A pipe coater needed a more environmentally friendly surface treatment to replace its current chromate based solution. The MSC was asked to screen greener adhesion promotors enabling durable steel/fusion bonded epoxy (FBE) primer interfaces for 3-layer polyethylene (3-LPE) pipe coatings.
Taking the chromate treatment as benchmark, chrome-free adhesion promotors were screened using pull-off tests on FBE primers and peeling tests on 3-LPE coatings. Both initial adhesion was measured as well as adhesion after immersion cycles in hot water.
Based on these results, a selection of best adhesion promotors were submitted to a 28-day cathodic disbondment (CD) test on 3-LPE coated samples.
From the tests, one adhesion promotor clearly outperformed the others and was found to be at least as durable as the reference chromate pretreatment. Furthermore, an excellent correlation was found between the 10-day wet adhesion test and the 28-day cathodic disbondment test.
Finally, the new treatment was validated after successful industrial application at the customers’ pipe mill.
Result after pull-off test
Peeling test on 3-LPE coating
Set-up for (left) and detail of (right) pull-off test