How Chemical Stress Can Lead To Polyethylene Tank Cracks

In most polyethylene chemical storage tank operating and loading applications, a tank failure is primarily due to two types of stresses: chemical stress or mechanical stress.

Let's explore how chemical stress can cause cracks in polyethylene chemical storage tanks and advanced tank solutions that resist cracking.

What Causes Chemical Stress?

Most polyethylene chemical storage tanks are inherently robust and resist chemical forces that cause degradation and cracks because the forces of the chemical stress are dispersed over a wide area of the tank. However, external stresses over a lifetime of use can break down the tank’s properties, potentially causing cracks. If cracks occur, it’s recommended that you replace the polyethylene tank.

Chemical stress occurs when the chemical stored in the tank oxidizes or "plasticizes" the polyethylene. It's a combination of stress and degradation of the polyethylene itself. The chemical pulls electrons from the molecular chain of the polyethylene. As a result, the polyethylene molecular chain becomes susceptible to oxygen attack. Over time, as oxygen attacks the polyethylene, the tank becomes brittle and leads to stress cracks. 

Plasticizing of polyethylene is not as prevalent as oxidation. A plasticizing chemical modifies the molecular structure of a polyethylene tank. As a result, the tank wall is softened, causing increased swelling and expansion. Fortunately, only a hand full of chemicals will plasticize polyethylene and are not recommended for use in a polyethylene tank. These include hydrocarbon based materials such as 2 cycle oil, gasoline, etc.