- Title
- Microbiological and abiotic marine corrosion of steel in sand media
- Creator
- Hossain, Md. Maruf
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- In many practical corrosion situations, steel infrastructure is exposed to sea or other sources of water while also being in direct contact with chemically inert particulate media, such as sand, pebbles, small rocks, non-cohesive soils, assorted detritus, rust particles, and various bulk cargoes, such as coal and iron ore. There is evidence from field operations that this type of exposure combination can be particularly severe, producing high, localized corrosion losses and deep corrosion pits. From established localised corrosion theory, crevice and/or pitting kinetics would be expected at the contact regions between sand and steel. But the observations so far available are insufficient to verify this. There are also suggestions that microbiologically influenced corrosion (MIC) occurs in the presence of nutrients critical to bacterial metabolism, but the available evidence is largely anecdotal. There is no well-organized body of knowledge to explain and quantify the various field observations at present. Therefore, the present project aims to develop an organized body of knowledge about the interaction between mild steel surfaces and different sizes of sand in both natural seawater and nutrient-dosed seawater immersion conditions, based on both directly relevant field exposure and laboratory observation by electrochemical testing. Field exposure considers the influence of particle size, burial type, and nutrient dosing on mild steel corrosion in coupons buried in different sizes of sand and immersed in natural and nutrient-dosed seawater for 24 months. Mass loss and pit depth have both been measured after the desired immersion period. The field testing was conducted at The University of Newcastle’s corrosion testing facilities, located at the fisheries research station at Taylors Beach, NSW. Moreover, electrochemical impedance spectroscopy (EIS) was performed for up to four months to measure corrosion rates of coupons under different sizes of sand in both natural and nutrient-dosed seawater immersion conditions in the laboratory at The University of Newcastle. Field exposure results reveal that the sand size does not have a significant and consistent influence on mass loss and general pit depth in either the natural or nutrient-dosed seawater immersion conditions. However, sand adhesions occurred in some places on the surfaces of a few coupon after 12 months of immersion, which acted as hard strata, and deep pitting occurred underneath the sand adhesions. Sand adhesion occurred randomly and was independent of particle size and nutrient dosing. Nutrient dosing slightly increased corrosion mass loss in early immersion periods for different burial types of mild steel coupons in various sizes of sand. However, sand adhesion on coupon surfaces and sediment deposition on coupon containers affected mild steel corrosion after 12 months of immersion. Therefore, the corrosion under sand adhesion and sediment deposition on the coupon containers was more significant than any difference in corrosion due to nutrient addition observed after the 12 months’ immersion, because sand adhesion and sediment deposition took time, and the coupons were most affected in the longer-term immersion period. Overall, nutrient addition does not have a significant and consistent influence on the mass loss and general pit depths for different burial types of mild steel coupons in various sizes of sand. Field exposure results also reveal that corrosion mass loss was consistently higher in coupons placed on the sand and for partially buried coupons compared to the coupons completely buried in sand in both the natural and nutrient-dosed seawater immersion conditions. The higher mass loss for the coupons placed on the sand and the partially buried coupons was due to oxygen depolarization, together with direct contact with seawater. Moreover, pit depth on the coupon surfaces that were in direct contact with seawater only was also higher than on the surface that was in contact with sand after 12 months of immersion. EIS test results reveal that the corrosion rate obtained was higher in the coarse sand than the medium and fine sand in natural seawater. This could be attributed to the difference in the surface area of the metal exposed to the electrolyte, i.e., the higher void space in coarse sand than medium and fine sand. However, particle size does not have that much influence on the corrosion rate in nutrient-dosed seawater. In fact, nutrient dosing reduces the corrosion rate in coarse sand. However, In the case of medium and fine sand, the corrosion rate was similar in both natural and nutrient-dosed seawater immersion conditions. Overall, the present study has contributed to the present state of knowledge about the effect of particle size, nutrient dosing, and burial type on mild steel coupons under different sizes of sand in seawater immersion conditions. Differential oxygen concentration cell formation due to sand adhesion and sediment deposition was one of the vital observations of this research, and was the critical factor making the difference in longer-term corrosion rather than nutrient dosing and particle size. These practical corrosion observations will undoubtedly help future researchers and industries working with steel infrastructure that interacts with particulate media, such as sand, particulate rusts, and detritus.
- Subject
- particulate media; microbiologically influenced corrosion (MIC); particle size; burial type; nutrient dosing; mild steel corrosion; marine environment
- Identifier
- http://hdl.handle.net/1959.13/1508802
- Identifier
- uon:56158
- Rights
- Copyright 2022 Md. Maruf Hossain
- Language
- eng
- Full Text
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| Thumbnail | File | Description | Size | Format | |||
|---|---|---|---|---|---|---|---|
| View Details Download | ATTACHMENT01 | Thesis | 5 MB | Adobe Acrobat PDF | View Details Download | ||
| View Details Download | ATTACHMENT02 | Abstract | 367 KB | Adobe Acrobat PDF | View Details Download |