The long term safe handling of Sodium Hypochlorite has long been a controversial discussion point with much conflicting information of which we address as follows:

As a general class of material, both PE and Polypropylene are recognised for their excellent resistance to harsh chemical environments, safely handling the commonly used products such as Caustic, Hydrochloric and low concentration sulphuric acids. This property has resulted in the successful utilisation of polyolefines in applications such as chemical tanks, industrial piping and of course pumps. The ability to measure and predict chemical resistance is extremely important. There are 2 basic types of chemical attack; Solvation and chemical reaction.

Solvation occurs when a chemical either dissolves the polymer, or more commonly, is absorbed, causing swelling and/or softening of the polymer, often resulting in mechanical failure or ‘ceasing’ of the rotating elements of a centrifugal pump for example. In this case, no chemical change occurs in the polymer and may even be reversible in very mild cases where swelling is minimal.

When a chemical reaction takes place, there is a change in the chemical structure of the polymer often causing a change in molecular weight and a loss in physical properties.
Another related mechanism is Environmental Stress Cracking (ESC). Although ESC is often described as a chemical attack, it is a very complex combination of plasticising, migration, low level stress and mechanical failure initiated by exposure to specific classes of liquids, primarily surfactants (soaps). ESC is a failure mechanism more commonly seen in PE, however in certain liquids such as Sodium Hypochlorite (bleach) , Polypropylene also suffers failure resembling ESC. The failure being caused by strong oxidising effect of the bleach that causes degradation and in turn failure.. Failure is commonly seen at specific cross section points, namely sharp corners in the components of pumps, valves and joints in pipework and edges of tanks.

While Polypropylene will provide a limited operational life, it is highly recommended to upgrade material specifications of items such as pumps to material such as PVDF, ETFE or even PFA to give provide a safe, long term installation.