Corrosion removal

Wet scrubbers rely on a liquid spray to remove dust particles from a gas stream. They are primarily used to remove gaseous emissions, with particulate control a secondary function. The major types are venturi scrubbers, jet (fume) scrubbers, and spray towers or chambers. Venturi scrubbers consume large quantities of scrubbing liquid (such as water) and electric power and incur high pressure drops. Jet or fume scrubbers rely on the kinetic energy of the liquid stream. The typical removal efficiency of a jet or fume scrubber (for particles 10 g. or less) is lower than that of a venturi scrubber. Spray towers can handle larger gas flows with minimal pressure drop and are therefore often used as precoolers. Because wet scrubbers may contribute to corrosion, removal of water from the effluent gas of the scrubbers may be necessary. 

Abrasion removes protective oxidized metal and polarized coatings to expose unoxidized metal, in addition to removing metal particles. Forms microscopic grooves and dents for concentration cell corrosion. Increases microscopic surface area exposed to corrosion. Removes strain-hardened surface layers. Cracks brittle metal constituents, forming sites for impact hydraulic splitting. Plastic deformation by high-stress metal-mineral contact causes strain hardening and susceptibility to chemical attack. 

Any system Small corrosion area or general corrosion over large area Localized corrosion Evaluate structural integrity. If fit for service, then apply coating to protect metal and inspect according to schedule Identify root cause of corrosion. Remove materials causing corrosion. Replace damaged material... 

Under certain corrosive conditions, many metals form covering layers. If these are sufficiently dense, they act as protective films against the corrosive removal of the material. An example of this is the protective layer of iron oxide formed in unalloyed or low-alloy boiler tubes. Corrosion with erosion is understood as the combined action of mechanical surface removal and corrosion. With some soft and loose layers, the shear forces obtained with pure flowing liqnids at medium flow velocities are sufficient to damage the protective layer without the involvement of abrasive solid particles. Where drop impingement or cavitation is involved, the mechanical removal of material is understandable. 

In Table 4.5.b. the values of the constants obtained from the experiments are given (K in im h ") by extrapolating these data to an integrated exposure period of 30 years, the cumulative corrosion removal from the materials shown in Table 4.5.C. results. 

Several authors have reported that recontamination rates are usually less severe when dilute chemical decontamination processes have been applied. The most likely explanation of the high recontamination rates observed after the use of concentrated reagents is that these solutions were corrosive, removing the entire protective film from the surfaces and roughening the underlying base material. Nevertheless, even when applying soft decontamination procedures, the phenomenon of recontamination is a severe handicap for further work. Numerous attempts, therefore, have been made to reduce the rate of recontamination in order to reduce... 

The initially apparently contradictory results of the experiments in [19] and [20] must be seen from the point of view of the types of corrosion. [19] deals primarily with uniform general corrosion (removal of iron) and the formation of msty water, while the conclusions in [20] primarily relate to wide or deep pitting corrosion. 

DR value means that the metal is readily coated with a thin protective film of the amine. Some amines commonly used and their pH and DR are given in Table 10.5. The amine is slowly lost, and it must be replaced continuously. Steam lines invariably have these amines, and the use of brass, bronze, or copper results in the corrosive removal of copper. 

For aqueous corrosion remove dissolved 0, increase the pH (for steels), add inhibitors. 

Chem. Descrip. Acids, wetting agents, and emulsifiers Uses Metal conditioner and corrosion remover removes It. oxidation and corrosion from metals... 

Corrosion problems often dictate that a particularly corrosive component be removed early to minimize the use of expensive materials of construction. 

HOCH2C = CCH2OH. White solid, m.p. 58 C, b.p. 238- C prepared by the high pressure reaction between ethyne and methanol and also from BrMgCCMgBr and methanal. Used in electroplating (Ni), as a corrosion inhibitor, and in paint and varnish removal. 

Other techniques to detennine the corrosion rate use instead of DC biasing, an AC approach (electrochemical impedance spectroscopy). From the impedance spectra, the polarization resistance (R ) of the system can be detennined. The polarization resistance is indirectly proportional to j. An advantage of an AC method is given by the fact that a small AC amplitude applied to a sample at the corrosion potential essentially does not remove the system from equilibrium. 

Erosion is the deterioration of a surface by the abrasive action of solid particles in a liquid or gas, gas bubbles in a liquid, liquid droplets in a gas or due to (local) high-flow velocities. This type of attack is often accompanied by corrosion (erosion-corrosion). The most significant effect of a joint action of erosion and corrosion is the constant removal of protective films from a metal s surface. This can also be caused by liquid movement at high velocities, and will be particularly prone to occur if the solution contains solid particles that have an abrasive action. 

Owing to the corrosive action of bromine upon corks j-jg 7, l. and rubber stoppers, ground glass joints are recommended in this preparation. The apparatus, depicted in Fig. Ill, 37, 1, is particularly convenient for the preparation of bromides from alcohols. A double surface condenser is fitted into D and a round-bottomed flask is fitted on to the ground glass joint at C R is a three-way stopcock f which permits the removal of the contents of A without disconnecting the apparatus. For preparations of moderate size, A has a capacity of 60 or 100 ml. and a 250 or 500 ml. flask is attached at C. 

Benzylatnine. Warm an alcoholic suspension of 118-5 g. of finely-powdered benzyl phthalimide with 25 g. of 100 per cent, hydrazine hydrate (CAUTION corrosive liquid) a white, gelatinous precipitate is produced rapidly. Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. Collect the phthalyl hydrazide which separates by suction filtration, and wash it with a little water. Concentrate the filtrate by distillation to remove alcohol, cool, filter from the small amount of precipitated phthalyl hydrazide, render alkaline with excess of sodium hydroxide solution, and extract the liberated benzylamine with ether. Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (compare Fig. //, 13, 4) on a water bath and finally distil the residue. Collect the benzylamine at 185-187° the 3ueld is 50 g. 

Weldments subjected to corrosive attack over a period of time may crack adjacent to the weld seams if the residual stresses are not removed. Gas—tungsten arc welding and gas—metal arc welding ate recommended for joining magnesium, the former for thinner materials and the latter for thicker materials. Maintaining a protective atmosphere is a critical issue in welding these alloys. 

Sweetening. Another significant purification appHcation area for adsorption is sweetening. Hydrogen sulfide, mercaptans, organic sulfides and disulfides, and COS need to be removed to prevent corrosion and catalyst poisoning. They ate to be found in H2, natural gas, deethanizer overhead, and biogas. Often adsorption is attractive because it dries the stream as it sweetens. 

Limestone slurry scmbs flue gas. SO2 absorbed, reacted to CaSO. Further ak-oxidized to CaSO settled/removed as sludge. Lower cost and simpler than other processes. Disadvantages abrasive/corrosive, plugging and scaling, poor dewatering of... 

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