Alternative Methodology for Elastomeric Seal RGD and Aging Testing Validates Long-Term Subsea Seal Performance and Integrity

摘要

Elastomeric sealing elements are used extensively throughout subsea production systems to providernbarriers between the wellbore and the environment. The long-term performance of elastomers is essentialrnwhen they are subjected to extreme temperatures, high pressures, and various chemical and wellborernfluids. This paper reviews current testing methodology and introduces a new validation program forrnelastomeric seals.rnTraditional elastomeric material evaluation methodology for oilfield applications focuses on Rapid GasrnDecompression (RGD) and aging. Industry standard testing protocols consist of testing per NORSOKrnM-710, ISO 23936-2, or API 6A. Since end users can select different validation criteria, overlappingrnvalidation testing often occur. Additionally, test medium, test temperature, test pressure, depressurizationrnrate, and exposure time vary between each standard. Traditional elastomeric material evaluation methodologyrnuses slab samples or O-rings as test specimens. Although this testing helps validate elastomericrnmaterials for a particular application, slab samples and O-rings are not always a true representation of thernactual elastomeric sealing element used in subsea production systems.rnValidation programs should compromise between realistic acceptance criteria and rigorous testingrnstandards to validate long-term performance in simulated operating conditions. NORSOK M-710 and ISOrn23936-2 RGD acceptance criteria (i.e., crack ratings) may be found subjective and impractical and arernindependent of whether or not the O-ring maintained a pressure-tight seal throughout testing. To bridgernthe gap between material testing and functional testing, the authors propose modifications to both agingrnand RGD testing industry standards. Using this approach, fixture testing would be conducted on the actualrnseal cross-section used in production with testing parameters similar to those specified in current industryrnstandards. The main deviation would be the acceptance criterion: The seal shall maintain pressure integrityrnas prescribed in API 6A following all testing. The authors further propose that this new testing protocolrnbe used in conjunction with existing API 6A/API 17D seal validation testing. This will make it possiblernto better understand a seal design’s actual pressure-containing functionality as opposed to solely a test ofrnits material properties. The aforementioned existing testing standards should not be disregarded, becausernthey establish a baseline for evaluating elastomeric materials. However, material test results should notrnalways be considered grounds for eliminating a particular compound if the actual seal design is able tornsurvive in a simulated environment.rnThe ultimate goal of a validation testing program shall be to select a functional seal design with anrnappropriate material that satisfies the end user’s requirements. With high pressures and extreme temperaturesrnpushing the limits of elastomer sealing technologies, long held validation assumptions need to bernreassessed.