Structure damaging and properties of steam line bends after long service

12Kh1MF steel tube bends and straight lengths are compared after long-term service under creep. Methods of light and electron microscopy and X-ray diffraction have been used. Tube bends fracture is found to occur preferably in a fine-grained (8-9 size) ferrite- carbide structure. Damaging in tubes is realized through the formation of micropores 0.05-3 mm in size. Presence of 1-3 mm pores and a network of pores at the grain boundaries decrease essentially a long-term rupture strength and a long-term plasticity