Acid Storage Department Editor: Kate Torzewski
Chemical Engineering
Most common acids can be stored in horizontal or vertical ASME-type tanks, as shown in the figures to the right, or vertical API-type tanks. Horizontal, carbon-steel ASME-type tanks of 10,000—40,000 gal capacity should have a plate thickness of 3/8 in. with dished heads of the same thickness. The thickness includes a corrosion allowance of 1/4 in., which provides a tank life of 15—20 years.
Sulfuric acid (H2SO4)
Storage
This acid is prone to enter into reactions that generate hydrogen, so in addition to keeping the vessel vented adequately, exclude potential sources of ignition from the vicinity.
Materials of construction
Carbon steel is satisfactory for concentrated technical grades of sulfuric acid at normal atmospheric temperature. H2SO4 solutions that are more dilute corrode carbon steel severely. To avoid inadvertent dilution of concentrated acid, keep acid away from contact with moist air.
Polyvinyl chloride pipe is recommended for ordinary sulfuric acid, but for oleum, Type 316 stainless steel or carbon-steel lined with a fluorocarbon is best.
Storage
This acid is prone to enter into reactions that generate hydrogen, so in addition to keeping the vessel vented adequately, exclude potential sources of ignition from the vicinity.
Materials of construction
Carbon steel is satisfactory for concentrated technical grades of sulfuric acid at normal atmospheric temperature. H2SO4 solutions that are more dilute corrode carbon steel severely. To avoid inadvertent dilution of concentrated acid, keep acid away from contact with moist air.
Polyvinyl chloride pipe is recommended for ordinary sulfuric acid, but for oleum, Type 316 stainless steel or carbon-steel lined with a fluorocarbon is best.
Phosphoric acid (H3PO4)
Storage
The tank bottom should be rolled to a height of 3 in. (upward). This allows welds to freely expand or contract. Corner welds should be avoided, as undue stresses can occur and aggravate corrosion [2].
Depending on the acid grade, the freezing point varies and may necessitate heating to avoid freeze-up in storage. In any case, to avoid corrosion, high-pressure steam should not be used; steam coils located several inches below the bottom of the tank are recommended. The space below the tank bottom should be enclosed to permit heating of the air to 50˚C, and the tank walls should be insulated.
Materials of construction
Tanks can be fabricated of Type 316 extra-low-carbon stainless steel, rubber--lined carbon steel or fiberglass-reinforced plastic. Carbon steel should not be used, as it will corrode.
Hydrochloric acid (HCl)
Storage
HCl of all strengths should be stored in tanks similar to those mentioned above. Containment areas should be provided around tanks, and storage facilities should include a pressure (and vacuum) relief service, primary and redundant level indicators, a high-level alarm, an overflow line, an emergency block valve at the tank outlet nozzle and a vent-fume scrubber.
Materials of construction
These storage tanks should be fabricated of rubber-lined carbon steel, glass-lined carbon steel or fiber-reinforced polymer (FRP). Soft natural-rubber compounds are used as liners for concentrated acid storage tanks at temperatures up to 60˚C with a minimum lining thickness of 3/16 in. Semi-hard rubber is used for lining equipment and piping for acid up to 70˚C with FRP tanks of vinyl-ester resin.
Nitric acid (HNO3)
Storage
Storage tanks for HNO3 of less than 95 wt.% concentration should be designed for at least a slight pressure and vacuum, permitting the venting of nitrogenoxide fumes to collection and disposal equipment, such as a scrubber or a flare.
When locating the tank vent and overflow pipe, consider that escaping vapors and liquid can corrode exterior welds as the acid is diluted with atmospheric moisture.
Materials of construction
For concentrations up to 95 wt.% at ambient temperature, storage units should be fabricated of Type 304L stainless steel. For concentrations of 95 wt.% and above, Type 3003 aluminum alloy should be used. Acid in the range of 52–55 wt.% should be stored in tanks of Type 347 stainless steel using No. 12 gage sheet. Above 90 wt.%, corrosion allowance in the tank-wall thickness may be necessary. Glass-lined carbon steel tanks are satisfactory for all acid grades.
Hydrofluoric acid (HF)
Storage
Because of anhydrous HF’s high vapor pressure, tanks are designed for a minimum pressure of 60 psig and have X-rayed and stress-relieved welds. Tanks holding 70 wt.% HF are also designed per ASME code, or for lower pressure, as its vapor pressure is much lower than that of anhydrous HF. These tanks should be equipped with a relief device, and discharge piping should be routed to a scrubber. Aqueous HF tanks should have a vent, with the vent line also going to the scrubber.
Materials of construction
Carbon-steel storage tanks can be used for anhydrous HF at temperatures up to 66˚C and 70 wt.% HF. Acid of concentrations greater than 60 wt.% may be handled in steel up to a temperature of 38˚C. In steel tanks, hydrogen blistering may be caused by the accumulation of H2, so periodic tank inspections are required to evaluate blistering.
References
1. Grossel, S., Safe Efficient Handling of Acids, Chem. Eng. December 1998, pp. 104–112.
2. Anon., Phosphoric Acid, Rhone-Poulene Basic Chemicals Co., Shelton, Conn. (1992).
Storage
The tank bottom should be rolled to a height of 3 in. (upward). This allows welds to freely expand or contract. Corner welds should be avoided, as undue stresses can occur and aggravate corrosion [2].
Depending on the acid grade, the freezing point varies and may necessitate heating to avoid freeze-up in storage. In any case, to avoid corrosion, high-pressure steam should not be used; steam coils located several inches below the bottom of the tank are recommended. The space below the tank bottom should be enclosed to permit heating of the air to 50˚C, and the tank walls should be insulated.
Materials of construction
Tanks can be fabricated of Type 316 extra-low-carbon stainless steel, rubber--lined carbon steel or fiberglass-reinforced plastic. Carbon steel should not be used, as it will corrode.
Hydrochloric acid (HCl)
Storage
HCl of all strengths should be stored in tanks similar to those mentioned above. Containment areas should be provided around tanks, and storage facilities should include a pressure (and vacuum) relief service, primary and redundant level indicators, a high-level alarm, an overflow line, an emergency block valve at the tank outlet nozzle and a vent-fume scrubber.Materials of construction
These storage tanks should be fabricated of rubber-lined carbon steel, glass-lined carbon steel or fiber-reinforced polymer (FRP). Soft natural-rubber compounds are used as liners for concentrated acid storage tanks at temperatures up to 60˚C with a minimum lining thickness of 3/16 in. Semi-hard rubber is used for lining equipment and piping for acid up to 70˚C with FRP tanks of vinyl-ester resin.
Nitric acid (HNO3)
Storage
Storage tanks for HNO3 of less than 95 wt.% concentration should be designed for at least a slight pressure and vacuum, permitting the venting of nitrogenoxide fumes to collection and disposal equipment, such as a scrubber or a flare.
When locating the tank vent and overflow pipe, consider that escaping vapors and liquid can corrode exterior welds as the acid is diluted with atmospheric moisture.
Materials of construction
For concentrations up to 95 wt.% at ambient temperature, storage units should be fabricated of Type 304L stainless steel. For concentrations of 95 wt.% and above, Type 3003 aluminum alloy should be used. Acid in the range of 52–55 wt.% should be stored in tanks of Type 347 stainless steel using No. 12 gage sheet. Above 90 wt.%, corrosion allowance in the tank-wall thickness may be necessary. Glass-lined carbon steel tanks are satisfactory for all acid grades.
Hydrofluoric acid (HF)
Storage
Because of anhydrous HF’s high vapor pressure, tanks are designed for a minimum pressure of 60 psig and have X-rayed and stress-relieved welds. Tanks holding 70 wt.% HF are also designed per ASME code, or for lower pressure, as its vapor pressure is much lower than that of anhydrous HF. These tanks should be equipped with a relief device, and discharge piping should be routed to a scrubber. Aqueous HF tanks should have a vent, with the vent line also going to the scrubber.
Materials of construction
Carbon-steel storage tanks can be used for anhydrous HF at temperatures up to 66˚C and 70 wt.% HF. Acid of concentrations greater than 60 wt.% may be handled in steel up to a temperature of 38˚C. In steel tanks, hydrogen blistering may be caused by the accumulation of H2, so periodic tank inspections are required to evaluate blistering.
References
1. Grossel, S., Safe Efficient Handling of Acids, Chem. Eng. December 1998, pp. 104–112.
2. Anon., Phosphoric Acid, Rhone-Poulene Basic Chemicals Co., Shelton, Conn. (1992).
4 comentarios:
Which tanks are vertical or horizontal cures?
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Very helpful information. Acid Storage structure is looking really great.
A manufacturer of steel tanks specializes in producing durable, high-capacity containers for various industries. These tanks are crafted from steel, known for its strength and longevity. Applications range from storing liquids like water, oil, and chemicals, to gases under pressure. Manufacturers often customize tanks to meet specific requirements, adhering to strict quality and safety standards.
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