利用光学显微镜、扫描电镜、能谱仪、拉伸及冲击试验机等对服役15 a的制氢转化炉中HP40Nb钢炉管的显微组织和力学性能进行了研究，依据高温持久试验结果估算了炉管剩余寿命。结果表明：长期高温服役后，炉管钢组织中晶界粗化并有G相析出，晶内二次碳化物析出明显，近内壁、近外壁和基体中均出现蠕变孔洞，近内壁和近外壁发生氧化和贫铬，外壁形成脱碳层；与原始铸态炉管相比，长期高温服役后炉管的室温抗拉强度降幅超30%，高温抗拉强度降幅约18%，室温冲击功下降明显，剩余寿命不足1 a。

The microstructure and mechanical properties of HP40Nb steel furnace tube in a hydrogen reformer after 15-year service were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, tensile and impact testers. Based on the high-temperature creep rupture testing results, the remnant life of the furnace tube was evaluated. The results show that after the long-term high-temperature service, in the microstructure of furnace tube steel, the grain boundaries coarsened with the G phase precipitation; secondary carbides precipitated in grains obviously; creep voids were observed near inner and outer wall and in matrix; oxidation and chromium depletion were observed near inner and outer wall; decarburization layer was formed on the outer wall. Compared with the as-cast steel furnace tube, the tensile strength of the furnace tube after the long-term high-temperature service reduced by 30% and 18% at room and high temperature, respectively, the impact energy at room temperature decreased significantly, and the remnant life was less than 1 a.