The test methods for assessing environment assisted cracking of metals in aqueous solutions are described. The advantages and disadvantages are examined and the interrelationship between results from different test methods is discussed. The source of differences in susceptibility to cracking observed occasionally from the varied mechanical test methods is often the variation in environmental parameters between the different tests and the lack of adequate specification, monitoring, and control of environmental variables. Time is also a significant factor when comparing results from short term tests with long exposure tests. In addition to these factors, the intrinsic difference in the important mechanical variables, such as strain rate, associated with the various mechanical test methods can change the apparent sensitivity of the material to stress corrosion cracking. The increasing economic pressure for more accelerated testing is in conflict with the characteristic time dependence of corrosion pr...

Test methods for environment assisted cracking

Test methods for environment-assisted cracking

The stress corrosion cracking (SCC) susceptibility of austenitic stainless steels (SS) in calcium chloride (CaCl2) solutions was studied using a constant-load method Initiation and propagation of stress corrosion cracks were examined using fractography The distribution of cracks was classified A physical cracking was introduced, and creep deformation measurements were performed The steady-state strain rate (E˙SS) obtained from the corrosion elongation curve (elongation-vs-time curve) showed a linear function of time to failure (tf) This implied that E˙SS can be applied as a parameter for prediction of tf Furthermore, E˙SS below which no failure occurs within a laboratory time scale was estimated Based on results obtained, the critical values of stress (σ) below which no SCC occurred were evaluated Based upon creep measurements in a noncorrosive environment, the influence of environment on E˙SS was more than fivefold Cracking characteristics were divided into three categories according to

Stress Corrosion Cracking and Life Prediction Evaluation of Austenitic Stainless Steels in Calcium Chloride Solution

This paper analyzes the effect of process history on K-dominance condition in hydrogen assisted cracking The performed study of stress-strain assisted diffusion reveals that hydrogenation of the fracture process zone is not a purely K-driven local autonomous phenomenon Hydrogenation and crack growth are shown to be coupled processes, one influencing the other Consequently, particular histories of stress intensity factor K and crack size evolutions affect crack growth rate ν that can occur at the same instantaneous K-value in a given material Thus the crack growth kinetics curve ν=ν(K) is not unique as an intrinsic material property must be

The Effect of History on Hydrogen Assisted Cracking: 1. Coupling of hydrogenation and crack growth

Stress corrosion cracking (SCC) is particularly important for aerospace vehicles, since it occurs, or can occur, in all major alloy systems used in their construction. The consequences of stress corrosion failures may be serious, even leading to loss of an aircraft. This chapter surveys the types of structures and materials used in aerospace vehicles and the environments encountered by them. Special mention is made of space vehicles and platforms, which pose unique problems with respect to avoiding stress corrosion cracking. Selected case histories from a wide variety of aircraft are included to illustrate the problems caused by SCC in service, and guidelines are given for preventing and alleviating these problems.

Stress corrosion cracking (SCC) in aerospace vehicles

This document provides guidelines for obtaining and using stress corrosion cracking (SCC) test data for high strength alloys, which are used typically in aerospace structures. Both fracture mechanics and non-fracture mechanics tests are considered, but the emphasis is on using fracture mechanics as part of an overall strategy - a fracture control plan - to prevent or control SCC in service. In fact, the control of SCC in aerospace structures is not feasible, and SCC fracture control planning for high strength alloys in aerospace structures must be directed to preventing SCC in service.

R.J.H. Wanhill

Papers

Fracture control guidelines for stress corrosion cracking of high strength alloys