Costs, corrosion control


Plastic Pumps for Corrosive Liquids. The main limitation is lower pressure and temperature capabiHties, although developments in new materials are likely to improve these limitations. If plain carbon steel or iron pump metallurgy is appHed for corrosive pumpage, the damage to shafts, impellers, casings, and other wetted parts can be quick and extensive, seriously affecting performance, efficiency, and reHabiHty (see Corrosion and CORROSIVE control). Although corrosive damage can be reduced upon the use of special alloys and/or metals, pump costs generally rise appreciably. For some appHcations, even a trace of metallic contamination caimot be tolerated. For these reasons, as weU as for extremely broad chemical resistance, a variety of polymer pump designs have been developed.  [c.297]

Once the MCLG is determined, EPA sets an enforceable standard. In most cases, the standard is a Maximum Contaminant Level (MCL), the maximum permissible level of a contaminant in water which is delivered to any user of a public water system. The MCL is set as close to the MCLG as feasible, which the Safe Drinking Water Act defines as the level that may be achieved with the use of the best available technology, treatment techniques, and other means which EPA finds are available(after examination for efficiency under field conditions and not solely under laboratory conditions) are available, taking cost into consideration. When there is no reliable method that is economically and technically feasible to measure a contaminant at particularly low concentrations, a Treatment Technique (TT) is set rather than an MCL. A treatment technique (TT) is an enforceable procedure or level of technological performance which public water systems must follow to ensure control of a contaminant. Examples of Treatment Technique rules are the Surface Water Treatment Rule (disinfection and filtration) and the Lead and Copper Rule (optimized corrosion control). After determining a MCL or TT based on affordable technology for large systems, EPA must complete an economic analysis to determine whether the benefits of that standard justify the costs. If not, EPA may adjust the MCL for a particular class or group of systems to a level that "maximizes health risk reduction benefits at a cost that is justified by the benefits."  [c.14]

Thorough assessment of the service environment and a review of options for corrosion control must be made. In severe, humid environments it is sometimes more economical to use a relatively cheap structural material and apply additional protection, rather than use costly corrosion-resistant ones. In relatively dry environments many materials can be used without special protection, even when pollutants are present.  [c.20]

When corrosion rates are mainly dependent on diffusion, especially of dissolved oxygen, carbon dioxide and/or hydrogen ions in weak acid solutions, then it is possible to relate corrosion rates in terms of hydrodynamic parameters, i.e. erosion corrosion. This makes corrosion allowance in design, at the drawing-board stage, a possibility. Engineers, who already carry out similar calculations to estimate the dimensions of pipelines and other flow systems, can use these concepts to predict erosion rates. Such calculations could be used as a guide to selection of materials or inhibitor type when more realistic estimations are made of the rate of corrosion damage. Thus, effective corrosion control might therefore be achieved by a larger pipe size, longer bends, more sophisticated tee junctions, and slower pump speeds as an alternative to the more formal methods of corrosion control which generally are more costly.  [c.317]

The direct chlorination reaction is very exothermic (Ai/ = —180 kJ/mol for eq. 1, Ref. 83) and requites heat removal for temperature control. Eady direct chlorination reactors were operated at moderate temperatures of 50—65°C to take advantage of lower by-product formation, and utilized conventional water cooling for heat removal. As energy costs became more significant, various schemes for recovering the heat of reaction were devised. A widely used method involves operating the reactor at the boiling point of EDC, allowing the pure product to vaporize, and then either recovering heat from the condensing vapor, or replacing one or more EDC fractionation column reboders with the reactor itself (84—86). An alternative method entails operation of the reactor at higher pressure to raise the boiling point of EDC in this case, the reactor operates without boiling, but at higher temperatures (75—200°C) to allow more efficient heat transfer to some other part of the process (87,88). For reactors equipped with Hquid product removal, the EDC is usually treated to remove ferric chloride. The latter, which would lead to rapid fouling of the EDC cracking reactor, can be removed by washing with water or by adsorption on a soHd. With dry feedstocks (<10 ppm water) and good temperature control, carbon steel can be used in direct chlorination reactors operating at low temperature and in auxiHary equipment. Higher temperature operation generally requites materials that are more resistant to erosion—corrosion in the reactor, eg, hard alloy cladding below the Hquid level and nickel alloy feed spargers.  [c.417]

The overall efficiency of electric power plants consisting of coal-fired boilers and steam turbines has plateaued at about 39%. The addition of pollutant control equipment has increased the internal power use on the stations and lowered the effective efficiency of the plant. The increased efficiencies have been achieved through use of larger units (up to 1500 MW) and higher pressures to 24.1 MPa (3500 psi) and reheat, but concerns about rehabdity and ability to match power generation and demand have kept plant sizes below these values. Maximum temperatures have not been increased because of the difficulties of corrosion owing to coal ash constituents, materials properties, and costs of better alloys. The advent of any future increases in efficiency depends on development of new systems of power generation, which might include fluid-bed boilers, gasification of coal to power a gas turbine having hot exhaust directed to a waste heat boiler in a combined cycle (gas turbine and steam turbine), or use of magnetohydrodynamics (qv) (see Furnaces, FUEL-FIRED).  [c.234]

Use of coil-coated stock reduces fire risk and hence iasurance costs for the metal fabricator. The problem of controlling VOC emissions is also avoided because no coating is done ia the factory. VOC emission control problems for the cod coater are minimal. The oven exhaust is used for the air needed for the gas heaters for the oven. In other words, the organic solvents are used as fuel rather than being allowed to escape iato the atmosphere. Film thickness of the coatings is more uniform than can be appHed by spray, dip, or bmsh coating of the final product. The coatings are all baked coatings, and when cod-coated metal is used, substantially greater exterior durabdity and corrosion protection can be achieved as compared with field-appHed air-dry coatings.  [c.355]

For Watts baths, nickel sulfate provides most of the nickel ion, (see Nickel compounds). Nickel chloride aids in anode corrosion, conductivity, and throwing power, but increases tensile stress. Boric acid is a buffer that works principally in the cathode film. It reduces burning and pitting, allows the use of higher currents, and contributes to smoother, more ductile deposits. Common impurities that affect nickel baths include iron, copper, zinc, chromium, and lead. Treatments and some additives for removal or control of these have been developed so that nickel plating baths can be used for many years with proper attention. When making up a new bath, it is often necessary to purify the solution before it can be used. Typically, high pH, 5.0—5.2, and activated carbon treatments are used along with several hours of low current density (LCD) electrolysis. Iron is removed by high pH precipitation, or sometimes complexed with citrates or gluconates. Anode efficiency is higher than cathode efficiency, and using closed loop systems, nickel ion builds up and eventually solution has to be withdrawn. Several methods are available for recovery of nickel from waste streams, or it is easily precipitated as the hydroxide sludge. Costs are becoming more favorable to recover the nickel.  [c.161]

Biological corrosion and deposition may be prevented by chemical treatment, system operation, and system design. Economics alone often favor chemical treatment. However, costs can usually be further reduced by appropriate system design and operation. Water treatment using chlorine, bromine, ozone, or other chemicals can control almost any biological problem. However, discharge limitations, associated corrosion, and other problems often restrict chemical use. Shocking with massive amounts of biocides may be effective in treating some systems, but not all systems will respond identically. Shocking heavily fouled systems may produce sloughing of large biological mats that plug components. After shocking, bacterial growth may be rapid, and the system can return to its previous state quickly. It is imperative that biological control not be erratic. It is much easier and decidedly less costly to maintain good control than to bring a seriously troubled system back into control.  [c.145]

Corrosion occurs in various forms and is promoted by a variety of causes, all related to process operating conditions. It is a continuous problem that can lead to contaminated process streams which leads to poor product quality and unscheduled equipment shutdowns, which leads to reduced production, and high maintenance and equipment replacement costs. Minimizing corrosion is a key consideration for the designer and can be accomplished in two ways (1) proper material selection for apparatus, and (2) preventive maintenance practices. Both these approaches must be examined by the designer. This chapter reviews principles of corrosion causes and control. It is important to recognize conditions that promote rapid material degradation to compensate for corrosion in designing.  [c.13]

Planned maintenance or regular replacement of plant equipment to avoid failure by corrosion, etc. is an essential adjunct to design, and constitutes the third phase of control. The design philosophy determines the emphasis placed on controlling corrosion by this means, as opposed to spending additional capital at the construction stage to prevent corrosion taking place at all. Where maintenance labour costs are high or spares may be difficult to procure, a policy of relying heavily on planned maintenance should be avoided.  [c.14]

Even with all these checks on design, fabrication and construction, errors are made which, with maloperation and changes in process conditions during the lifetime of the plant, can all lead to corrosion. The fourth phase of control therefore lies in monitoring the plant for corrosion in critical areas. Corrosion monitors should be regarded as part of plant instrumentation and located in areas of high corrosion risk or where corrosion damage could be particularly hazardous or costly. Monitoring should include a schedule of inspections once the plant is commissioned.  [c.14]

Deposit control is important because porous deposits, under the influence of heat flux, can induce the development of high concentrations of boiler water solutes far above their normally beneficial bulk values with correspondingly increased corrosion rates. This becomes an increasingly important feature with increase in boiler saturation temperature. In addition, deposits can cause overheating owing to loss of heat transfer. Finally, carryover of boiler water solutes, which can be either mechanical or chemical, can lead to consequential corrosion in the circuit, either on-load or off-load. Material so transported can result in corrosion reactions far from its point of origin, with costly penalties. It is therefore preferably dealt with by a policy of prevention rather than cure.  [c.832]

Fouling organisms attach themselves to the underwater portions of ships and have a severe impact on operating costs. They can increase fuel consumption and decrease ship speed by more than 20%. Warships are particularly concerned about the loss of speed and maneuverabiHty caused by fouling. Because fouling is controUed best by use of antifouHng paints, it is important that these paints be compatible with the system used for corrosion control and become a part of the total corrosion control strategy.  [c.363]

Significant savings can be achieved by optimum material selection (guidance is given in Section 53.3), by considering corrosion at the design stage (Section 53.4), by employing corrosion-control techniques (Section 53.7) and corrosion monitoring (Section 53.8). In the industrialized countries of the Western world, corrosion is estimated to cost some 4 per cent of a country s GNP. This represents 6 billion per annum, of which a significant proportion could be saved by the use of existing knowledge. It cannot all be saved, since the gradual deterioration of a plant over its operational life is one of the costs incurred in the process.  [c.896]

With metals used as construction materials corrosion control may be regarded as the regulation of the reaction so that the physical and mechanical properties of the metal are preserved during the anticipated life of the structure or the component. In relation to the term anticipated life it should be noted that this cannot be precise, and although the designer might be told on the basis of information available at that time that the plant should last, say, 10 years, it might be scrapped much earlier or be required to give more prolonged service. It is also evident that, providing there are no restrictions on costs, it is not difficult to design a plant to last at least 10 years, but quite impossible to design one that will last exactly 10 years. Thus although underdesign could be catastrophic, over-design could be unnecessarily expensive, and it is the difficult task of the corrosion engineer to avoid either of these two extremes. A further factor that has to be considered is that in the processing of foodstuffs and certain chemicals, contamination of the environment by traces of corrosion products is far more significant than the effect of corrosion on the structural properties of the metal, and under these circumstances the materials selected must be highly resistant to corrosion.  [c.1454]

There are some disadvantages to wet precipitators. Water can enhance latent corrosion problems and require the utilisation of expensive alloy constmction instead of the carbon steel often used in a dry precipitator. Some wet precipitators using plastic components have been developed to lower costs in corrosive situations. Additionally, the collection of pollutants in aqueous media may create water treatment and waste handling problems which can equal the cost and complexity of the precipitator installation itself. Spray rate and distribution can be critical in a wet precipitator and must be carefully apphed so as not to restrict operating voltage. Recirculated spray water may become supersaturated with low solubiUty compounds which plate out on surfaces or build up in critical parts of the precipitator. Recirculated suspended soHds can erode or plug spray no22les. Wet precipitators have been most useful in treating mixtures of gaseous and submicrometer particulates such as aluminum pot line and carbon anode baking fumes, fiberglass fume control, coke oven and metallurgical fumes, and phosphate fertili2er emissions.  [c.402]

Cartridge Filters Cartridge filters are used in a multitude of solid-liquid filtration applications ranging from laboratory scale operations to industrial flows in excess of 5,000 gpm. These units are typically operated in the countercurrent mode. Common configurations consist of a series of thin metal disks that are 3 to 10 inches in diameter, set in a vertical stack with very narrow uniform spaces between them. The disks are supported on a vertical hollow shaft, and fit into a closed cylindrical casing. Liquid is fed to the casing under pressure, whence it flows inward between the disks to openings in the central shaft and out through the top of the casing. Solid particles are captured between the disks and remain on the filter media. Since most of the solids are removed at the periphery of the disks, the unit is referred to as an edge filter. The accumulated solids are periodically removed from the cartridge. As with any filter, careful media selection is critical. Media that are too coarse, for example, will not provide the needed protection. However, specifying finer media than necessary can add substantially to both equipment and operating costs. Factors to be considered in media selection include the solids loading, the nature and properties of the particles, particle size, shape and size distribution, the amount of solids to be filtered, fluid viscosity, slurry corrosiveness, abrasiveness, adhesive qualities, liquid temperature, and flowrate. Typical filter media are wire mesh (typically 10 to 700 mesh), fabric (30 mesh - 1 /i), slotted screens (10 mesh to 25 fi) and perforated stainless steel screens (10 to 30 mesh). Multiple filters are also common, consisting of two or more single filter units valved in parallel to common headers. The distinguishing feature of these filters is the ability to sequentially backwash each unit in place while the others remain on stream. Hence, these systems are continuous filters. These units can be fully automated to eliminate manual backwashing. Backwashing can be eontrolled by changes in differential pressure between the inlet and outlet headers. One possible arrangement consists of a controller and solenoid valves that supply air signals to pneumatic valve actuators on each individual filter unit. As solids eollect on the filter elements, flow resistance increases. This increases the pressure differential across the elements and, thus, between the inlet and outlet headers on the system. When the pressure drop reaches a preset level, an adjustable differential pressure switch relays information through a programmer to a set of solenoid valves, which in turn sends a signal to the valve actuator. This rotates the necessary valve(s) to backwash the first filter element. When the first element is cleaned and back on stream, each successive filter element  [c.359]

This system is called wet NO control. Water or steam is injected into the primary combustion zone. This method has been used ef fectively in the past. Current installations are using this system when the water or steam is readily available or if they are already part of the process. Maintenance costs are higher when compared with dry control, because this method requires high quality water. If high quality water is not used, the corrosion associated with dissolved minerals in the water may prematurely damage the turbine.  [c.491]

The ever-increasing research into corrosion, and the knowledge that this produces is driven to a small part by the corrosion scientist him- or her-self in seeking a detailed understanding of the intricacies of the interfacial processes driving corrosion and passivation. Such a self-fulfilling drive cannot of itself however, be indefinitely sustainable, despite the fascination that this science engenders, since research is costly. Such advances are led primarily by the continuing need to predict, control and prevent corrosion as an engineering imperative. Corrosion science, multidisciplinary in itself, is probably unique in crossing the borders of almost all the technologies environmental stability of all components of those technologies remains a prime requirement for their success. New technologies, new engineering practices, new materials and new processes can succeed only if the behaviour of their components with the environment is satisfactory, and predictably so. The eighties and nineties, and beyond, see a further need to underpin research and development into corrosion and protection - the growing awareness of the necessity for conservation, of materials and of energy, the so-called green issues. Most materials and components made from them require large energy resources to produce clearly the quest for longevity and reliability of structures is a significant and worthy contribution towards conserving energy and materials, quite additional to minimising the heavy cost of corrosion failures.  [c.1404]

The broad principles of design that should be followed in order to effectively and economically control corrosion in marine and offshore engineering should also be subject to the overriding necessity to regard designing against corrosion as an integral part of the total planning and costing procedure which should be continuously followed at all stages from the initial plans to the finished construction. Failure to do so is likely to result in breakdown of plant (with consequential losses), costly maintenance or modifications in design (if these are practicable) and a possible reduction of safety factors. An attempt to design against corrosion as an afterthought is generally unsatisfactory, costly and often impractical.  [c.66]

Economically the installation of anodic protection is often very good. The advantages include a reducton in capital investment, lower maintenance and replacement costs and an improvement in the product quantity and value. The use of a potentiostat and its associated equipment involves a high installation cost but low operating costs, because only very small current densities are required to maintain passivity. In some circumstances the passive condition may persist for several hours after the current has been switched off. If this is the situation it is possible to use a relatively inexpensive switching mechanism with one control and power-supply system to anodically protect three separate tanks, and therefore reduced the high initial cost. Four storage vessels, volume 160 m , containing aqueous ammonia have been protected simultaneously by one system by switching the current on for 2 min and off for 6 min. The rate of corrosion with this technique decreased from about 0186mmy" to less than 0-001 mmy . It can be seen from Table 10.38 that it is more economical to anodically protect mild steel than to use mild steel with a p.v.c. lining or to use a more resistant and expensive metal or alloy such as aluminium or stainless steel. It is worth noting that because most of the expense of an anodic-protection system is due to the cost of the potentiostat, it is more economical per unit volume to use a larger instrument and a bigger tank.  [c.272]


Corrosion, Volume 2 (2000) -- [ c.2 ]