Novel multi-layer FBE pipe coating system announced

Pipeline & Gas Journal, Nov, 2007 by Denis Grimshaw

Fusion bond epoxy (FBE) has long been used as a protective coating for oil and gas pipelines with one consistent and major drawback--mechanical resistance. As FBE is a relatively thin, hard coat, it is prone to damage during handling and installation, as well as during operations. Some progress in improving this has been made over the years. The major improvement has been the dual-layer abrasion-resistant overcoat systems. These systems have improved impact and gouge resistance but at the expense of flexibility.

New Multi-layer FBE System

To take the performance to a higher level using a different concept, a new system for a multi-layer FBE-based coating has been developed by Jotun Powder Coatings resulting in a tough resilient, anti-corrosion coating. This new system is commercially branded J-trac.

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The Concept

The concept can be visualized by the model shown in Figure 1.

The system consists of three layers, each providing a different characteristic. The combination of these three layers work together to deliver high levels of performance.

The outer layer is a tough layer resisting damage arising from impacts and gouges. The middle layer is a resilient layer functioning as a cushion to absorb impacts and protect the inner layer. The inner layer is an FBE optimized to ensure good wetting, adhesion and anti-corrosion properties and designed to work with the protection of the outer layers.

The three layers are applied in a continuous coating operation similar to that employed for dual-layer epoxies. This results in the three layers being fused together.

Performance Delivery

How does the system work to deliver performance? By improving impact resistance, abrasion and gouge resistance and flexibility.

Impact Resistance

The tough outer layer minimizes impact damage. The middle resilient layer spreads the impact over a wider area, ensuring the impact energy is dissipated. The anti-corrosion inner layer is thereby protected from damage (Figure 2).

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The value of an energy absorbing process can be clearly seen in the comparison of two well-known impact test procedures. A standard FBE panel tested for impact, for example, in accordance with the AWWA C213 method, is required to meet a requirement of 11.J, but the same coating tested using the CSA Z245.20.06 method will only yield 2-3J. Why such difference? Because the energy is absorbed differently.

The AWWA method allows the energy to be absorbed by deforming the metal panel. In CSA, it is absorbed only by the FBE. With the new system, it is absorbed by the resilient layer, which also spreads the load, ensuring that it does not damage the anticorrosion layer.

Abrasion And Gouge Resistance

In this case, the tough outer layer resists penetration and the inner resilient layer absorbs and spreads the load (Figure 3).

When the load is heavy enough to penetrate the tough outer layer, the resilient middle layer acts as a lubricant to smooth the gouge and protect the anti-corrosion inner layer (Figure 4).

Flexibility

Stress on the tough outer layer is spread evenly. The resilient middle layer absorbs the bending force, reducing stress raisers, which can break the outer layer, ensuring the anti-corrosion inner layer is well protected (Figure 5).

The J-trac system features a combination of FBE powders providing all the benefits--and none of the weaknesses, of stand-alone FBE and multi-layer extruded coatings. In addition to long term anti-corrosion protection the J-trac system provides:

* Mechanical protection matching or exceeding multi-layer capabilities.

* Compatibility with traditional girth welds coating solutions for FBE.

* Negligible damage on concrete weight coating application.

* Advanced abrasion and impact performance.

* Compatibility with anti slip coatings.

* High flexibility at low temperatures.

* Cathodic protection transparency.

* Raised weld coverage.

* Pipe stress tolerance.

A full performance evaluation of J-trac against CSA Z245.20-06 is shown in Figure 6.

By Denis Grimshaw, Jotun Powder Coatings, UAE

Author: Denis Grimshaw is a manager of Jotun Powder Coatings. He can be reached at denis.grimshaw@jotun.ae, www.jotun.com.

Figure 6:

Property                                 Result          Specification

24 hours CDT at 65[degrees]C             4.0 mm          6.5 mm

28 days CDT at 65[degrees]C              4.0 mm          20 mm

28 days CDT at 23[degrees]C              2.0 mm          8.5 mm

X-section porosity                       1               1-4

Interface porosity                       1               1-4

2 degrees flexibility at -30[degrees]C   pass            No cracking

3 degrees flexibility at -30[degrees]C   pass            No cracking

Flexibility at 23[degrees]C              Results up to
                                         4.8 degrees
                                         per pipe
                                         diameter
                                         achieved        No cracking

3.0J impact resistance                   Pass            No holidays

Impact resistance                        Results up
                                         to 10J
                                         achieved        No holidays

24 hours at 75[degrees]C adhesion        1               1-3

28 days at 75[degrees]C adhesion         1               1-3

1.5 degrees strained CDT                 pass            No cracking

Cure conversion                          > 95%           > 95%

Property                                 Comments

24 hours CDT at 65[degrees]C             System 2 test

28 days CDT at 65[degrees]C              System 2 test

28 days CDT at 23[degrees]C              System 1A test

X-section porosity                       System 2 test

Interface porosity                       System 2 test

2 degrees flexibility at -30[degrees]C   System 2 test

3 degrees flexibility at -30[degrees]C   System 1 A test

Flexibility at 23[degrees]C

3.0J impact resistance                   System 2 test

Impact resistance

24 hours at 75[degrees]C adhesion        System 2 test

28 days at 75[degrees]C adhesion         System 2 test

1.5 degrees strained CDT                 System 2 test

Cure conversion                          System 2 test