Uncontrolled variables lower disbonded FBE test's reliability

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Uncontrolled variables lower disbonded FBE test's reliability

Neal, D. / Cox, G.

Uncontrolled variables cause high-temperature pipe coating cathodic disbonding performance data from the same material to be unrepeatable. Research into the cause of disbonding has shown that changes in the electrolyte and high pH in the disbond crevice cause coating to disbond. Three variables, holiday diameter, the use of a salt bridge (the separation of the anode from the cell) and aeration of the electrolyte, were evaluated both individually and combined in a preliminary test to determine their effect on the disbonding of a high-temperature FBE (fusion bonded epoxy) coating. It was found that replicate samples showed significant differences in disbonding. All three variables significantly affect the amount of disbonding. Disbonding increases when the anode is separated from the cell, when the electrolyte is aerated and when the holiday diameter is increased. The largest amount was observed when the cell is aerated. Changes in multiple variables have similar effects, but do not appear do be additive. Disbonding ranged from 1.5 to 6.3 mm radius, showing the major effect of the variables on the FBE disbonding. The results indicate that test parameters have a major effect on the extent of disbonding. Further work is necessary.