Novel Pressure Vessel for Pressurizing Corrosive Liquids With Applications in Accelerated Life Testing of Composite Materials

A system was designed for high-pressure accelerated life testing (ALT) of composite materials exposed to saline water solutions or other potentially corrosive media. The system was comprised primarily of a large stainless steel pressure vessel with the capability to perform extended pressure holds of up to 41.3 MPa at temperatures up to 70 °C. Using a nylon fabric-reinforced Buna-N rubber diaphragm as a media isolator and an inert ceramic coating on all wetted surfaces of the vessel, 3.5% saline water solutions were successfully held at test pressures and temperatures for extended periods with no evidence of corrosion or other degradation even after several days of exposure. Pressurization was achieved through a hydraulic pump system, which contained pressure monitoring equipment and valves and was isolated from the saline water by the diaphragm. The temperature of the entire vessel and contents was maintained by complete immersion in a heated, filtered water bath. The efficacy of using an elastomeric diaphragm to transfer large pressures between two near-incompressible fluids without mixing was shown, provided adequate reinforcement in the form of an interwoven fabric was provided to prevent tearing and extrusion from the extreme through-thickness stresses, particularly at clamping locations. Discussion on the effects of temperature, material, thickness, reinforcement, and sealing methods on the effectiveness and repeatability of the system is provided, and a demonstration of an accelerated test on a carbon–fiber composite is also presented.