Are Polyethylene (HDPE) Tanks UV Resistant?
Anytime a chemical storage tank is located outside, it’s exposed to harmful elements, such as sun, wind, and rain. Poly Processing recommends taking special considerations to protect the life of your storage tank, especially from damaging ultraviolet rays.
Let’s explore solutions you can implement to protect polyethylene chemical storage tanks from damage due to UV exposure.
UV Exposure Is Bad for Your Storage Tanks
When crosslinked polyethylene tanks are manufactured, bonds form between atoms on polyethylene molecules. The molecular chains become linked together in a vast network, which gives the material its durability and strength. UV light can attack these molecular bonds.
Extended exposure to sunlight radiation and ultraviolet rays results in weathering of all polyethylene storage tanks. Without proper protection, UV light causes a compound breakdown of the polyethylene elements, making the polyethylene tank brittle. This can cause microcracks, leading to leaks and potential failure of the chemical storage tank.
Exposure to UV light is a problem for any plastic product when long term performance is essential. However, some polymers are more resistant to serious degradation than others. Crosslinked polyethylene (XLPE) chains can provide more protection than linear polyethylene. Poly Processing’s XLPE chemical tanks in most cases aren’t susceptible to the serious reactions of linear polyethylene, such as potential catastrophic failure and unzipping. See the illustration below to see the difference between linear polyethylene which is a thermoplastic polymer and crosslinked polyethylene which is a thermoseting polymer.
Download our Carbon Black & Plastics technical bulletin for more information about the impact of ultraviolet light on various resins.
If you can’t place your chemical storage tank indoors or under a lean-to shelter or covering, manufacturing the tank with carbon black resin is a great option for UV protection.
Carbon Black Is a Great Choice for UV Protection
Carbon Black is a nearly pure, elemental carbon. When used as a resin in the molding of the polyethylene tank, it acts as an absorber of ultraviolet light. UV energy is absorbed, transformed into heat, and dissipated throughout the tank. While Carbon Black polyethylene tanks tend to have slightly higher temperatures than light-colored tanks, the difference is nominal.
The UV index value or rating of carbon black, according to an ExxonMobil study, supports carbon black as a superior UV resistant material.
Adding carbon black is a simple, inexpensive solution. It’s the preferred pigment of many of our customers especially when storing harsh chemicals outdoors.
What About Temperature Concerns?
While black tanks have a slightly higher overall temperature than natural or white tanks, the UV protection that carbon black provides outweighs the effects of slightly elevated temperature levels. The useful life of the tank is extended and the potential for catastrophic failure is reduced significantly. As a result, carbon black is the preferred compounded pigment for storing harsh chemicals such as sodium hypochlorite and other aggressive materials.
It takes a tremendous amount of energy to heat up all of the chemical in a storage tank, no matter what color the tank is. That’s because by the time the temperature starts to rise, the sun is already setting, and ambient temperatures are cooling down.
Ambient temperature, or external atmospheric temperature, has little effect on the tank or the chemical content in the tank. That’s because ambient temperatures fluctuate too quickly to affect the chemical. First, the heat needs to penetrate the plastic tank, then it needs to heat hundreds or thousands of gallons of chemical.
Even in the hottest areas of the country, by the time the environmental temperature begins to warm the chemical, the sun is already descending and the ambient temperature is falling.
So black tanks are a great choice for UV protection.
For questions regarding outdoor polyethylene storage tanks, or for a custom storage tank system solution, contact a Poly Processing storage tank specialist.
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