Analysis of the variation of metals mechanical properties depending on operation time

A safe and long term exploitation of various steel structures is a relevant engineering problem. In design calculations of structures and pipelines the materials features, which will be used for their production of structures, are assessed. Unfortunately in practice we face with ill-timed structures and their elements failure, which always are associated with economical losses and environmental damages. One of the main problems is to predict the changes of materials mechanical characteristics after particular. However, it is complicated to make aging test of materials tests in laboratory and this kind of tests requires plenty of time. One of the ways how to solve this kind of problem is to perform tests with exploited material. Often from the practical or scientific point of view only single cases are studied when it is necessary to identify the reason of failure, but there is no systematic data analysis yet. It is known, that characteristics of materials vary according to time, but relationships between materials mechanical characteristics and exploitation time are not defined. For new steel with high plasticity features various kinds of defects are not very unsafe, because in defected place plastic strains asserts and fracture processes are blocked. When materials plastic features decrease, even the same size defects can be the reason of material failure.