Historically highly pigmented metallic zinc primers have been selected for highly corrosive environments such as the offshore and petrochemical industries. These primers gave excellent performance in accelerated corrosion tests and this correlated with what was seen in the field. The primer described in the paper has a long track record in offshore maintenance and repair, and for the first time it has been used in a new construction project for an offshore installation in the Caspian Sea. Until recently conventional anti-corrosive pigments have been unable to meet the performance levels of zinc rich primers in the offshore and petrochemical environments. This paper describes the evaluation of a metallic zinc free anti-corrosive primer which has been formulated to meet the requirements of today's aggressive marine environments, and come close to the performance of certain metallic zinc primers.
The cost of zinc on the global metal markets has increased significantly over the past 2-3 years (see Figure 1) and, indeed, the consolidation of zinc dust suppliers has fuelled the shortage of good quality zinc dust, i.e. conforming to ASTM D520 Type 2.
FIGURE 1 - Zinc Prices(available in full paper)
This has meant that the paint industry has had to increase prices of zinc primers and therefore pass on the cost to their customers. Zinc primers are generally formulated to meet detailed specification regarding zinc content, and a number of these can be seen in Table 1.
TABLE 1 SUMMARY OF ZINC RICH STANDARDS(available in full paper)
However, this is not the only option, as it has been shown from internal and external tests over many years that a zinc metal free primer can give some good anti-corrosive properties in certain paint formulations when used as a primer in a system containing HB intermediate and topcoat. Therefore, from work that has been carried out over the last 5 years, it has been observed that performance coming close to that of some zinc epoxies can be achieved. This paper details the performance of a 2K epoxy zinc phosphate (EZP), with comparisons to a SSPC 20 Level 1 zinc epoxy.
Testing was carried out to assess the suitability of a 2K EZP primer as part of a maintenance system and then later because of the good performance was tested as a high performance system for new construction.
A 2K epoxy zinc phosphate (EZP) has been evaluated as an offshore maintenance primer as part of an independent project. Initial testing showed that the system primed with the 2K EZP performed similar to that of the zinc rich epoxies. The work has been repeated to see whether this was a true reflection of the performance of the 2K EZP primer and therefore whether it could be used as an alternative to zinc rich epoxies for maintenance.
ISO 20340 is a cyclic corrosion test to evaluate a coating system's suitability to perform in marine environments classified as C5-M as per ISO 12944, Part 2.