Fremgangsmåte og anordning for sentrering av et rör ned i en brönn

A system for centralizing casing pipe in a wellbore includes lateral pistons in the side wall of the casing string which are movable by force applied to their inner end, from a retracted position within the maximum exterior profile of the casing pipe string to a predetermined extended position which will move the casing pipe string toward a central position in the borehole. Various well operations can be performed using the pistons in addition to the centralizing function. When a predetermined deploying force is applied to the pistons, they are released from their retracted position for movement to a fixed extended position. The deploying force is accurately determined by a simple retaining mechanism involving a snap ring and groove on the pistons.