Protective gas blanket

Regulators may be used in gas blanketing systems to maintain a protective environment above anv liquid stored in a tank or vessel as the liquid is pumped out. When the temperature of the vessel is suddenly cooled, the regulator maintains the tank pressure and protects the waUs of the tank from possible collapse. Regulators are known for their fast dynamic response. The absence of time delay that often comes with more sophisticated control systems makes the regulator useful in applications requiring fast corrective action. 

Where process, safety, and environmental considerations permit, vacuum protection may be provided by properly sized ever-open vents. Alternatively, active protective devices and systems are required. Vacuum breaker valves designed to open and admit air at a predetermined vacuum in the vessel are commonly used on storage tanks, but may not be suitable for some applications involving flammable liquids. Inert gas blanketing systems may be used if adequate capacity and reliability can be ensured. Where the source of the vacuum can be deenergized or isolated, suitably reliable safety instrumented systems (e.g, interlocks) can be provided. 

A final aspect of GPC solvent delivery relates to the solvent reservoirs themselves. The ability to perform in situ helium degassing of solvents, provide inert gas blankets over solvents, and protect solvents from contamination from external sources are worth consideration from the standpoints of convenience and safety alone. If these features are provided for, it is a small step to also provide a small positive pressure, say 10 psi or so, to the solvent reservoir. This positive pressure helps minimize the formation of solvent vapors in the pump chamber during the refill part of the pump stroke, and improves the flow rate reproducibility of rapid-refill type pumps delivering high-vapor-pressure solvents. 

To prevent oxidation of substances on the layer, protective measures must be taken even before the samples are applied. Using the CAMAG Linomat IV with inert gas blanket, nitrogen (for example) can be applied before and during application of the sample. To develop thin-layer chromatograms with exclusion of O2, the chamber is purged with CO2 if the substances are not affected by this gas, or alternatively with N2. For this, a lid fitted with a tube with a double-valve gas supply system is useful [20, p.69]. 

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. 

Zinc carboxylates have considerably increased catalytic ability as compared with cadmium. This extends in a positive sense to promotion of the costabilizing effects of phosphites and epoxidized oils, and to need for lower levels (also from its lower atomic weight). Thus, the overall amount of Zn in a liquid stabilizer is likely to be in the range of 1-2 percent, whereas Ba/Cd and Ba/Cd/Zn liquids used Cd levels often reaching 5-10 percent. The associated disadvantages of Zinc versus cadmium are an increased tendency to fail catastrophically instead of gradually, referred to as zinc bum. In addition, zinc salts catalyze hydrolysis of phosphites and promote condensation of the chlorohydrin products of the reaction of ESO with HCl, as well as the development of chromophores from the oxidation of antioxidants. As a result, Ba/Zn and Ca/Zn liquids must be protected from moist air. Some users employ inert gas blankets over liquid stabilizer tanks. 

Gas blanket A protective environment formed by an inert gas surrounding the surface. 

Nickel—beryllium casting alloys are readily air melted, in electric or induction furnaces. Melt surface protection is suppHed by a blanket of argon gas or an alumina-base slag cover. Furnace linings or cmcibles of magnesia are preferred, with zirconium siUcate or mullite also adequate. Sand, investment, ceramic, and permanent mold materials are appropriate for these alloys. Beryllium ia the composition is an effective deoxidizer and scavenger of sulfur and nitrogen. 

Many austenitic stainless steels have failed during downtime because the piping or tubes were not protected from chlorides. A good precaution is to blanket austenitic stainless steel piping and tubing during downtime with an inert gas (nitrogen). 

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