Storage tanks corrosion allowance

A storage tank for concentrated nitric acid will be constructed from aluminium to resist corrosion. The tank is to have an inside diameter of 6 m and a height of 17 m. The maximum liquid level in the tank will be at 16 m. Estimate the plate thickness required at the base of the tank. Take the allowable design stress for aluminium as 90 N/mm2. 

The V-03 is the equipment number. The type of equipment is a horizontal storage tank. It is used to store methanoi. The capacity is 20,000 gal (76 m3) and the size is 11 ft (3.35 m) in diameter by 31 ft (9.5 m) long. The tank is to be made of carbon steel and will not be insulated. It should be built to withstand a pressure of 10 psig (1.8 kg / cm2). Any vessel with a rating of under 15 psig (2 kg / cm2) is not considered a pressure vessel. No information is given on temperature or corrosion allowances because neither of these factors presents any special problem. The rate of corrosion... 

A spherical carbon-steel storage tank has an inside diameter of 30 ft. All joints are butt-welded with backing strip. If the tank is to be used at a working pressure of 30 psig and a temperature of 80°F, estimate the necessary wall thickness. No corrosion allowance is necessary. 

When the specified corrosion allowance is less than 1/8 in., the thickness must be adjusted accordingly. It must be noted that on flat bottom atmospheric storage tanks, the bottom and top thickness need not be more than 1/4 in. 

Water content varies from 0.5 to 1%. Water is introduced into residual fuels by poor storage. The standards allow water up to a maximum of 1% in residual fuels. However, the majority of fuel deliveries have water contents below 0.5%. The problems with high water levels in fuel can be complex and include sludging of fuel tanks, filter blockage, corrosion of fuel injection equipment, exhaust valve corrosion, etc. 

C. Storage and Transfer. Concentrated sulfuric acid up to about 99% H2SO4 can be handled in ordinary ferrous-metal equipment. The rate of corrosion reaches a minimum at about 96%. In 93% acid at about 50°C, the rate is 0.6-0.65 mm yr For a 10-year life, a corrosion allowance of 6.5 mm should be specified. Anodic protection can cut the rate of corrosion approximately in half and extend tank life, but it is not often used by chlor-alkali producers. Above 99% and 50°C, the corrosion rate of carbon steel is greater than 1.5mmyr , and stainless steel is often specified. 

Pamphlet 78 calls for the same sort of fabrication techniques recommended for pressurized storage. It also gives instructions for commissioning, inspection, and maintenance. It covers single-wall as well as double-wall tanks and horizontal as well as vertical or spherical tanks. The minimum design pressure for a single-wall tank should be about 175 kPa (25 psig). The corrosion allowance for the internal tank and connections usually is about 2 mm this should also apply to the external vessel when one of its functions is containment. 

The methyl isocyanate had escaped when a valve in the plant s underground storage tank broke under pressure and allowed water to enter and react with the organic compound. This caused a cloud of lethal gas to diffuse from the factory over Bhopal. The release was made worse because the hydrolysis reaction was catalysed by iron from corrosion of the stainless steel tank. 

Fig. 10.22 The influence of design factors on corrosion, (a) Storage tanks should be fabricated to allow complete drainage and access to outside surface for painting, (b) The insulation of cool pipe supports may prevent internal or external condensation of an electrolyte film. Insulation may prevent bimetallic corrosion tight insulation may prevent water ingress, (c) Full length, continuous welds are preferred to intermittent, tack ones. Slag and surface oxides must be removed prior to surface coating.

Slow evaporation (70 to 80°C) allowed storage of all the product in one tank. This slow evaporation was successful in controlling the corrosion due to chromium in the product. 

It is desirable and inherently safer to use fire-safe valves whenever it is necessary to isolate flammable or combustible fluids in a pipeline, tank, or other type of equipment. Fire-safe valves should be considered for handling most fluids that are highly flammable, highly toxic, or highly corrosive and that cannot be allowed to escape into the environment. Fire-safe valves should also be used to isolate reactors, storage vessels, and pipelines. They can be used wherever EBVs are required. 

Wet storage, alternating climate, and salt fog test are used to test for corrosion. The latter is typically applied when metallic accessories or inserts for plastics fuel containers are qualified. Alternating moisture tests allow sufficient swelling of the plastic containers and help detect any loosening of welded-on fixtures or potential corrosion on the metallic parts inside the tank [515],... 

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