Tank Application: Storage of Sodium Hypochlorite
Wagner Enterprise has been designing and selling storage tanks for the containment of sodium hypochlorite (bleach) for many years.
The standard practice for the past 30 years has been to use a premium grade vinyl ester resin such as Derakane 411 with BPO/DMA hardener. BPO/DMA is used in lieu of the traditional MEKP hardener as MEKP contains a percentage of metal which is detrimental to the chemical compatibility for bleach.
The inner face of the corrosion barrier has always been specified with a synthetic veil (Nexus®). After an extensive study, Ashland Inc. — who produces Derakane resins — has found that the lifespan of fiberglass bleach tanks is similar when using Derakane 441-400 vinyl ester resin and two plies of C-veil in lieu of a synthetic veil on the internal corrosion barrier at a more economical cost to the end user.
When built using the above resin and veil system, the lifespan of a fiberglass bleach tank could be expected to last roughly 18-20 years when built in accordance with ASTM D-3299-10. Other materials of construction for the storage of bleach include cross-linked polyethylene (XLPE), high-density linear polyethylene (HDLPE), rubber lined steel, and fiberglass lined steel tanks.
Although rubber linings are used, the cost and life expectancy are inferior to fiberglass. Due to a change in resin formulation of polyethylene tanks within the last 15 years, the life span when storing bleach has decreased from 15-20 years to 9-12 years. However, using polyethylene at capacities up to ≈5,000 gallons is a very economical way to store bleach in comparison to the alternate aforementioned materials of construction.
Rubber lined steel tanks have also experienced the similar decrease in life expectancy due to environmental changes in the formulation of the rubber lining material. A fiberglass lining such as Ceilcote’s Lining 652 is an excellent alternative for lining steel tanks. This type of lining can last with no maintenance for 15 to 20 years.
Fittings are also an issue that have pros and cons in regards to rubber, fiberglass, and steel storage tanks. A fiberglass tank has integral fiberglass flanges which are produced using the same resin and layup technique as the tank itself. Smaller diameter flanges (4” and below) also include conical or plate gusseted reinforcements following ASTM standards. Side manways are also available and recommended for future inspection of the vessel.
On polyethylene tanks, the fittings are a compression style using PVC or Polypropylene. These compression style fittings typically include the use of an EPDM gasket and titanium fasteners. Side manways are not available on polyethylene tanks due to the strength limitations of the material.
All tanks should be inspected after five years, and every one to two years after that. Wagner Enterprise can inspect any and all tanks as required.
Please contact us if you would like to discuss a new tank application or an inspection of an existing vessel at your facility.