Extension of life of steam pipelines, operated under creep conditions, determines the necessity of evaluation of their damageability and in many respects depends on carbide transformations in metal. The work considers peculiarities of diffusion and structure of carbide phases in metal of welded joints of pearlite steels after long-term operation. It is determined that concentration of coagulating carbide phases (M23C6, M7C3 etc.) Metal of welded joints of steam pipelines is characterized by structural, chemical and mechanical inhomogeneity, formation of which is promoted by welding heating at their manufacture. Namely, inhomogeneity under conditions of long-term operation provides for more intensive physical-chemical processes in welded joint metal than in the base metal, that, respectively, provokes its degradation and limits the life.Evaluation of damageability level in welded joints of steam pipelines of long-term operation, which allows specifying their residual life, is of current importance. Investigation of peculiarities of physical-chemical processes, taking place in welded joint metal, is relevant for evaluation.It is a well-known fact that welded joints of elements of steam conduit channel from 15Kh1M1F and 12Kh1MF steels, being operated under 545-585 °C temperature and 20-25 MPa pressure [1][2][3][4][5][6][7], mostly suffer from damages at long-term running. Transfer of power generating units in cycling operation mode provides for acceleration of their damageability. Damageability of metal of welded joints mainly takes place by creep and fatigue mechanisms, which are forced by corrosion constituent (Figure 1). Damageability by creep mechanism is characterized by formation of nucleation (critical) pores of around 0.03-0.07 μm size as well as their coarsening up to 3-7 μm, further branching and transformation of pores in creep cracks.The most intensive formation of creep pores is observed in areas of incomplete recrystallization and fusion of HAZ of welded joints in their external, most elongated area. The fatigue cracks

The peculiarities of degradation of structure and damageability of metal of welded joints of the steam pipelines of heat power plants of long-term operation period (more than 250,000 h) under the conditions of creep and low-cyclic fatigue are given. It is shown that welded joints of steels 15Kh1M1F and 12Kh1MF are damaged mostly along the areas of fusion, overheating and partial recrystallization of metal in the near-weld zone and also in the places of joining pipe elements of different thicknesses. 13 Ref., 1 Table.

EffEct of amplitudE and frEquEncy of plasmatron oscillations on chEmical and structural inhomogEnEity of mEtal dEpositEd by plasma-powdEr mEthod i.a. ryabtsEV 1 , E.f. pErEplyotchiKoV 1 , i.a. bartEnEV 2 , g.n. gordan 1 , i.l. bogaJchuK 1 and l.m. KapitanchuK 1 1

No abstract

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