Effect of microstructures on SCC of steel: field failure analysis case study and laboratory test result

Abstract

Based on continuum mechanics approach, the first step on the modeling of the stress corrosion cracking (SCC) is to understand the morphology of the cracks. Later on, it is followed by other considerations such as the chemical interaction, and electron diffusion. This paper investigates the morphology of the SCC behavior of steels with the main purpose of developing the basis of computational modeling. It also aims to give the basic sense for practical engineers in the fields as well. It mainly focuses on the morphology of the SCC on three basic common microstructures of steel: austenite, ferrite–pearlite, and martensite. The objects were taken both from real field works and from accelerated laboratory tests. The field samples were extracted from actual failed parts at known operating conditions and lifetimes. The laboratory test was an immersion in sodium hydroxide solution. The experimental parameters were controlled in such away to simulate accelerated field failures with all three microstructures. The crack depth and behavior of the stress corrosion cracking (SCC) were then analyzed after immersion test and subsequently, the mechanism of stress corrosion cracking was studied with the focus on their morphological observations. The result shows that each microstructure produces unique shape that can be used as a basis for computational model creation. Field engineers can also take advantage of the results for materials selection.