Editors Note: : This article was presented at the 16th International Conference on Pipeline Protection in Paphos, Cyprus, November 2 - 4, 2005, and is published in the conference Proceedings.

Fusion-bonded epoxy (FBE) coatings have been applied to pipeline for more than 40 years. They have been used as stand-alone corrosion protection as well as the first layer in three-layer polyolefin systems. Typical application temperatures are in the range of 230 to 240 C for standalone FBE, while 200 C is commonly the application temperature for FBE when applied as the primer in polyolefin systems.

Fusion-bonded epoxy is a one-part, heat-cured thermosetting epoxy resin. The pipe is heated before application so that the applied powdered epoxy will melt, flow, adhere to the substrate, and cure within a defined time. Conventional products require temperatures generally in excess of 200 C to achieve good flow and wetting of the substrate. In order to produce a protective coating film, the powder reacts as it melts and flows. Therefore the powder must have the correct balance of reactivity and viscosity development in order to be acceptable as a pipe coating.

Developments in epoxy resin technology have now allowed formulators to develop powders that can achieve a good balance between these properties at lower application temperatures.

A preheat temperature reduction of approximately 50 degrees C represents a potential energy reduction of 20 to 30%.

Low application temperature FBE may also offer significant benefit s related to polyolefin waste reduction during application of three layer polyethylene and poly propylene products: the lower heat content enables more effective cooling of the coated pipe.

In addition, in upcoming pipeline projects in North America, such as the McKenzie Delta pipeline system and the PNG Australia pipeline, companies are investigating the use of high-strength steel with yield strengths in excess of X80 grade 1. The tensile strength of such steels can be influenced by induction heating at the normal application temperatures of conventional FBE.2 Therefore; lower application temperature products may be required for corrosion protection of such steels.

The work presented in this article addresses the performance of an FBE developed for application in the temperature range of 150 to 200 C. Data from laboratory work and application trials under full-scale conditions will be presented. The benefits obtained by using such a product are also discussed.

FBE formulations designed for applications at low temperature were qualified in accordance with CSA Z245.20-02³. Powders were applied onto steel panels that had been blast cleaned to achieve a surface cleanliness of Sa 2.5 (SSPC-SP10/NACE No. 2). No other surface pretreatment was used. The panels were heated in an oven to the desired temperature before application; the powder was applied by a conventional electrostatic spray gun. Panels were prepared at temperatures between 140 and 200 C. Third party testing of the product as a standalone coating was performed by I.T.I laboratories of Houston, TX, on panels that were coated at 190 C.

Plant trials were performed using the new low application temperature FBE as part of a three-layer polyethylene coating system. The coating system was applied to spiral welded pipe (24-inch diameter, 7.9 mm wall thickness). Application line speed was 1.7 m/min, the same as a standard system, and the FBE layer was applied at a thickness of 100 microns. A polyethylene copolymer adhesive was applied at a thickness of 300 microns, and a polyethylene topcoat was applied at 3.5 mm total thickness. Application temperatures of 150 and 160 C were investigated. The primary goal of these trials was to evaluate the benefits of such powders in the application of side-extruded, three layer polyethylene in terms of energy savings and reduction in polyethylene use over raised welds.

Melt viscosity data for a typical epoxy resin used in pipe formulations was measured with a cone and plate viscometer and compared with the new low application temperature resin. The average of four viscosity readings was taken at each temperature. The results are shown in Fig. 1. Resin A is the new low application temperature resin.

Table I outlines the acceptance criteria for testing of FBE coatings in accordance with CSA Z245.20-02 (3). Tables 2 and 3 present a portion of the results of independent laboratory testing of steel panels coated at 190oC using the low application temperature epoxy; the coating passed the acceptance criteria. [Editor’s Note: More results are presented in the original paper]

 

However, the formulation was further modified to improve adhesion. Adhesion testing of the modified formulation for the stand-alone FBE was carried out at various temperatures to identify the critical application temperature limit. Figure 2 presents cathodic disbondment test results obtained at 65 C after 7 and 14 days of exposure, Table 4 presents cathodic disbondment test results for additional long-term exposure of panels coated at 180 and 200 C. Figure 3 shows the results of the testing.

 

Table 4: Long-term cathodic disbondment results for low-temperature FBE

Many aspects of the pipe coating process depend on time and temperature. Whether used as a stand-alone product or as the primer in a three layer system, the FBE powder is electro statically sprayed onto the heated pipe and, to achieve good adhesion, has to melt and flow into the anchor profile of the cleaned pipe surface. At the same time the epoxy is reacting and cross linking to form a stable film. The ability to wet the steel surface is a combination of effects that are related to the melt viscosity of the epoxy resin as well as the gel time or reactivity of the powder. Conventional FBE has a relatively high melt viscosity at temperatures below 200 C, and it is difficult for such epoxies to wet the steel surface at low application temperatures. In contrast, the newly developed formulation described here has much lower melt viscosity, even below 140 C (Fig. 1).

The results of third party evaluation of panels coated with the new low application temperature epoxy at 190 C met or exceeded the requirements of CSA Z245.20-02 for stand-alone FBE coatings (Tables 2 and 3). The obvious benefit is that the performance of a conventional FBE coating can be achieved at almost 50 C lower application temperature without a loss of productivity. Additional testing data presented in Table 4 and Fig. 2 suggest that as a standalone coating, the new FBE could be applied at temperatures as low as 180 C.

The results presented in Table 5 indicate acceptable performance of the FBE in a three-layer, side-extruded coating. In addition, application temperatures of 150 to 160 C can be used. Short term cathodic disbandment testing also exceeded the requirements of CSA Z245.20-02. Figure 3 depicts some of those results. Measurement of polyethylene usage at these lower application temperatures indicated that polyethylene waste could be reduced by more than 10%. Optimization of process parameters could result in further savings. In addition to savings in polyethylene material, the lower application temperature also reduces energy use by about 10%.

Low application temperature epoxies also offer advantages for coaling girth welds, including

• Faster cycle times due to the need for a lower peak temperature
• less stress on the parent pipe coaling during the heating stage, and
• lower energy requirement in the field situation.

Development of high-strength steels has been the subject of research for many years. Recently, several papers have described the development of XI00 and X120 steels for high-pressure gas transmission pipelines.4-7 One of the issues with these steels is that the yield-to-tensile ratio of the steel can be adversely affected during the induction heating processes for coating pipe with either stand-alone FBE or with three-layer polyethylene. The development of this new low application temperature FBE allows the design engineer to select an option that enables the pipe to be coated at temperature s well below 200 C, the temperature at which it is believed that yield to tensile properties are altered.

A low application temperature FBE has been developed that meets or exceeds the requirements of CSA Z 245.20-02. This FBE can be used as either a stand-alone product or as a primer in a three layer coating system to coat oil and gas pipelines. As a stand -alone coating, the FBE can be applied at temperatures around 190 C. and, as a primer, it can be applied at temperatures as low as 150 C without a reduction in productivity.

The low application temperature enables savings in energy and, in the case or a three layer polyethylene system, savings in material use. The lower application temperature FBE should also provide benefits for girth weld coating, specifically reducing cycle time and stress on the parent coating. The lower application temperature should make this FBE product suitable for coating of high strength steels currently being developed for high pressure, strain-based design pipelines.

• P Singh. S Haberer. N Gritis, R Worthingham and M Cetiner;  "New Developments in High Performance Coatings," 16th International Conference on Pipeline Protection. Cyprus 2 - 4 November 2005, Published by B1IR Group Limited, Editor David lorman.

• Australian Pipeline Industry Association Private Communication CSA Z245.20-02 "External Fusion Bond Epoxy Coaling For Steel Pipe," Canadian Standards Association, Etobicoke, Ontario. 2003

• Hans-Georg Hillenbrand, Andreas Liessem, Karin Biermann, Carl Justus Heckmann and Volker Schwinn, "Development of High strength material and Pipe Production Technology For X120 Line Pipe: ' Proceedings of IPC 2004, IPC04-0224, International Pipeline Conference, October 4-8, 2004,Calgary, Alberta, Canada.

• Hitoshi Asahi et al, "Development and Properties of Ultra-High Strength UOE Linepipe", Proceedings of IPC 2004, IPC04-0230, International Pipeline Conference, October 4-8, 2004, Calgary, Alberta, Canada.

• G Demonfonti, G Mannucci. H.G.Hillenbrand and D Harris, "Evaluation of the Suitability of XI00 Steel Pipes For High Pressure Gas Transportation Pipelines by Full Scale Tests: ' Proceedings of IPC 2004, IPC04-0145, International Pipeline Conference, October 4-8, 2004, Calgary, Alberta, Canada.

• Alan Glover, David Horsley, David Dorling, and Junichiro Takehara, "Construction and Installation of XI00 Pipelines." Proceedings of IPC 2004, IPC04-0328, International Pipeline Conference, October 4-8, 2004, Calgary, Alberta, Canada .