In April 2016 Manchester eScholar was replaced by the University of Manchester’s new Research Information Management System, Pure. In the autumn the University’s research outputs will be available to search and browse via a new Research Portal. Until then the University’s full publication record can be accessed via a temporary portal and the old eScholar content is available to search and browse via this archive.

Effect of Platinum Group Metal (PGM) additions on the stress corrosion cracking resistance of type 304 stainless steel in pressurised water reactors

Necib Ammour, Ouarda

[Thesis]. Manchester, UK: The University of Manchester; 2010.

Access to files

Abstract

In pressurised water reactors (PWRs), hydrogen overpressure is used to keep the corrosion potentialbelow the threshold for onset of intergranular stress corrosion cracking (IGSCC) in type 304 SS. However, some regions may contain higher oxygen levels resulting in an increase in the potential. These “dead space” regions are difficult to access and during refuelling; oxygen may become trapped in these locations. The objective of this study was to investigate the influence of PGM additions on IGSCC susceptibility of type 304 stainless steels (SS) in the sensitised state within PWRs.The work presented herein investigates several aspects of the IGSCC problem. Virgin and platinum group metal (PGM)-modified (Ru and Pd) 304 SS have been studied. Material characterisation, including microstructural, tensile properties, hardness and grain size measurements, has been conducted. Crack initiation studies using U-bend samples in autoclaves simulating PWR environments have also been performed. In addition, crack propagation studies using circumferential cracked bar (CCB) specimens under constant extension in potassium tetrathionate solutions, a well-known medium to promote IGSCC on sensitised stainless steels, have been conducted in order to evaluate cracking resistance. Electrochemical studies using model solutions for PWR chemistry (containing boric acid and lithium hydroxide) and also potassium tetrathionate were carried out to look at the influence of the PGM on the kinetics of the main electrochemical reactions.The results revealed that PGM additions appeared to reduce crack initiation on sensitised type 304 SS under oxygenated conditions in high temperature water containing sulphate and chloride. PGM-doped and standard sensitised type 304 stainless steels revealed susceptibility to IGSCC propagation in 0.01 M K2S4O6, at pH=1.5 and 25°C. Electrochemical studies in potassium tetrathionate media showed smaller anodic dissolution peaks with PGM additions and metallography indicated less intergranular attack with PGM additions. In PWR model electrolytes, PGM additions, particularly 1 wt% Ru, were shown to catalyse the oxygen reduction reaction or hydrogen oxidation reaction, depending on the oxygen /hydrogen level. Overall findings showed that Ru additions can improve the IGSCC resistance of sensitised type 304 SS in PWR, while Pd additions are less effective.

Keyword(s)

304SS; PGMs; PWR; SCC

Bibliographic metadata

Type of resource:
Content type:
Form of thesis:
Type of submission:
Degree type:
Doctor of Philosophy in Materials Science
Degree programme:
PhD Materials Science
Publication date:
Location:
Manchester, UK
Total pages:
312
Abstract:
In pressurised water reactors (PWRs), hydrogen overpressure is used to keep the corrosion potentialbelow the threshold for onset of intergranular stress corrosion cracking (IGSCC) in type 304 SS. However, some regions may contain higher oxygen levels resulting in an increase in the potential. These “dead space” regions are difficult to access and during refuelling; oxygen may become trapped in these locations. The objective of this study was to investigate the influence of PGM additions on IGSCC susceptibility of type 304 stainless steels (SS) in the sensitised state within PWRs.The work presented herein investigates several aspects of the IGSCC problem. Virgin and platinum group metal (PGM)-modified (Ru and Pd) 304 SS have been studied. Material characterisation, including microstructural, tensile properties, hardness and grain size measurements, has been conducted. Crack initiation studies using U-bend samples in autoclaves simulating PWR environments have also been performed. In addition, crack propagation studies using circumferential cracked bar (CCB) specimens under constant extension in potassium tetrathionate solutions, a well-known medium to promote IGSCC on sensitised stainless steels, have been conducted in order to evaluate cracking resistance. Electrochemical studies using model solutions for PWR chemistry (containing boric acid and lithium hydroxide) and also potassium tetrathionate were carried out to look at the influence of the PGM on the kinetics of the main electrochemical reactions.The results revealed that PGM additions appeared to reduce crack initiation on sensitised type 304 SS under oxygenated conditions in high temperature water containing sulphate and chloride. PGM-doped and standard sensitised type 304 stainless steels revealed susceptibility to IGSCC propagation in 0.01 M K2S4O6, at pH=1.5 and 25°C. Electrochemical studies in potassium tetrathionate media showed smaller anodic dissolution peaks with PGM additions and metallography indicated less intergranular attack with PGM additions. In PWR model electrolytes, PGM additions, particularly 1 wt% Ru, were shown to catalyse the oxygen reduction reaction or hydrogen oxidation reaction, depending on the oxygen /hydrogen level. Overall findings showed that Ru additions can improve the IGSCC resistance of sensitised type 304 SS in PWR, while Pd additions are less effective.
Keyword(s):
Thesis main supervisor(s):
Funder(s):
Language:
en

Institutional metadata

University researcher(s):

Record metadata

Manchester eScholar ID:
uk-ac-man-scw:84669
Created by:
Necib Ammour, Ouarda
Created:
29th June, 2010, 17:49:58
Last modified by:
Necib Ammour, Ouarda
Last modified:
7th April, 2011, 10:22:17

Can we help?

The library chat service will be available from 11am-3pm Monday to Friday (excluding Bank Holidays). You can also email your enquiry to us.