Oxygen content, pipeline

Soft waters attack pipeline materials and cause extensive leakage in many drinking water pipe systems. In this connection it has been recommended that the ratio between the concentration of bicarbonate HCO3 and the concentration of SO/ and Cr, respectively (in mg/1) should be higher than 1. The pH value should be between 7.4 and 8.3, the oxygen content about 6 mg/1, and the water velocity > 0.5 m/s. The bicarbonate content should normally be increased to 50-60 mg/1, e.g. by addition of CO2 and calcium compounds. 

If inert gas is available on site, gas blanketing of solvents stored within their explosive range is usually justifiable. Solvents such as toluene, heptane, isopropanol and ethyl acetate fall into this classification. Air with its oxygen content reduced to below 10% win not support combustion but it is normal practice to err on the safe side and use 2-3% oxygen for tank blanketing and clearing pipelines. Solvents which are particularly prone to form peroxides, e.g. THF, must be protected by pure nitrogen if they have to be stored uninhibited. 

A metal pipeline was unlikely to be satisfactory in this application. Cast iron would be expected to last perhaps 20-30 years, whereas the design life was to be 50 years. It would be subject to internal attack from the effluent and external attack from the sea water. Protection against this type of corrosion would be difficult. Similar objections apply to use of mild steel, where again predictable protection would be difficult to achieve mild steel would also suffer rapid internal corrosion. A suitable grade of stainless steel could probably be selected to resist internal attack by the effluent but the problem of external corrosion would remain. Stainless steel is subject to corrosion pitting in sea water, especially when the oxygen content is low. In quiet water the rate of pitting can be 6.9 mm per year. 

Another example is the very useful flow diagram proposed by Krooneman et al. for the assessment and reducing the risk of MIC in pipelines [6], In this simple yet very clever flow diagram, the possibility of different factors leading to the risk of MIC is addressed. Some of these factors are oxygen content, pH, sulphate content, total organic carbon content, salt concentration and temperature. While the model is certainly a useful tool, it does not consider, for example, the possible effect of thermophilic corrosive bacteria, or the risk of corrosion when the tenperature is above 40°C. This model may not be useful in assessing MIC in, say, geo-thermal power plants [7]. 

Suppose, a pipeline is buried in a completely uniform soil and that some areas of the line have a free supply of oxygen and other areas have a restricted supply. The part of the pipe buried in the soil with a free supply of oxygen (high oxygen content) would form the cathode and the part with a less supply of oxygen or poorly aerated forms that anode (Fig. 5.5). The current (Fe ions) would flow in the soil from anode to cathode resulting in the corrosion of the pipe end buried in poorly aerated soil. Such a cell is commonly called a differential aeration cell... 

The butanols and their methyl and ethyl ethers have several advantages as oxygenates over methanol and ethanol in gasoline blends. Their energy contents are closer to those of gasoline the compatibility and miscibility problems with petroleum fuels are nil excessive vapor pressure and volatility problems do not occur and they are water tolerant and can be transported in gasoline blends by pipeline without danger of phase separation due to moisture absorption. Fermentation processes (Weizmann process) have been developed for simultaneous production of 1-butanol, 2-propanol, acetone, and ethanol from... 

The escape of natural gas from the gas distribution networks also exerts a considerable effect on physical, chemical and biological processes in the soil. The extent of the gas zone depends greatly on the rate of its escape, depth of the groundwater level, type of pipeline, the nature and moisture of the soil, treatment of its surface, etc. The composition of the gaseous phase in the soil is affected by the microbiological oxidation of methane. The rate of this depends on the soil temperature, presence of oxygen and the content of nutrients. At low temperatures, this microbial process is restricted, which also restricts the anaerobic zone. 

It is important to control the surface area of manganese sulfide inclusions. During the rolling process for pipeline manufacture, for example, these inclusions get flattened to form platelets. This ino-eases the available surface area for hydrogen adsorption and therefore increases material susceptibility to HIC. One way to control this is the addition of calcium to ladle steel. Calcium reduces the oxygen and sulfur content of the steel. Calcium also results in the spheroidization of sulfide inclusions, thereby decreasing the available surface area for adsorption of atomic hydrogen. 

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