There are two types of coating failure; predictable and unpredictable. All coatings are designed to provide a certain level of performance in a specified environment. If failure occurs prematurely, something has gone wrong!
If failure occurs, it is generally the result of a problem associated with the selection or application of the coating. It is possible to evaluate the chances of a coating failing prematurely using statistical methods to determine the Reliability Factor of a particular coating system. This work was done initially by Dr. J.F.H. van Eijnsbergen in the Netherlands to develop simple statistical methods for evaluating the reliability of any applied coating.
Dr. van Eijnsbergen developed a scale of Relative Importance in which a factor (I) can be allocated to each and every element in the coating process. This factor is logarithmic and rates the importance of a particular element in relation to the coatings performance.
Factor
8
4
2
1
0.25
0.125Importance
Very high or dominating in comparison to all other parameters
High or dominating in comparison with all other parameters
Significant over other parameters
Equivalent value to other parameters
Of minor significance over other parameters
Of no significance in comparison to other parameters
By allocating Relative Importance Factors (IR) to the elements making up a coating system, a Total Reliability Factor (FT) can be obtained from the sum of these. The lower the FT, the higher the reliability of the coating system.
By applying Relative Importance (IR) factors to such elements as steel surface condition, weather conditions, presence of soluble salts, surface preparation and other elements to whatever level is deemed necessary for a particular analysis (there are more than 100 factors to which Relative Importance (IR) factors could be applied in relation to coatings), the particular coating system's reliability can be given some statistical significance.
To assist in logically rating performance, a Degree of Reliability (RT) factor can be produced using the formula RT = 100 / FT. The higher the Degree of Reliability (RT), the higher the level of coating reliability in relation to other coatings.
Reliability Parameters
There are six basic parameters that impact coating reliability. These are;
|
1. Steel surface and shape |
4. Application of coating system |
Each of these parameters has its own set of parameters which is important in determining the reliability of a coating system.
Why is Hot Dip Galvanizing so Reliable?
Both Factory applied paint coatings and especially field applied paint coatings will always be less reliable than factory applied galvanizing. A simple test is to observe the performance of paint coatings vs galvanizing coatings in service today. In the entire USA area there are VERY few examples of galvanized coating failure on millions of items that are in service throughout the United States. Signposts, fence posts, guardrail, mesh fencing, trailers, transmission towers and countless other hot dip galvanized items are still doing there job preventing rust with the intact coatings after 20, 30 or 40 years.
When you look around at painted steel surfaces you also will find a major repainting industry, thriving and very profitable attempting to address the major and frequent paint failures in the public domain. However, In today's market it is nearly impossible to find a maintenance galvainzing industry as it is NOT needed.
The reason manufacture or field applied paint coatings are far less reliable than hot dip galvanized coatings can be shown statistically by applying the Reliability Factor analysis above to each system using the parameters that are relevant to the application of the coatings.
Conclusion
When the numbers are worked it illustrates that PAINTING IS Almost 400% more likely to fail in a typical paint application. Another way to say it is Galvanizing is 400% better than painting. On the other hand, once the hot dip galvanized coating is present it will NEVER FAIL due to application related factors as the galvanized coating will not form unless the steel surfaces is prepaired and fluxed before dipping. Hot dipped Galvanizing molecules have interelaced with the steel molecules at the surface and pentrated below the surface. Bottomline is galvanizing is molecule bonding or marriage of metals, at and below the surface. No painted application can compete with galvanizing for protection against the elements and mother nature. Paint looks good until you drive it off the dealers lot. Once the unit is put to work, the rust battle is lost.
In rugged appliations such as dump bodies, painted coat will reliabliity last as long as the first rugged use of the equipment. As soon as the paint coat is pentrated, or nicked rusting will pentrate under the paint coat. The laws of nature are time honored and the rusting process will destroy the best paint job quickly. Hot dipped galvanizing never fails due to poor applications and their performance is not subject to handling or transportation.
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