A multiple cap arrangement is provided to seal the open end of a container. The multiple cap seal includes a sealing cap and locking cap which are hingedly coupled to the open end of a container such as a disposable centrifuge container. The sealing cap is lodged in the open end of the container and the locking cap coupled to the sealing cap by a mechanism that retains the caps essentially fixed relative to one another. With the caps coupled in this way, stress, resulting from pressure in the container, is transferred through the caps to the hinges. The hinges are sized to prevent axial movement of the interlocked sealing and locking cap structure away from the container. Since the hinges resist stretching even under substantial tension, the container remains reliably sealed even when the pressures in the container are very high.