Fluid containment pressure vessel that eliminates the outer support housing present in certain conventional vessels, and provides an improved cap-to-body interface. In certain embodiments, the cap is threaded and configured to threadingly engage with the body of the pressure vessel, and has sufficient structural integrity to withstand the pressures in the device without the need for a support housing. In certain embodiments, an interlock mechanism is provided that prevents the cap from being opened (e.g., removed from the body) while the device is under pressure. In certain embodiments, a pressure relief valve is provided with a pre-loaded biasing mechanism to achieve the required pressure release rate. The vessel can be used for sample preparation, including purification or concentration of samples, particularly protein samples.