Unified Model of Steady-State and Transient Creep and Identification of Its Parameters

Durability of bends in high-temperature steam lines under the conditions of long-term operation

“…The following creep model adequately describing both the first and second stage under the conditions of gradual hardening (softening) of material was proposed for the conditions of long term (300000 h and more) operation [4]:…”

“…Creep model (1) makes it possible to describe the slowdown of creep rate with time, which is character istic of long term tests [4] due to the power depen dence of creep deformation rate on time contained in the second summand.…”

“…Its further generalization for the case that makes it possible to take into account the dif ferences in the parameters of material for the ranges of stresses higher and lower than the elasticity limit with retaining the model structure is given in [4].…”

“…Matters concerned with identifying the parameters of creep model (1) based on the least squares method using the optimal search for solution according to the Levenberg-Marquardt algorithm were considered in [4,5]. Two methods for determining six constants appearing in equation (1) were proposed: the first one is based on creep test results, and the second is based on the results of stress relaxation tests.…”

“…specific features relating to the stress strain state (SSS) of a bend using more sophisticated creep models ori ented at providing a more accurate description of creep processes under long term loading conditions [4]. The fracture conditions are systematically analyzed, and the lifetime in a wide range of temperatures is evalu ated for two design versions of bends: a curved bend and a steeply curved bend made of steel grades 12Kh1MF, 15Kh1M1F and 10Kh9MFB according to the Central Boiler and Turbine Institute (TsKTI)'s standards 321.05 2009 and 321 06 2009 (Fig.…”