Microstructure Optimization to Prevent Hydrogen-Induced Cracking of API X70 Pipeline Steels in Sour Environments
type: CreativeWork
description: These days, by increasing the demand for oil and gas resources, the failure of pipeline steels has become one of the crucial topics in the oil and gas transportation industry. The failure of pipeline steels is divided into two major categories: stress corrosion cracking (SCC) and hydrogen assistant cracking (HAC). Hydrogen-induced cracking (HIC) is the main cause of pipeline steels failure in sour environments, which is categorized as a type of HAC. In this type of failure, hydrogen atoms accumulate in the steel and cause cracking by different mechanisms. The main focus of this thesis is to find the effects of texture and microstructural parameters on HIC nucleation and propagation in steels exposed to sour environments and also the effect of such environment on the mechanical properties of steels with different microstructure and texture. In this thesis, the electrochemical hydrogen charging experiment was used to introduce HIC in API 5L X70 pipeline steels with four different thermo-mechanical control processing (TMCP) parameters. Using the scanning electron microscope (SEM), HIC cracks at the cross-section of samples were observed. The SEM observations indicate that the sample which had more finish rolling steps and smaller grain size was more susceptible to HIC. However, the specimen with larger grains was more susceptible to hardness increment than the steels with smaller grains. The energy dispersive Spectrometer (EDS) results showed that two types of inclusions, namely calcium sulfide (CaS) and aluminum oxide (Al2O3), were responsible for the nucleation of HIC in all examined API 5L X70 samples in sour environments. Comparing the length and quantity of the cracks in the middle and top layers of all samples, it could be concluded that the middle layer was more susceptible to HIC. The martensite phase accumulated around the HIC crack was recognized as the weakest phase that could resist HIC propagation and the specimen which had more deformed grains was more su…
abstract: These days, by increasing the demand for oil and gas resources, the failure of pipeline steels has become one of the crucial topics in the oil and gas transportation industry. The failure of pipeline steels is divided into two major categories: stress corrosion cracking (SCC) and hydrogen assistant cracking (HAC). Hydrogen-induced cracking (HIC) is the main cause of pipeline steels failure in sour environments, which is categorized as a type of HAC. In this type of failure, hydrogen atoms accumulate in the steel and cause cracking by different mechanisms. The main focus of this thesis is to find the effects of texture and microstructural parameters on HIC nucleation and propagation in steels exposed to sour environments and also the effect of such environment on the mechanical properties of steels with different microstructure and texture. In this thesis, the electrochemical hydrogen charging experiment was used to introduce HIC in API 5L X70 pipeline steels with four different thermo-mechanical control processing (TMCP) parameters. Using the scanning electron microscope (SEM), HIC cracks at the cross-section of samples were observed. The SEM observations indicate that the sample which had more finish rolling steps and smaller grain size was more susceptible to HIC. However, the specimen with larger grains was more susceptible to hardness increment than the steels with smaller grains. The energy dispersive Spectrometer (EDS) results showed that two types of inclusions, namely calcium sulfide (CaS) and aluminum oxide (Al2O3), were responsible for the nucleation of HIC in all examined API 5L X70 samples in sour environments. Comparing the length and quantity of the cracks in the middle and top layers of all samples, it could be concluded that the middle layer was more susceptible to HIC. The martensite phase accumulated around the HIC crack was recognized as the weakest phase that could resist HIC propagation and the specimen which had more deformed grains was more su…
author: Pourazizi, Reza
keywords: Pipeline steel, Hydrogen induced cracking, Corrosion, API X70, Sour environment
date published: 2021-01-05
date modified: 2026-07-24T04:27:11Z
provider: University of Saskatchewan
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Saskatchewan

PropertyValue
property ID: Handle
value: https://hdl.handle.net/10388/13186