Choosing the right polyethylene tank involves more than just selecting size or capacity. For demanding applications such as potable water, wastewater, and chemical storage, the grade of resin, wall thickness, and overall tank design play a critical role in ensuring long-term performance, safety, and durability. Misjudging these factors can result in premature failure, environmental risks, and increased maintenance costs.

Wall Thickness and Resin Quality: Not All Tanks Are Created Equal

Resin Quality Drives Performance: The quality of polyethylene resin directly influences a tank’s mechanical properties. Higher-grade resins with enhanced tensile strength and chemical resistance allow for optimised wall thickness without compromising structural integrity.

Engineered Thickness Variability: Polyethylene tanks are designed with varying wall thicknesses at strategic locations to meet specific structural and performance demands. For example, sidewalls are thicker at the bottom to support hydrostatic pressure, while the top and bottom have optimised thickness to balance weight and strength.

Wall Thickness Consistency: Critical to Long-Term Reliability

Why Uniformity Matters: Consistent wall thickness prevents weak spots and ensures even stress distribution. Tanks manufactured with lower weights often result in thinner wall sections, increasing the risk of weak points due to the inherent variability of the rotational moulding process. Thin or inconsistent areas become stress concentration points, leading to deformation, cracking, and premature failure.

Impact of Manufacturing Processes: Rotational moulding can lead to thickness inconsistencies if not properly controlled. High-quality manufacturers implement precise moulding techniques and rigorous quality control to ensure uniform thickness and structural integrity. This attention to detail is particularly critical when penetrations, such as flanged connections, are part of the design.

Stress Distribution: Why Wall Thickness and Resin Quality Matter

Load and Stress Management: In applications involving large volumes or dense materials (e.g., wastewater), thicker walls help distribute internal stresses more effectively. However, performance also depends on the resin’s mechanical properties. High-grade resins enhance a tank’s ability to withstand internal pressure and cyclical loading without cracking or bulging.

Localised Stress Points: Penetrations, such as flanged or threaded connections, concentrate stress around openings, increasing the risk of failure in tanks with insufficient wall thickness or subpar resin. Selecting tanks with adequate wall thickness and high-quality polyethylene minimises these risks.

Application-Specific Considerations

Potable and Raw Water Storage: In potable water applications, tank degradation can compromise water quality. Increased wall thickness and high-grade resins provide added protection against stress fractures and leaks, extending the tank’s lifespan and ensuring safe water storage.

Wastewater and Chemical Storage: Tanks used for wastewater or chemical storage experience mechanical and chemical stresses. Properties such as fluid density and temperature place additional loads on the tank, requiring thicker walls and chemically resistant resins to ensure long-term reliability.

Engineering and Finite Element Analysis (FEA)

Advanced Engineering for Enhanced Performance: Finite Element Analysis (FEA) is an essential tool in the design and validation of polyethylene storage tanks. FEA enables engineers to simulate structural behaviour under various conditions, ensuring that wall thickness, material selection, and stress distribution are optimised.

Failure Prevention and Optimisation: This analytical approach identifies potential failure points, evaluates the effects of penetrations, and ensures the tank can withstand operational stresses. Through FEA, manufacturers can design tanks that meet and exceed industry standards, providing reliable storage solutions.

For more information on engineered polyethylene tank designs, visit:

https://www.coerco.com.au/coerco-updates/poly-water-chemical-tanks-engineered-certified-to-last

Installation Considerations: Foundations and Flexible Connections

Proper Foundations for Stability: A stable and level foundation is critical for polyethylene tanks. Inadequate foundations cause uneven load distribution, leading to stress cracking and deformation. Concrete pads, compacted gravel, or engineered bases should be specified based on tank size and application.

Flexible Connections to Minimise Stress: Plumbing connections should include flexible couplings to absorb movement and vibration, preventing undue stress on tank walls. Rigid connections transfer mechanical loads to the tank shell, increasing fatigue over time.

Long-Term Benefits of Optimised Wall Thickness and Resin Selection

Durability and Reliability: Thicker-walled polyethylene tanks made with high-grade resins exhibit superior resistance to cracking, bulging, and chemical attack. Tanks designed with high-quality polyethylene can handle stress cycles more effectively, reducing maintenance requirements.

Cost Savings Over Time: While heavier-duty tanks have higher initial costs, their increased lifespan and lower maintenance expenses result in long-term savings. Tanks built for demanding applications prevent costly leaks, failures, and environmental damage.

The Risk of Under-Specifying Tanks

"Rainwater-Grade" Tanks vs. Industrial Applications: Some manufacturers supply standard-weight, rainwater-grade tanks for projects involving penetrations or higher-stress conditions. These lightweight tanks, often produced with lower wall thicknesses, are not suited for applications involving wastewater, chemicals, or industrial processes.

Safety and Compliance Risks: Underspecified tanks with insufficient wall thickness and substandard resins can lead to failures that result in environmental damage, safety incidents, and regulatory violations. Selecting tanks with the appropriate specifications ensures safety and compliance.

Making the Right Choice: Certified, Experienced, and Fit for Purpose

A polyethylene storage tank is a long-term investment. Choosing the right supplier ensures the tank meets all required specifications and performs reliably over its lifecycle. Consider the following when selecting a supplier:

Certification: Ensure compliance with AS/NZS 4766:2020, the standard governing polyethylene storage tanks for water and chemicals.

Technical Expertise: Work with a supplier that understands the requirements for safe and reliable storage solutions.

Engineering Capability: Choose a manufacturer with dedicated engineering resources and expertise in polyethylene materials and tank design.

Watch the video below to understand why AS/NZS 4766 certification and WaterMark approval matter when selecting a polyethylene storage tank.

Selecting a tank that is fit for purpose, with an appropriate design life and maintenance plan, is essential for long-term performance. The right supplier helps ensure a safe, efficient, and cost-effective storage solution.

Selecting polyethylene tanks for critical applications goes beyond size or cost—it’s about ensuring engineering reliability, safety, and long-term performance. Wall thickness, resin quality, and tank grade directly impact a tank’s ability to handle stress, penetrations, and environmental conditions. By partnering with certified and experienced suppliers, you safeguard your investment and ensure a technically sound storage solution designed for lasting success.