When it comes to providing you with the newest innovations in polyethylene chemical storage tanks, Poly Processing stays ahead of the curve. From linear polyethylene parts and cross-linked polyethylene to full drainage systems and tank fittings - we’ve uncovered everything you need to know to safely store chemicals in our article featured in Environmental Science & Engineering Magazine’s June publication. Our marketing team is sharing these insights and more in today’s blog, but you can also access the article on pages 40 to 42 by browsing here.
At a glance, it’s impossible to gauge the life of your chemical storage tank, there are many things to know and consider that will help you extend the life of your tank to its fullest potential. It is important to know that from the production of the raw materials through installation, it is expertly manufactured with all of the right gaskets and fittings.
The goal of this article is to update the reader with the latest in material technology. We will discuss new engineered polyethylene tank resins, innovative tank configurations, and engineered fittings.
High-density polyethylene chemical storage tanks can be made of linear polyethylene or cross-linked polyethylene. They are both made with resins that are heated to create a hollow plastic part, yet the differences in their development create very different polyethylenes of structural strength.
Linear polyethylene parts are created when thermoplastic resin pellets are ground and then heated to create the fluid plastic that will harden and cure into a linear, high-density polyethylene surface. Envision a rope where the individual threads of fiber are twisted together, but not tied. The result is a linear resin that has polymer chains “tangled” together, rather than tied. Linear polyethylene is cost-efficient, and is safe for storage of benign and non-corrosive chemicals.
Cross-linked polyethylene (XLPE) is high-density polyethylene that is manufactured by adding a catalyst to the thermoplastic resin which turns it into a thermoset. The catalyst causes a covalent bond that links the molecules together. Picture a chain linked fence where the metal is actually linked together. The result is a plastic that possesses impact, tensile strength and resistance to fracture which makes cross-linked polyethylene an excellent choice for chemical storage applications when tank integrity is of utmost importance. The chemical resistance, heat resistance, and dimensional stability is unparalleled.
Because cross-linked polyethylene offers longer tank life and more protection in the long run, there is a little more upfront investment. Cross-linked polyethylene offers 20 times the environmental stress crack resistance of high-density linear polyethylene, has 10 times the molecular weight and greater impact and tensile strength as well. Another difference comes in testing the two plastics. When linear polyethylene fails, it fails catastrophically, because the linear polymer chains “unzip.” Cross-linked polyethylene might develop a small tear or pinhole but cannot catastrophically fail due to the covalent bonds that connect the polymers together. Poly Processing is a leader in the design and manufacturing of crosslinked polyethylene tanks.
If you’re storing an oxidizing chemical like sulfuric acid or sodium hypochlorite in a polyethylene tank, an antioxidant barrier will give you much greater life of the tank. Polyethylene, whether it be linear or cross-linked, has excellent chemical compatibility compared to other choices. An antioxidant barrier is all about extending the life expectancy of normal polyethylene.
Antioxidants are additives to the polyethylene; molecules which can safely interact with free radicals and terminate the chain reaction they cause before more vital ethylene molecules are damaged. Antioxidants exist, for example, as enzyme systems within the human body, where they scavenge free radicals. Likewise, vitamin C is an antioxidant in the same way. They simply interact with free radicals and stop the stealing of electrons.
Antioxidant resins contain saturated amounts of antioxidants. Most polyethylene resin already contains some antioxidant to start with. Resin producers intend to protect the plastic resin itself from heat created in the molding process. It is spent during the heating process and non-existent at the completion of the molded part. Having performed the task it was charged with (protecting the plastic during production); it is no longer available for any post-production purpose.
The presence of antioxidant resin in a completed storage tank, however, addresses the chemical resistance of oxidizing chemicals for 15-20 years after the tank ships. Poly Processing Company has developed the OR-1000 antioxidant system and is the world’s leader in rotational molding of antioxidant materials for chemical storage.
There are several different polyethylene tank configurations available in the marketplace today. The leading rotational molding tank companies have innovated over the past few years to develop “state of the art” technology in tank performance, safety, and ease of use. Two of the innovative tank configurations are full drain tanks and double wall tanks. Let’s take a look at each one to determine what design works best for the end user.
One of the biggest challenges in vertical tank design is maintaining the tank’s integrity while still allowing for the tank to be fully drained, cleaned, and properly maintained. Some companies create tanks out of one substance and insert or mold a flange, post-production or during production, for drainage. This works fine, to a point, but there are other alternatives such as an IMFO (Integrally Molded Flanged Outlet).
One-piece construction enhances long-term integrity, both for the tank as a whole and in the knuckle radius, which is the point where the floor of the tank meets its sidewall. The knuckle radius is the thickest part of the tank; so adding an insert post-production or during construction can compromise the tank. An insert can impact the tank's hoop integrity as well, which puts the entire tank at risk of structural stress from volatile chemicals. When the insert is made of metals or alloys, you can run into a whole new set of problems. Chemical reactions in the place where the tank material meets the metal or alloy of an insert can create a stress point for the plastic itself. This can cause leaks or cracks over time.
With an IMFO® system, the drainage flange is molded while the tank is processing, making it a one-piece, stress- free integrated part of the tank. The flange is created using the same material as the tank cross-linked high density polyethylene. It’s not an insert “added on” during or after tank production. An Integrally Molded Flanged Outlet has several key advantages:
Poly Processing has developed the IMFO® system on tanks from 200 gallons to 13,650 gallons.
Safe operation and minimizing the risk and hazards associated with spills and leaks is vital in storage of chemicals. An effective way to contain the spill or leak is a secondary containment system called a double wall tank, or "tank-within-a-tank." We'll explore the advantages of a secondary storage tank containment system in this article.
A properly designed "tank-within-a-tank" system keeps contaminants, such as debris and rainwater, from entering the interstitial area. These tanks provide secondary containment to avoid damaging equipment or property, loss of chemical, or injury to employees in the event of a spill. This design provides a leveraged investment that offers peace of mind and environmental care.
Poly Processing Company is an innovator in double wall tank designs. They have developed the SAFE-Tank systems from 55 Gallons to 8700 Gallons.
Selecting the right fittings for a polyethylene chemical storage tank is crucial. The proper fittings ensure optimum function, personnel safety, and maximum life of the polyethylene tank. Proper sidewall fittings avoid tank leaks and spills. Selecting sidewall fittings purely based on cost can lead to an expensive mistake. Let’s explore two engineered options that will give the end user a peace of mind knowing that chemical compatibility and environmental safety is handled.
The outlet on a double wall tank becomes the most vulnerable and most commonly used component for wear, but with the way some tank manufacturers address the need, they end up compromising the containment itself. A cost savings technique employed by a few is to use a rubberized doughnut between the inner and outer tank, which bridges the two tanks together. The challenge with this compromise is it reduces flex which the tank needs, but greatly compromises true secondary containment. The pressure that the bottom of the tank experiences in combination with an inflexible fitting creates a hinge point, which commonly fails from wear and leads to compete siphoning of the tank outside of the containment to the outside ground. This creates a dangerous environment, which can result in a workplace.
Adding the enhanced bellows transition fitting will maximize your double wall tank system's performance by allowing you to safely drain the primary tank through single or double-wall piping.