Major corrosion problems

Lubricants are specially formulated to meet all manner of requirements and the major corrosion problems associated with important classes of lubricants will now be outlined. 

Is the plant suitable or can it be altered to make it so The most likely reason that the answer to this query would be negative is that there is a major corrosion problem, but lack of traced lines, the presence of odours and also regulatory barriers are other common problems. 

Chloride corrosion is the major corrosion problem. The other major specific problem area is assuring that materials used comply with FDA/USDA regulations for contact with foods and/or beverages during manufacture, processing, and handling [2,7]. 

The major corrosion problems with titanium alloys appear to be crevice corrosion, which occurs in locations where the corroding media are virtually stagnant. Pits, if formed, may progress in a similar manner. A general comparison of corrosion resistance for titanium is provided in Fig. 1(a). 

A complete description of stainless steels and major corrosion problems encountered by steels have been described in Chapter 4. Here, a brief description of stainless steels with reference to their corrosion resisting properties in certain selected environments is presented. 

In many practical situations, carbonation- and chloride-induced corrosion can occur in tandem. Research studies have shown that corrosion caused by carbonation was intensified with increasing chloride ion concentration, provided that the carbonation rate itself was not retarded by the presence of chlorides. According to these studies, chloride attack and carbonation can act synergistically (the combined damage being more severe than the sum of its parts) and have been responsible for major corrosion problems in hot coastal areas. 

High temperature sulfidation can be found in primary, secondary and even downstream chemical processing units. Therefore, corrosion attack associated with sulfur is one of the major corrosion problems and can occur in the whole refining process. The total sulfur content in crude oils is not directly correlated with their corrosivity. Actually the corrosivity is mainly dependent... 

The Steam Injection Cycle Steam injection has been used in reciprocating engines and gas turbines for a number of years. This cycle may be an answer to the present concern with pollution and higher efficiency. Corrosion problems are the major hurdle in such a system. The concept is simple and straightforward Steam is injected into the compressor discharge air and increases the mass flow rate... 

The three major forms of concentration cell corrosion are crevice corrosion, tuberculation, and underdeposit attack. Each form of corrosion is common in cooling systems. Many corrosion-related problems in the cooling water environment are caused by these three forms of wastage. The next three chapters—Chap. 2, Crevice Corrosion, Chap. 3, Tuberculation, and Chap. 4, Underdeposit Corrosion — will discuss cooling water system corrosion problems. 

Water injection, or steam injection systems, are being used extensively to augment power. Corrosion problems in the compressor diffuser and combustor have not been found to be major problems. The increase in work and efficiency with a reduction in NO makes the process very attractive. Split-shaft cycles are attractive for use in variable-speed mechanical drives. The off-design characteristics of such an engine are high efficiency and high torque at low speeds. 

In a combined cycle plant, high steam pressures do not necessarily convert to a high thermal efficiency for a combined cycle power plant. Expanding the steam at higher steam pressure causes an increase in the moisture content at the exit of the steam turbine. The increase in moisture content creates major erosion and corrosion problems in the later stages of the turbine. A limit is set at about 10% (90% steam quality) moisture content. 

The process is similar to the catalytic liquid-phase oxidation of ethylene to acetaldehyde. The difference hetween the two processes is the presence of acetic acid. In practice, acetaldehyde is a major coproduct. The mole ratio of acetaldehyde to vinyl acetate can he varied from 0.3 1 to 2.5 1. The liquid-phase process is not used extensively due to corrosion problems and the formation of a fairly wide variety of by-products. 

Table 1.29 tabulates most known examples of erosion corrosion problems occuring in aqueous systems. Historically, erosion corrosion first became a problem with the copper alloy (70%Cu 29%Zn l%Sn) condensers of naval shipsErosion corrosion of copper alloys has been an ongoing problem since then. The other major problem areas are (a) power plants where steels are exposed to water or water/steam mixtures in the temperature range 90°-280°C (b) the oil and gas industry where steels are exposed to various liquid, gas, and sometimes solids combinations containing carbon dioxide. 

In duplex steels, ferrite is a major intentional constituent. The features noted above are relevant the two phases do have differing analyses but not to such an extent as to cause serious corrosion problems. A further... 

Major Industry Corrosion Problems A number of specific problems have achieved industry status over the past ten years, owing to their cost and/or threat to plant integrity. All have significant design implications. 

A major goal in wall cooling is to spread out the hot zone and prevent very high peak temperatures. High peak temperatures cause poor reaction selectivity, cause carbon formation, deactivate catalysts, and cause corrosion problems in the reactor walls. CocuJTent flows spread out the hot zone and cause lower peak temperatures, but many additional design features must be considered in designing jacketed reactors. 

The motivation for the vast majority of radiation chemical studies has been provided by considerations other than the desire to develop economically feasible processes. The approach has been fundamental, with the result that many data exist on systems having no possible application in the chemical process industry, while data on potential systems are lacking. Though extensive work on aqueous systems has been motivated by practical applications of these data to corrosion problems and biological systems, the approach has still been a fundamental one and the systems studied have been chosen so as to yield information... 

Localized corrosion is the direct result of the breakdown of passivity at discrete sites on the material surface. As was stated above, once passivity is established on a surface, one might expect either that it would remain passive or that a complete activation of the surface would occur. However, what is often observed in practice is the appearance of discrete areas of attack that begin to corrode actively while the vast majority of the surface remains passive. These isolated regions of attack are more than mere annoyances the local penetration rates can be on the order of 10 mpy or higher, leading to rapid perforation of any reasonably sized container. Since the original intent in using passive materials (e.g., CRAs) in any application is to exploit their low dissolution rates, localized corrosion can be a major operational problem. 

The major stray-current corrosion problems now result in cathodic protection systems. Current from an impressed-current cathodic protection system will pass through the metal of a neighboring pipeline at some distance before it returns to the protected surface. Increased anodic corrosion is frequently localized on the pipe at the zone where the current leaves the pipe back to the protected steel tank. 

Description Ammonia and carbon dioxide react at 155 bar to synthesize urea and carbamate. The reactor conversion rate is very high under the N/C ratio of 3.7 with a temperature of 182-185°C. Unconverted materials in synthesis solution are efficiently separated by C02 stripping. The milder operating condition and using two-phase stainless steel prevent corrosion problems. Gas from the stripper is condensed in vertical submerged carbamate condenser. Using an HP Ejector for internal synthesis recycle, major synthesis equipment is located on the ground level. 

The formation of chlorinated by-products and the processing of aqueous chloride solutions are putting heavy ecological constraints on this technology nowadays. Additionally corrosion problems related to the use of highly acidic solutions have always been a major drawback for the Wacker-Hoechst process. 

---