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

Elastomeric sealing elements are used extensively throughout subsea production systems to provide barriers between the wellbore and the environment. The long-term performance of elastomers is essential when they are subjected to extreme temperatures, high pressures, and various chemical and wellbore fluids. This paper reviews current testing methodology and introduces a new validation program for elastomeric seals. Traditional elastomeric material evaluation methodology for oilfield applications focuses on Rapid Gas Decompression (RGD) and aging. Industry standard testing protocols consist of testing per NORSOK M-710, ISO 23936-2, or API 6A. Since end users can select different validation criteria, overlapping validation testing often occur. Additionally, test medium, test temperature, test pressure, depressurization rate, and exposure time vary between each standard. Traditional elastomeric material evaluation methodology uses slab samples or O-rings as test specimens. Although this testing helps validate elastomeric materials for a particular application, slab samples and O-rings are not always a true representation of the actual elastomeric sealing element used in subsea production systems. Validation programs should compromise between realistic acceptance criteria and rigorous testing standards to validate long-term performance in simulated operating conditions. NORSOK M-710 and ISO 23936-2 RGD acceptance criteria (i.e., crack ratings) may be found subjective and impractical and are independent of whether or not the O-ring maintained a pressure-tight seal throughout testing. To bridge the gap between material testing and functional testing, the authors propose modifications to both aging and RGD testing industry standards. Using this approach, fixture testing would be conducted on the actual seal cross-section used in production with testing parameters similar to those specified in current industry standards. The main deviation would be the acceptance criterion: The seal shall maintain pressure integrity as prescribed in API 6A following all testing. The authors further propose that this new testing protocol be used in conjunction with existing API 6A/API 17D seal validation testing. This will make it possible to better understand a seal design’s actual pressure-containing functionality as opposed to solely a test of its material properties. The aforementioned existing testing standards should not be disregarded, because they establish a baseline for evaluating elastomeric materials. However, material test results should not always be considered grounds for eliminating a particular compound if the actual seal design is able to survive in a simulated environment. The ultimate goal of a validation testing program shall be to select a functional seal design with an appropriate material that satisfies the end user’s requirements. With high pressures and extreme temperatures pushing the limits of elastomer sealing technologies, long held validation assumptions need to be reassessed.