Visions of the IT enterprise in the 21st century (panel session): managerial issues and research opportunities

A releasable coupling or safety sub for a drill string including an inner tubular member piloted within an outer tubular member, the inner member including expansible lock members shiftable laterally of the tubular member into locking engagement with a transverse shoulder on the outer member, a retaining member holding the lock members outwardly in engagement with the shoulder, release of the retainer member from the lock members enabling the latter to move laterally inwardly to a position released from the shoulder, permitting the tubular members to be separated from one another. The coupling includes a device acting between the lock members and outer member for imposing an axial preload on the inner and outer members to place the outer member in compression and the inner member in tension to provide a rigid structure.