Voltage-Induced Void Formation in High-Temperature Oxide Scales of Boiler Tubes
Corrosion monitoring remains a significant challenge at high temperatures. Understanding the varying factors in high-temperature cathodic protection is crucial for developing mitigation strategies and predictive maintenance. This study assesses how cathodic protection influences oxidation in T91 al...
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| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IIUM Press, International Islamic University Malaysia
2025-05-01
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| Series: | International Islamic University Malaysia Engineering Journal |
| Subjects: | |
| Online Access: | https://journals.iium.edu.my/ejournal/index.php/iiumej/article/view/3577 |
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| Summary: | Corrosion monitoring remains a significant challenge at high temperatures. Understanding the varying factors in high-temperature cathodic protection is crucial for developing mitigation strategies and predictive maintenance. This study assesses how cathodic protection influences oxidation in T91 alloys at elevated temperatures by evaluating the effects of exposure duration and voltage-induced void development in the oxide layer. It is hypothesized that polarizing the sample affects the diffusivity of cations and anions in the oxide scale, which is the rate-determining step of the oxidation process. This study measured the number of voids directly on T91 alloys exposed at 823K under various induced voltages. T91 alloy was externally induced with voltages of 0V, 50V, and 300V for 43.2 ks, 259.2 ks, and 432 ks at 923 K in air ( = 0.21 atm = 2.1×104 Pa). The presence of oxide layers was analysed using X-Ray Diffraction (XRD), and the void formed was inspected using Scanning Electron Microscopy (SEM). XRD results reveal that Fe2O3, Fe3O4, FeCr2O3, and Cr2O3 peaks were formed on all samples. The parabolic rate constant, Kp, was calculated as 3.83 × 10-14 m2/s, 2.17 × 10-14 m2/s, and 9.25 × 10-14 m2/s, respectively, verifying that the reaction occurred by solid-state diffusion. Changes in Kp at different induced voltages are clear evidence that the diffusivity was altered by external electrical potential. It was observed that the overall void formation decreased by 17%. Inducing voltage onto T91 alloy affects the ionic diffusivity. It changes the void formation, suggesting it may promote the diffusivity of more inert species, such as Cr, to form a protective layer at the early oxidation stage.
ABSTRAK: Pemantauan hakisan kekal sebagai cabaran utama pada suhu tinggi. Memahami pelbagai faktor perlindungan katodik pada suhu tinggi adalah penting untuk membangunkan strategi pengurangan dan ramalan penyelenggaraan. Kajian ini menilai perlindungan katodik mempengaruhi pengoksidaan dalam aloi T91 pada suhu tinggi dengan melihat kesan tempoh pendedahan dan pembangunan rongga yang disebabkan oleh potensi elektrik luaran pada lapisan oksida. Pemolaran sampel mempengaruhi keberaliran kation dan anion dalam oksida, yang menentukan kadar dalam proses pengoksidaan. Melalui kajian ini, jumlah ruang kosong diukur secara langsung pada aloi T91 yang didedahkan pada suhu 823K di bawah pelbagai voltan teraruh. Aloi T91 dikenakan voltan luaran sebanyak 0V, 50V, dan 300V bagi tempoh 43.2 ks, 259.2 ks, dan 432 ks pada suhu 923K dalam udara ( = 0.21 atm = 2.1 × 104 Pa). Kehadiran lapisan oksida dianalisa menggunakan Pembelauan Sinar-X (XRD), dan ruang kosong yang terbentuk diperiksa menggunakan Mikroskop Elektron Imbasan (SEM). Dapatan XRD menunjukkan bahawa puncak Fe2O3, Fe3O4, FeCr2O3, dan Cr?O? terbentuk pada semua sampel. Pemalar kadar parabola, Kp, dikira masing-masing sebanyak 3.83 × 10-14 m²/s, 2.17 × 10-14 m²/s, dan 9.25 × 10-14 m²/s, mengesahkan bahawa tindak balas yang berlaku adalah penyebaran keadaan pepejal. Perubahan dalam Kp pada voltan teraruh berbeza membuktikan bahawa keberaliran telah diubah oleh potensi elektrik luaran. Hasil kajian mendapati bahawa pembentukan ruang kosong secara keseluruhan berkurangan sebanyak 17%. Proses penguraian voltan pada aloi T91 mempengaruhi keberaliran ionik dan mengubah pembentukan ruang kosong, mencadangkan bahawa ia mungkin digunakan bagi mempromosi keberaliran spesies yang lebih lengai seperti Cr bagi membentuk lapisan pelindung pada peringkat awal pengoksidaan.
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| ISSN: | 1511-788X 2289-7860 |