Оцінювання залишкового ресурсу зварних з’єднань паропроводів з тріщинами

Abstract

Задача про визначення залишкового ресурсу зварних з’єднань труб паропроводів з тріщинами розв’язана з допомогою сформульованого раніше авторами енергетичного підходу. При цьому для спрощення розв’язку такої складної просторової задачі застосований метод еквівалентних площ.

The method for determination of residual resource of steam pipeline pipes the welded connections with cracks is proposed. The method is based on the first low of thermodynamic on energy balance and the balance of energy change rate in a metallic body, containing a macro crack and subjected to long-term loading tension under high-temperature field. It is assumed, that the period of well-established creep dominates here. In this case the main mechanism of fracture is high temperature creep fracture. We assume that crack propagation occurs by jumps during incubation periods of high temperature creep in the prefracture zone near the crack tip. Then the crack growth rate can be represented as the average ratio of the length of its jump to the time of incubation period. Basing on it and some ideas of fracture mechanics available in literature the equation has been obtained for description of high temperature creep cracks growth kinetics. This equation together with initial and final conditions form a mathematical model for determination of the period of high temperature creep crack subcritical growth in the metallic materials. This equation depends on the stress intensity factors, which for welded joints with cracks are defined as follows. Stress intensity factors for weld crack pipe represent the approximate as stress intensity factor for plates with semielliptical surface crack on the surface of which is applied the amount of residual stress of welded joints and stress in the wall of the pipe. This stress intensity factor is found on the basis of published data. Substituting this value of this stress intensity factor in the above-mentioned equation we obtain a mathematical problem to determine the residual life of the pipe, in the weld joint which is semielliptical surface crack. Solution of this problem is associated with considerable mathematical difficulties.Thus for simplification of decision of such intricate spatial problem the method of equivalent areas is applied. Numerically and graphically it was shown that the residual life of welded connections of steam crack strongly depends on the initial value of the size of the defect