Long-Term Performance - Bredero Shaw

( protecting against corrosion )Corrosion is the primary factor affecting thelongevity and reliability of buried oil andgas pipelines. Fusion Bonded Epoxy (FBE)and 3-layer polyolefin (3LPO) (polyethylene PE orpolypropylene PP) are the most widely used externalcoating systems for corrosion protection of newlyconstructed pipelines. Over the past decade, severalincidents of coating failures have been reported withmassive disbondment of 3-layer polyolefin coatings1-5(both 3LPE and 3LPP). These coating failures haveraised concerns in the industry worldwide about thelong-term performance of 3LPO coatings, resulting inseveral initiatives to determine the failure mechanisms6and corrective measures.Current national, international and companystandards and specifications often have a specificvalue of tested properties as an acceptance criterionDisbonded Radius (mm)403530252015105Disbondment Vs Time00 20 40 60 80 100DaysSeries1Series2Figure 1. Cathodic disbondment - time behaviour of twodifferent coatings.Tg in °C120110100908070Glass Transition Temperatures for Coatings at 65°Cfor material qualification. However, tests identifiedin these documents are relatively short-term andpredictive models for long-term performance are notavailable. Adding to the problem is that the data onlong-term behaviour of pipe coating materials, even ifavailable, are often scarce.As with any other pipeline coating systems,materials evaluation and process controls can makea significant impact on the long-term performanceof FBE and 3LPO pipeline coatings. This paperdiscusses the results of our study on some relatedcritical parameters, which include the qualification andapplied thicknesses of FBE, surface cleanliness andblasting profile, surface treatment, pipe temperatureduring coating application, weld-seam coverage andfinished coating inspection.Two examples reveal the need forlong-term evaluationsThe draft ISO 21809-1 for 3LPO pipe coatings willprobably contain a short-term (24 hours at 65 ˚C)cathodic disbondment (CD) test. China’s SY/T 0413-2002 standard also calls for a 48 hour CD test at65 ˚C. These short-term tests are intended for in-plantCathodic disbondment (mm)2520151050Cathodic disbondment test at 6550 100 150 200 250 3002 4 6 8 10 12FBE Primer Thickness (microns/mils)o C14 days28 daysFigure 3. Cathodic disbondment of a multi-layer PE coatingat various FBE primer thicknesses.600 7 14 28 60 90 120Duration of DaysFigure 2. T gof two FBE materials after exposure to wetservice environment.Table 1. Correlation of hot water soak results with thickness of aFBE coating at 75˚CThickness (µmor mil)7 days 14 days 28 days 60 days100 µm (4 mil) 2 2 2 4 - 5150 µm (6 mil) 2 2 2 4200 µm (8 mil) 1 1 1 3 - 4250 µm (10 mil) 1 1 1 3300 µn (12 mil) 1 1 1 3Figure 4. Two different blasted surfaces show an identicalprofile reading by Testex measurements.REPRINTED FROM WORLD PI PELINES November2008www.worldpipelines.com