Тривала міцність зварних швів теплостійких сталей у газоподібному водні

Abstract

Оцінено тривалу міцність різних зон зварного з’єднання за статичного та повторно-статичного навантаження сталі 15Х2МФА й характеристики повзучості після випроб на повітрі та в середовищі газоподібного водню металу різних зон зварних з'єднань жароміцних конструкційних сталей 15Х2МФА і 2.25Cr-1Mо у вихідному стані й після деградації за лабораторних та експлуатаційних умов. Показано, що найслабшою зоною є зона термічного впливу, але найінтенсивніше деградує метал шва. Залишковий ресурс різних зон зварного з'єднання оцінили, використавши параметр Ларсона-Міллера.

The features of service regime of the oil hydrocracking reactors is associated with the high stress in its body due to fluctuations in temperature and pressure of the environment during the technological process. To understand the influence of such fluctuations of stress on the degradation characteristics of the weld joint of the steel 15Kh2MFA at static and re-static strength in gaseous hydrogen was investigated. It is established that metal of heat-affected zone is the weakest area of the weld joint at static and re-static loading under the basis of 250 hours of testing. It was established the steady creep rate of 15Kh2MFA steel in hydrogen already in the initial state was worse than steel 2,25Cr-1Mo. At the same initial stress level (σ0 = 330 MPa) the steady creep rate of the 15Kh2MFA steel was more than an order of magnitude higher than obtained for the 2,25Cr-1Mo steel (7,4*10-3 and 3*10-4% / h respectively). The same tendency of change of the steady creep rate was saved in degraded steels at the same initial stress level (σ0 = 330 MPa). The long-term strength data for the metals of different zones of the weld joint on the 15Kh2MFA steel and for the base metal and weld metal on the 2.25Cr-1Mo steel were analyzed using the Larson-Miller parameter. The data obtained at higher loadings was extrapolated to its worker levels. Analysis of these results showed that the time to failure of the weld metal specimens of the 2.25Cr-1Mo steel degraded in operating conditions for 79*103 hours and tested at 290 MPa stress level and temperature of 450 °C, practically coincided with the such time of the base metal, degraded during 60*103 hours in service. It was revealed that the long-term strength of the metal from all weld joint zones under re-static loading is lower than in a purely static one. The weld metal was the most sensitive to the effects of re-static loading. Using of the Larson-Miller parameter it was shown that long-term strength of the metal of different zones of the welded joint tested in hydrogen already in the initial state reached the lower limit of the regulated range for guarantee safe operation of the heat resistant steels.