某材料为35Cr45Ni高镍铬奥氏体耐热钢的循环乙烷裂解炉炉管在停炉后发生开裂，通过对其进行宏观形貌、微观形貌、显微组织以及化学成分等方面的分析和理论计算，找出了炉管开裂失效的原因，并提出了相应的预防措施和建议。结果表明：炉管长期在高温下服役，导致其强度降低，塑性和韧性变差；同时炉管内形成了很厚的结焦层，由于结焦层的热膨胀系数和炉管的热膨胀系数相差很大，使其在停炉冷却过程中对炉管内壁产生了很大的环向应力，当其超过炉管的抗拉强度时，就会导致炉管发生纵向全管开裂。

Failure causes of the cycle ethane ethane pyrolysis furnace tube with material of 35Cr45Ni high nickel-chrome austenitic heat resistance steel which cracked in the shutdown process were presented based on theory calculation and a series of test including macro and micro morphological observation, metallographic examination, chemical compositions analysis and mechanical properties test. The corresponding protective measures were also put forward. The results show that long-term working at high temperatures resulted in the formation of a thick layer of coke inside the tube surface and the decrease of strength, plasticity and toughness of the furnace tube. Large difference of thermal expansion coefficient between the coke and the furnace tube led to the hoop stress exceeding the furnace tube strength in the shutdown process and the longitudinal cracking of the whole furnace tube.