Chloride salts, corrosion caused

Most simple inorganic salt solutions cause virtually no attack on aluminium-base alloys, unless they possess the qualities required for pitting corrosion, which have been considered previously, or hydrolyse in solution to give acid or alkaline reactions, as do, for example, aluminium, ferric and zinc chlorides. With salts of heavy metals —notably copper, silver, and gold —the heavy metal deposits on to the aluminium, where it subsequently causes serious bimetallic corrosion. 

Sulfate ions have reactions similar to those of chloride. They are corrosion-causative agents (similar to oxygen and hydrogen) of the various types of concentration cell corrosion. In addition, they also are depassivation agents and may greatly accelerate the risk of stress corrosion mechanisms. Saline corrosion pits resulting from high concentrations of chloride and sulfate salts also may be associated with low pH corrosion because hydrochloric acid and sulfuric acid can form within the pit, under deposits. 

Removal of salts from the crude is important to avoid corrosion and plugging of the overhead system. Any plugging is normally caused by ammonium chloride. Salt wateV in crude is usually similar to ocean water. Sodium chloride, which is quite soluble in hot water, is easily removed. Magnesium chloride,... 

Nanofiltration or reverse osmosis treated water is needed in the most demanding places of the null such as for the high-pressure showers in a paper machine. Surface water used in the mill as intake freshwater may also need NF or RO treatment. Permeation of monovalent ions, in particular chloride ions, is both an advantage and a disadvantage of NF compared to RO. Monovalent salts cause significant osmotic pressure when retained in RO. In NF their permeation keeps the osmotic pressure lower and thus the transmembrane pressure needed to overcome the osmotic pressure is lower. The permeation of chloride ions in NF may restrict the reuse of the permeate because of concerns regarding corrosion caused by chloride. On the other hand, the concentrate then contains less chloride and its reuse or incineration is safer. 

Button batteries are small disk-shaped batteries used in watches, calculators, and cameras. They contain caustic metal salts such as mercuric chloride that may cause corrosive injury. 

In water, corrosion limits the use of aluminum to temperatures near 100°C, unless special precautions are taken. In air, corrosion limits its use to temperatures slightly over 300°C. Failure is caused by pitting of the otherwise protective Al(OH)3 film. The presence of chloride salts and of some other metals that form strong galvanic couples (for example, copper) can promote pitting. 

Stainless steels are resistant to corrosion by most salts. The exceptions are the halide salts that cause pitting, crevice corrosion, and SCC. Of these salts, those containing chlorides are the most corrosive, followed by fluoride, bromide, and iodide salts. Stainless steels with higher chromium, molybdenum, and nitrogen concentrations will resist pitting and crevice corrosion more effectively. Austenitic stainless steels with higher molybdenum and nickel, ferritic stainless steels with no nickel or copper, and duplex stainless steels will resist SCC. 

Reinforced concrete electrochemical protection methods used against corrosion caused by contamination with chlorides or the carbonization process may be used for new structures, as well as those already used in soil, water, and atmospheric environments. The first practical CP application was realized in the U.S. A. for the protection of a bridge contaminated with deicing salts (Stratfull, 1974). 

Metallic chloride salts, such as ferric chloride and cupric chloride, can be very corrosive to CF8M. Above 160°F (71°C), chloride can also cause SCC. The combination of chlorides, water, oxygen, and surface tensile stress can result in cracking at stresses far below the tensile strength of all austenitic SSTs. Although a threshold chloride level may exist, one is difficult to set because chlorides concentrate in pits, crevices, and under deposits until the minimum concentration is reached. One must be concerned about SCC any time a few hundred ppm chlorides is present and the temperature exceeds about 160°F (71 °C). SCC may develop at lower temperatures if the pH is low. 

If the salt concentration of the crude oil is over (1 lb/1000 bbls) of crude, consideration needs to be given to the problem of chloride fouling and corrosion caused by hydrochloric acid resulting from the hydrolysis of MgClj and CaClj in the distillation-tower crude preheating exchangers, as follows ... 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

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