Corrosion condensed water

Sulfur. Sulfur in diesel fuel should be kept below set limits for both environmental and operational reasons. Operationally, high levels of sulfur can lead to high levels of corrosion and engine wear owing to emissions of SO that can react with condensed water during start-up to form sulfuric acids. From an environmental perspective, sulfur bums to SO2 and SO, the exact spHt being a function of temperature and time in the combustion chamber. 

Examples of the sacrificial-anode method include the use of zinc, magnesium, or aluminum as anodes in electrical contact with the metal to be protected. These may be anodes buried in the ground for protection of underground pipe lines or attachments to the surfaces of equipment such as condenser water boxes or on ship hulls. The current required is generated in this method by corrosion of the sacrificial-anode material. In the case of the impressed emf, the direct current is provided by external sources and is passed through the system by use of essentially nonsacrificial anodes such as carbon, noncor-rodible alloys, or platinum buried in the ground or suspended in the electrolyte in the case of aqueous systems. 

For several years now, cable ducts have been manufactured from plastic pipes, which are watertight and form a continuous run of piping. In laying the ducts, low points can occur in which condensed water or water penetrating from the ends can collect. In many cases this water has led to corrosion damage in lead-sheathed cables. Lead-sheathed cables must therefore only be used in such ducts with an additional PE sheath of type A-PM2Y. Cathodic protection of these cables is not possible because of their complete insulation by the plastic pipe. 

Carbon Dioxide CO2 Corrosion in water lines and particularly steam and condensate lines Aeration, deaeration, neutralization with alkalies, filming and neutralizing amines... 

Carbon dioxide COj Results in the corrosion of water lines, especially steam and condensate lines. 

Dehydration to dew points below the temperature to which the gas will be subjected will prevent hydrate formation and corrosion from condensed water. The latter consideration is especially important in gas streams containing CO2 or H2S where the acid gas components will form an acid with the condensed water. 

The main febricated parts of the units are carbon steel, with suitable corrosion allowance for the conditions of the chilled and condensing water. When brackish or sea water is used in a barometric condenser, steel construction with a V4 -in. to -in. corrosion allowance is suggested, and minimum wall plates of V2 -in. to -in. may be justified. Internal splash plates should be V2 -in. to -in. minimum, because the atmosphere of water vapor-air is very corrosive. Alloy construction is not justified except in exceptional cases. 

Condensing economizers are constructed from corrosion-resistant materials (notably aluminum or stainless steel), since the condensed water vapor in the gas is slightly acidic (typically, with a pH of 3-5). This is... 

The main corrosion processes that occur in these items arise from condensing liquids on the internal surface. Although often lagged, heat loss frequently causes internal skin temperatures to fall below the dewpoint of one or more components of the gas stream, albeit locally, such as at support points. Even at temperatures above its dewpoint a gas can dissolve in condensed water. Rapid corrosion can then occur in this thin film of corrosive liquid. 

Condensing species of relevance to corrosion include water and all acid gases. The dewpoint of water is obtained from standard tables, requiring only the water content (i.e. relative humidity) of the gas stream. Above the water dewpoint, corrosion problems include condensing acids (Section 53.3.2), dry acid gases (Section 53.3.3) and erosion. Below the water dewpoint acid gases dissolve in the water film to create an acidic solution, including ... 

The data on which Fig. 8.74 is based are for tests carried out in carbonate well-water. McAdam made the further interesting discovery that if mild steel were tested in condenser water and a similar graph constructed, the set of contours corresponded more closely to the right-hand side of Fig. 8.74, i.e. the behaviour of mild steel in condenser water was similar to that of Monel in carbonate water. The apparent universality of this diagram is an interesting observation, but it has not provoked a basic theory of corrosion fatigue. 

Burning of sulfur to produce SO can create both burner system corrosion problems as well as atmospheric air emission concerns. About 1% to 5% of the fuel sulfur burned is converted to S03 and the remainder is converted to S02. If a system operates below its dew point, the SO, can react with condensed water to form sulfuric acid. Much work is being done through hydrodesulfurization, neutralization, and engineering to reduce the amount of sulfur oxides produced through burning of residual fuel. 

A more serious threat to the materials compatibility of CNG fuel systems is condensed water vapor. Water can cause steel and cast iron to rust and aluminum to corrode. Any corrosion of components that must withstand high pressures is a concern, since corrosion stress cracking can occur which can result in failure of the component with disastrous results. The presence of water greatly accelerates the corrosion properties of the hydrogen sulfide that might be found in the natural gas. For these reasons it has been recommended that the way to control corrosion in CNG systems is to remove sufficient water vapor to prevent it from condensing in the system under static conditions [3.13]. Natural gas dryers have been developed to help reach this goal. 

Figure 10-14 An inspector examines the condition of the tubes on a condenser. Water-side corrosion can occur if water treatment is insufficient.

Other examples of such mixed potential models include that developed by Macdonald and Urquidi-Macdonald to predict water radiolysis effects in thin condensed water layers on metal surfaces (24), and the models of Marsh and Taylor (25), and Kolar and King (22) to predict the corrosion of carbon steel and copper waste containers surrounded by a low permeability material such as clay. 

Austenitic irons are used for valve and pump bodies condenser water boxes in refineries, cryogenics, marine and electricity generation systems. In general austenitic irons have better corrosion resistance than unalloyed or low-alloy irons. 

The fact that the aluminum cylinder is constantly under pressure is believed to be a contributing factor for stress corrosion. The moisture content is very critical since condensation occurs when pressure changes rapidly. Therefore, moisture content and slow refilling procedure are strictly regulated. Carbon dioxide content is also critical since it increases its dissolubility as pressure increases. As a result, it could bring the pH value of condensed water below the level where aluminum oxide is no longer stable. 

Corrosion rate of steel vs temperature of atmospheric tower sour condensate water. 19... 

Reprinted from Corrosion of Steel by Sulfides and Cyanides in Refinery Condensate Water," Materials Protection, December 1968.)... 

For cross country lines containing oil or gas, the corrosive constituents such as water, carbon dioxide, and hydrogen sulfide are usually reduced to a very low level before the fluid enters the line. The lost efficiency required to pump the unwanted constituents and the extra wall thickness required for corrosion allowance usually cannot be economically justified. Even with cleanup systems, some water will get into pipelines. In oil lines, oil soluble corrosion inhibitors usually prevent attack by water settling in low spots, etc. Gas lines are usually dehydrated to 60% of saturation to avoid corrosion from condensing water containing dissolved carbon dioxide. Molecular sieves that reduce water to 5 ppm have proved necessary in lines containing 100% carbon dioxide. 

Aluminum pistons in an engine that bums H2 will be exposed to not only H2 but also H2O at temperatures of 80 to 120°C. Aluminum alloys can be totally immune to H2 embrittlement and H2-induced crack growth if the natural AI2O3 oxide is intact. However, there are processes that can disrupt this film, and it is known that aluminum alloys will absorb H2 when exposed to H2O vapor at 70°C. There will also be periods when the engine is cool and condensed water will be present so that aqueous corrosion could occur, but this is not expected to be any different than with an engine with cast aluminum pistons that bums gasoline. 

Condensation and Corrosion Prevention Water vapor in air condenses on surfaces whose temperature is below the dew point, and the outer surfaces of the tanks or pipes that contain a cold fluid frequently fall below the dew-point temperature unless they have adequate insulation. The liquid water on exposed surfaces of metal tanks or pipes may promote corrosion as well as algae growth,... 

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