Distinctive features of fatigue crack growth in 14Mo V63 pipe steel after service

We study the influence of technological parameters of operation of the bends of steam pipelines made of 14Mo V63 steel on the kinetic characteristics of fatigue crack growth. We show that an increase in the steam pressure in the pipeline determining the stress-strain state of the pipe wall promotes a decrease in the threshold characteristics of crack resistance. The tests carried out for the constant range of the stress intensity factor revealed the acceleration of crack growth in internal layers of the pipe wall for the metal operating under higher service steam pressure and near the external surface of the metal operating under lower service pressure. We propose a mathematical model of growth of grain-boundary cracks at high temperatures. It is assumed that the crack propagates by the mechanism of merging of pores ahead of the crack tip. The appearance and growth of these pores are governed by the vacancy mechanism.