Development of bonded composite doublers for the repair of oil recovery equipment.

Abstract

An unavoidable by-product of a metallic structure's use is the appearance of crack and corrosion flaws. Economic barriers to the replacement of these structures have created an aging infrastructure and placed even greater demands on efficient and safe repair methods. In the past decade, an advanced composite repair technology has made great strides in commercial aviation use. Extensive testing and analysis, through joint programs between the Sandia Labs FAA Airworthiness Assurance Center and the aviation industry, have proven that composite materials can be used to repair damaged aluminum structure. Successful pilot programs have produced flight performance history to establish the durability of bonded composite patches as a permanent repair on commercial aircraft structures. With this foundation in place, this effort is adapting bonded composite repair technology to civil structures. The use of bonded composite doublers has the potential to correct the difficulties associated with current repair techniques and the ability to be applied where there are no rehabilitation options. It promises to be cost-effective with minimal disruption to the users of the structure. This report concludes a study into the application of composite patches on thick steel structures typically used in mining operations. Extreme fatigue, temperature, erosive, and corrosive environments induce an array of equipment damage. The current weld repair techniques for these structures provide a fatigue life that is inferior to that of the original plate. Subsequent cracking must be revisited on a regular basis. The use of composite doublers, which do not have brittle fracture problems such as those inherent in welds, can help extend the structure's fatigue life and reduce the equipment downtime. Two of the main issues for adapting aircraft composite repairs to civil applications are developing an installation technique for carbon steel and accommodating large repairs on extremely thick structures. This study developed and proved an optimum field installation process using specific mechanical and chemical surface preparation techniques coupled with unique, in-situ heating methods. In addition, a comprehensive performance assessment of composite doubler repairs was completed to establish the viability of this technology for large, steel structures. The factors influencing the durability of composite patches in severe field environments were evaluated along with related laminate design issues.