nuclear power station cracked. The causes of cracking on heat transfer tube of high temperature sampling cooler in nuclear power plant were analyzed by means of macro observation, chemical composition analysis, metallographic examination and hardness test. The results show that the cracking of heat transfer tube is alkali stress corrosion cracking caused by phosphate. The main reason was that there was local superheated leading to water boiling at the top of the heat transfer tube, resulting in phosphate concealment. The concentration and deposition of phosphate products, the enrichment and alkalization of local OH^- under the deposited products, the further dissolution of Fe₃O₄ oxide film, and even the direct reaction with fresh metal matrix, led to the formation of uneven corrosion pits on the surface, and eventually led to the leakage of heat transfer tube due to alkali induced stress corrosion cracking under the effect of residual stress. In addition, the higher hardness of heat transfer tube also promoted the crack initiation.