A Subscale Experimental Test Method to Characterize Extrusion-Based Elastomer Seals

Extrusion-based elastomer seals are used in many applications, such as the seal in a variable bore ram valve used in offshore oil and gas drilling. Performing full-scale closing pressure experiments of such valves to characterize the seal performance and material failure of elastomer, especially under various temperature conditions, are quite expensive and time consuming. Conversely, simple coupon tests to characterize the elastomer mechanical properties and failure do not capture the complex deformation associated with the extrusion and subsequent sealing type that these materials undergo in the valves. In view of this, a simple subscale experimental test method capable of simulating the extrusion and sealing type deformation is developed. The extrusion and sealing deformation are realized by bonding the rectangular elastomer sample to metal pieces on top and bottom surfaces, and then compressing the sample in the vertical direction, while the deformation of the three lateral surfaces is kept constrained. As a result, sample deforms and extrudes out of the front surface, eventually forming the seal against a flat rigid metal plate placed at an appropriate distance. Simple scaling rules to determine the appropriate sample size and initial sealing gap, equivalent to the full-scale valve in terms of similar strain conditions, are derived and then verified using finite element analysis (FEA). Finally, the experimental test method is demonstrated by characterizing the contact pressure of nitrile (NBR) samples under different operating temperatures, ranging from 21 °C to 160 °C using pressure-sensitive film sensor.