Acid initiated corrosion

Control acid-initiated corrosion and erosion of fuel injector nozzle orifices... 

Attempts made to produce an alloy more resistant to hydrochloric acid have resulted in alloys containing 17-18% silicon or 14-5% silicon and chromium plus 3% molybdenum. The first is produced in Britain, and the second in the United States. The reason for the increase in resistance to hydrochloric acid of the Fe-18 Si alloy is thought to lie primarily in the increased density of the silica-rich film left on the metal by initial corrosion. The addition of 6% chromium with some molybdenum to Fe-14-5 Si causes the formation of extremely stable complex carbides with the consequent complete elimination of graphite plus the formation of a more penetration-resistant silica film, probably containing chromium in substantial quantity. 

The atmospheric corrosion data in Table 4.34 (and also Table 13.8) is related to historic environments. Current use in the industrial areas listed with acidic pollution would show much lower corrosion rates as the corrosion of zinc in the atmosphere is essentially related to the SOj content (and the time of wetness) and in many countries the sulphurous pollution has been greatly reduced in the past 20 years. Zinc also benefits from rainwater washing to remove corrosive poultices thus, although initial corrosion rates are usually not very different on upper and lower surfaces, the latter tend —with time—to become encrusted with corrosion products and deposits and these are not always protective. 

Both iron- and copper-based alloys are corroded more easily on either side of the neutral pH band. In low pH conditions e.g. due to carbon dioxide, the acidic environments attack the alloys readily, causing damage both at the points of initial corrosion and perhaps, consequentially, further along the system, by screening the surface with corrosion products and permitting the development of differential aeration cells. 

In fuel combustion systems, S02 and S03 can form upon the burning of fuel sulfur. When sulfur oxides combine with water vapor, acids form. This problem of acid formation and accumulation is a known phenomena and usually occurs under low-speed and load operating conditions. The acids which condense on fuel system components can initiate corrosion of valves, piston rings, and fuel injector nozzles. 

Together, water and SO can combine to form sulfur-bearing acids. These acids can accumulate to initiate corrosive wear, oxidation of lubricating oil, and the formation of piston lacquer deposits within the combustion chamber. Engine deposits can result in operability problems such as preignition knock, dieseling, and wear. 

Water contamination of fuel occurs. Water can originate from fuel processing, atmospheric condensation, or external sources. Water may contain dissolved salts, may be acidic or basic, or may contain solubilized organic compounds. Water-initiated corrosion can result. 

Sulfuric acid and hydrofluoric acid are used as catalysts in the production of gasoline alkylate. After processing, this acid must be removed from the finished alkylate. This is typically accomplished by water washing or caustic washing the alkylate. However, if residual sulfuric acid or hydrofluoric acid remains in the fuel or alkylate, the acid can initiate corrosion. The acid is very aggressive toward initiating corrosion of ferrous metal. It is difficult for filming-type corrosion inhibitors to overcome acid attack of metal. 

When a corrosive medium contacts the edge of a bonded joint and finds an extremely active surface, such as that produced by a fresh acid treatment of the metal substrate to improve adhesion, corrosion at the metal-adhesives interface can occur. This initial corrosion and the subsequent penetration can take several forms. 

The key point for atmospheric steel corrosion is to make an initial corrosion product of soluble ferrous ions air-oxidized as soon as possible into an insoluble ferric hydroxide aggregate, which eventually turns into anticorrosive mst. The air-oxidation of hydrated ferrous ions is fast in neutral water but slow in acidic water. Once corrosion-produced ferrous ions are oxidized into gel-like... 

The spray formulation appears to be nontoxic because both fish and algae grow readily in the ponds. The pH level of the water in the ponds has remained constant, which indicates that bacteria are not converting sulfur to sulfuric acid. Samples of the formulation were exposed to bacterial attack in a controlled environmental chamber maintained at a high moisture level to accelerate the rate of attack. No evidence of bacterial attack on the samples has been detected after 1 yr of exposure under aerobic conditions. Initial corrosion tests showed that samples of the formulation did not lose weight after exposure in 1 and 5% sulfuric acid solutions for 4 months. 

Second precondition. Dissolution of iron will take place only when the current circulates for sufficiently long periods and in high enough intensity to produce acidity that can destroy the conditions of passivity. For instance, Figure 9.6 show the results obtained with laboratory tests on specimens of cement paste subjected to the circulation of current densities of 1 and 10 A/m [5]. Corrosion initiated on steel embedded in cement paste without chloride ordy after more than 200 h of ap-pHcation of an anodic current density of 10 A/m. A current density of 1 A/m could not initiate corrosion even after 14 months (i. e. more than 10000 hours) of continuous application, although the charge that circulated (> 10000 A -h/m )... 

Initial corrosion rates are modified by the subsequent formation of corrosion products, particularly in atmospheric exposure, where there is the beneficial effect of periodic drying periodic drying may, however, have a detrimental effect when dissolved salts become more concentrated in areas that remain moist after most of the water has evaporated, especially when evaporation results in increased acidity of the residual solution. 

Protection of Austenitic Stainless Steel from Polythionic Acid Stress Corrosion Cracking During Shutdown of Refinery Equipment Collection and Identification of Corrosion Products Initial Conditioning of Cooling Water Equipment On-Line Monitoring of Cooling Waters... 

The material distilled in some towers becomes super-corrosive when exposed to moisture. Some depropanizers in sulfuric-acid alkylation service are quite susceptible to moisture-initiated corrosion. One such depropanizer had a long history of corrosion failures. Most frequently, the overhead condenser tubes would start leaking. When this occurred, propane vapors rose from the cooling tower. Often, the effects of corrosion were less subtle clouds of hydrocarbons would burst forth from leaking lines. 

On a weight basis in many locations, dust is the primary air contaminant. When in contact with metallic surfaces and combined with moisture, dust can promote corrosion by forming galvanic or differential cells that, because of their hygroscopic nature, form an electrolyte on the surface. Suspended particles of carbon and carbon compoimds, metal oxides, sulfuric acid, ammonium sulfate, sodium chloride, and other salts will be foimd in industrial atmospheres. It is these materials, when combined with moisture, that initiate corrosion. 

The atmospheric corrosion of zinc starts with the instant formation of a thin film of zinc hydroxide, which seems to occur in different crystal structures, and the subsequent formation of a protective layer of basic zinc carbonate, Zn5(C03)2(0H)g. The pH of the aqueous layer controls the stability of initial corrosion products and results in the dissolution of Zn +. From the HSAB principle one expects Zn, classified as an intermediate acid, to coordinate with a number of different bases. In accordance with this, the prolonged exposure of zinc can proceed along a variety of different paths of reaction sequences depending on the actual deposition rates of atmospheric constituents. Among these Cl and SO2 seem to be the most important. 

The generation of CO is beheved to proceed through the intermediate formation of carbon surface oxides, as suggested in earlier studies in phosphoric acid fuel cells (Kinoshita and Bett 1973). It was reported that formation of surface oxides and evolution of CO occur simultaneously during the initial corrosion of high surface area carbon blacks. Similar conclusions are also reported by recent studies of PEMFCs (Kangasniemi et al. 2004). These studies showed that the surface oxides... 

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