The Influence Of Repair Welded Joint On The Life Of Steam Pipeline Made Of Cr-Mo Steel Serviced Beyond The Calculated Working Time

Abstract

The aim of the paper was to examine the influence of repair welded joints on the service life of steam pipelines for over 220 000 hours of service in creep conditions. The research included the study of the microstructure using scanning microscopy, the tests on mechanical properties at room and elevated temperature, determining the nil ductility transition temperature, and short-time creep tests to determine the residual life of the material. The tests allowed determining the time of further safe operation of elements of the steam pipeline with a repair welded joint, with reference to the base material, and the welded joint after service. The assessment of residual life and disposable residual life, and at the same time determining the possible time of further safe operation, has an essential meaning in the case of elements serviced considerably beyond the calculated working time.Keywords: creeping, material diagnostics, welded joints after service, Cr-Mo steel, residual life Celem pracy było zbadanie wpływu naprawczych złączy spawanych na trwałość eksploatacyjną rurociągów pary przez ponad 220 000 godzin eksploatacji warunkach pełzania. Wykonano badania mikrostruktury z wykorzystaniem mikroskopii skaningowej, badania właściwości mechanicznych w temperaturze pokojowej i podwyższonej, wyznaczono temperaturę przejścia w stan kruchy, przeprowadzono skrócone próby pełzania celem wyznaczenia trwałości resztkowej materiału. Przeprowadzone badania pozwoliły na wyznaczenie czasu dalszej bezpiecznej eksploatacji elementów rurociągu pary z wykonanym naprawczym złączem spawanym w odniesieniu do materiału rodzimego i złącza spawanego po eksploatacji. Ocena trwałości resztkowej i resztkowej trwałości rozporządzalnej, a tym samym oszacowanie lub wyznaczenie możliwego czasu dalszej bezpiecznej eksploatacji ma zasadnicze znaczenie w przypadku eksploatacji elementów znacznie poza obliczeniowy czas pracy.

Forecasting in the presence of microstructural changes for the case of P91 steel after long-term ageing

“…Recorded images of microstructure were used in the analysis of mean diameter of precipitates observed mainly on boundaries of martensite laths and grains of former austenite, where, according to the conducted internal research, confirmed with reference data [1,12], mainly M 23 C 6 carbides and Laves' phase are present.…”

“…A crucial tool in diagnostic testing of material condition, not only within the design work time, but also beyond the design work time is a database of material characteristics. It takes into consideration changes in the processes of microstructure and mechanical properties degradation [9][10][11][12]. A significant factor having impact on the changes in microstructure, and thus functional properties, is the temperature, and in particular, its changes during exploitation.…”

The effect of temperature on the changes of precipitates in low-alloy steel

“…[6][7][8] describing the structure of the data set change in time, and the analysed distributions show right-side asymmetry and concentration around the mean that are stronger than those in the normal distribution. Then, the probability density distributions were determined by non-parametric methods.…”

The Procedure for Determining the Time of Safe Service beyond the Design Service Time Based on Creep Testing

“…Out of them, the components working at above the limit temperature, that is, under creep conditions, are of particular importance. In the assessment of these components, it is important and necessary to assess the condition of their materials [1][2][3][4][5][6][7]. Such an assessment is carried out based on nondestructive materials testing, and its result is referred to the available characteristics of materials after service [8][9][10][11][12][13][14][15].…”