Salt water corrosion

K. N. Reichek, K. J. Clark, and J. E. HiUis, Controlling the Salt Water Corrosion Peformance of Magnesium AZ91 Alloy, paper 850417, Society of Automotive Engineers, Detroit, Mich., 1985. 

Composition These copper alloys can contain from 10% to 30% nickel. They are excellent heat exchanger tubes because of their resistance to salt water corrosion at high temperatures. 

Alloys containing principally copper and tin are referred to as true bronzes. Tin increases hardness and wear resistance more than zinc. It also improves salt water corrosion resistance. Common uses of copper-tin bronze are described in TABLE 9-5. 

W.E. Mercer and J.E. Hillis, The Critical Contaminant Limit and Salt Water Corrosion Performance of Magnesium AE 42 Alloy, SAE Technical Paper No. 920073, 1992. 

The initial corrosion control system used in a crude unit is a desalter. Modern desalters separate oil and water electrostatically. The internals used to accomplish electrostatic separation are normally of a proprietary design. The vessel itself is usually carbon steel. The bottom is often cement lined to protect it from salt water corrosion. The payout on a desalter is difficult to establish. Desalters are normally used when the salt content of the crude exceeds 20 lb per 1,000 barrels (ptb). When high reliability of the unit is desired, crudes with salt contents of 8 to 10 ptb are desalted. When desalting is used, the target is 1 ptb or less. Fluctuations in salt content are particularly troublesome to the downstream equipment therefore, the desalter should be designed for the maximum anticipated salt content. 

Salt water, corrosion anticaking agent (see YPS below)... 

Hillis, J. E. and Reichek, R. N., High Purity Magnesium AM60 Alloy The Critical Contaminant Limits and the Salt Water Corrosion Performance, Paper 860288, International Congress and Exposition of the Society of Automotive Engineers, Detroit, Ml, 1986. 

The salt-water corrosion test is used to evaluate submarine splice closures. For this test a spUce closure tuid its outer housing are immersed in aerated 3.5 % sodium chloride solution for 180 days. The test is described in TA-TSY-041 [17]. The same closures are also exposed to a similar test using artificial fresh water (ASTM D 2570, Method for Simulated Service Corrosion Testing of Engine Coolants). 

Mercer, W. E. II, Hillis, J. E. (1992), The Critical Contaminant Limits and Salt Water Corrosion Performance of Magnesium AE42 Alloy, Society of Automotive Engineers Technical Paper Series 920073, Detroit. 

As an example of the effect that corrosion can have on connnercial industries, consider the corrosive effects of salt water on a seagoing vessel. Corrosion can drastically affect a ship s perfonnance and fiiel consumption over a period of time. As the hull of a steel boat becomes corroded and fouled by marine growths, the... 

Pure vanadium is a bright white metal, and is soft and duchle. It has good corrosion resistance to alkalis, sulfuric and hydrochloric acid, and salt water, but the metal oxidizes readily above 660oC. 

Titanium has potential use in desalination plants for converting sea water into fresh water. The metal has excellent resistance to sea water and is used for propeller shafts, rigging, and other parts of ships exposed to salt water. A titanium anode coated with platinum has been used to provide cathodic protection from corrosion by salt water. 

Corrosion occurs when the metallic iron in DRI is wetted with fresh or salt water and reacts with oxygen from air to form mst, Ee(OH)2- The corrosion reactions continue as long as water is present. Because water evaporates at approximately 100°C, corrosion reactions have a low temperature limit even though the reactions are exothermic. Small amounts of hydrogen may be generated when DRI reacts with water. However, this poses no safety problem as long as proper ventilation is provided. 

Allowing DRI to become wet does not necessatily cause it to overheat. When large pdes of DRI are wetted with rain, the corrosion reactions are limited to the outer surface area of the pde and the resultant heat from the corrosion reactions is dissipated into the atmosphere. However, if water penetrates into the pde from the bottom, or if wet DRI is covered with dry DRI, the heat from corrosion reactions can budd up inside the pde to the point where rapid reoxidation begins. Corrosion occurs significantly faster with salt water than with fresh water. DRI saturated with water can cause steam explosions if it is batch charged into an electric arc furnace. 

Although most greases offer some inherent protection against msting, additives, eg, amine salts, sodium sulfonate, cycloparaffin (naphthenate) salts, esters, and nonionic surfactants (qv), are often used to provide added protection against water and salt-spray corrosion. A dispersion of sodium nitrite has been particularly effective in some multipurpose greases. 

G lv nic Corrosion. Galvanic corrosion is an electrochemical process with four fundamental requirements (/) an anode (magnesium), 2) a cathode (steel, brass, or graphite component), (J) direct anode to cathode electrical contact, and (4) an electrolyte bridge at the anode and cathode interface, eg, salt water bridging the adjacent surfaces of steel and magnesium components. If any one of these is lacking, the process does not occur (133,134). 

Addition of one mole of P,P -dipheny1methy1enediphosphinic acid to tetraisopropyl titanate gives a chelated product, the solutions of which can be used as a primer coat for metals to enhance the adhesion of topcoats, eg, alkyds, polyalkyl acylates, and other polymeric surface coating products, and improve the corrosion resistance of the metal to salt water (102). 

The marine environment is highly aggressive. Materials in marine service are constantly exposed to water, corrosive salts, strong sunlight, extremes in temperature, mechanical abuse, and chemical pollution in ports. This climate is very severe on ships, buoys, and navigational aids, offshore stmctures such as drilling platforms, and faciUties near the shore such as piers, locks, and bridges. 

Atmospheric exposure, fresh and salt waters, and many types of soil can cause uniform corrosion of copper aHoys. The relative ranking of aHoys for resistance to general corrosion depends strongly on environment and is relatively independent of temper. Atmospheric corrosion, the least damaging of the various forms of corrosion, is generaHy predictable from weight loss data obtained from exposure to various environments (31) (see Corrosion and CORROSION CONTKOL). 

It is a consequence of the action of different pH values in the aeration cell that these cells do not arise in well-buffered media [4] and in fast-flowing waters [5-7]. The enforced uniform corrosion leads to the formation of homogeneous surface films in solutions containing Oj [7-9]. This process is encouraged by film-forming inhibitors (HCOj, phosphate, silicate, Ca and AP ) and disrupted by peptizing anions (CP, SO ") [10]. In pure salt water, no protective films are formed. In this case the corrosion rate is determined by oxygen diffusion [6,7,10]... 

The annular space between the outer pipe and the surrounding rock is filled with cement over the whole depth up to the ground in new wells. The purpose of this is to seal the deposits at the top and to keep the fresh water and salt water zones separate. In addition, it serves as a protection against pressure from the rock and as corrosion protection which, however, is only effective so long as there is no current exit caused by extended corrosion of cells or due to foreign anodic influences. The cement Ailing of the borehole casing is usually not uniformly spread over the pipe surface. It has to be remembered that there can be sections which are either not covered or are only thinly covered with cement. 

Hot corrosion is a rapid form of attack that is generally associated with alkali metal contaminants, such as sodium and potassium, reacting with sulfur in the fuel to form molten sulfates. The presence of only a few parts per million (ppm) of such contaminants in the fuel, or equivalent in the air, is sufficient to cause this corrosion. Sodium can be introduced in a number of ways, such as salt water in liquid fuel, through the turbine air inlet at sites near salt water or other contaminated areas, or as contaminants in water/steam injections. Besides the alkali metals such as sodium and potassium, other chemical elements can influence or cause corrosion on bucketing. Notable in this connection are vanadium, primarily found in crude and residual oils. 

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