Cold Formed Steel
Types and Durability
|
Description Cold Formed Steel |
Expected Lifespan ( Years ) |
Adjustment Factors
|
|
Internal
|
||
| Austenitic stainless steel to BS 970: Part 1, grade 316 or 304. |
35+
|
1st stage adjustment factor: In industrial areas (heavy polluted): -15% years In urban areas: -10% years In suburban areas: -0% years 2nd stage adjustment factor: Within 20m from express way: -20% years Within 20m from major arterial road: -10% years Within 20m from light traffic road: – 5% years Test certificate from approved local testing authority : +15% years Through dip in bitumen: +15% years. |
| Post-galvanized mild steel, minimum 600g/m² zinc coating weight. |
35+
|
|
| Pre-galvanized mild steel, minimum 600g/m² zinc coating weight. Factory applied organic coating, 25-50 microns nominal thickness. |
35+
|
|
| Mild steel, molten zinc sprayed after fabrication, minimum 700g/m² zinc coating weight. |
35+
|
|
| Pre-galvanized or post-galvanized mild steel, minimum 450g/m² zinc coating weight. Factory applied organic coating, 25-50 microns normal thickness. |
35
|
|
| Pre-galvanized or post-galvanized mild steel, minimum 275g/m² zinc coating weight. Factory applied organic coating, 25-50 microns normal thickness. |
30
|
|
| Pre-galvanized or post-galvanized mild steel, minimum 275g/m² zinc coating weight. |
25
|
|
| Mild steel protected with an appropriate Micaceous Iron Oxide, Chlorinated Rubber or similar high performance finish to give a minimum dry film thickness of 250 microns. |
25
|
|
| Unclassified, ie mild steel ‘factory primed’ or less than above specifications. |
< 25
|
Combination of adjustment factors (1st stage and 2nd stage) should be added to obtain the durability values. Refer to durability calculator.
Corrosion life of unpainted steel in atmospheric environment
| Atmospheric classification | Short term
(2-5 years) |
Medium term
(5-10 years) |
Long term (10-20 years) |
| Mild | Suitable | Suitable | Suitable |
| Moderate | Suitable | Suitable | Suitable |
| Tropical* | Suitable | Suitable | Suitable |
| Industrial | Unsuitable | Unsuitable | Unsuitable |
| Marine | Suitable | Unsuitable | Unsuitable |
| Severe Marine | Unsuitable | Unsuitable | Unsuitable |
* Not suitable when affected by sea salt spray
Note: The range of options for protecting steel is huge; therefore the classes listed are indicative only.