Mar 22 2002
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Failure of a coating can be either predictable or unpredictable. All coatings are meant to provide a specific performance level in a particular environment. A premature failure specifies that there is an issue.
Failure mostly happens because of a problem associated with the application or the choice of the coating. The probability of a premature coating failure can be assessed using statistical methods to examine the “Reliability Factor” of a particular coating system. Dr. J.F.H. van Eijnsbergen from the Netherlands was the first person to conduct this study to develop easy statistical methods for evaluating the dependability of any applied coating.
Relative Importance Scale
Dr van Eijnsbergen developed a scale of “Relative Importance” where a factor (I) can be assigned to each element in the coating process. This logarithmic factor rates the importance of a particular element concerning the coating’s performance.
| Factor |
Importance |
| 8 |
Very high or dominating in comparison to all other parameters |
| 4 |
High or dominating in comparison with all other parameters |
| 2 |
Significant over other parameters |
| 1 |
Equivalent value to other parameters |
| 0.25 |
Of minor significance over other parameters |
| 0.125 |
Of no significance in comparison to other parameters |
A Total Reliability Factor (FT) can be gained from the sum of the Relative Importance Factors (IR) by assigning them to the elements that make up a coating system. The dependability of the coating system is inversely proportional to FT.
Some statistical importance can be given to the dependability of a specific coating system by applying IR to elements, such as surface preparation, steel surface condition, weather conditions, presence of soluble salts, and other elements to a level that is believed to be necessary for a particular analysis (IR could be applied to more than 100 factors in relation to coatings).
Coating performance can be logically rated by generating a Degree of Reliability (RT) factor using the formula RT = 100/FT. RT is directly proportional to the level of coating reliability, with regard to other coatings.
Reliability Parameters
The six standard parameters that impact the reliability of coating are listed below:
- Application of coating system
- Pre-treatment of the steel surface
- Coating or coating system
- Surface and shape of steel
- “Youth” period of the system
- Service exposure period
Each parameter stated above has its own set of parameters that are vital in determining the dependability of a coating system.
Why is Hot-Dip Galvanizing so Reliable?
In contrast to field-applied coatings, factory-applied coatings are more dependable as the same control cannot be implemented for an application in the field. A simple test would be to observe the performance of coatings being used.
Among the millions of items that are in use, there are very few instances of failure relating to galvanized coating. Fence posts, guardrails, signposts, transmission towers, mesh fencing, trailers, and several other hot-dip galvanized items remain rust-free, where the coating is not damaged even after 40 years.
While observing painted surfaces, failures are clearly seen almost everywhere. Flaking paint, rust, and other indications of paint failure are accountable for the sustenance of the maintenance painting sector. However, a maintenance galvanizing industry is not present.
Reliability Factor analysis can be applied to expose the reason behind the relative unpredictability of field-applied paint coatings compared to hot-dip galvanized coatings. This can be achieved by evaluating each system and applying the parameters applicable to the coating application.
| Parameter |
Relative Importance (IR) |
| Paint |
Galvanizing |
| Surface condition |
4 |
1 |
| Surface preparation |
8 |
8 |
| Humidity/dew point |
8 |
0.125 |
| Coating Composition |
8 |
1 |
| Applicator skill |
4 |
0.25 |
| Curing conditions |
1 |
0.125 |
| Transport/handling |
8 |
1 |
| Total reliability (FT) |
41 |
10.5 |
| Degree of reliability (RT) |
2.44 |
9.5 |
Summary
This research shows that hot-dip galvanized coatings are approximately 400% more dependable when compared to paint coatings in a standard application. However, it does not expose the true dependability of galvanized coatings since it is only involved with the application stage of the process.
Once the hot-dip galvanized coating is applied, it will never fail because of application-related factors. This is because the galvanized coating forms only on flawlessly prepared steel surfaces, and it is possible to apply any paint on any surface to give an acceptable initial appearance.
The type of application largely decides the reliability of the paint coating. Furthermore, statistically, paint coatings have a 400% greater chance of failure when compared to galvanized coatings. Even if hot-dip galvanized coatings are applied in a substandard way, they never fail and their performance is also not impacted by handling and shipping.