Forecasting the Corrosion Fatigue Life of Structural Materials in Chemical Engineering

Abstract

Introduction: The most important task in the development of modern chemical engineering is to improve the quality of metal products and parts made from them, increase their efficiency, reliability, and fatigue life, bring these indicators to the level of world standards, and ensure the competitiveness of domestic products in the foreign market. The structural safety of chemical engineering equipment is largely determined by the operational reliability of its component elements. The most common and progressive way of their manufacture is cold pressing methods, the quality and reliability of which are largely defined by the condition of the gauged bars' surface. At the same time, the performance characteristics of machinery parts and mechanisms are determined mainly by the properties of the surface layers of metal, since all destruction processes, especially during cyclic loading, usually start from the surface and depend on its structure and physical and chemical status. The role of the type of metal surface imperfection increases greatly with corrosion fatigue, which is determined by the formation of protective barrier films. In the absence of stress, these films reduce the rate of corrosion, and during cyclic loading, they are continuously destroyed. In addition, a stress concentration appears that is caused by surface damage, leading to the formation of corrosive cavities on it. In this paper, based on theoretical research, a physical parameter is proposed that controls the corrosion fatigue life of strain-hardened structural materials of chemical engineering, serving as an indicator of the degree of strain hardening under static tension. An analysis of experimental data has confirmed that the technological plastic processing of structural materials, leading to a decrease in the value of this indicator, causes an increase in their resistance to corrosion-fatigue failure. Purpose: The purpose of this work was to identify a physical parameter that controls the corrosion fatigue life of technologically processed structural materials of chemical engineering. Methods: The experimental test procedure included mechanical tests under static and cyclic loading. Structural materials widely used in chemical engineering, prestrained at different degrees, were selected for the study. Static tension tests of standard samples were carried out on ZD 10/90 and UME-10TM machines with a strain rate of 2 × 10-3 sec–1. The samples were loaded at a frequency of 50 Hz using the MIP-8 machine. A widely spread 3% aqueous solution of sea salt was used for testing in a corrosive environment. Results: It has been established that a physical parameter that controls the corrosion fatigue life of materials is the exponent in the equation of the strain hardening curve under static tension. It has been shown that the process of plastic treatment of material, leading to a decrease in its size, causes an increase in its resistance to corrosion-fatigue failure. Conclusion: It has been shown that in order to assess the feasibility of a particular process treatment in order to increase the resistance to corrosion fatigue of structural materials, it is necessary to trace its impact on the value of the strain hardening index under static tension.