Use of wave compensators with flexible elements in grade Kh18N10T steel

Abstract

ELEMENTS UDC 621.643.43 The widely used wave compensators with flexible elements in grade KhlSN10T steel, the use of which is associated with considerable temperature changes, must be able to undergo deformation. However, experience in the use of these compensators has shown that in certain cases the flexible elements in grade Kh18N10T steel, undergo intensive corrosion cracking. This type of corrosion cracking of wave compensators is observed at certain petroleum reprocessing factories on atmospheric and atmospheric-vacuum setups for the primaryprocessing of petroleum. Figure I shows one of the damaged compensators. Through, annular cracks are clearly visible on the wave crests of the flexible element, in the zone of maximum tensile stresses and strains. The cracks propagate both as intercrystallites and intracrystallites, which is characteristic of the corrosion cracking of austenitic steels, with the combined action of chlorides and H2S (Fig. 2).In investigating the deposit removed from the internal walls of the compensator, C1-and S 2-ions were observed. In other words, it is from this surface, adjacent to the corrosion medium that the first corrosion cracking of items of equipment in grade 18-18 chromium steel has been observed with other technological equipment, for example the breakup of cooler condensers in equipment for the primary processing of petroleum [1]. Corrosion cracking in this equipment is determined by the increased aggressive character of the medium, which contains chlorides, H2S , and condensed water, while the complex stress state in which the flexible elements have to operate also has an effect.Under such conditions it is necessary to use compensators with flexible elements made not from grade Kh18N10T steel but from materials of increased resistance to corrosion cracking, for example, Cr-Ni anstenitic steels, containing Mo, and of higher Ni content, and Ni based alloys.At the All Union Scientific Research Institute for Petroleum Engineering (VNIIneftemash) work has been carried out on finding media for the petroleum reprocessing industry in which industrially produced wave compensators with flexible elements in grade Kh18N10T steel can be used without fear of breakdown. With this in view, the ability of the main technological media used in the petroleum reprocessing industry to induce corrosion cracking of stressed grade KhlSN10T steel was investigated under industrial conditions. A large batch of stressed, loop-shaped specimens in grade KhlSN10T steel were subjected to previous treatment producing the maximum susceptibility of the metal to corrosion cracking; for example, preliminary cold deformation under tension, sensitization of the steelby annealing, and so on. The specimens were then stored in the equipment for 12 months, which increased the reliability of the results. Table 1 shows that the cracking of indicator loops was observed in technological media used for the primary processing of petroleum and was absent in media used for secondary processes, i.e. catalytical reforming a...