Localized Corrosion of Stainless Steel in a Nuclear Waste Cooling Water System—Part 6: Testing for Stress Corrosion Cracking Susceptibility

CORROSION ◽  
10.5006/0417 ◽  
2013 ◽  
Vol 69 (1) ◽  
pp. 9-14 ◽  
Author(s):  
G.O.H. Whillock ◽  
C.J. Donohoe
Keyword(s):  
Stainless Steel ◽  
Stress Corrosion ◽  
Nuclear Waste ◽  
Stress Corrosion Cracking ◽  
Water System ◽  
Cooling Water ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
Cooling Water System ◽  
System Part

Localized Corrosion of Stainless Steel in a Nuclear Waste Cooling Water System—Part 2: Plant Inspection Findings

CORROSION ◽  
10.5006/0413 ◽  
2012 ◽  
Vol 68 (9) ◽  
pp. 844-852 ◽  
Author(s):  
C.J. Donohoe ◽  
G.O.H. Whillock ◽  
P.J. Apps
Keyword(s):  
Stainless Steel ◽  
Nuclear Waste ◽  
Water System ◽  
Cooling Water ◽  
Chloride Ions ◽  
Localized Corrosion ◽  
Water Radiolysis ◽  
Cooling Water System ◽  
System Part ◽  
Plant Inspection

Parts of a nuclear waste cooling water system, constructed from an austenitic stainless steel, are known to be susceptible to localized corrosion. This is attributed to the presence of chloride ions in the water, albeit only at low concentration (<10 mg/L), and oxidants produced by water radiolysis. Plate samples were cut and taken for examination from downstream tanks located in man-access areas out of the radiation field. Large pits were found. The largest were highly elongated but had failed to form through-wall penetrations. Smaller pits that were spheroidal in shape were found that had formed through-wall penetrations. The pits were sectioned and their internal morphologies examined by scanning electron microscopy. The elongated pits were found to have a crystalline internal morphology associated with the mechanism of etch-type pitting. The spheroidal pits had a smoother interior morphology but it was not bright or distinctive-like classic pits formed by a salt-filming mechanism. Formation of the spheroidal pits is attributed to corrosion by a quasi-salt-filming mechanism.

Localized Corrosion of Stainless Steel in a Nuclear Waste Cooling Water System—Part 4: Artificial Pit Investigation of Nitrate Inhibition

CORROSION ◽  
10.5006/0415 ◽  
2012 ◽  
Vol 68 (11) ◽  
pp. 967-981 ◽  
Author(s):  
G.O.H. Whillock ◽  
T.J. Binks ◽  
C.J. Donohoe
Keyword(s):  
Stainless Steel ◽  
Nuclear Waste ◽  
Water System ◽  
Cooling Water ◽  
Bulk Water ◽  
Localized Corrosion ◽  
Water Radiolysis ◽  
Wire Electrode ◽  
Cooling Water System ◽  
The Wire

A nuclear waste cooling water system, constructed from an austenitic stainless steel, is known to be susceptible to localized corrosion because of the combined presence of low concentrations of chloride (Cl−) ions in the water (<10 mg/L) and oxidants produced by water radiolysis. Corrosion propagates in the system as pitting corrosion, and inspections of accessible components indicated that large pit cavities could form. To investigate possible inhibition options, an artificial pit, termed the wire-electrode artificial pit, was developed and shown to be capable of sustaining corrosion under representative conditions. Tests carried out using this artificial pit to investigate the effect of sodium nitrate (NaNO3) added to the bulk water are reported here. The results showed that nitrate (NO3−) was capable of affecting inhibition at 60°C, although large concentrations and long times were required, e.g., inhibition took up to 20 days at 60,000 mg/L NO3−. Complimentary polarization tests were also carried out in a range of artificial pit solutions as a function of nitrate concentration to aid interpretation of the wire-electrode tests. The existence of a threshold molar NO3−/Cl− ratio for passivation to occur was identified but not clearly defined.

Localized Corrosion of Stainless Steel in a Nuclear Waste Cooling Water System— Part 1: Crevice Corrosion Studies

CORROSION ◽  
10.5006/0412 ◽  
2012 ◽  
Vol 68 (8) ◽  
pp. 677-687 ◽  
Author(s):  
G.O.H. Whillock ◽  
S.E. Worthington ◽  
C.J. Donohoe
Keyword(s):  
Stainless Steel ◽  
Nuclear Waste ◽  
Crevice Corrosion ◽  
Water System ◽  
Cooling Water ◽  
Chloride Ions ◽  
Localized Corrosion ◽  
Stainless Steel Surface ◽  
Water Radiolysis ◽  
Cooling Water System

Parts of a nuclear waste cooling water system, constructed from an austenitic stainless steel, are known to be susceptible to localized corrosion. This is attributed to the presence of chloride ions in the water, albeit only at low concentrations (<10 mg/L), and oxidants produced by water radiolysis. Experiments were carried out using an engineered crevice connected to a large passive stainless steel surface to demonstrate the viability of crevice corrosion. Similar tests were undertaken to investigate the efficacy of nitrate as an inhibitor. In irradiated water containing up to 300 mg/L Cl− and at temperatures of up to 60°C, crevice corrosion of UNS 30403 and 18Cr-13Ni 1Nb was inhibited by nitrate added at molar ratios of approximately 2.9 to 5.7 with respect to chloride. Once corrosion is inhibited, the nitrate/chloride ratio can be reduced to maintain passivity, but a nitrate:chloride ratio of approximately 0.6 or lower is unlikely to be effective.

Effect of Long-Term Service Exposure on the Localized Corrosion and Stress Corrosion Cracking Susceptibility of Type 347 Stainless Steel

CORROSION ◽  
10.5006/2612 ◽  
2017 ◽  
Vol 74 (3) ◽  
pp. 350-361 ◽  
Author(s):  
K. Ravindranath ◽  
N. Tanoli ◽  
B. Al-Wakaa
Keyword(s):  
Stainless Steel ◽  
Stress Corrosion ◽  
Stress Corrosion Cracking ◽  
Corrosion Cracking ◽  
Localized Corrosion ◽  
X Ray Diffraction ◽  
Degree Of Sensitization ◽  
Corrosion Susceptibility ◽  
Service Exposure

The paper presents the results of a study conducted on the effects of long-term service exposure of Type 347 stainless steel (SS) on the microstructure and corrosion susceptibility. The material subjected to the study was in service in a petroleum refinery as heater tube at 620°C for 31 years. The microscopic and x-ray diffraction studies of the service-exposed specimen revealed the precipitation of chromium-rich carbides along the grain boundaries. The microstructural changes that occurred as a result of service exposure affected the ductility and toughness of the alloy. The sensitization of the alloy was assessed by scanning electron microscopy and double loop electrochemical potentiodynamic reactivation. The studies have indicated some degree of sensitization in the alloy. The service exposure resulted in a marginal increase in the susceptibility of Type 347 SS to pitting in environments containing NaCl and NaCl + H2S. Environments such as H2SO4 and K2S4O6 at the tested concentrations did not differentiate between service-exposed and solution annealed specimens for their corrosion susceptibility. Slow strain rate testing of Type 347 SS in both the service-exposed and solution annealed conditions showed susceptibility to stress corrosion cracking in environment containing NaCl + H2S, while the alloy did not show susceptibility to SCC in H2SO4 and K2S4O6. The long-term service exposure did not noticeably influence the SCC susceptibility of Type 347 SS under the tested conditions.

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