Guide to Maximizing Bleach and Bleach Tank Service Life
Sodium hypochlorite (bleach, NaOCl) is a strong oxidizing agent with various breakdown concerns that present specific considerations for the proper storage of this widely used chemical solution. Bleach is defined as a hazardous chemical by the U.S. EPA, and one that is capable of corrosive damage to person and material, particularly at high concentrations. Therefore, the right storage and handling requirements are important to maximize safety as well as the service life of both the bleach solution and its container.
In North America, sodium hypochlorite is frequently stored, used, and distributed within polyethylene plastic tanks and IBC totes. Bleach is commonly kept for use as a whitening agent, for sanitization, or to drive a variety of chemical reactions. The solution has extensive use in the food industry, healthcare, and in drinking water, wastewater, and water management systems.
Under the right conditions, polyethylene tanks can provide up to and potentially beyond 10 years of safe use. To achieve these results, it is necessary to follow the right storage guidelines that take into account NaOCl’s unique chemical characteristics and properties.
In this Chemical Tanks Series, we will cover six main points on how to effectively and safely store sodium hypochlorite in polyethylene tanks to achieve long-term, successful results.
6 Points on How to Properly Store Bleach in Polyethylene
1) Use HDPE, Not Other Polyethylene Variants
Polyethylene is a synthetic material, i.e., plastic, that is engineered into various forms. The most common are high density, low density and cross linked polyethylene; abbreviated HDPE, LDPE and XLPE, respectively. These polyethylene variants differ in their manufacture and their resulting properties, meaning each can be better suited for certain chemical storage applications. In bleach storage, studies have demonstrated HDPE is more durable and with greater total resistance against NaOCl damage than the other poly types, particularly XLPE. Therefore, when selecting a poly bleach tank, choose HDPE.
High density poly tanks are acceptable for ≤ 16.5% NaOCl solutions kept beneath 100°F and at atmospheric pressure. HDPE bleach storage tanks should be manufactured to 1.9 specific gravity (SG) according to ASTM D-1988 to 600 PSI hoop stress standards. Bleach is well suited for storage in HDPE tanks up to 12,500 gallons in vertical style tanks, horizontal tanks, cone bottom tanks, and double walled containment tanks.
The service life of a poly bleach tank falls between 3 to 12 years. This wide range is due to the number of variables involved in NaOCl storage, proper care and maintenance as well as workmanship of the poly tank brand. This therefore makes it important to select quality tank manufacturers and store bleach under ideal conditions. HDPE tanks are also capable of thermoplastic welding, while XLPE is not, allowing for tank repair when needed; a further benefit should the work case require.
2) Protect From Sunlight Ultraviolet (UV) Radiation
Storing bleach in polyethylene tanks can leave solutions susceptible to decomposition reactions resulting from UV sun exposure unless preventive actions are taken. UV rays can penetrate an unprotected polyethylene tank and reach the molecular NaOCl structure where an energy transfer occurs that causes NaOCl molecules to react. The reaction produces oxygen gas, O2, and leaves behind sodium chloride, NaCl, water, and sodium chlorate, NaClO3, an undesired impurity.
The UV to bleach interaction is a chemical breakdown that reduces bleach concentration, solution purity, and therefore the chemical’s relative effectiveness. The oxygen gas produced is a potential safety hazard. Extensive oxygen buildup can cause a tank to rupture if left unchecked and unmitigated under scenarios of high concentrations, extended UV exposure, and bleach decomposition.
Note the following conditions on how to best protect a poly bleach tank from sunlight UV effects:
- To limit or largely reduce UV exposure ‒ store bleach tanks inside.
- To limit or even negate UV exposure ‒ keep bleach indoors in UV stabilized black colored tanks.
- To limit UV for outside storage ‒ keep bleach in opaque, white colored tanks formulated with HDPE resin #880059. (Note, black is not recommended for outdoor UV protection due to the increased contribution of heat to solution.)
- To eliminate UV effects inside or outside ‒ use a tank with polyurethane foam insulation covered with a mastic weatherproof coating.
The most effective means to preserve both bleach and poly tank service life from sun damage is to protect with insulation and mastic coating. If insulation is chosen, the poly tank can be fabricated in its natural color, which will also reduce purchase costs. Additionally, bleach tank insulation contributes significantly to solution temperature maintenance, which is another important point in proper bleach storage.
3) Protect From Elevated Temperatures | Maintain Low Temps
Sodium hypochlorite is sensitive to high temperatures and low temps should be maintained to improve shelf life and usefulness. Proper bleach storage in poly tanks will include methods to control or mitigate temperature fluctuations. Protecting against temperature extremes and regular elevated temperatures will in turn limit the rate of NaOCl decomposition as well as potential poly tank damage. HDPE tanks are rated for service temperatures up to 130°F (54°C) but are best kept beneath 100°F (38°C), while bleach solutions are best kept at temperatures beneath 60°F (15°C).
Keeping bleach solutions under 60°F greatly lowers the rate of NaOCl breakdown. The exact rate reduction depends on solution concentration, where higher concentrations will decompose faster than more dilute solutions. Temperature maintenance methods for poly bleach tanks include: (1) Tank insulation; (2) Indoor installation in climate control; (3) Outside out of direct sunlight within an opaque, white colored tank made from HDPE resin #880059.
4) Understand Bleach Properties and Interactions | Factors of NaOCl Breakdown
Each polyethylene variant expresses some degree of reactivity with sodium hypochlorite solutions. High density polyethylene is the most resistant to NaOCl oxidation. The extent of poly to bleach tank chemical interactions can be reduced by following proper storage guidelines. Factors that increase interactivity include stronger NaOCl concentrations, greater temperatures, and bleach breakdown reactions.
Limiting sodium hypochlorite breakdown reactions will lengthen solution usability and can extend tank service life. In addition to UV and increased temperatures, impure bleach solutions are known to break down much more rapidly than pure, filtered solutions. Organic matter, suspended solids of calcium, magnesium and heavy metals, particularly copper, nickel, cobalt and iron, if present in a bleach solution will amplify the rate of breakdown. To avoid this, purchase or manufacture bleach products purified through quality filtration methods that remove these contaminants and do not use any system components made from or that can potentially leach any of these materials.
Solution pH also plays a vital role in bleach stability for storage and use. The pH of bleach is best kept at 10 and above. NaOCl breakdown into hypochlorous acid begins as pH begins to drop below 9 to 10, which can be a result of dilution or an aging bleach stock. Bleach interactions with strong acids can drop pH to 4 or below and can generate toxic chlorine gas as a result and should be avoided.
5) Perform Regular Tank Inspections & Maintenance
Similar to many storage tank applications that involve aggressive and/or hazardous chemicals, bleach tanks can fail over time. The question of when is dependent on the storage conditions, length of time, and solution specifics of concentration and purity. If a poly tank system has been engineered to maximize bleach shelf life, then the service life of the tank itself will also be maximized. Even so, regular tank inspections should be performed and are likely required by OSHA in the United States.
With bleach volumes that exceed 1000 gallons, annual tank inspections are recommended. Inspections should evaluate a poly tank for signs of cracks, fractures, bubbles and/or thinning; the symptoms of environmental stress cracking (ESC). Satisfactory inspections will verify continued tank durability and chemical resilience. Holes and/or failing fittings can be repaired or replaced but are a sign that tank replacement will soon be needed.
Regular flushing of poly bleach tanks can assist in lengthening both the service life of the storage tank and stored bleach solution. When the stored bleach stock is low or depleted and scheduled for refilling, take the opportunity to rinse and flush the bleach tank. Regular flushing will ensure the old solution is removed and will not potentially dilute or contaminate the incoming new bleach stock.
6) Install Chemically Compatible Fittings & Plumbing
For bleach tanks, compatible fittings and plumbing are necessary to prevent a chemical release. For tank fittings: PVC, CPVC and polypropylene are frequently used with encapsulated titanium metal bolts. For sealing gaskets: Viton®, EPDM and Teflon® are compatible. For pipes / plumbing fixtures: CPVC, Teflon® or FRP types are recommended. When sodium hypochlorite will be used in water treatment ‒ a common bleach use ‒ full tank systems and components must meet ANSI / NSF 61 equipment standards.
If not required, secondary containment tanks are recommended for bulk volumes of bleach stock in the event of unexpected tank failure. Secondary containment is designed to contain any spilt bleach and prevent release to the environment and effectively protect personnel and equipment.
Properly Storing Bleach in Polyethylene Takeaways
In summary, all bleach solutions up to 16.5% are recommended for storage in high density polyethylene containers. Whenever choosing between the modern synthetic plastic options, preference is for HDPE. Containers should be airtight but have built-in auto vent features or dedicated vent pipes for release of any oxygen gas buildup from bleach breakdown. Bleach tanks are recommended with insulation and mastic coating for sunlight and temperature protection.
NaOCl storage is best indoors, in climate controlled, lower temperature conditions. Factors such as sunlight, heat, and solution impurities can affect bleach stability, reduce shelf life, and should be avoided. Regular maintenance schedules are important in bleach storage to verify the continuous integrity of the poly tank. Under ideal conditions and inspections, proper poly bleach storage can provide years of successful service at appreciably reduced costs to materials and installation.
If looking for certified bleach tanks made in the USA by leading manufacturers, we offer them here. For more information on sodium hypochlorite poly storage tanks, assistance, or multi-tank orders, contact us, our support professionals are always ready to help.