Twenty years ago, the availability of commercial grade cross-linked polyethylene (XLPE) for chemical storage tanks was limited to a small number of sources. The limited supply, as well as a wide variation in quality, made it challenging to find quality resin for chemical storage tanks.
To control manufacturing quality and create a steady supply source, Poly Processing led the charge in developing a robust, high-density cross-linked polyethylene that could be used successfully in large storage vessels.
Innovating Better Cross-Linked Polyethylene Solutions
The quest to develop an industry-leading high-density cross-linked polyethylene resin began in 2003. In conjunction with the Pennsylvania College of Technology, the process consisted of developing a variety of resins, as well as rigorous short-term and long-term testing.
Once a number of resin compound variations were developed, they were subjected to impact, hoop stress, environmental stress crack, tensile, and several other tests in the lab. This lab work produced new resin compounds that were ready for testing in the field.
In order to get an idea of how these new resins would perform in real-world scenarios, we manufactured test tanks with the new resin compounds. Numerous resin variations were field-tested over several years with fertilizer applications in agriculture.
In these tests, the tanks were not only required to successfully contain the chemical being stored, they were also subjected to the demands of frequent movement.
We also recruited distributors to test and monitor the performance of these tanks in controlled storage situations. The tanks were placed under various chemical applications to verify the longevity and performance of each tank.
The result of this extensive testing and development is a high-density cross-linked polyethylene resin custom-tailored for large, thick-walled chemical storage tanks. It’s a robust, long-lasting material that meets strict quality specifications.
Read more: Discover the latest innovations in chemical storage
What Makes Cross-Linked Polyethylene Unique?
Crosslinking is simply the formation of bonds between the polymer chains. These bonds are equal in strength and stability to the principal bonds along the polymer backbone. During the crosslinking process, the bonds tie the polymers together, thus dramatically increasing molecular weight.
As a result, the length of the polymer chains, and the physical properties, are much better than can ever be achieved without crosslinking.
The result is a plastic that possesses impact resistance, tensile strength, and resistance to fracture that linear polyethylene just can’t match. These qualities make cross-linked polyethylene an excellent choice when tank integrity is critical. The structural integrity, heat resistance, and useful life in most cases are unparalleled.
Strength and Durability: Linear Vs. Cross-Linked Polyethylene
Both linear and cross-linked polyethylene resins are rotational molding-grade resins that have been ground into a powder to allow the material to melt easily during the molding process. Both types of resins are available in standard colors as well as some custom colors. Both resins are corrosion-resistant polyethylene.
However, the differences are critical. Compared to linear polyethylene, XLPE provides:
- 10 - 20 times the environmental stress crack resistance
- 10 times the molecular weight
- 3-5 times the impact and tensile strength
The four most important factors of high-density linear tanks and cross-linked tanks include:
- Environmental stress crack resistance/notch sensitivity
- Long-term hydrostatic strength
- Toughness and Durability
- Useful Life
In all four of these areas, testing and measurements show cross-linked resins are more durable than linear resins.
The Drop Test: Putting Our Money Where Our Mouth Is
We're always working to improve the strength and longevity of our polyethylene tank solutions. In a measure to see just how much force a cross-linked polyethylene storage tank could stand up to, we performed a series of tests. Originally, these tests were designed as part of the NFPA (National Fire Protection Association) testing protocol for designing plastic gas tanks.
We performed a drop test on a variety of storage tanks that were built using different materials — fiberglass reinforced plastic (FRP), linear polyethylene, and XLPE. The 2,800 gallon vertical test tanks were filled with over 28,000 pounds of water and raised to a height of 18 feet. We then dropped each tank.
As you can see in the video below, the FRP tank catastrophically fails. The linear polyethylene tank suffers the same fate. The cross-linked polyethylene tank, however, survives the impact due to its superior strength of construction.