The limitations of fusion bond epoxy

Denis Grimshaw looks at why fusion bond epoxy (FBE) is not a universal solution for corrosion protection.

FBE has been widely used as a stand-alone coating in North America and certain other parts of the world. With a well satisfactory performance and a good track record covering over 30 years, stand-alone FBE has not been however a universal solution to the pipelines need for protection against corrosion.

Over the years, the application of FBE has developed with improvements in procedures and processes as well as increase in quality assurance processes to a level that ensures reliable anti corrosion performance. Many girth weld coating systems are compatible with FBE; cathodic protection is compatible with FBE with little or no perceived risk of cathodic shielding. So why is FBE not a universal solution?

The resistance of FBE to mechanical damage could probably be the major reason. Resistance to mechanical damage during handling in the pipe coating yard, resistance to damage in the transportation to the right of way, resistance to damage during the installation and in particular during the backfill operation when the most arduous mechanical forces are placed on the coating. During this stage the coating is subjected to many impacts from falling stones while the trench is filled and the pipe buried.

This lack of resistance to mechanical damage gives rise to many extra processes in the laying of a pipeline. It increases the need for holiday testing, and each holiday test increases the likelihood of a failure. This is especially true if the pipeline coating is tested damp. Any detected damage gives rise to a requirement for repairs, which need to be carried out in the field. Often hurried and not well executed these repairs can compromise the integrity of the pipeline.

To reduce the effects of backfill it is frequently necessary that a special backfill is carried to the right of way pipeline in order to reduce the damage. In areas where FBE is the coating of choice the procedures developed over the decades have minimized these problems to an acceptable level.

FBE systems have also improved in their performance to eliminate this damage risk. An example of which are the mechanical overcoat systems, MPS or ARO. These systems consist of two layers of FBE-based materials. The first layer consists of the anticorrosion FBE coating while the second is an FBE modified for improved impact resistance overcoat.

The latest in these improvements is a three-layer system where all the layers are FBE-based. The first layer being the primary anticorrosion layer, the middle layer being a resilient epoxy, and the top-coat being a tough skin based on epoxy. This synergistic combination provides a performance similar to three-layer polyethylene coating in many respects.

Such systems provide the benefits of FBE for protection against corrosion, girth weld compatibility, and cathodic protection compatibility while at the same time improving the handling ability of the coated pipes during storage and installation.

Denis Grimshaw is Product Manager at Jotun Powder Coatings. Currently based in Dubai, with over thirty years’ experience in the powder coatings industry, Grimshaw has global responsibility for the functional powder business at Jotun. An active member of NACE’s technical committee, he is also a member of British Standards, European Standards and ISO committees, responsible for writing specificiations for the pipe coating industry. Grimshaw can be contacted at Jotun Powder Coatings AS, PO Box 51033, Dubai, United Arab Emirates, on + 971 4 347-2515, or denis.grimshaw@jotun.com.