Salt formation with corrosion inhibitor

The original design and structure of the Statue of Liberty, built about 100 years ago, took into accoimt the need to avoid using different metals in direct contact with each other. However, the salt sea spray penetrated the structure and corroded the iron frame which supported the outer copper shell. Chloride ions catalyzed the corrosion of iron. The use of brass in a steam line valve resulted in corrosion and the formation of a green solid product. The architect was apparently unaware of the standard practice to use amines such as morpholine as a corrosion inhibitor for steam lines. Amines react with copper in the brass at high temperatures in the presence of oxygen to form copper-amine complexes similar to the dark blue copper ammonium complex, Cu(NH3)J. ... 

Inhibitors of corrosion and salt-formation based on the complexes of or-ganophosphonic acids with <7-metals, mainly with zinc, ate rather widespread [1-4]. However, the preparation of the inhibitors of this particular class with a prespecified structure and high-repeatability anticorrosive efficiency is very difficult because oiganophosphonic acids similar to other oxygen compounds of phosphor tend to the formation of spatial polymer structures [5]. Therefore, known maiketable products contain particles of an inhibitor with nonstable structure and demonstrate changing inhibiting properties. 

Formation of lead soaps appears to be the mechanism by which lead-based paints inhibit corrosion of clean steel. When formulated with linseed oil, lead reacts with components of the oil to form soaps in the cured film in the presence of water and oxygen, these soaps degrade to, among other things, salts of a variety of mono- and di-basic aliphatic acids. The lead salts of azelaic, suberic, and pelargonic acid act as corrosion inhibitors lead azelate is of particular importance in LBP. These acids may inhibit corrosion by bringing about the formation of insoluble ferric salts, which reinforce the metal s oxide film until it becomes impermeable to ferrous ions, thus suppressing the corrosion mechanism. 

In this case, the ion-association model predicted that the connate water would require a minimum dilution with boiler feedwater of 15 percent to prevent halite precipitation (Fig. 8.23). The model also predicted that over-injection of dilution water would promote barite (barium sulfate) formation (Fig. 8.24). Although the well produced F1,S at a concentration of 50 mg/L, the program did not predict the formation of iron sulfide because of the combination of low pH and high temperature. Boiler feedwater was injected into the bottom of the well using the downhole injection valve normally used for corrosion inhibitor injection. Injection of dilution water at a rate of 25 to 30 percent has allowed the well to produce successfully since startup. Barite and iron sulfide precipitation have not been observed, and plugging with salt has not occurred. 

Sodium polyphosphate is often used in a concentration of about lO-lOOppm, sometimes with added zinc salts to improve inhibition. The pH value is adjusted to 5-6 in order to minimize pitting and tubercle formation, as well as scale deposition. Polyphosphates decompose slowly into orthophosphates, which, in the presence of calcium or magnesium ions, precipitate insoluble calcium or magnesium orthophosphate, causing scale formation on the warmer parts of the system. Unlike chromates, they favor algae growth, which necessitates the addition of algaecides to the water. Corrosion inhibition with polyphosphates is less effective than that by chromates, but polyphosphates in low concentration are not toxic, and the required optimum amount of inhibitor is less than that for chromates. 

Flash rusting is the phenomenon of formation of small brown rust spots that appear very soon after application of waterbased systems directly to steel. The problem is more prominent when the steel surface is active (for example, after blasting) and the pH is <7. To combat this problem, flash-rust inhibitors are added to waterbased coatings. They should have good water solubility. Flat surfaces are relatively easy to protect, while weld areas are considered difficult. Flash-rust inhibition at a weld area can be achieved by a combination of different products. Flash-rust inhibitors are typically based on ammonium and sodium nitrites, benzoates, metaborates and phosphates, occasionally in combination with materials such as morpholine and amino methyl propanol. Some other organic salts are also used, such as amine salts of 2-mercaptobenzothiazolyl succinic acid and calcium or barium salts of linear alkyl naphthalene sulfonic acids. Typically they are used at levels of 0.1 to 1.0 % of the total mass of paint. They also help in preventing in-can corrosion upon storage of aqueous paint. 

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