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Corrosion deposition erosion

Galvanic corrosion may also occur by transport of relatively noble metals, either as particulate or as ions, to the surface of an active metal. For example, ions of copper, perhaps resulting from corrosion or erosion-corrosion at an upstream site, may be carried by cooling water to the surfaces of aluminum, steel, or even stainless steel components. If the ions are reduced and deposit on the component surfaces, localized galvanic corrosion may result. [Pg.358]

Steam drums and water-wall headers should be inspected for evidence of pitting corrosion, chelant corrosion, cracks, erosion, thinning, sludge fouling, and scale deposition. Also, the waterline should be checked for surging and priming problems. [Pg.618]

Ash deposition in biomass combustion systems has been the focus of numerous research efforts.559,659 The basic mechanism for deposit formation in biomass combustion systems starts with the vaporization of alkali metals, usually chlorides, in the combustor. Fly ash particles, which are predominantly silica, impact and stick to boiler tube surfaces. As the flue cools the alkali metal vapors and aerosols quench on the tube surfaces. When the ash chemistry approaches equilibrium on the surface and the deposit becomes molten, the likelihood increases that additional fly ash particles will stick, and deposits grow rapidly. Ash deposits can also accelerate the corrosion or erosion of the heat transfer surfaces. This greatly increases the maintenance requirements of the power plant often causing unscheduled plant interruptions and shutdown. [Pg.1522]

Erosion corrosion is caused by the conjoint action of corrosion and mechanical abrasion by a moving fluid or suspended material in the fluid. Turbulent flow or jets of liquid on a metal surface may lead to erosion corrosion. The mechanical action of the fluid removes the protective corrosion deposit, thus exposing fresh metal to the corrosive. As corrosion products build up, they are removed and so the process continues. The surface of a piece of metal exposed to this type of corrosion has a characteristic structure (Fig. 8). [Pg.252]

These deposits not only reduce the efficiency of the boiler drastically, but also promote corrosion and erosion (Honea et al.,... [Pg.3675]

Benson, S., Steadman, E. N., Zygarlicke, C. J. Erickson, T. A. (1996), Ash Formation, Deposition, Corrosion, and Erosion in Conventional Boilers. Applications of Advanced Technology to Ash-Related Problems in Boilers, Plenum Press, New York, p. 1. [Pg.571]

The flame imprinted characteristics of pulverized coal ash relevant to boiler slagging, corrosion and erosion have been discussed previously (1,2). Silicate minerals constitute between 60 and 90 per cent of ash in most coals and boiler deposits are largely made up from the silicious impurity constituents. This work sets out first to examine the mode of occurrence of the silicate mineral species in coal followed by a characterization assessment of the flame vitrified and sodium enriched silicate ash particles. The ash sintering studies are limited to investigations of the role of sodium in initiating and sustaining the bond forming reactions to the formation of boiler deposits. [Pg.138]

C/OKE FORMATION IS AN UNDESIRABLE SIDE EFFECT of many chemical operations because it leads to costly decoking steps, reduced efficiency of operation, and increased rates of metal corrosion and erosion. There is, therefore, a tremendous incentive to minimize or at least better control coke deposition in numerous commercial units. [Pg.1]

At high temperature, erosion becomes more complicated due to the involvement of corrosion, deposition, and chemical reactions such as oxidation. The presence of an oxidized layer or deposit may reduce the apparent erosion rate in some cases. [Pg.915]

Radioactive tracers have been used in the study of equilibrium and reactions in various branches of chemistry, including inorganic and organic and also basic and industrial. Solubility, vapor pressure, diffusion, precipitation, deposition, erosion, corrosion, etc., have been extensively studied with the use of radioactive tracers. Early studies were extensively compiled by Wahl and Bonner (1951). [Pg.1777]

The turbine shell is generally removed for a warranty inspection after the first year s operation. Shutdowns thereafter can be at intervals of 3,4, or 5 yr. Long periods of operation with minimal maintenance require steam of high purity. Carryover of certain contaminants in the steam can cause deposits, erosion, and stress cracking. A list of common deposit- and corrosion-causing contaminants is given in Table 6.27. [Pg.986]

Fig. 10.16 Types of localized corrosion initially associated with the environment, (a) Crevice corrosion, (b) Deposit corrosion, (c) Waterline attack, (d) Filiform corrosion (e) Erosion corrosion, (f) Drop corrosion, (g) Turbulent-flow corrosion, (h) Fretting. Fig. 10.16 Types of localized corrosion initially associated with the environment, (a) Crevice corrosion, (b) Deposit corrosion, (c) Waterline attack, (d) Filiform corrosion (e) Erosion corrosion, (f) Drop corrosion, (g) Turbulent-flow corrosion, (h) Fretting.
Arc vapor deposition processes are used for vaporizing all forms of conductive materials with low radiant thermal energy from cathodic arc deposition. Non-conductive materials cannot be processed. However, the process is effective in depositing high-wear, corrosion and erosion-resistant thin-film coatings on precision parts. Pure metals, metal nitrides, carbides and carbo-nitrides, for example, can be deposited as a monolayer, multilayer, graded, or alloy film. [Pg.70]

These materials can damage equipment by means of corrosion, erosion, deposits, plugging, catalyst poisoning, etc. [Pg.326]

High Water Velocities. The abiUty of high water velocities to minimize fouling depends on the nature of the foulant. Clay and silt deposits are more effectively removed by high water velocities than aluminum and iron deposits, which are more tacky and form interlocking networks with other precipitates. Operation at high water velocities is not always a viable solution to clay and silt deposition because of design limitations, economic considerations, and the potential for erosion corrosion. [Pg.271]

Indirect attack can also occur because of turbulence associated with flow over and around a deposit. Increased turbulence may initiate attack (see Chap. 11, Erosion-Corrosion and Chap. 12, Cavitation Damage ). [Pg.69]

Shells, clams, wood fragments, and other biological materials can also produce concentration cell corrosion. Additionally, fragments can lodge in heat exchanger inlets, locally increasing turbulence and erosion-corrosion. If deposits are massive, turbulence, air separation, and associated erosion-corrosion can occur downstream (see Case History 11.5). [Pg.126]

After only 4 months of service, the main condenser at a large fossil utility began to perforate. Initial perforations were due to erosion-corrosion (see Case History 11.5). Small clumps of seed hairs entering the condenser after being blown into the cooling tower were caught on surfaces. The entrapped seed hairs acted as sieves, filtering out small silt and sand particles to form lumps of deposit (Fig. 6.24A and B). Immediately downstream from each deposit mound, an erosion-corrosion pit was found. [Pg.152]

Figure 11.4 Deposits covering intact metal surfaces at sites of horseshoe-shaped erosion-corrosion depressions. (Magnification 15x.)... Figure 11.4 Deposits covering intact metal surfaces at sites of horseshoe-shaped erosion-corrosion depressions. (Magnification 15x.)...
Affected areas are essentially free of deposits and corrosion products, although these may be found nearby (Fig. 11.4). Affected areas may be covered with deposits and corrosion products if erosion-corrosion occurs intermittently, and the component is removed following a period in which erosion-corrosion was inactive. [Pg.242]

Favored locations for erosion-corrosion are areas exposed to high-flow velocities or turbulence. Tees, bends, elbows (Fig. 11.5), pumps, valves (Fig. 11.6), and inlet and outlet tube ends of heat exchangers (Fig. 11.7) can be affected. Turbulence may be created downstream of crevices, ledges (Fig. 11.8), abrupt cross-section changes, deposits, corrosion products, and other obstructions that change laminar flow to turbulent flow. [Pg.242]

The classic signature of erosion-corrosion is the formation of horseshoeshaped depressions, comet tads, grooves, or sand dunelike surface contours oriented along the direction of fluid flow (Figs. 11.1,11.2,11.3,11.5, and 11.8). Occasionally, erosion-corrosion will produce smooth, almost featureless, surface contours (Fig. 11.15), although even in this case oriented metal loss often exists around the perimeter of the affected region. If erosion-corrosion has been recently active, affected surfaces will be free of accumulated deposits and corrosion products. [Pg.248]


See other pages where Corrosion deposition erosion is mentioned: [Pg.464]    [Pg.1274]    [Pg.125]    [Pg.220]    [Pg.183]    [Pg.464]    [Pg.217]    [Pg.464]    [Pg.206]    [Pg.397]    [Pg.1384]    [Pg.319]    [Pg.866]    [Pg.403]    [Pg.283]    [Pg.149]    [Pg.22]    [Pg.130]    [Pg.418]    [Pg.371]    [Pg.496]    [Pg.404]    [Pg.188]    [Pg.313]    [Pg.511]    [Pg.126]    [Pg.176]   
See also in sourсe #XX -- [ Pg.180 ]




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