Effect of curing time on physical and mechanical properties of MIO/synthetic rubber primer as weld joint coating of gas pipeline

The influence of curing time on adhesion and flexibility of a synthetic primer reinforced with different ratios of micaceous iron oxide (MIO) is the aim of this study. MIO particles in the vol. % of 2.2, 8.2, 17.2 and 30 were added to the synthetic rubber based primer. The coatings were applied on low carbon steel plates and also on 8 inch outer diameter steel pipes. The morphological properties of the coated primers was determined using an optical microscope. In order to evaluation of the curing time on adhesion of the primers to top-coat (cold applied tape) and also on steel substrate, sequence peel and cross-cut adhesion tests, was done. Cupping test in different times after applying the samples on steel substrates were employed to investigate the effect of curing mechanism on flexibility of the coatings. The experimental results, indicated that the completing of curing of the synthetic rubber based primer is too long in room temperature (more than 3 moths). Cross-cut test results revealed that, when the coatings were completely cured, no change was observed by adding different ratios of MIO. Peel adhesion test results, presented that adding 2.2 vol. % of MIO particles into the primer improved the adhesion of the primer to the upper layer tape. Also, cupping tests showed that the samples containing 2.2 and 8.2 vol. % of MIO pigments has not any negative effect on flexibility of the coated primers.