Comparison study of dicyandiamide-cured epoxy bonded steel joints and polyamidoamine-cured epoxy bonded steel joints

There are instances where efficiency and safety may be compromised as a res ult of deteriorating fluid transport systems. Thus, it is worth evaluating other methods that can repair the damage for a temporary period without shu tting down the operation. The objective was to evaluate the durability of a n epoxy-bonded steel in aqueous environments that would represent such a re pair. EPON(R) 828 was chosen as the epoxy resin, and dicyandiamide and poly amidoamine were two types of curing agents evaluated in this study. The epo xy-bonded steel joints were exposed in either distilled water or 3.4% NaCl solution for various times. The mechanical strength of the bonded joints wa s evaluated using a three-point flexure test. The interfacial shear strengt h of unaged samples ranged from 0.93 to 0.32 MPa. It was found that the int erfacial shear strength decreased with aging time for both epoxy-bonded sys tems. Scanning electron microscopy (SEM), optical microscopy, and X-ray pho toelectron spectroscopy (XPS) were used to determine the locus of failure o f the bonded joints. It was concluded that failure occurred cohesively with in the oxide layer if oxides were present on the substrate surface prior to the bonding procedure. (C) 2000 Elsevier Science Ltd. All rights reserved.