 |
| Example of pitting corrosion |
Whereas pitting is characterized by extremely localized attacks that, over time, create holes in the material, uniform corrosion takes place as an evenly distributed reduction of the material’s thickness. The nature of these two forms of corrosion may have quite different consequences because pitting corrosion causes small, sometimes almost invisible damage that may go deep into the design’s structure.
 |
| Example of uniform corrosion |
Uniform corrosion, on the other hand, reduces the overall thickness of the design. Uniform or pitting corrosion occurs when the material is exposed to conditions that attack the material surface, such as acids, salts and flow conditions in a tube. Thus, the choice of material is vital to achieve a good design against corrosion.
Uniform and pitting corrosion in all-aluminium heat exchangers can be avoided. Design against corrosion prescribes selection of the right aluminium alloy for the specific environment in which the design will be used.
| Environment vs corrosion rate (μm/year) |
Copper |
SX 316 |
Aluminium |
Mild steel |
SX 304 |
| Rural |
0.5 |
0.0025 |
0.025 |
5.8 |
0.0025 |
| Marine |
0.8 |
0.0076 |
0.432 |
34.0 |
0.0076 |
| Marine-industrial |
1.0 |
0.0051 |
0.686 |
46.2 |
0.0076 |
As displayed in the table, the corrosion rate of aluminium is very low when the design is correct. The automotive and oil industries are examples of areas where aluminium has been successfully introduced due to well-considered design of aluminium systems.
