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Erosion corrosion, also known as impingement damage, is the combined effect of corrosion and erosion caused by rapid flowing turbulent water.It is probably the second most common cause of copper tube failures behind Type 1 pitting which is also known as Cold Water Pitting of Copper Tube.
Inside the cracks, the water evaporates and the amount of hydroxide keeps increasing progressively. The concentrated area with high stress works as anode and diluted area works as cathode. At anode, sodium hydroxide attacks the surrounding material and then dissolves the iron of the boiler as sodium ferrate forming rust. This causes ...
Another example is the cathodic protection of buried or submerged structures as well as hot water storage tanks. In this case, sacrificial anodes work as part of a galvanic couple, promoting corrosion of the anode, while protecting the cathode metal.
In brief, corrosion is a chemical reaction occurring by an electrochemical mechanism (a redox reaction). [1] During corrosion of iron or steel there are two reactions, oxidation (equation 1), where electrons leave the metal (and the metal dissolves, i.e. actual loss of metal results) and reduction, where the electrons are used to convert oxygen and water to hydroxide ions (equation 2): [2]
In addition to being cold hard and organically pure, the water needs a specific chemistry. The effect of the water chemistry can be empirically determined though use of the Pitting Propensity Rating (PPR) a number that takes into account the sulfate, chloride, nitrate and sodium ion concentrations of the water as well as its acidity or pH. A ...
Over time the galvanic anode continues to corrode, consuming the anode material until eventually it must be replaced. Galvanic or sacrificial anodes are made in various shapes and sizes using alloys of zinc, magnesium, and aluminum. ASTM International publishes standards on the composition and manufacturing of galvanic anodes. [10] [11] [12]
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