Metal oxidation
Limiting corrosion and reducing costs

Oxidation damage is the number one enemy of the most common ferrous metals used in the manufacture of mechanical components. Despite being an unavoidable phenomenon, it is still possible to reduce the effects through appropriate measures to be taken during the production process and handling.

The process of atmospheric oxidation only occurs in the presence of:

• A ferrous or otherwise non-self-passivating metal substrate
• Water in a liquid state
• An oxidising environment, with dissolved oxygen in the air-water medium

Corrosion of ferrous metals by oxidation is an inexorable and progressive process since rust (mainly oxidised iron or Fe2O3) is a friable and porous material that tends to flake off, freeing the underlying surface and making it vulnerable to further attack.

Amongst the hidden costs that manufacturers of valves, pumps and fluid interception components in general have to bear, those related to oxide formation have a considerable impact on company budgets. By taking certain measures, it is possible to reduce or even eliminate its occurrence.

Prior to the application of any permanent coatings, the semi-finished products may be subjected to wet corrosion attacks. This can happen during:

• Machining, such as by chip removal
• Handling in the production cycle
• Testing whereby involving the use of aqueous solutions, such as for valves, pumps or hydrostatically-tested parts
• Warehouse storage outdoors and/or indoors in damp locations
• Transport by land or sea, being truly critical in the case of the transfer of goods by sea

Ferrous alloys subject to atmospheric oxidation can be protected during their production cycle with coatings of various types and compositions, namely:

• Temporary > consist of the application and/or protection of surfaces exposed to atmospheric corrosion by removable protective barriers, recommended when subsequent passivation, coating or painting operations are planned
  
  
• Permanent > applied to metal surfaces to prevent the formation of iron oxides during the production cycle

Which lubricant composition is best suited to your logistics and production process?

• Pastes and gels > grease compounds with high protective power, suitable for use in mechanical devices such as actuators, gears and kinematics operating in external parts, usually also used as lubricants
  
• Dry film coatings > dispersions of protective waxes in a fast-evaporating solvent, leaving a dry film on metal surfaces that is particularly resistant to wash-off
  
• Protective oils > fluids of an oily consistency of a mineral or synthetic nature, enriched with corrosion-inhibiting additives
  
• Corrosion inhibitors > concentrated salt solutions to be diluted in mains water to 3>5%, suitable for testing valves, pumps, heat exchangers and pressure equipment
  
• Emulsifiable > mineral or synthetic oils formulated with surfactants for easy suspension in water, being suitable for testing, such as corrosion inhibitors
  
• VpCI > polyethylene-coated paper impregnated with corrosion inhibitors to create a protective barrier against salt spray and produce a reducing (protective) atmosphere around the semi-finished product