Process units carbonate corrosion

On older process units, you may still encounter piping with sentry holes. Let s say I have a Vfc-in thick pipe. The corrosion allowance for the pipe is Vi in. A number of small holes are drilled into the pipe, to a depth of in. When we start leaking at these small holes, this means that the pipe has corroded to its discard thickness in the area of the sentry hole. Incidentally, you can stop the resulting leak, at least in carbon steel water lines, with a brass wood screw and a screwdriver. I have also done this on hydrocarbon lines under an 80 psig pressure, but perhaps that is not too smart. 

Shortening units are constructed of carbon steel. The water phase in margarine is corrosive, and sanitation procedures require that all of the equipment used to manufacture it must be chemically cleaned. Margarine processing units contain chromium-plated commercially pure nickel heat transfer tubes and stainless steel for all product-contacted metal surfaces. 

Corrosion problems on process units often first show up as weld leaks. More precisely, the failures occur in the heat-affected zone adjacent to the weld. The welding procedure lowers corrosion resistance at the metal grain boundaries in the heat-affected zone. Stress relieving and improved welding techniques will not necessarily mitigate the problem. Use of low-carbon steels or Type 321 stainless (contains titanium) and Type 347 stainless (contains columbium) for replacement piping subject to frequent weld leaks will minimize the rate of failure. 

This input to design refers to the long-term stability of the raw material sources for the plant. It is only of importance where the raw materials can or do contain impurities which can have profound effects on the corrosivity of the process. Just as the design should cater not only for the norm of operation but for the extremes, so it is pertinent to question the assumptions made about raw material purity. Crude oil (where HjS, mercaptan sulphur and napthenic acid contents determine the corrosivity of the distillation process) and phosphate rock (chloride, silica and fluoride determine the corrosivity of phosphoric acid) are very pertinent examples. Thus, crude-oil units intended to process low-sulphur crudes , and therefore designed on a basis of carbon-steel equipment, experience serious corrosion problems when only higher sulphur crudes are economically available and must be processed. 

Low levels of resistance have been reported for some populations of Indian meal moth, almond moth, and red flour beetle populations in stored peanuts in the southeastern United States (Zettler et al., 1989), but no assessments are available for phosphine resistance in insect populations in mills, warehouses, processing plants, and other structural facilities. Phosphine can be corrosive to metals, particularly copper, electrical wiring, and electronic equipment (Bond et al., 1984), which limits its application in food processing facilities and warehouses. A new formulation of phosphine, in which phosphine gas is combined with carbon dioxide and released from a cylinder, alleviates some but not all of the corrosive effects of phosphine and is labeled for use as a structural treatment. 

Chlorination of natural rubber (NR) is carried out with chlorine in carbon tetrachloride solution at 60-90°C to yield a chlorinated rubber containing about 65% chlorine, which corresponds to 3.5 chlorine atoms per repeat unit. The process is complex and includes chlorine addition to the double bond, substitution at allylic positions, and cyclization. Chlorinated rubber has high moisture resistance and is resistant to most aqueous reagents (including mineral acids and bases). It is used in chemical- and corrosion-resistant paints, printing inks, and textile coatings. Bromination of butyl rubber is also practiced [Parent et al., 2002]. 

There are many options for barrel material construction with most extruder barrel designed to withstand up to at least 10,000 psi (69 MPa) internal pressures higher pressure units [30,000 psi (210 MPa)] are manufactured for the injection molding processes since they operate at higher pressures. They have a minimum safety burst pressure of at least 50,000 psi (350 MPa). The need for corrosion and/or wear protection, cost, repair, or their combinations may determine the choice of materials. They can be made from a solid piece of metal. The most common material is carbon steel.6... 

Figure 1.12 Comparison of sulfur levels vs carbon steel corrosion rates.9 Petroleum Refining Process Corrosion, Crude Fractionation Units, and Utilities 21...

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