Assessment of the In-Service Degradation of Pipeline Steel by Destructive and Nondestructive Methods

Abstract

We analyze the influence of the long-term operation of API X52 pipeline steel on the degradation of its mechanical properties. It is established that, after operation for 30 years, its strength and plasticity characteristics decrease substantially, and the fatigue toughness decreases particularly abruptly, which is connected with the development of the damageability. We use indentation methods for comparing the states of the operated and nonoperated material. It is shown that the indices of spread of the results of measurements (the coefficient of variance) of the mechanical properties (hardness, wear, etc.) are more sensitive to the damage of the material in the initial state and the damage after operation than their averaged values. Some correlations between the Vickers hardness, cyclic hardness, strength, and plasticity of the steel are established.