Guide to Safely and Effectively Storing Muriatic Acid
Hydrochloric acid, HCl, also known as Muriatic Acid and Aqueous Hydrogen Chloride, is a colorless, corrosive liquid that produces vapors with increasing concentrations. Federal guidelines outline the safe handling and storage requirements of hydrochloric acid. Concentrated HCl is a hazardous material capable of causing harm, and generated fumes are regulated air pollutants where exposure is considered harmful to health.
Hydrochloric acid is heavily used across markets and industries in North America and is commonly stored in polyethylene from small bottles to large, bulk volume tanks. HCl solutions see use in the food industry, pharmaceuticals and lab work, paper and pulp production, semiconductor production, stone, clay, and glass processing, oil well acidification, steel pickling, and the chemical production industry (CPI) in synthesizing chemical compounds and solutions. HCl has many other uses not listed here.
In this Chemical Tanks Series, we focus on how to properly store hydrochloric acid in polyethylene tanks.
6 Points on How to Properly Store HCl in Polyethylene
1) HDPE Tanks are Compatible and Frequently Used with HCl
Polyethylene is a synthetic material widely used in item production and is made in various density versions of the material. Polyethylene storage tanks come in high density polyethylene (HDPE), low density polyethylene (LDPE), and cross-linked polyethylene (XLPE). However, the best polyethylene variant for hydrochloric acid storage is high density polyethylene based on test results and real-world reports on long-term resistance and service durability.
For HCl, HDPE poly tanks are chemically compatible and frequently used to store concentrations ≤ 37%. HDPE is frequently selected as it provides an excellent balance of tank durability, cost effectiveness, and ability for thermo-welding repair. Poly tanks made from XLPE are not recommended for HCl acid based on Snyder Industries’ position statement, a renowned manufacturer of HDPE tanks, XLPE tanks, metal tanks and more.
Due to the chemical nature and hazards of muriatic acid, poly tanks should be built with a tank specific gravity (SG) rating of 1.9 SG. Common tank volumes range from 35 gallons to 12,500 gallons. Storage tanks can be purchased with capacities exceeding 12,500 gallons. However, when storing HCl in poly tanks, it is recommended to never store volumes greater than 12,500 due to regulations associated with safety concerns. Instead, it is ideal to store bulk solutions in several tanks and with secondary containment should tank failure or an accident occur.
Common hydrochloric acid storage tanks are vertical and double wall tanks. Double wall tanks are often chosen for their built-in safety features and compliance with secondary containment measures.
2) Install Tanks in Ideal, Compliant Locations
All volumes of hydrochloric acid must be stored in a manner that is compliant with federal, local, and any company-specific regulations. Hydrochloric acid is long-term stable with an extended shelf life, especially in airtight containers. HCl should be stored in a designated, well-ventilated area, be clearly labeled, and kept away from incompatible materials, including oxidizers.
HCl reacts energetically with organic bases, inorganic bases, and carbonates. Contact with various metals can produce flammable hydrogen gas and should be avoided. Muriatic acid can produce toxic and/or flammable gasses on reaction with chemicals of boride, carbide, phosphide, and sulfide. Additional examples of incompatible chemical materials include acetic anhydride, sodium hydroxide, ammonium hydroxide, perchloric acid, propylene oxide, and carbon tetrachloride.
Outdoor storage is recommended for bulk HCl storage tanks. If indoor storage is necessary, containers should be clearly labeled and kept in a well-ventilated area with limited access. Depending on the bulk indoor volume amount, a fume scrubber system is highly recommended and may be required per regulations.
Storing bulk volumes of hydrochloric acid outdoors helps reduce the risk of exposure by personnel or equipment to fumes or in the case of a spill. However, storing HCl outside can increase fume production as a result of sun exposure that can increase solution temperatures.
For outside installations, tank insulation and coating are recommended. Insulating an HCl tank can efficiently reduce heating effects to maintain solution temperature and significantly lower vapor generation. Tank insulation is often a polyurethane foam shell with a weatherproof mastic coating.
Airtight manways should be maintained on hydrochloric acid storage tanks to reduce generation of and potential exposure to vapors. These fumes can be corrosive to the environment around the tank. For this reason, a bolted and sealed, fume tight manway should be considered for hydrochloric acid tanks and special considerations should be taken for venting the tank to a scrubber system.
See this pamphlet on safe handling of hydrochloric acid for even more info on HCl storage.
3) Employ Vapor Mitigation / Fume Scrubber Systems
As mentioned above, concentrated solutions of hydrochloric acid can generate hazardous vapors of hydrogen chloride. The rate of fume production and strength directly correlates with HCl concentration and solution temperature. The reaction begins to occur immediately on contact with air. Hydrogen chloride fumes are considered toxic, hazardous and are an EPA regulated pollutant. Depending on the stored volume and the extent of vapor generation, a fume mitigation system for hydrochloric acid is often required. Large volumes and high concentrations are common scenarios for using an HCl fume scrubber.
Fume scrubber systems are frequently employed in proper HCl storage for successful vapor mitigation. Fume scrubbers work by connecting to a tank and diverting storage fumes through a media that will either deactivate the targeted control vapors or lower the concentration to regulation approved levels. Deactivating target vapors can be done by completely removing them from the exhaust through binding with another chemical compound (often activated carbon) or by driving a chemical reaction that changes target vapors into a safe or non-regulated chemical exhaust.
Sodium hydroxide (NaOH, lye) or plain water are frequent media choices used in HCl fume scrubbers. Sodium hydroxide is used to deactivate gaseous HCl by driving the formation of water and sodium chloride. Water can be used as an HCl fume scrubber medium to dilute the vapors to levels considered acceptable by governing agencies.
Hydrochloric acid fume scrubber systems are commonly made from thermoplastic materials, including CPVC, PVC, and HDPE, are ideal for HCl fume mitigation. Our company also specializes in fume scrubber systems and can produce custom made systems on request to match application needs and design requirements.
4) Prepare and Protect in Case of Spill or Accidental Release
Most, if not all, regulatory bodies and guidelines require secondary containment for bulk volumes of hydrochloric acid due to the presented hazards to personnel, equipment and the environment should a spill occur. Most secondary containment guidelines require a system or equipment that is sized to handle at least 110% the volume of solution or solutions held within the storage area. Examples of secondary containment include double walled storage tanks, containment basins, structural berms, dikes and retaining walls.
The secondary containment solution best for HCl storage will vary by application, the storage environment, and total volume. Double wall tanks often make excellent choices for secondary containment needs in hydrochloric acid storage. For more on secondary containment, see this document from the EPA, or this page from the SCDHEC.
5) Conduct Regular Tank Inspections
With aggressive, corrosive or hazardous chemicals, regular tank integrity inspections are an important safety measure and are often required by local regulation. Polyethylene HCl tanks are no exception. Only storage tanks made from expensive, rare materials or applications that hold wholly inert or non-hazardous chemicals may never experience tank failure. Even poly water tanks do not last indefinitely. With these considerations and the damage potential of catastrophic HCl release, conducting regular tank inspections should never be neglected. Regular inspection of an HCl poly tank will promote tank service life and usefulness.
With hydrochloric acid volumes that exceed 600 gallons, annual tank inspections, at minimum, are recommended. Ideally, inspections are most thorough and best performed when the tank has been fully drained and cleaned. An inspection should evaluate a poly tank for any cracks, fractures, bubbles and/or thinning in tank walls or around fittings as these are signs of environmental stress cracking (ESC). Satisfactory inspections will verify a tank’s remaining strength, projected service life and approve the tank for continued use.
High density polyethylene chemical storage tanks manufactured by Snyder Industries provide a full drain option with upgrade to a SUMO™ tank outlet fitting. The SUMO™ fitting (Snyder Unitized Molded Outlet) is available on standard, single wall tanks from 2,000 gallons up to 12,500 gallons. The fitting features an HCl compatible encapsulated Hastelloy™ ring and PVC adapter. The SUMO™ molded outlet is recommended as it promotes full tank draining and makes an excellent choice for HCl poly storage tanks.
6) Install Chemically Compatible Fittings & Plumbing
Muriatic acid is compatible with polyethylene based tanks, but many material options exist for the fittings and plumbing of HCl storage tanks and handling systems. It is vital to ensure the resistance, reactivity, and longevity of components that will encounter hydrochloric acid as well as potential vapors.
Polyethylene tanks experience thermal flexibility and can expand or contract vertically and laterally with changing temperatures. Joints and fittings that are designed to accommodate these shifts in tank rigidity should be installed on poly HCl tanks to avoid leaks and failed fittings.
Chemical compatibility tests and resistance measurements have been performed many times in detail to verify and approve certain materials for use with HCl solutions. For tank fittings: PVC and CPVC are common, popular choices. ABS plastic and PVDF Kynar® are also excellent, compatible fitting options. For sealing gaskets: Viton™ is the top rated material of choice. PTFE, FKM and EPDM are also suitable. If bolted connections are required, Hastelloy™ encapsulated bolts are recommended.
*Disclaimer
The storage recommendations here for proper hydrochloric acid storage in poly tanks are recommendations only. Information is presented and collaborated based on research provided by leading authorities, governing agencies, chemical suppliers, and manufacturers. HCl storage guidelines are presented in good faith and for informative purposes to detail safe storage practices for hydrochloric acid.
The author maintains no warranty or guarantee as to the fail-proof security of any HCl storage handling system. Accidents and unforeseen scenario circumstances can always arise with chemicals, especially in bulk volumes. As with all bulk chemical storage and handling, always verify with the proper authority, such as governmental regulatory oversight, the tank manufacturer, an engineer, and/or chemical supplier, prior to any bulk chemical storage and use.
Properly Storing Muriatic Acid in Polyethylene Takeaways
In summary, hydrochloric acid up to concentrated 37% solutions can be stored in high density polyethylene tanks successfully, safely and long term. When choosing between the different polyethylene variants, HDPE is the best recommended option that is also highly cost-effective and durable. Cross linked polyethylene can be used but in general, is not recommended.
Storing HCl is best outdoors due to safety reasons from spills and fumes. Tanks should be maintained at atmospheric pressure and fitted with a fume scrubber system. Thermoplastic fume scrubbers are recommended to regulate vapors, pressure and exposure concerns. To avoid undesirable heating, outdoor poly HCl tank installations are best with double walled tanks or coated with insulation. Double wall tanks also provide built-in secondary containment for spill protection and safety compliance.
If looking for certified HCl tanks made by leading U.S. manufacturers, we offer them here. For more information on hydrochloric acid storage in poly tanks, assistance, or multi-tank orders, contact us, our support professionals are always ready to help.
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External Resources:
- https://cameochemicals.noaa.gov/chemical/3598
- https://www.dec.ny.gov/regulations/38102.html
- https://www.snydernet.com/Portals/0/PDF/Industrial-PDF/technical/sumo-ad.pdf
- https://www.epa.gov/sites/production/files/2014-04/documents/4_secondarycontainment_impracticability_2014.pdf
- https://www.jsia.gr.jp/data/handling_02e.pdf
- https://www.nj.gov/health/eoh/rtkweb/documents/fs/1012.pdf
- https://ofmpub.epa.gov/apex/guideme_ext/guideme_ext/guideme/file/hydrochloric%20acid.pdf
- https://www.osha.gov/semiconductors/solutions/toxic-gases
- https://www.rila.org/retail-compliance-center/regulations/storage-tanks-regulations
- https://scdhec.gov/secondary-containment
- https://www.snydernet.com/Portals/0/PDF/Industrial-PDF/technical/chemical-resistance/hydrochloric-acid.pdf