Is mechanical resistance a limitation to using FBE?

An Ask the Expert feature with Jotun Powder Coatings

FBE has been widely used as a standalone coating in North America and certain other parts of the world. Performing well with a good track record covering 30+ years stand alone FBE has however not been a universal solution to the corrosion protection needs of pipelines.

Application of FBE has, over the years 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 is probably the biggest 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 during the backfill operation. Particularly 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 as 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 minimised these problems to an acceptable level.

FBE systems are also improving in their performance to elimination 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 layer is an FBE modified for improved impact resistance overcoat. The enhanced mechanical resistance can be demonstrated

With stone drop tests such as ASTM G13 of with a heavy duty scratch test called a gouge test which involves a load on a defined tip being dragged over the coating and the load to penetration being evaluated. Typical loads for a standard FBE would be 25Kg but for a protected FBE would be double that.

The latest systems such as Jotun’s J-trac which feature an engineered multilayer FBE system which gives performance comparable to three three-layer PE and even superior on some measures such as gouge resistance.

Such systems give the benefits of FBE for corrosion protection, Girth weld compatibility and CP compatibility while at the same time improving the handle ability of the coated pipes during storage and installation.

The answer is therefore no, mechanical resistance need not be a limitation to the use of FBE.

Written by Denis Grimshaw, Jotun Powder Coatings A/S, P.O. Box 51033, Dubai, United Arab Emirates. For more information please contact Tel: 971-4-347-2515 or email denis.grimshaw@jotun.com.