Long-Term Performance - Bredero Shaw

( protecting against corrosion )of 1 - 3 for 28 days). It is interesting to note that thehot water soak exposure did not reveal any differenceamong the applied coating systems until 60 days.Figure 3 shows the cathodic disbondment(65 ˚C, -1.5 V, 14 and 28 days) behaviour of a multilayerpolyethylene coating system at different FBEprimer thicknesses. It was found that the cathodicdisbondment performance of the multi-layer PEcoating system using a 200 µm (8 mil) FBE primerexhibited comparable results to a stand-alone 350 µm(14 mil) FBE coating, under the similar applicationprocess conditions. Together with the results givenin Table 1, it demonstrates that with current FBEtechnology, there is a threshold minimum thicknessof FBE primer for multi-layer polyolefin coatings toprovide a good balance of anti-corrosion properties. Aminimum of 150 µm (6 mil) is needed and 200 µm(8 mil) should be the specified value.Surface preparationMany reported pipeline coating failures have occurreddirectly as a result of poor surface preparation of thepipe substrate before coating application. Figure 4illustrates two blasted pipe surfaces, which had anidentical profile reading by Testex measurementsbut were quite different in their microstructures, witha distinct profile-peak count difference by surfaceprofilometer. Unfortunately, long-term tests will haveto be used to differentiate the performance of pipecoatings applied onto correctly or incorrectly preparedpipe substrate surfaces. Table 2 shows the adhesionproperties of two commercial FBE coatings after 75 ˚Chot water soak testing as per CSA Z245.20, appliedto three different steel substrates using two differentgrades of steel grits and power grinding. It suggeststhat short-term hot water soak testing would not beable to differentiate the adhesion performance of thetwo coatings and the impact of surface preparation.Table 3 shows the 65 ˚C cathodic disbondmentresults of FBE#1 coating samples after applied ontosteel substrates with two distinctly different profiles.Neither short-term cathodic disbondment nor watersoak testing can reveal the impact of differentsurface preparation on the performance of the samecommercially qualified coating.Phosphoric acid treatment is one of the popularmethods of preparing a blasted steel pipe surfacebefore receiving a coating. Table 4 compares theresults of hot water soak testing and cathodicdisbodment testing of the FBE#1 coating appliedonto a steel surface with and without phosphoric acidtreatment. Short-term cathodic disbondment testingdid not give out significantly different results, but longtermhot water soak testing suggested much improvedadhesion property of the coating system with the acidtreatment.Coating application temperatureMany reported failure case histories of 3LPO coatingswere related to inappropriate application temperatures7of the FBE primer. Potential solutions have beensuggested, 7 for example, correct application of theFBE primer to the full standard applied to FBE standalonecoatings and the adopting of low applicationtemperature FBE (LAT-FBE) formulations developedfor use in 3LPO systems. An international brand nameregular FBE coating was applied at 190 - 200 ˚C ontoproperly applied steel substrate surfaces. The resultsof hot water soak testing and cathodic disbondmenttesting are given in Table 5. We also investigatedtwo LAT-FBE coatings and two regular FBE coatingsapplied at different application temperature rangesbetween 160 and 240 ˚C. Results of cathodicdisbondment testing at 65 ºC for 28 days are given inTable 6. The results suggest that unless a fully testedlow application temperature FBE powder and itsTable 5. Evaluation tests for a regular FBE coating applied at 190 - 200˚CTest CSA Z245.20 - 2006 criterion Test duration and average resultsAdhesion rating (hot water soak, 75 ˚C)24 hours and 28 days adhesionrating of 1 - 324 hours 7 days 14 days 28 days1 1.2 2 2Cathodic disbondment (28 days, 65 ˚C) 28 days. CD radius < 20 mm N/A 6 mm 14 mm 24 mmTable 6. Cathodic disbondment of four FBE coatings at different application temperatures (65 ˚C, 28 days)Application temperature ˚C LAT FBE 1 LAT FBE 2 Regular FBE 1 Regular FBE 2160 19 mm 12.75 mm N/A N/A170 20 mm 12.75 mm N/A N/A180 15.5 mm 12.75 mm 17.5 mm 25.75 mm190 15.25 mm 14.25 mm N/A N/A200 16 mm 14.25 mm N/A N/A240 11 mm 5.0 mm 9.5 mm 11 mmREPRINTED FROM WORLD PI PELINES November2008www.worldpipelines.com