The enamelling of air preheater elements

In Spain, Howden have pioneered a dry electrostatic technique to enamel heater elements. You can watch a video of the process in action.


​The enamelling of air preheater elements, particularly those destined for oil fired stations, has long been common practice. This helps combat sulphuric acid corrosion; however the widespread adoption of flue gas desulphurisation demanded that the elements of the gas reheaters be enamelled to a higher grade than was previously possible.

Working in conjunction with specialist suppliers, Howden has perfected both an enamel and an application technique that meets these higher standards. To properly protect the steel elements, the enamel has to form a robust, corrosion resistant barrier on their surface. It must make a strong and lasting bond with the steel and it must be flexible enough to remain undamaged when the elements are compressed into their basket. The chemical composition of the frit, the enamelling compound itself is critical, but so is the grade of the steel and the method of application.  After years of development, Howden has pioneered a dry electrostatic technique. Electrostatic coating ensures that all parts of the elements including the edges are covered evenly, it keeps the coating in place with no downward flow as the element is taken to the oven.

The finished coatings are regularly tested for properties such as acid resistance, porosity and adherence, to make sure they continue to meet the most stringent European and International standards.  But quality assurance depends on rigorous pre-application tests too. Before any enamel is applied both the batch of frit and the steel coil are tested to ascertain that they meet their required specifications.  During production random samples are taken and tested to check the performance of the finished coating. The dossier of test results is passed on to the customer on delivery of the job.