{"id":32609,"date":"2024-09-23T15:50:24","date_gmt":"2024-09-23T14:50:24","guid":{"rendered":"https:\/\/www.hawkins.biz\/?post_type=insight&p=32609"},"modified":"2025-07-29T15:09:33","modified_gmt":"2025-07-29T14:09:33","slug":"forensic-steel-corrosion-analysis","status":"publish","type":"insight","link":"https:\/\/www.hawkins.biz\/insight\/forensic-steel-corrosion-analysis\/","title":{"rendered":"Not Just Rust: A Forensic Investigator’s View of Corrosion in Steels"},"content":{"rendered":"\t\t
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What do I see when I look at rusty steel?\u00a0 Lots… and potentially much more if I can take samples to examine in the laboratory.<\/span> \u00a0<\/span><\/p>

At any scene where something has broken, exploded, leaked, or injured someone, and I have been asked to find out \u2018<\/span>What happened?<\/span><\/i>\u2019, I often find that materials science will lead me to the root cause of the failure.<\/span>\u00a0<\/span><\/p>

As an engineer specialising in steel structures, metals and welds, this often means there will be some kind of corrosion.\u00a0 In shipping, corrosion damage can be a significant factor in the claims managed, and some examples of common types of incidents<\/a> investigated by Hawkins are; corrosion of steel cargo, hull corrosion, and wire rope damage.<\/span>\u00a0<\/span><\/p>

Rust and corrosion are a natural consequence for steels, and corrosion must be kept at bay through the constant application of corrosion protection methods.\u00a0 For a ship\u2019s hull, deck and machinery, the most commonly used methods are paints and coatings, often used in conjunction with sacrificial anodes for cathodic protection below the water line.\u00a0 For steels used in fluid containment or transport, corrosion inhibitor chemicals can be added to the fluid to prevent internal corrosion.\u00a0 For cargoes of steel products, keeping the goods dry and protected from rain, sea water or sea spray is vital to maintaining the product quality to prevent rusting during transport, so that they arrive in the best condition to be manufactured into their finished product such as may be cars, building frame beams or other machinery or structures. The iron in steel wants to corrode, and we need to actively prevent it from doing so for the duration of the service life, while we exploit the strength and performance of modern steels.<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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Figure 2: Rolls of steel coils in a warehouse.<\/figcaption>\n\t\t\t\t\t\t\t\t\t\t<\/figure>\n\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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But is it Art?\u00a0<\/span><\/h4>

The first \u2018rust\u2019 that forms when iron or steel start to corrode when exposed to moist atmospheric conditions is the bright orange powdery oxide that can be brushed off.\u00a0 Over time another oxide starts to form that is darker bronze or brown colour that forms more evenly over the surface of the iron.\u00a0 While the bright orange coloured oxide is loose and falls off, the brown oxide remains on the surface and provides a more protective patina.\u00a0 Iron can also corrode in water under low-oxygen conditions to form a black coloured oxide.\u00a0 Steel radiators corrode internally to produce this black oxide, which flakes off to form the black sludge inside heating systems.\u00a0 In principle, once the oxygen in the water inside the closed system has been used up, the corrosion rate reduces.<\/span>\u00a0<\/span><\/p>

In cast irons, the brown oxide patina can be sufficiently stable to provide permanent protection from further corrosion.\u00a0 Some iron and steel objects make use of progression of corrosion to deliberately create a \u2018weathered\u2019 surface appearance.\u00a0 Some garden ornaments are intended to rust, and give a nostalgic charm to a garden design. So rust is not always a problem, and can even be aesthetic.<\/span>\u00a0<\/span><\/p>

One of the tempting questions to ask when looking at rust is \u201cHow long has it been corroding?\u201d<\/em>, and\/or \u201cHow long will it survive?\u201d<\/em> These are questions that are almost impossible to answer in practise, because the thermodynamics of corrosion depends on a large number of variables, such as:<\/span>\u00a0<\/span><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t

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