Increase coating lifetime by optimising pipe surface preparation

Coatings or adhesive bonded systems are used in different environments, for various applications. All have been designed and developed for a specific lifetime. As such, adhesion is a critical link.

To improve the lifetime of 3-layer polyethylene (3 LPE) coated pipes for burried or submerged use, the pipe surface preparation procedure was evaluated by OCAS.

First, the right test methodology was developed together with the steel abrasive and coating suppliers.

Samples were then prepared in the lab by applying the 3 LPE coating system on test panels. The test panels were submitted to abrasive blasting. Furthermore, different levels of residual dust and/or salt contamination were applied to the bare surface of the test panels, prior to painting.

Coating lifetime was evaluated through cathodic disbondment test according to ISO 21809-1 annex H (-1,5V at 80°C during 28 days). The measured disbondment distance should not exceed 15 mm.

It was found that the cathodic disbondment distance significantly improves when reducing the residual dust level of the panels. Presence of residual dust seemed to have a stronger effect than salt contamination for the tested contamination levels. Using the cathodic disbondment distance to characterise the adhesion, enabled to define the acceptable process window.

The obtained results furthermore allowed to validate a new blasting process for the customer.

 

Being able to measure the influence of contamination levels not only allows to optimise surface preparation, it also provides the customer with a valuable tool to estimate the coating lifetime.”

    

Barbara Van Langenhove, technician Inorganic and Organic Chemistry, Electrochemistry & Corrosion team, OCAS