The effect of sodium hydroxide on niobium carbide precipitates in thermally sensitised 20Cr-25Ni-Nb austenitic stainless steel

Clark, Roy W.; Chan, Choen May; Martin, T.; Walters, William; Engelberg, Dirk; Burrows, Robert; Williams, Geraint

doi:10.1016/j.corsci.2020.108596

Cited by 3 publications

(5 citation statements)

References 22 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The simple PREN calculation accounts for the beneficial impact of alloying elements: Cr which is the passivating element within a stainless steel, as well as Mo and N. Given that it is a simple calculation, it cannot be used to predict the performance in any given environment. 30 For example, As observed in prior studies, 8,16,25,34 NbC precipitates in this 20Cr-25Ni-Nb alloy do not dissolve preferentially. Imaging of as-received and stabilized specimens following corrosion experiments in current work shows that localized corrosion can initiate around NbC precipitates, which can then develop into pits.…”

Section: Discussionmentioning

confidence: 50%

“…The composition of the alloy is given in Table 1 for both the end cap and tube material. 16 Both end cap flat strip and tube material were used within this work. Heat treatments were conducted to both stabilize and thermally sensitize the alloy (end cap and tube) following the procedure described in.…”

Section: Methodsmentioning

confidence: 99%

“…Past work has revealed that NbC precipitates present within the 20Cr-25Ni-Nb stainless steel microstructure are linked to localized corrosion initiation. 8,16 Application of the scanning vibrating electrode technique (SVET), combined with scanning electron microscopy energy-dispersive X-ray spectroscopy (SEM-EDS) and focused ion beam SEM (FIB-SEM) apparatus has shown an abundance of Nb-rich precipitates at pit sites. This research also showed the propagation of IGC along grain boundaries, with NbC appearing unaffected using the time-lapse microscopy (TLM) technique.…”

Section: Introductionmentioning

confidence: 99%

“…SEM-EDS characterization following polarization showed corrosion initiation around NbC precipitates. 16 What is required is information to link the corrosion pit initiation to the propagation of IGC, which in turn will help explain how intergranular stress corrosion cracking (IGSCC) initiates when sufficient residual stresses are present. 17 In this paper an electrochemical investigation is conducted to give insight into the dependence of key parameters ([Cl -], temperature, pH) on the corrosion of this austenitic 20Cr-25Ni-Nb stainless steel in an as-received, ( i ) Dungeness B fuel stringers utilise 7 fuel elements ( ii ) AGR coolant (CO2 gas) enters from the bottom of the core, and as such, lower elements are cooler, and within the temperature range for RIS.…”

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Intergranular and Pitting Corrosion in Sensitized and Unsensitized 20Cr-25Ni-Nb Austenitic Stainless Steel

et al. 2021

Self Cite

View full text Add to dashboard Cite

Advanced gas-cooled reactor (AGR) oxide fuels used in the UK are clad in bespoke grade 20%Cr-25%Ni-Nb austenitic stainless steel. Electrochemistry was first applied to correlate the breakdown potential with chloride ion concentration, temperature and pH for this alloy. At near-neutral pH the unsensitized material exhibited a linear Eb = A + B log10[Cl-] relationship, where A = 0.7 V (vs. SCE), and B = 0.098 V/decade. Scanning Kelvin probe force microscopy revealed grain boundary regions in the heat-treated material up to 65 mV less noble to the matrix, whereas un-dissolved niobium carbide (NbC) precipitates were up to 55 mV more noble to the matrix. In-situ time-lapse microscopy and post-corrosion observations confirmed that sensitized grain boundaries were susceptible to pitting corrosion, further developing along intergranular corrosion pathways. It has however been shown that micro galvanic coupling between the Nb precipitates and matrix and / or sensitized grain boundary regions is not a factor in corrosion initiation as all experiments were performed under external potential control. Post corrosion observations showed the presence of pits at NbC precipitates promoting grain boundary corrosion. It is postulated that corrosion initiates at NbC precipitates as a pit, and when in close vicinity to Cr-depleted grain boundaries, then propagates along grain boundaries as intergranular corrosion.

show abstract

Section: Discussionmentioning

confidence: 50%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Intergranular and Pitting Corrosion in Sensitized and Unsensitized 20Cr-25Ni-Nb Austenitic Stainless Steel

et al. 2021

Self Cite

View full text Add to dashboard Cite

show abstract

“…The dosing of storage ponds with NaOH to prevent corrosion in the UK is a routine practice, both for Magnox and advanced gas-cooled reactor (AGR) fuel cladding materials. 16,19,20 Hence the interest in deducing if this procedure affects the surface film, compared to native air-formed films. The spectrum showed peaks for Mg and Mg(OH)2 (also known by the mineral name brucite), confirming the formation of a corrosion film.…”

Section: Characterizationmentioning

confidence: 99%

A Study into the Localized Corrosion of Magnesium Alloy Magnox Al-80

et al. 2020

Self Cite

View full text Add to dashboard Cite

Magnesium (Mg) non-oxidizing alloy, known as Magnox, was historically used as a fuel cladding material for the first-generation of carbon dioxide (CO2) gas-cooled nuclear reactors in the UK. Waste Magnox is currently stored in cooling ponds, pending final disposal. The corrosion resistance of Mg and its alloys is relatively poor, compared to modern cladding materials such as zirconium (Zr) alloys, so it is important to have a knowledge of the chloride concentration/pH dependence on breakdown and localized corrosion characteristics prior to waste retrievals taking place. Our results show that Magnox exhibits passivity in high pH solutions, with charge transfer resistance and passive film thicknesses showing an increase with immersion time. When chloride is added to the system the higher pH maintains Magnox passivity, as shown through a combination of potentiodynamic and time-lapse/post corrosion imaging experiments. Potentiodynamic polarization of Magnox reveals a -229 mV-decade linear dependence of breakdown potential with chloride ion concentration. The use of the scanning vibrating electrode technique (SVET) enabled the localized corrosion characteristics to be followed. At high pH where Magnox is passive, at low chloride concentrations, the anodes which form predominantly couple to the visually intact surface in the vicinity of the anode. The high pH however means that visually intact Magnox in the vicinity of the anode is less prone to breakdown, restricting anode propagation such that they remain largely static. In high chloride concentrations the higher conductivity means that the anode and cathode can couple over greater distances and so propagation along the surface can occur at a much faster rate, with the visually intact surface acting as a distributed cathode. In addition, the chloride anion itself, when present at high concentration will play a role in rapid passive film dissolution, enabling rapid anode propagation.

show abstract

AGR fuel corrosion: SIMFUEL-based method development in preparation for electrochemical studies of real spent AGR nuclear fuel electrode

et al. 2022

View full text Add to dashboard Cite

Electrochemical corrosion of lower-activity spent fuel simulants, SIMFUELs, has been investigated in support of on-going analogous studies of a real AGR spent nuclear fuel electrode. Two electrode coupling methods have been investigated, to study the coupling of a sample of 25 GWd/tU SIMFUEL pellet to a sample of 20/25/Nb AGR cladding to replicate the real AGR fuel electrode setup. Method-1 involves coupling of individual standalone electrodes, while Method-2 involves coupling of the cladding and SIMFUEL within the same electrode. For both coupling methods, open circuit potentials and linear sweep voltammetry measurements were conducted in electrolyte solutions containing 30 μmol/m3 NaCl, dosed with NaOH to pH 8, 11.4 and 12.5. Resultant data were compared with single-component studies of SIMFUEL and cladding electrodes. Method-1 presents inconsistent electrochemical behaviour which we attribute to pitting/crevice corrosion effects on the cladding, whereas Method-2 shows a consistent behaviour that most resembles that of the SIMFUEL component. Graphical abstract

show abstract

The effect of sodium hydroxide on niobium carbide precipitates in thermally sensitised 20Cr-25Ni-Nb austenitic stainless steel

Cited by 3 publications

References 22 publications

Intergranular and Pitting Corrosion in Sensitized and Unsensitized 20Cr-25Ni-Nb Austenitic Stainless Steel

Intergranular and Pitting Corrosion in Sensitized and Unsensitized 20Cr-25Ni-Nb Austenitic Stainless Steel

A Study into the Localized Corrosion of Magnesium Alloy Magnox Al-80

AGR fuel corrosion: SIMFUEL-based method development in preparation for electrochemical studies of real spent AGR nuclear fuel electrode

Contact Info

Product

Resources

About