Low alloy steel susceptibility to stress corrosion cracking in hydraulic fracturing environment

Date of Award

2014

Degree Name

M.S. in Chemical Engineering

Department

Department of Chemical and Materials Engineering

Advisor/Chair

Advisor: Douglas. C. Hansen

Abstract

The pipelines used for hydraulic fracturing (aka. fracking") are often operating at a pressure above 10000psi and thus are highly susceptible to Stress Corrosion Cracking (SCC). This is primarily due to the process of carrying out fracturing at a shale gas site, where the hydraulic fracturing fluid is pumped through these pipes at very high pressure in order to initiate fracture in the shale formation. While the fracturing fluid is typically more than 99% water, other components are used to perform various functions during the fracturing process. Research into the occurrence of SCC reveals that SCC is engendered by a number of factors, of which two main contributors are stress in the pipe steel and a particular type of corrosive environment in contact with the pipeline in the service setting. The variety of fracturing fluid formulas which could be used and the insufficient reported information about the fracturing fluid chemistry makes it very important to carry out analysis to ensure the integrity of the pipelines used for this process. The current research described here is focused on the evaluation of the susceptibility of low alloy steel (AISI 4340) to stress corrosion cracking in different environments as it relates to hydraulic fracturing fluid chemistry and operating conditions. These different environments are achieved by varying the solution pH, the pH adjusting agent and the applied stress. Electrochemistry and stress measurements showed that at near neutral pH solution, AISI 4340 showed a higher SCC susceptibility in solutions where Na2CO3 was used as the pH adjusting than in solutions where NaOH was used as the pH adjusting agent. Scanning electron microscopy and Auger electron spectroscopy was used to analyze the oxide film in solution with the two pH adjusting agents at a pH of 7. Depth profiles of the passive film formed in a solution with pH adjusted to 7 using NaOH pH adjusting agent suggests the presence of a complex, FeOCl, which dissolves actively and thus reduces the SCC susceptibility of AISI 4340 in this environment. It is inferred from the SEM image of AISI 4340 material after testing and stress measurements showed that low alloy steel is more susceptible to SCC in solutions with Na2CO3 as the pH adjusting agent than solutions with NaOH pH adjusting agent especially at near neutral pH. Whereas, at high pH environment AISI 4340 showed a higher SCC susceptibility in solution with NaOH as the pH adjusting agent."

Keywords

Steel alloys Effect of chemicals on, Stress corrosion, Pipelines Cracking, Hydraulic fracturing Equipment and supplies, Chemical Engineering, Chemistry, Materials Science, Stress Corrosion Cracking, Hydraulic Fracturing, Solution Chemistry, Slow Strain Rate Tests, Low Alloy Steel, AISI 4340, Localized Corrosion, Surface Film Analysis

Rights Statement

Copyright © 2014, author

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