Location

J. Erskine Love Room 295 and/or Virtually via Zoom

Abdullah Alzubail

(Advisor: Prof. Preet Singh)

will propose a doctoral thesis entitled,

 

 

Corrosion and Environmental Assisted Cracking of Carbon and Austenitic Stainless Steel in Thiosulfate-Containing Environments

On

 Tuesday, November 26 at 9:00 a.m. (EST)
 J. Erskine Love Room 295
and/or
Virtually via Zoom
https://gatech.zoom.us/j/93232314638?pwd=tbtsp1CMsozNVwZsa46s58xRF8AZcU.1

Committee 

  • Prof. Preet Singh – School of Materials Science and Engineering (advisor)
  • Prof. Hamid Garmestani – School of Materials Science and Engineering
  • Dr. Josh Kacher – School of Materials Science and Engineering
  • Dr. Matthew McDowell – School of Materials Science and Engineering
  • Dr. Christian Canto Maya - Saudi Arabian Oil Company

 

Abstract

Thiosulfate (S2O32-) is used across various industrial applications, including oil and gas, pulp and paper, nuclear, and mining. Given thiosulfate's versatile nature and wide range of uses, this proposed research explores a broad range of environmental conditions involving thiosulfate and its potential redox transformation products. Understanding thiosulfate’s interactions with materials is essential for enhancing material performance, particularly in improving corrosion resistance. In this study, the surface reactions and films formed on carbon steel X-65 and austenitic stainless steel 316L are systematically characterized to understand their role in corrosion and stress corrosion cracking (SCC). Furthermore, this study introduces a novel approach for electrochemically generating an H₂S environment from thiosulfate, independent from steel dissolution.

The environmental testing conditions include oxic and anoxic environments, with varying concentrations of S₂O₃²⁻ (10⁻² M, 10⁻¹ M, and 1 M), sodium chloride (0%, 2.5%, and 5%), and pH levels (2.5, 6, and 10). These environmental parameters directly impact the thermodynamic stability of the combined thiosulfate-steel system, with further implications for the corrosion and SCC of steel alloys.

Corrosion films formed on carbon steel and stainless steel in various thiosulfate environments were characterized using electrochemical impedance spectroscopy (EIS) to estimate the film's impedance, assess its ability to inhibit further corrosion, and determine its structural layers. Energy-dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) are considered for validating the film's structure and composition.

Chronoamperometry was used to evaluate the repassivation kinetics of steel alloys by monitoring the electric current flow after film disruption. These tests help identify environmental conditions that are likely to promote SCC. To further assess SCC susceptibility, Slow Strain Rate Testing (SSRT) is being considered for both steel alloys. The fracture surfaces from SSRT samples will be examined using SEM and EDS to determine fracture modes and analyze the composition of reaction products.

Hydrogen sulfide (H₂S) is one of the potential redox products of thiosulfate. In various studies, thiosulfate has been used to simulate H₂S environments for investigating H₂S-induced corrosion and SCC. This approach is preferred in several studies as an alternative to directly handling H₂S gas, due to its high toxicity and severe health risks. However, a major limitation noted in the literature is the requirement for initial steel dissolution to generate H₂S. In this study, the electrochemical generation of H₂S from thiosulfate was demonstrated independently of steel dissolution. This was achieved by applying specific potentials to thiosulfate to target H₂S production. Sulfide generation in the solution was measured using a sulfide-selective electrode at different applied potentials.

This research could benefit various industries by enhancing the understanding of thiosulfate's role in corrosion and its interactions with material surfaces across a range of environmental conditions. Insights from this study could support decision-making for developing new corrosion-resistant alloys or optimizing control processes to prevent or mitigate corrosion and SCC.