Increased consumer awareness has allowed corrosion prevention products to develop and improve significantly. Through the application of existing or emerging technologies, advances are being made in all methods for corrosion control and its application. These prevention methods include temporary and permanent coatings, material selection, inhibitors, cathodic protection, and design.
Each closed system differs depending on several factors including size of facility and application. When designing the system consideration should be given for the mechanical and strength requirement, together with an allowance for corrosion.
The design of a system should take into account the materials to be used for various components within the system.
At design stage it is important that the correct metals that make up a system are given thought. At construction stage and pre-commissioning stage that the most suitable cleaner, inhibitor and biocide are selected. For commissioning and hand over it is vital that the water treatment company is aware of all the metals in the system so they can formulate a site specific water treatment plan for the site.
The implications of adding a high pH corrosion inhibitor to a system with aluminium is detrimental.
The technique of adding inhibitors to the environment of a metal is a well-established method for controlling corrosion. A corrosion inhibitor may act in a number of ways: it can restrict the rate of the anodic process or the cathodic process by simply blocking active sites on the metal surface.
Alternatively, it may act by increasing the potential of the metal surface so that the metal enters the passivation region where a natural oxide film forms.
The protection is achieved by supplying electrons to the metal structure to be protected. There are two ways to cathodically protect a structure; by an external power supply or by appropriate galvanic coupling.
On the ground there are several modifications to the environment which can help control corrosion:
- Lowering the temperature can slow down the rate of corrosion
- Adjusting the concentration of a corrosion solution will reduce the rate of corrosion
- Removal of oxygen or oxidizers in most environments decreases corrosion rate, but it is not favourable for active—passive metal or alloys since they require oxidizers to form and maintain protective films.
- Avoid high velocities as this will increase the rate of corrosion.
To help reduce the cost and the environmental impact of corrosion, and enhance the sustainability of materials, the use of any or all these methods are recommended and could lead to savings from 10 – 35% of the cost of corrosion.