The thermal history and stress state of a fresh steam-pipeline influencing its remaining service life

Abstract

The service life of thick-walled power plant components exposed to creep, as is the case with pipelines of fresh- and re-heated steam, depend on the exhaustion rate of the material. Plant operation at elevated temperatures and at temperatures below designed temperatures all relates to the material exhaustion rate, thus complicating remaining life assessment, whereas the operating temperature variation is a most common cause in the mismatching of real service- and design life. Apart from temperature, the tube wall stress is a significant variable for remaining life assessment, whose calculation depends on the selected procedure, due to the complex pipeline configuration. In this paper, a remaining life assessment is performed according to the Larson-Miller parametric relation for a Ø324×36 pipe bend element of a fresh steam-pipeline, made of steel class 1Cr0.3Mo0.25V, after 160 000 hours of operation. The temperature history of the pipeline, altogether with the pipe bend, is determined based on continuous temperature monitoring records. Compared results of remaining life assessment are displayed for monitored temperature records and for designed operating temperature in the same time period. The stress calculation in the pipe bend wall is performed by three methods that are usually applied so to emphasize the differences in the obtained results of remaining life assessment

Pragmatic optimisation methods for determining material constants of viscoplasticity model from isothermal experimental data

“…This is accounted for through the definition of a viscous stress, σ v , assumed to take the form of a power law 7 such as equation (4), where Z and n are viscous material coefficients. The viscous stress, along with the kinematic and isotropic internal variables, defines the total stress (σ) given in equation (4).…”

“…These fluctuations may be periodic or cyclic in nature. Additionally, focusing particularly on the future trends of power plant operation, these fluctuations will become more pronounced as operators attempt to generate in a highly strategic manner, maximising generation effectiveness 3,4 . Variations in loading or temperature present serious complications when analysing such components due to the cyclic hardening behaviour of materials if the material works within the plastic range.…”

Remaining life assessment of a high pressure turbine casing in creep and low cycle service regime

“…The time of continuously recorded temperatures during this period is systematized into temperature intervals of T = 10°C for the sake of extrapolating onto the total service life of 150 000 h [17,18]. The time of continuously recorded temperatures during this period is systematized into temperature intervals of T = 10°C for the sake of extrapolating onto the total service life of 150 000 h [17,18].…”

“…Since the sixties of the last century, it is massively used in cast and rolled states for developing of parts that work at temperatures up to 565°C and pressures up to 25.5 Mpa, hence it a large amount of data on it is available from real exploitation, for various elements used in thermal power plants [6,[18][19][20]. This steel cast is designated as 15H1M1FL, in accordance with GOST standard, and has been in use for a long time.…”

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

“…Moreover, other factors that also have an influence on it are as follows: the mean creep-rupture strength, whose actual value cannot be higher than the mean value assumed for calculations, the actual thickness of wall bigger than the calculated thickness, and actual parameters of work (temperature, pressure), most frequently lower than the assumed calculated ones. The above-mentioned factors in practice or normal service, with fairly performed routine diagnostics and economically grounded modernization works, allow extending the working time considerably beyond the calculated time [6][7][8][9]. It should be mentioned that in the case of extension of the service time of critical elements of a boiler above 200 000 hours, it is necessary to determine the residual creep strength [1,10].…”