Cement-lined pipes of increased flexibility and method of making same

Claim 1

A METHOD OF PROVIDING A METAL PIPE HAVING A CONTINUOUS INTERIOR WALL WITH A LINER OF HYDRAULIC CEMENT, COMPRISING THE STEPS OF: (A) LINING THE INTERIOR WALL OF SAID PIPE WITH SAID HYDRAULIC CEMENT IN A PLASTIC CONDITION, (B) THEREAFTER AND WHILE SAID CEMENT IS IN A PLASTIC CONDITION INSERTING AN EXPANSIBLE SLEEVE HAVING CLOSED ENDS IN THE INTERIOR OF SAID PIPE AND CONNECTING THE ENDS OF SAID SLEEVE TO SAID PIPE AT LONGITUDINALLY SPACED POSITIONS THEREOF, (C) THEREAFTER APPLYING SUFFICIENT PRESSURE INSIDE SAID SLEEVE TO CAUSE TRANSVERSE AND LONGITUNDINAL ELASTIC ENLARGEMENT OF SAID PIPE, (D) MAINTAINING SAID PRESSURE UNTIL SAID CEMENT HAS SET SUFFICIENTALY TO RENDER IT ESSENTIALY NONDEFORMABLE, AND (E) THEREAFTER RELEASING SAID PRESSURE WHEREBY THE ELASTIC RESTORING FORCE OF SAID PIPE PLACES SAID CEMENT IN COMPRESSION.