2009

Copyright ©2009 by NACE International. Requests for permission to publish this manuscript in any form, in part or in whole must be in writing to NACE International, Copyright Division, 1440 South creek Drive, Houston, Texas 777084. The material presented and the views expressed in this paper are solely those of the author(s) and are not necessarily endorsed by the Association. Printed in the U.S.A.

SOLUTIONS FOR SURFACE TOLERANT COATING AND REPAIR APPLICATIONS

Ivan Ordaz Belzona, Inc.

2000 NW 88th Court Miami, FL 33172

iordaz@belzona.com

ABSTRACT

The corrosion process requires four key factors: an anode, a cathode an electrical connection, and an electrolyte. Removing any one of these factors will effectively halt corrosion. Polymeric coatings act as electrical insulators between the substrate and the electrolyte. The insulating barrier blocks the exchange of ions therefore halting corrosion of the metal substrate. Adhesion is critical to such a system. Good adhesion is achieved by a rough angular profile on the substrate to allow the polymer to physically grip the substrate. Common standards require at least a 3.0 mil (76 microns) angular profile and a NACE No. 2 /SSPC-SP 10 surface cleanliness. Unfortunately, in the field, it is difficult to meet all these requirements. New technology in polymeric materials has led to the development of epoxy-based products that can be applied onto wet and oily surfaces, therefore easing some of the typical surface preparation requirements. These materials are effective at displacing contaminants from the substrate via a strong electronic affinity with the metallic substrate, thus allowing the epoxy to penetrate the profile and create a strong mechanical bond.

Keywords: epoxy, coatings, surface, tolerant, underwater, contaminated, surface, polymer, solvent, free, offshore, preparation, substrate, adhesion, profile

INTRODUCTION

Corrosion is a thermodynamically driven process, chemically represented by a series of reactions leading to a state of equilibrium. Unfortunately, human nature seeks to create complex ordered structures through technological advances, which nature constantly attempts to degrade and destroy to reach its desired equilibrium. It is an arduous battle which will never be won, but there are measures that can be taken to delay the unavoidable, and protect valuable industrial assets. The corrosion process requires four key factors: an anodic material,

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a cathodic material, an electrical connection, and an electrolytic solution. Removing any of these factors will effectively halt the process. Polymeric coatings act as electrical insulators between the metallic substrate and the electrolyte. The insulating barrier blocks the exchange of ions, therefore halting the corrosion of the metal substrate.

For such a system to be effective the polymeric coating must possess certain critical properties. The polymer coating must be impermeable to create a true isolating barrier between the electrolyte and the substrate, and must be an electrical insulator. In addition, the coating must have a high adhesion force to the substrate. These factors are critical in any coating meant to protect assets from the destructive effects of corrosion. The coatings industry is constantly implementing new technological solutions to meet such essential properties. Most notably, solvent-free epoxies with excellent mechanical properties and high degree of polymeric cross-linking have been lately introduced to minimize permeability and maximize mechanical and chemical strength. A key factor is the solvent-free composition; similar but solvented counterparts have porosity as a distinct disadvantage. During the cure of a solvented coating the solvents must escape. This has been known to produce negative properties such as porosity of the coating and induced internal stress, caused by the thickness change during the cure process.

Adhesion of a coating is critical. Regardless of how mechanically strong or chemically resistant a coating might be, if it does not adhere to the substrate it will fail to protect the asset. Adhesion testing is a good measure of quality as it can quantify both the strength of the coating and the degree of surface preparation. Common coating standards require a minimum of 3.0 mil (76 microns) angular profile, a NACE No. 2 / SSPC 10 surface cleanliness, and SSPC-SP 1 solvent cleaning. Unfortunately, in the field there are situations where it is difficult to conform perfectly to these requirements. New technology in polymeric materials has led to the development of solvent free epoxy based products that can be applied onto wet and oily surfaces, therefore easing some of the typical surface preparation requirements.

Solvent-free epoxies are highly cross-linked polymers that minimize permeability, and are non-conductive materials. Due to recent introduction of plasticizers, these epoxies can now be applied to wet and oily surfaces. New additives and plasticizers allow the polymer to absorb water and oil contaminants that remain trapped between the surface profile and the coating material. The contaminants are consumed and become part of the polymer themselves. As the contaminants are absorbed, the polymer takes their place into the profile, hence improving the adhesive strength of the coating.

PROCEDURE

Laboratory adhesion testing has been performed to quantify the effectiveness of surface tolerant coatings. The objective of this test was to compare the effect of surface contamination and surface preparation methods on the tensile adhesion force of the coating, measured as per ASTM D4541 standards. An adhesion tester was used to determine the adhesion force in pounds per square inch (psi); six dollies were used per test to establish repeatability. The surface contaminants compared were tap water, cutting oil, and a 50/50 water-oil emulsion. A

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control was also tested without any contaminants as per SSPC-SP 1 solvent cleaning procedure to establish a base line. The surface preparation tools evaluated were wire-brush, grinder, and bristle blaster.

FIGURE 1 – Adhesion testing

The steel plates were prepared with the respective tool and contaminated with the corresponding contaminant. Aluminum adhesion test dollies were roughened and solvent cleaned. The epoxy material was mixed conforming to manufacturer specified ratios. Then it was applied onto the steel plates using a short bristle brush as a two coat system of 12 mils (305 microns) per coat as suggested by manufacturer’s specifications. Once the epoxy had been applied, the test dollies were embedded into the material normal to the plate surface, and left to cure for full mechanical cure as per manufacturer specifications. Once cured, the dollies were pulled off with the adhesion tester and the values were recorded along with the mode of failure.

RESULTS

The adhesion forces are shown in Table 1 and the modes of failure in Table 2. Since only one layer of material existed and the dollies were embedded in the material, there were only three possible modes of failure: adhesive failure of the material to the substrate, cohesive failure of the material, and adhesive failure to the dollies. All the tests resulted in either

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cohesive failure of the material or adhesive failure to the substrate. No adhesion failure was observed to the dollies. Table 2 indicates the mean failure modes for each test.

TABLE 1 ADHESION FORCE (PSI)

Control Water Emulsion Oil Wirebrush 2074 1800 906 1609

Grinder 2277 2082 1557 1721 MBX 2572 2151 1547 1201

TABLE 2 FAILURE MODE

Control Water Emulsion Oil

Wirebrush100%

Cohesive 80%

Cohesive 100%

Adhesive 100%

Adhesive

Grinder100%

Cohesive 90%

Cohesive 100%

Adhesive 100%

Adhesive

MBX100%

Cohesive 90%

Cohesive 100%

Adhesive 100%

Adhesive

A clear trend can be seen from both tables of results. Figure 2 shows a graph of the adhesion forces with corresponding 95% confidence intervals. As expected, wirebrush was the least effective form of preparation, followed by grinding. The best of these three was bristle blaster. The contaminants also showed a clear effect on the adhesion of the product. The contaminant-free control, as expected, showed the highest adhesion, followed by water. The water/oil emulsion and the oil did not show a clear difference or trend. It was observed from the tests and the raw data that adhesion when oil is present depends heavily on how well the oil gets displaced when the material is being applied.

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FIGURE 2 – Adhesion test graph

Per manufactured recommendations, their products must be always applied by bush and continuous force must be exerted to physically displace the contaminants. The remaining thin film that is trapped between the substrate and the product is absorbed by the product’s plasticizers. The same applies to water contamination. It was observed though that the hydrophobic nature of the product tends to displace water much more efficiently.

CONCLUSION

From Table 1 it can be seen that the lowest and highest adhesion values were 906 psi, and 2572 psi respectively. These products clearly provide a high level of adhesion even when application conditions are not ideal. These products have proven to be very effective not just in lab testing but in the field as well.

FIGURE 3 - Riser surface preparation using a grinder

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FIGURE 4 – Riser coating application using surface tolerant product

These coatings were developed particularly for offshore drilling where corrosion is a serious problem in the splash zones. Surface tolerant epoxies can be used to coat jetty legs, pylons and other splash zone surfaces. In these areas, the only other solutions for corrosion protection involve removing the equipment from water, which is not always possible; or constructing coffer dams, which are not economically attractive. As it can be seen in Figure 3 and Figure 4 above surface tolerant coatings allow for simpler applications on hard to reach splash zones. In areas such as these simplicity is very valuable since scaffolding is not always possible. Coating Preparation can be done with simple hand tools and application can take place over wet contaminated surfaces. These applications have been performed for over a decade and have been shown to be a very effective solution. The repair shown in Figure 3 and Figure 4 was performed in Indonesia on August 2005 and is still protecting the risers to this day.

These products are bringing new life and practicality to the coating industry with fast, effective solutions that remove some impractical steps required by traditional coatings and polymeric repair materials.

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