某油田甲醇厂锅炉给水预热器在投入使用14个月后，管箱内外壁近焊缝处出现了多处裂纹。通过宏观检验、化学成分分析、力学性能试验、金相检验以及能谱分析等方法，对该锅炉给水预热器管壁开裂原因进行了分析。结果表明：预热器管壁材料的铬元素和镍元素含量过低，导致材料硬度增大，韧性降低；同时，材料中磷元素含量超标，进一步降低了材料的塑性和韧性；晶界贫铬区极易遭受腐蚀并产生微裂纹，在锅炉给水预热器材料本身存在的残余应力和工作内压引起的应力作用下，晶界微裂纹不断扩展连接，最终引发预热器管壁开裂失效。

After 14 months of operation, multiple cracks appeared near the weld of inner and outer walls of a boiler feed water preheater of an oilfield methanol plant. Through macroscopic inspection, chemical composition analysis, mechanical property test, metallographic examination, energy spectrum analysis and other methods, the causes of cracking of the boiler feed water preheater were analyzed. The results show that the contents of chromium and nickel in the material of the preheater were too low, which led to the increase of hardness and the decrease of toughness of the material. Meanwhile, the phosphorus content exceeded the standard requirement, which further reduced the plasticity and toughness of the material. The chromium-poor region of the grain boundary was highly susceptible to corrosion and microcracks produced. Under the action of the residual stress existing in the boiler feed water preheater material and the stress caused by the working internal pressure, the grain boundary microcracks continuously expanded and connected, and finally caused the preheater to crack.