NACE Resource Center
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| Resource Library - (Materials Selection) |
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Steel Corrosion Pages on this web site related to steel Iron and steel, the most commonly used metals, corrode in many media including most outdoor atmospheres. Usually they are selected not for their corrosion ance resist but for such properties as strength, ease of fabrication, and cost. These differences show up in the rate of metal lost due to rusting. All steels and low- alloy steels rust in moist atmospheres. In some circumstances, the addition of 0.3% copper to carbon steel can reduce the rate of rusting by one quarter or even by one half. The elements copper, phosphorus, chromium and nickel have all been shown to improve resistance to atmospheric corrosion. Formation of a dense, tightly adhering rust scale is a factor in lowering the rate of attack. The improvement may be sufficient to encourage use without protection, and can also extend paint life by decreasing the amount of corrosion underneath the paint. The rate of rusting will usually be higher in the first year of atmospheric exposure than in subsequent years, and will increase significantly with the degree of pollution and moisture in the air. Ordinary steels are essentially alloys of iron and carbon with small additions of elements such as manganese and silicon added to provide the requisite mechanical properties. The steels are manufactured from a mixture of pig iron and scrap, which is treated in the molten state to remove excess carbon and other impurities. The steel may be continuously cast into strands or cast into individual ingots. The final product is then produced by rolling, drawing or forging. During hot rolling and forging the steel surface is oxidized by air and the scale produced, usually termed millscale. In air, the presence of millscale on the steel may reduce the corrosion rate over comparatively short periods, but over longer periods the rate tends to rise. In water, severe pitting of the steel may occur if large amounts of millscale are present on the surface. Stress corrosion cracking (SCC) in passivating environments Carbon and low alloy steels can suffer from SCC in a wide range of environments that tend to form a protective passivating film of oxide or other species. Cracking will not normally occur when there is a significant corrosion rate (note that this is not the case for hydrogen embrittlement - see below). A wide range of environments have been found to cause SCC, including strong caustic solutions, phosphates, nitrates, carbonates, and hot water. The problems are important for both economic and safety reasons. Caustic cracking of steam-generating boilers was a serious problem in the late 19th century (the necessary strong caustic solution was produced by evaporation of the very dilute solution inside the boiler as it escaped through leaks in the riveted seams) and boiler explosions led to significant loss of life. More recently gas transmission pipelines have cracked in carbonate solutions produced under protective coatings as a result of cathodic protection systems. In this case the crack runs along the length of the pipe, and may propagate for very long distances by fast fracture. If the gas cloud that is released ignites, the resultant fireball is devastating. High strength low alloy steel (HSLA) HSLA Steel is a type of steel alloys that provide many benefits over regular steel alloys. In general they are much stronger and tougher than ordinary carbon based steel. It is used in cars, trucks, cranes, bridges and other structures that must be able to handle a lot of strain. HSLA Steel only contain a very small percentage of carbon, less than one percent, and only small amounts of other added metals. Stress corrosion cracking (SCC) of HSLA steel All steels are affected by hydrogen, as is evidenced by the influence of hydrogen on corrosion fatigue crack growth, and the occurrence of hydrogen-induced cracking 5 under the influence of very high hydrogen concentrations. However, hydrogen embrittlementunder static load is only experienced in steels of relatively high strength. There is no hard-and-fast limit for the strength level above which problems will be experienced, as this will be a function of the amount of hydrogen in the steel, the applied stress, the severity of the stress concentration and the composition and microstructure of the steel. As a rough guide hydrogen embrittlement is unlikely for modern steels with yield strengths below 600 MPa, and is likely to become a major problem above 1000 MPa. The hydrogen may be introduced into the steel by a number of routes, including welding, pickling, electroplating, exposure to hydrogen-containing gases and corrosion in service. The effects of hydrogen introduced into components prior to service may be reduced by baking for a few hours at around 200 °C. this allows some of the hydrogen to diffuse out of the steel while another fraction becomes bound to relatively harmless sites in the microstructure.
Cathodic protection: Coatings: Corrosion inhibitors: Corrosion monitoring: Corrosion rates: Corrosion testing: Galvanic corrosion: Materials selection: Microbiological corrosion: Passivation: Scaling: Seawater: Steel in concrete:
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See also: Equilibrium reactions of iron in water, Iron corrosion products, Iron species and their thermodynamic data, Pourbaix diagram of iron, KTS Thermo demo, Rust chemistry, Rust converters, Steel corrosion
Numerous pages on this web site discuss passivation related topics: Beer, Biomaterials, Blocking, Calcareous deposits, Electrochemical noise, Electrode passivation, Galvanized, Inhibitors, Iron, Nickel aluminum bronze, Oxidizers, Passivation layer, Passive curve, Passivity, pH, Pickling, Pitting, Potentiodynamic polarization, Rouging, Stainless steels, Steel, Stress corrosion cracking, Surface contaminants
Or: Aluminum, Aluminum alloys, Brass, Bronze, Cadmium, Chromium, Cobalt, Copper, Gold, Iron, Lead, Magnesium, Molybdenum, Nickel, Nickel alloys, Silver, Stainless steels, Steel, Tantalum, Tin, Titanium, Zinc, Weathering steel
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