Corrosion problem

There is a background of relevant knowledge arising from the nuclear power industry and the Energy Laboratory at the Massachusetts Institute of Technology (Boston) is a centre for supercritical water corrosion studies. A workshop on Corrosion in Supercritical Water Oxidation Systems was held in May 1993. A copy of the report subsequently produced is available from Professor Latanision at MIT. 

Gallagher, J.S. and Kell, G.S. (1984) NBSjNRC Steam Tables, Hemisphere, Washington. 

Franck, E.U. (1987) in High Pressure Chemistry and Biochemistry (eds R. van Eldik and J. Jonas), D. Reidel, New York, p. 93. 

Brunner, G. and Perrut, M. (eds) (1994) Proc. 3rd Int. Symp. on Supercritical Fluids, Institut National Polytechnique de Lorraine, Nancy. 

Penninger, J.M.L. and Kolmschate, J.M.M. (1988) in Supercritical Fluid Science and Technology ACS Symposium Series 406 (eds K.P. Johnston and J.M.L. Penninger), American Chemical Society, Washington DC, p. 242. 

---

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

Carbon dioxide (CO2) is a very common contaminant in hydrocarbon fluids, especially in gases and gas condensate, and is a source of corrosion problems. CO2 in the gas phase dissolves in any water present to form carbonic acid (H2CO3) which is highly corrosive. Its reaction with iron creates iron carbonate (FeCOg) ... 

The most common contaminants in produced gas are carbon dioxide (COj) and hydrogen sulphide (HjS). Both can combine with free water to cause corrosion and H2S is extremely toxic even in very small amounts (less than 0.01% volume can be fatal if inhaled). Because of the equipment required, extraction is performed onshore whenever possible, and providing gas is dehydrated, most pipeline corrosion problems can be avoided. However, if third party pipelines are used it may be necessary to perform some extraction on site prior to evacuation to meet pipeline owner specifications. Extraction of CO2 and H2S is normally performed by absorption in contact towers like those used for dehydration, though other solvents are used instead of glycol. 

The near drum corrosion problem is relatively newly identified in Scandinavia. This paper presents the experience from many years of inspections in North America. 

Corrosion problems are particularly important when two metals are in contact. The more reactive metal becomes the cathode of the cell and goes into solution when the cell is activated by an electrolyte. A typical cell is shown in Figure 13.7. When the metal in contact with iron is more reactive than iron itself, the iron is protected from corrosion. This is important when mechanical strength... 

The practical problems He ia the separatioa of the chlorine from the hydrogea chloride and nitrous gases. The dilute nitric acid must be reconcentrated and corrosion problems are severe. Suggested improvements iaclude oxidation of concentrated solutions of chlorides, eg, LiCl, by nitrates, followed by separation of chlorine from nitrosyl chloride by distillation at 135°C, or oxidation by a mixture of nitric and sulfuric acids, separating the... 

Because an excess of ammonia is fed to the reactor, and because the reactions ate reversible, ammonia and carbon dioxide exit the reactor along with the carbamate and urea. Several process variations have been developed to deal with the efficiency of the conversion and with serious corrosion problems. The three main types of ammonia handling ate once through, partial recycle, and total recycle. Urea plants having capacity up to 1800 t/d ate available. Most advances have dealt with reduction of energy requirements in the total recycle process. The economics of urea production ate most strongly influenced by the cost of the taw material ammonia. When the ammonia cost is representative of production cost in a new plant it can amount to more than 50% of urea cost. 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

The basic seed processing plant design is based on 70% removal of the sulfur contained in the coal used (Montana Rosebud), which satisfies NSPS requirements. Virtually complete sulfur removal appears to be feasible and can be considered as a design alternative to minimize potential corrosion problems related to sulfur in the gas. The estimated reduction in plant performance for complete removal is on the order of 1/4 percentage point. The size of the seed processing plant would have to be increased by roughly 40% but the corresponding additional cost appears tolerable. The constmction time for the 500 MW plant is estimated to be ca five years. 

Ma.rine. In the presence of an electrolyte, eg, seawater, aluminum and steel form a galvanic cell and corrosion takes place at the interface. Because the aluminum superstmcture is bolted to the steel bulkhead in a lap joint, crevice corrosion is masked and may remain uimoticed until replacement is required. By using transition-joint strips cut from explosion-welded clads, the corrosion problem can be eliminated. Because the transition is metaHurgicaHy bonded, there is no crevice in which the electrolyte can act and galvanic action caimot take place. Steel corrosion is confined to external surfaces where it can be detected easily and corrected by simple wire bmshing and painting. 

Other acids, eg, hydrochloric or nitric acid, are more seldom used because of higher costs and corrosion problems. 

Boron, in the form of boric acid, is used in the PWR primary system water to compensate for fuel consumption and to control reactor power (3). The concentration is varied over the fuel cycle. Small amounts of the isotope lithium-7 are added in the form of lithium hydroxide to increase pH and to reduce corrosion rates of primary system materials (4). Primary-side corrosion problems are much less than those encountered on the secondary side of the steam generators. 

The quantity of boric acid maintained in the reactor coolant is usually plant specific. In general, it ranges from ca 2000 ppm boron or less at the start of a fuel cycle to ca 0 ppm boron at the end. Most plants initially used 12-month fuel cycles, but have been extended to 18- and 24-month fuel cycles, exposing the materials of constmction of the fuel elements to longer operating times. Consequendy concern over corrosion problems has increased. 

Historically, ferrous sulfamate, Fe(NH2S02)2, was added to the HNO scmbbing solution in sufficient excess to ensure the destmction of nitrite ions and the resulting reduction of the Pu to the less extractable Pu . However, the sulfate ion is undesirable because sulfate complexes with the plutonium to compHcate the subsequent plutonium purification step, adds to corrosion problems, and as SO2 is an off-gas pollutant during any subsequent high temperature waste solidification operations. The associated ferric ion contributes significantly to the solidified waste volume. 

Ha/ogenation. Heats of reaction are highly exothermic for halogens, particularly fluorine (qv), and chain reactions can result in explosions over broad concentration ranges. Halogens also present severely challenging corrosion problems (see Corrosion and corrosion control). 

The monohalide vapors are conveyed to a slightly cooler zone (700—800°C) where the reaction reverses, resulting in the condensation of pure aluminum. The monochloride process was carried to the demonstration plant stage but was abandoned because of corrosion problems (24). 

Isopropyl Alcohol. Propylene may be easily hydrolyzed to isopropyl alcohol. Eady commercial processes involved the use of sulfuric acid in an indirect process (100). The disadvantage was the need to reconcentrate the sulfuric acid after hydrolysis. Direct catalytic hydration of propylene to 2-propanol followed commercialization of the sulfuric acid process and eliniinated the need for acid reconcentration, thus reducing corrosion problems, energy use, and air pollution by SO2 and organic sulfur compounds. Gas-phase hydration takes place over supported oxides of tungsten at 540 K and 25... 

C. S. Tedmon, Jr., Corrosion Problems in Energy Conversion Generators, Electrochemical Society, Princeton, N.J., 1974. 

The formation of acids from heteroatoms creates a corrosion problem. At the working temperatures, stainless steels are easily corroded by the acids. Even platinum and gold are not immune to corrosion. One solution is to add sodium hydroxide to the reactant mixture to neutralize the acids as they form. However, because the dielectric constant of water is low at the temperatures and pressure in use, the salts formed have low solubiHty at the supercritical temperatures and tend to precipitate and plug reaction tubes. Most hydrothermal processing is oxidation, and has been called supercritical water oxidation. 

Process air in sulfur-burning plants is dried by contacting it with 93—98 wt % sulfuric acid in a countercurrent packed tower. Dry process air is used to minimise sulfuric acid mist formation in downstream equipment, thus reducing corrosion problems and stack mist emissions. 

Both types of babbitt ate easily cast and can be bonded rigidly to cast iron, steel, and bton2e backiags. They perform satisfactorily when lubricated against a soft steel shaft, and occasional corrosion problems with lead babbitt can be corrected by increasing the tin content or shifting to high tin babbitt. 

Accelerator in Ready-Mix Concrete. Calcium chloride accelerates the set time of concrete giving it a high early strength development. It is not an antifreeze, but by using it duriag cold weather protection can proceed in a timely manner (31—34). In Russia, calcium chloride forms a component of several antifreeze admixtures (33). Reviews of the concerns and possible remedies of calcium chloride corrosion problems in concrete are available (21,35). There is no consensus on what the safe levels of calcium chloride in concrete are. 

The process is capable of achieving higher solubiHties of CO2 in the solution without the corrosion problems encountered with amine systems before the advent of Amine Guard. The Sulfinol process is used in over 50 plants worldwide nevertheless, it is used less often than the amine or carbonate processes. 

---