Rubber - steel interface failure in pipeline

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Rubber - steel interface failure in pipeline

Gnatowski, Marek

The technology of bonding rubber to steel has been developing for many years but industry is still confronted with unexpected and expensive failures caused by unusual service conditions or strange behavior of materials in some environments. The objective of this presentation is to create awareness in scientific and technical societies about certain issues in bonding rubber to steel that may lead to premature interface and rubber failure. These issues seemed to be detected during investigation of the failure of a long industrial steel pipeline located in North America and lined with natural rubber compound. The materials and process used in pipeline manufacturing could be accepted as industry standard. Large blisters, combined with steel corrosion and rubber cracking, developed in the steel/rubber interface after approximately 5 years of pipeline exploitation at an elevated temperature of approximately 50 deg C. The rubber, steel/rubber interface, chemistry of pipeline fluid, and blister water were evaluated, including optical and electron microscopy, mechanical testing, pH, chromatography and mass spectroscopy. It was found that the blister water chemistry was significantly affected by the chemistry of the adhesive system used in pipeline manufacturing. Large concentrations of bromide and chloride ions were detected in samples of water taken from the blisters. This most likely caused accelerated degradation of the interface, including steel corrosion. The 'cold wall' effect also likely contributed to the interface failure. Significant aging of the rubber liner under the service conditions, possibly accelerated by the presence of corrosion products, was identified as well, including high water absorption by the rubber. This further contributed to degradation of the rubber/steel interface. Most of the standard testing procedures for evaluation of bonding rubbers to metal do not take into consideration long term water absorption by rubbers. General conclusions related to the failure mechanism, and the need for future research work, were drawn based on the results evaluation.