Why Chemical Storage Tank Wall Thickness Matters and How to Get It Right

Wall thickness is one of the most important factors in a safe and reliable chemical storage system. The thickness of a polyethylene tank wall determines how well the vessel can handle the weight of the chemical, the specific gravity rating, process temperatures, and long-term mechanical stress. Getting wall thickness right protects people, equipment, and the environment.

This blog helps to explain how chemical storage tank wall thickness is determined, how it is verified, and what operational conditions can change the thickness you need. It also answers common questions that operators and engineers raise when evaluating new or replacement storage systems.

Why Wall Thickness Is a Critical Design Factor

Polyethylene tank walls are engineered to handle a defined load based on the chemical’s specific gravity, temperature, and oxidation potential. A tank with insufficient wall thickness can deform, creep, or fail prematurely. A tank with excessive thickness may add cost without improving performance.

Poly Processing designs tanks to meet or exceed ASTM D1998, the industry standard for upright, atmospheric polyethylene tanks. ASTM D1998 outlines minimum wall thicknesses, hoop stress requirements, impact testing, and proof pressure guidelines. These checks ensure every tank meets structural expectations.

How Wall Thickness Is Determined

Several factors drive the required wall thickness for a polyethylene chemical tank:

Specific Gravity of the Chemical

The chemical itself, and its operating temperature, determine a tank’s specific gravity rating (SPG). Chemicals that are dense and warm have a higher specific gravity than lighter, cooler chemicals. Your tank needs to be rated for the correct specific gravity, or it could fail. We manufacture our standard tanks with SPGs of 1.35, 1.65, 1.9 and 2.2.

A fluid’s SPG and operating temperature are directly proportional to the weight and pressure the chemical exerts at the bottom sidewall of a tank. Customers often ask how thick a chemical storage tank wall needs to be in a 1.65 SPG tank. It will vary based on the geometry of the tank, and our engineers can work with you to determine what you need.

Tank Diameter and Height

Larger diameter tanks distribute stress differently than smaller ones. The taller the tank, the higher the hydrostatic pressure at the bottom. These forces determine the needed thickness to prevent bulging and long-term creep.

Tank walls can range from .15 inches thick to 2 inches thick or thicker, depending on size, dimensions, and where the measurements are taken. A 1.65 SPG tank that is very short and flat will have a thinner wall than a 1.65 SPG tank that is tall and narrow. That’s because of the third factor, size dimensions. As the diameter of a tank base decreases and the height increases, the pressure on the bottom sidewall of the tank increases. As a result, you need a thicker wall to handle the extra pressure on the sidewall of the tank.

Operating Temperature

Polyethylene tanks storing chemicals at elevated temperatures require thicker walls to maintain structural strength. We advise limiting process temperature to 100°F for standard polyethylene tanks. Higher temperatures may require a thicker wall or a different system design.

Chemical Oxidation Potential

Aggressive oxidizers, such as sodium hypochlorite, can degrade polyethylene over time. Poly Processing’s OR-1000 system provides added protection and extended useful life, but some applications may still require a thicker wall or higher SG-rated tank for long-term safety.

Calculating Wall Thickness

The calculation for this geometry comes down to the allowable hoop stress of the construction material. Hoop stress is the force applied to the tank wall from inside the tank. Hoop stress is higher on a tall tank with a small diameter, because it is measured in pounds per square inch of pressure in that tank.

A six-foot diameter tank holding the same chemical and gallonage as a twelve-foot diameter tank will have less surface area on the bottom sidewall, so it will require thicker walls to compensate for the greater hoop stress. We make our calculations and design each tank based on the ASTM D 1998-13 standards. You can download an explanation of the ASTM standard for more information.

How Wall Thickness Is Measured and Verified 

Poly Processing uses multiple methods to verify wall thickness during and after manufacturing.

Ultrasonic Testing

Ultrasonic gauges measure wall thickness at defined points without cutting or damaging the tank. This method is standard for verifying consistency and identifying thin spots.

ASTM D1998 Hydrostatic and Impact Testing

Tanks undergo impact and hydrostatic testing to confirm that material thickness and strength meet ASTM requirements. These tests validate both the resin performance and the finished tank’s structural integrity.

Rotational Molding Control

Wall thickness is controlled by precise resin loading and real-time temperature monitoring throughout the molding cycle. Telemetry systems track the heating and cooling curve, ensuring uniform wall formation.

How Wall Thickness Varies by Tank Design

Not all polyethylene tanks have the same structural profile. Different configurations require different wall thickness strategies.

Vertical Tanks

Standard vertical tanks use the ASTM D1998 profile: thicker in the lower third and thinner near the top. This matches the pressure distribution created by the chemical column.

IMFO Tanks

IMFO tanks include an integrally molded flanged outlet. Because the flange sits below the knuckle radius, the tank must maintain structural strength in the discharge area. The molding process creates uniform, enhanced thickness around the IMFO outlet.

SAFE-Tank Systems

SAFE-Tank double-wall systems include an inner tank with an ASTM-designed wall profile and an outer tank that acts as integrated containment. The combined system handles both chemical weight and emergency containment loads.

Cone-Bottom Tanks

Cone-bottom designs require extra structural strength near the cone transition. Load-bearing demands and complete-drain requirements drive thicker wall sections in the lower cone area.

Signs That a Tank Wall May Be Too Thin

Early detection of compromised wall thickness can prevent a costly failure. Watch for:

• Excessive bulging or out-of-round geometry
• Localized thinning detected during ultrasonic testing
• New stress cracks, especially near fittings
• Soft or chalky surface indicating chemical or UV degradation
• Leaks around threaded connections where stress has increased

If any of these signs appear, take the tank offline and conduct a full evaluation.

When to Upgrade to a Thicker-Wall Tank

A thicker-wall or higher SG-rated tank may be required when:

• You change the chemical to one with higher specific gravity
• Process temperatures rise above typical limits
• The chemical has strong oxidative properties
• You increase batch volumes or tank cycling frequency
• You experience accelerated wear near fittings or the tank bottom
• Your application now requires additional safety margin or extended service life

Selecting the correct chemical storage tank wall thickness at the beginning of a project reduces long-term operational risk and lowers lifecycle cost.

Get Expert Support

Correctly specifying wall thickness for a polyethylene chemical tank protects your people, equipment, and chemical inventory. If you need help evaluating your current tanks or planning a new system, our technical team can review your application and recommend a safe, compliant solution.

Contact us to discuss your chemical storage needs.