Corrosive scale

The heat-transfer quaUties of titanium are characterized by the coefficient of thermal conductivity. Even though the coefficient is low, heat transfer in service approaches that of admiralty brass (thermal conductivity seven times greater) because titanium s greater strength permits thinner-walled equipment, relative absence of corrosion scale, erosion—corrosion resistance that allows higher operating velocities, and the inherently passive film. 

While the ambient-temperature operation of membrane processes reduces scaling, membranes are much more susceptible not only to minute amounts of scaling or even dirt, but also to the presence of certain salts and other compounds that reduce their ability to separate salt from water. To reduce corrosion, scaling, and other problems, the water to be desalted is pretreated. The pretreatment consists of filtration, and may include removal of air (deaeration), removal of CO2 (decarbonation), and selective removal of scale-forming salts (softening). It also includes the addition of chemicals that allow operation without scale deposition, or which retard scale deposition or cause the precipitation of scale which does not adhere to soHd surfaces, and that prevent foam formation during the desalination process. 

The importance of being able to predict the effect of a specific gas analysis on the formation of the corrosive scale is essential in the prevention of blade failures. Again, competent manufacturers have successfully developed a means of achieving this through the application of modern computer programs. However, the gas analysis provided must be as accurate as possible if the program and calculations performed are to have any real value. 

Since competent manufacturers can accurately predict the susceptibility for the formation of the corrosive scale Ni3S2 for any gas analysis, it is possible to implement preventive measures. The preventive measure that is presently being used by Elliott and others is the use of a steam barrier. The principle of the steam barrier design is to inject steam into the inlet and exhaust chambers of the disc/blade area. The injection of steam into both these chambers creates a barrier of... 

Carryover of oils (e.g., compressor lube oils), brine, corrosion inhibitors, well treating chemicals sand, corrosion scales, etc., from inlet separator... 

Higher than design strain rates in service (> lO s ) can also cause disruption of the corrosion scale, leading to enhanced metal loss and corrosion-assisted cracking of the substrate "". Laboratory exposures show parabolic... 

The NACE corrosion scale is a visual rating of surface rusting from 0% to 100%. Most refiners, product pipeline companies, and marketers of fuel require an NACE surface rust rating of 5% or less. The NACE corrosion rating scale is outlined in TABLE 7-1. 

Chemical inhibitor. Any of a wide range of blended chemical formulations, sold with the benefit of technical services and other products, and designed for particular water treatment applications, to inhibit the occurrence of corrosion, scaling, fouling, or other disruptive processes. 

The analysis of corrosion scale or product may be done by wet chemical methods such as spectrophotometry or atomic absorption spectrophotometry in cases where the removal of corrosion scale is permitted, or by surface analytical techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, electron microprobe analysis, by energy dispersive X-ray analysis in the case of samples which need to be preserved. 

Electron probe microanalysis is also used in the analysis of corrosion scales, and the probe along with wavelength dispersive attachments can detect elements of the order of 0.01 wt %. 

Commercially available pipes differ from those used in the experiments in that the roughness of pipes in the market is not uniform and it is difficult to give a precise description of it. Equivalent roughness values for some commercial pipes are given in Table 8-3 as well as on the Moody chart. But it should be kept in mind that these values are for new pipes, and the relative roughness of pipes may increase with use as a result of corrosion, scale... 

The experiments have proved that membrane distillation can be applied for radioactive wastewater treatment. In one-stage installation the membrane retained all radionuclides and decontamination factors were higher than those obtained by other membrane methods. The distillate obtained in the process was pure water, which could be recycled or safely discharged into the environment. It seems the process can overcome various problems of evaporation such as corrosion, scaling, or foaming. There is no entrainment of droplets, which cause the contamination of condensate from thin-film evaporator. Operation at low evaporation temperature can decrease the volatility of some volatile nuclides present in the waste, such as tritium or some forms of iodine and ruthenium. The process is especially economic for the plants, which can utilize waste heat, e.g., plants operating in power and nuclear industry. 

The corrosion resistance of stainless steels and nickel-based alloys in aqueous solutions can often be increased by addition of chromium or aluminum. " Chromium protects the base metal from corrosion by forming an oxide layer at the surface. Chromium is also considered to be an important alloying metal for steels in MCFC applications. Chromium containing stainless steel, however, leads to the induced loss of electrolyte. Previous studies done to characterize the corrosion behavior of chromium in MCFC conditions have shown the formation of several lithium chromium oxides by reaction with the electrolyte. This corrosion process also results in increased ohmic loss because of the formation of scales on the steel. Aluminum additions similarly have a positive effect on corrosion resistance. " However, corrosion scales formed in aluminum containing alloys show low conductivity leading to a significant ohmic polarization loss. 

The nature of the corrosion scale is very important in deciding the corrosion resistance of the component. Surface modification or alloying alters the composition and complexity of the corrosion scales, which prevents further corrosion and outward diffusion of alloy components. Vossen et al. have shown the complex scale formation in the case of stainless steel and nickel-based alloys in comparison to pure metals.These scales are understood to cause transport problems to the outward diffusion of alloy components and thereby decrease the dissolution of the steel components. Therefore, any improvement to the corrosion resistant properties of the current collector has to come by way... 

The corrosion scales on the archaeological artefacts have been shown to consist primarily of siderite (FeC03) visible as large yellow-brownish crystals on the surface of some of the artefacts. Analysis of cross-sections of a few artefacts also showed that the inner corrosion layers consisted of siderite with some magnetite or maghemite. Importantly, only very low contents of sulfur were found, indicating that corrosion by sulfate-reducing bacteria is not a problem at this site. Siderite was also found on modern iron samples that had been exposed for a few years in the soil at Nydam. 

Ethylene glycol provides the best freezing-point and heat-transfer characteristics. However, the quality of the water it is mixed with and the high temperatures involved cause many problems that chemists must control. Water usually contains Ca Mg, Cl, S04, and dissolved O2. The engine and radiator are made of many metals, all of which can corrode. Corrosion is an oxidation process, so O2 must be removed. Acids produced also tend to dissolve away the metal. This corrosion scale reduces the heat transfer and, if the scale falls away, then these particles can bombard other sections of the metal and either remove more scale or "sand blast" away any inhibitor film and expose more metal to corrosion. These particles eventually plug up the radiator or wear out the water pump. 

CWT. [Drew Ind. Div.] Corrosion, scale inhibitor, slime preventives, and antifoams for cooling towers. 

Chromium obviously has an effect on the scale appearance, too. Compared to alloy Fe-A16-Cr2 alloy Fe-A16-Crl0 shows much lower corrosion rates and a thinner corrosion scale. The scale appearance, however, is similar to that found on Fe-A16-Crl() the scale consists of an external scale with some cracks and a multi-component subscale which adheres to the base metal. 

EPMA and XRD of the thicker hot salt corrosion scales, shows that the majority of the scale is rutile. Alumina is present as a discrete phase within the scale, but does not form a continuous layer. Further alumina is present as whiskers on the scale surface. Aluminium is also detected within the rutile rich regions, at a low level, inferring that it is either in solution or distributed as micro particles below the resolution of the SEM. 

Treatment of cooling water to combat corrosion, scale formation and biofouling can be achieved by a suitable programme. The cost may be high and for a modest cooling water system the cost may run into tens of thousands of pounds. 

There are a number of features in the design of cooling water plant that need attention in order to reduce or even eliminate the incidence of fouling. The extent of the individual mechanisms of particulate deposition, corrosion, scale formation and biofouling, will depend on the quality of the cooling water, the temperature and the material of construction. 

Fig. 10.11 Illustration of the possible scale phenomena as they pertain to membrane transport (a) Cross section of a corrosion free membrane, (b) membrane with porous corrosion scale, (c) membrane with cracked corrosion scale, (d) membrane with spalling corrosion scale, (e) membrane with continuous, dense corrosion scale...

Additionally, the corrosive nature of the syngas stream can have significant impacts on the mechanical and chemical stability of the membrane. Researchers have shown that a pure palladium membrane can develop a corrosion scale as thick as 35 microns after only 5 days of operation in the presence of 0.1%H2S-H2, making thin film palladium membrane technologies impractical in such an environment [91]. 

First, let us consider thin-film systems such as emulsions at interfaces. An emulsion is a quasi-stable suspension of fine drops of one liquid dispersed in another liquid. Emulsions, together with microemulsions, can be found in technology, and in almost every part of the petroleum production and recovery process in reservoirs, produced at wellheads, in many parts of the refining process, and in transportation pipelines [1-4]. Understanding the chemistry involved in the stabilization of emulsions and in crude oil emulsions in particular is important both for economic and environmental reasons. The presence of water in oil (w/o) and oil in water (o/w) results in several costly byproducts, such as corrosion, scale, and dissolved metals. Water-in-crude oil emulsions are responsible for the enormous increase in the viscosity of the crude oils produced in reservoirs. Transportation of the viscous crude oil through pipelines is difficult and adds to the cost of production of the oil. With increasing... 

Sulfite pulping chemical recovery consists of greater amounts of sulfite, hydrogen sulfide, and hydrochloric acid than those used in the Kraft process. Because of these corrosive species, the internal portions of the recovery boilers and the evaporators are generally constructed of reinforced plastics, type 316L stainless steel, type 317L stainless steel, or nickel-based alloys. To prevent pitting and crevice corrosion, scale build-up should be prevented, wet-dry zones should be avoided, and chloride concentration should be kept to a minimum. 

The most common failure modes of these pipes are uniform corrosion (both external and internal), graphitization, and pitting under unprotected corrosion scales. Loose tubercles may cause blockage of pipes. The corrosion control of loose particles is by the addition of corrosion inhibitors, which protect the inside pipe walls or internal lining of the pipe. Other protective linings are specialty cement mortars, epoxies, polyethylene, and polyurethane. 

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