Galvanizing equipment

The total annual loss of silver to the environment from industrial wastes has been estimated at > 2500 tons. Of this amount, about 150 tons were found in sewage sludge and about 80 tons in surface water. Processes are available for the recovery of Ag from photographic chemical residues, from amalgam wastes, and from galvanizing equipment (Petering and McClain... 

Zinc is also used extensively to galvanize other metals such as iron to prevent corrosion. Zinc oxide is a unique and very useful material for modern civilization. It is widely used in the manufacture of paints, rubber products, cosmetics, pharmaceuticals, floor coverings, plastics, printing inks, soap, storage batteries, textiles, electrical equipment, and other products. Lithopone, a mixture of zinc sulfide and barium sulfate, is an important pigment. 

Tungsten has Htde effect on recrystallization temperature or the high temperature properties of molybdenum. However, the Mo—30% W alloy is recognized as a standard commercial alloy for stirrers, pipes, and other equipment that is required to be in contact with molten zinc during processing of the metal and in galvanizing and die casting operations. 

Incorrect information can result if the probe is made of the wrong material and is not heat treated in the same way as the process equipment (as well as because of other problems). The probe must be as close as possible to the material from which the equipment of interest is made. Existence of a critical condition, such as weldments or galvanic couples or occluded cells in the eqmpment of concern, makes the fabrication, placement, and maintenance of the probes and monitoring system or critical importance, if accurate and useful data are to be obtained. 

Sufficient temperature differences between sites on the same component can cause a galvanic current flow. In these cases, the site with the higher temperature is usually the corrosion site (see Case History 16.3). Galvanic corrosion of this form can potentially affect heat exchangers and refrigeration equipment. 

The nature of galvanic corrosion is such that successful avoidance generally requires implementing preventive rather than corrective techniques. Therefore, consideration of galvanic corrosion problems must be integrated into the design of equipment. Corrective techniques applied to existing equipment can be expensive and less than satisfactory. 

In the food production and OTC (Over the Counter) Drug industries, like milk, soups, cough syrup, and juices, outside balanced seals are quite popular. Their design permits easy cleaning of the equipment without pump disassembly. These seals are prominent in the chemical processing industry because all metal components in the seal are located outside the fluid. This avoids problems of galvanic eorro.sion. 

Examples of the Design of Protective Installations 11.3.3.1 Equipment Using Galvanic Anodes... 

Tanks that are enamelled or that have other high-resistance coatings with volumes below 4 m do not require automatic exhausts if they are equipped with galvanic anodes in which the surface area does not exceed 5 dm per square meter of surface to be protected, or with controlled impressed current anodes with a low current output of 150 mA. 

Organic coatings are applied mainly to mild steel structures and equipment. They are also used on aluminum, zinc-sprayed and galvanized steel, but to a lesser extent. The applications for organic coatings can be divided into three areas corrosion by atmospheric pollution, protection from splash by process liquors, and linings for immersion in process liquors [70-74]. 

In areas where electrical equipment is exposed to contaminants, the selection of equipment whose contacts are oil-immersed or hermetically sealed can increase reliability and equipment life. Similarly, providing environmentally-controlled equipment rooms can greatly increase equipment life at locations where contaminants are prevalent. In offshore and other areas exposed to salt, type 316 stainless steel is often preferred over types 303 and 304, which will pit with time. Likewise, in similar locations, equipment fabricated from galvanized steel will corrode much more rapidly than equipment hot-dip galvanized after fabrication. 

Solar water heating declined in Southern California in the 1920s due to the development of natural gas, but it continued in Florida where natural gas was very expensive. In 1941 more than half Miami s population had solar water heaters, and more than 80 percent of new homes built then were equipped with solar water heaters. By the end of the 1950s in Florida, solar water heating was displaced by electricity as the price dropped and the storage tanks of solar water heaters failed because of galvanic corrosion from connecting steel tanks to copper collectors. 

Corrosion may take various forms and may combine other forms of damage (erosion, wear, fatigue, etc.) to cause equipment failure. The forms of corrosion most encountered in drilling equipment are uniform corrosion and galvanic corrosion. 

Sheet steel for ductwork, general air-conditioning components, and outdoor equipment is galvanized. 

Several items of pre-boiler equipment (and post-boiler equipment) may suffer from selective forms of galvanic corrosion. One fairly common... 

These galvanic corrosion processes take place when one or more elemental constituents of an alloy is leached, often leaving a weak, porous structure, although the component dimensions often are unchanged. Dealloying particularly affects equipment constructed of cupronickels, bronzes, brasses, and gunmetal, such as FW heaters, strainers, valves, and pump impellers. 

Liquid-Metal Corrosion Liquid metals can also cause corrosion failures. The most damaging are liquid metals which penetrate the metal along grain boundaries to cause catastrophic failure. Examples include mercury attack on aluminum alloys and attack of stainless steels by molten zinc or aluminum. A fairly common problem occurs when galvanized-structural-steel attachments are welded to stainless piping or equipment. In such cases it is mandatory to remove the galvanizing completely from the area which will be heated above 260°C (500°F). 

Galvanic corrosion is a frequent source of trouble on a large scale. Not only is the use of different metals in the same piece of equipment dangerous, but the effect of cold working may be sufficient to estabhsh potential differences of objectionable magnitude between different... 

The life of equipment subjected to corrosive environments can be increased by proper attention to design details. Equipment should be designed to drain freely and completely. The internal surfaces should be smooth and free from crevasses where corrosion products and other solids can accumulate. Butt joints should be used in preference to lap joints. The use of dissimilar metals in contact should be avoided, or care taken to ensure that they are effectively insulated to avoid galvanic corrosion. Fluid velocities and turbulence should be high enough to avoid the deposition of solids, but not so high as to cause erosion-corrosion. 

Certain ores or metals may contain traces of arsenic. If water or acid contacts these ores or metals, they may release small amounts of arsine gas. Arsine is widely used in manufacturing of fiberoptic equipment and computer microchips. It is sometimes used in galvanizing, soldering, etching, and lead plating. 

A variety of feeders are commercially available for rats and mice. These include various-sized glass jars and stainless steel or galvanized feed cups, which can be equipped with restraining lids and food followers to preclude significant losses of feed due to animals digging in the feeders. Slotted metal feeders are designed so that animals cannot climb into the feed, and they also contain mesh food followers to prevent digging. 

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