Corrosion is one of the biggest causes of early failure of metal parts and, where appropriate, the use of the right coating can add years to the life of a part in harsh conditions.
Which Materials Give the Best Protection
For corrosion protection, commonly used thermal spray coating materials are Zinc, Aluminium and Zinc-Aluminium (pseudo-alloy, 85%Zn 15%Al) sprays. Zinc coatings are suitable for use in mildly aggressive environments. Aluminium coatings provide good corrosion resistance at higher temperatures and in acidic or marine environments.
How Sacrificial Protection Works
The corrosion coating is sprayed on as a sacrificial anode. The sacrificial coating protects the substrate metal by corroding slowly instead. If the coating has suffered damage by scratching or by having developed small cracks, then the area around the affected portion will continue to corrode in its place. This form of protection is far superior to paint in regards to cut-edge corrosion, since paint cannot self-heal when it has been scratched through to the underlying metal.
Environments and Industries That Benefit Most
Marine structures, offshore platforms, chemical plant pipework, bridges, and port structures are typical applications for corrosion protection. A thermal spray corrosion coating offers greater resistance to salt, moisture, and chemical exposure than paint, and can even withstand continuous salt spray testing which would strip a conventional paint system within a few years.
How Thickness Affects Corrosion Life
Coating thickness can significantly impact corrosion protection, and typically would be specified in the region of 100 to 200 microns for corrosion protection. However, in offshore/marine exposure (e.g. standing seawater) the coating thickness could be increased to 200+ microns. Information on process controls to ensure consistent and acceptable coatings is given in the UK government’s metal powder and other thermal spraying: process guidance note 6/35.
Surface Preparation Before Coating
Thermal spray coatings are sensitive to surface preparation which is critical for adhesion. In order to achieve a suitable bond to steel surfaces, they must be clean and free from oil, mill scale and rust. The surface profile of blasted surfaces should be approximately 60-100 microns Ra and ideally cleaned to a Sa3 surface (white metal cleanliness). If you want Thermal Sprays, https://www.poeton.co.uk/surface-treatments/thermal-metal-sprays is a good place to start.
If the right choice of material is applied at the correct thickness to the relevant application, then thermal spray coatings are among the most durable corrosion protection solutions available to metal structures and components.
Leave a Reply