We often think of metal as a timeless material, but this opinion is not always true. Measures must be taken to protect metal surfaces from corrosion. In the US, the direct cost of corrosion damage exceeds $280 billion per year (according to ASM International). From the moment a metal surface becomes shiny and exposed during machining, thermodynamic and kinetic factors are constantly destroying it. Water and oxygen, necessary for human life, are not your friends when it comes to corrosion of metals. Acids, corrosives and suspended solids will also join and dance in Deathwatch.
Any type of equipment requires protection and storage procedures to protect the investment. The company policy, discipline and culture required to integrate procedures and properly store goods is critical. In my November 2016 column, I described the proper steps to store pumps and spare parts. For more information, see the 2016 column cited and/or the pump and seal manufacturer.
First of all, pay attention to the difference: rust is a type of corrosion, but not all corrosion is rust. There are at least 10 major types of corrosion and at least 7 types of pitting that attack the metal surfaces of pumps. Generally, corrosion is divided into two different types: general corrosion and localized corrosion. General corrosion problems are usually easy to detect and fix, but localized corrosion problems can be more difficult to diagnose and fix.
The easiest thing you can do to protect your pump externally is to make sure it is properly painted/coated. Paint or other technical coating systems are a relatively inexpensive but effective protection system. Painted surfaces damaged during transport, installation or maintenance must be refinished before the pump is put into service. Paint system defects will never heal on their own and will inevitably lead to corrosion damage. Special coatings are available for high temperature applications, as well as hazardous chemicals and marine environments. There are many companies that do not paint the metal surface on alloy steel equipment.
Be aware that corrosive elements can come into contact with pump surfaces in a variety of ways, including mist/fog/dew/steam, drips and splashes. Understand that water doesn’t have to be in visible or liquid droplets; humidity can provide all the moisture needed for corrosion to occur.
An initial and important decision is to determine which material is best suited for a given application. This includes wetted parts (impeller, stuffing box and housing) and other components. Remember that even non-wetted parts are exposed to aggressive media.
Post time: Apr-07-2023