Abstract: This locking mechanism incorporates mechanical objects such as pipe flanges having locking receptacles through which extend a retaining pin having a retaining sleeve threadedly received thereby and secured by means of a locking ring. Both the retaining pin and retaining sleeve can be installed and removed only by means of specifically designed installation tools. A locking plug is also received within one of the flange receptacles and is secured by a plug retainer pin. The locking plug can be installed and removed only be means of a removal key which is retained by authorized personnel. Sealing plugs secure the retaining pin and plug retainer pin in encapsulated position within the pipe flanges and thereby prevent tampering.