07003 INTERNAL STRESS AND MECHANICAL PROPERTIES OF PAINT FILMS

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Product Number: 51300-07003-SG

ISBN: 07003 2007 CP

Author: Ole Øystein Knudsen, Astrid Bjørgum, Mario Polanco-Loria, Anne Øyen, and Roy Johnsen

Publication Date: 2007

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Since the introduction of the NORSOK M-501 standard some incidents of major coating failure by cracking and flaking have been reported for offshore installations in the Norwegian sector. Internal stress has often been mentioned as an important factor in these types of degradation. The purpose with this investigation has been to investigate formation of internal stress and to look into other mechanical properties of paint films that may affect cracking and flaking. Internal stress has been studied by the beam deflection method, while mechanical properties, i.e. fracture strength and flexibility, have been studied by tensile testing of free films. Internal stress in epoxies depended on film thickness, curing conditions and exposure. The polysiloxane developed less internal stress than the epoxy, and internal stress was less dependent on film thickness. Flexibility and tensile strength varied over a wide range for different types of coatings. High strength films tend to be less flexible, which was found for epoxy, acrylic and polysiloxane coatings. The polyurethanes were very flexible. The main conclusion from this work is that internal stress and flexibility of paint films may play an important role for cracking and flaking, but other parameters are also important. Adhesion is probably the most important parameter.