An isolation device for use with a pressure vessel penetrator. The isolation device is formed from a high performance thermoplastic having low creep properties and includes a central cylindrical portion, a lower inner flange portion and, preferably, an upper outer flange portion. The cylindrical portion has an inner diameter adapted to receive an upper larger diameter portion of the penetrator. The lower inner flange portion is coupled to a lower portion of the central cylindrical portion and forms an aperture for receiving a lower smaller diameter portion of the penetrator. The upper outer flange portion is coupled to an upper portion of the central cylindrical portion and may include clocking apertures. The high performance thermoplastic may be 30% glass-filled PEEK or TORLON®. A custom tapered nut may be provided to secure the penetrator in an internal tapered recess of the pressure vessel.