The effects of application temperature, degree of cure, film thickness on cathodic disbondment of FBE coatings are examined to see which has the largest effect. These three factors were examined because they are all thought to have some effect on cathodic disbondment (CD), a low application temperature has been blamed as causes as loss of adhesion. These effects were examined for conventional (a commercially available FBE with twenty years track record) and a new generation (a commercially available FBE with two years track record) FBE. CD was selected as the key performance test for adhesion because it simulates field conditions for disbonding of a coating from a pipeline with applied cathodic protection. The new generation FBE coating performs significantly better for CD test than conventional FBE under all application conditions examined. Thickness of the coatings has more impact on the CD performance than application temperature especially for the new generation FBE. The CD performance of both conventional and new generation FBE coatings improves with an increase of cure percentage as determined by differential scanning calorimetry (DSC). The new FBE should be used where superior cathodic disbondment properties is needed.
Fusion bonded epoxy is considered a superior coating material for underground pipeline protection since it has excellent adhesion to steel, good chemical resistance, low oxygen permeability and good flexibility [1]. FBE has been used for this purpose for decades on pipes to transport gas, oil and water. As pipelines go deeper and longer to cross areas with limited maintenance facilities for cathodic protection, requests for FBE to work under higher temperatures and with longer life are increasing. There are many factors that can affect the long term performance of the coating, one of them is the formulation of the coating, another one is the surface preparation of the metal substrate before the coatings are applied [2]. It is known that improved adhesion would enhance the FBE/cathodic protection performance. Adhesion comes from mechanical, polar-polar (e.g. hydrogen bonding) and chemical bonding to the substrate [3]. FBE manufacturers continue to develop products with enhanced adhesion to meet different market needs. Edmondson recently reported a new generation FBE with exceptional adhesion and cathodic disbondment results [4, 5]. Six Sigma methodology was used to optimize the formula leading to a new range of products which tolerate more surface contamination and a wider steel application temperature window than a conventional FBE.
As part of the effort to understand this new technology for pipe, valve and rebar application, the study focused on the influence of application variables on the cathodic disbondment test. CD was selected as the key performance test for adhesion because it simulates field conditions for disbonding of a coating from a pipeline with applied cathodic protection. In this paper, the effects of application temperature, degree of cure and film thickness on cathodic disbondment of conventional FBE and new generation FBE coatings are reported. A conventional FBE was chosen as a benchmark and compared to a next generation FBE which offers better adhesion at lower application temperature [4]. Application temperature ranged from 180 to 240°C, thickness from 75 to 350 microns, and cure from 70% to 100%. Long term CD test with phosphoric acid treatment to remove containment is also studied.
Experiment
Materials. Both conventional and new generation FBE powders used here were Nap-Gard®1 products and produced by DuPont Powder Coatings, Houston, TX. Both products had a 22 second gel time per CSA Z245.20-98. Panels for CD
