Environmentally Assisted Cracking Behavior of S420 and X80 Steels Containing U-notches at Two Different Cathodic Polarization Levels: An Approach from the Theory of Critical Distances

Pablo González,Sergio Cicero,Borja Arroyo,José Álvarez

doi:10.3390/met9050570

Abstract

This paper analyzes, using the theory of critical distances, the environmentally assisted cracking behavior of two steels (S420 and API X80) subjected to two different aggressive environments. The propagation threshold for environmentally assisted cracking (i.e., the stress intensity factor above which crack propagation initiates) in cracked and notched specimens (KIEAC and KNIEAC) has been experimentally obtained under different environmental conditions. Cathodic polarization has been employed to generate the aggressive environments, at 1 and 5 mA/cm2, causing hydrogen embrittlement on the steels. The point method and the line method, both belonging to the theory of critical distances, have been applied to verify their capacity to predict the initiation of crack propagation. The results demonstrate the capacity of the theory of critical distances to predict the crack propagation onset under the different combinations of material and aggressive environments.

Highlights

It is expected that fossil energies, such as gas and petroleum, will remain the main source of energy for the two decades
The aim of this paper is to extend the validation of the use of the theory of critical distances (TCD) in environmentally assisted cracking (EAC) assessments, analyzing the effect of two cathodic current densities on two different steels (S420 and X80) that are commonly used in offshore components, power plants and pipes
This study analyzes, through the application of the point method (PM) and the Line Method (LM), the effect of the environment on the EAC behavior of two steels: a weldable thermo-mechanically treated S420 medium-strength steel [28], and API X80 medium-strength steel obtained by means of control rolling and accelerate cooling [29]

Summary

Introduction

It is expected that fossil energies, such as gas and petroleum, will remain the main source of energy for the two decades. Predictions estimate that energy demand will present an increase of 48% by 2040 [1] This increasing energy demand has led to the development of other energy sources (e.g., nuclear power and renewables), and to the extraction of fossil energies in more demanding locations. The failure of structural components that operate in aggressive environments is often related to environmentally assisted cracking (EAC) processes, such as stress corrosion cracking (SCC) and hydrogen embrittlement (HE) [2,3]. Both phenomena lead to brittle and unexpected failures caused by the degradation of the mechanical properties of the materials [4,5]

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