Abstract: An explosive activated assembly for repairing a heat exchange tube in which a grooved metal casing is inserted into the tube to be repaired and has a plurality of projections extending from the outer surface thereof. A force-transmitting member extends within a bore formed in the casing and contains an explosive member so that, upon detonation of the explosive member, the force-transmitting member and the casing are expanded radially outwardly to drive the projections against the tube. A booster is located within the casing and adjacent the charge and is activated by a transfer cord connected to an externally located detonator. The casing is formed with an extension that extends over a portion of the transfer cord and has a hole through which the cord extends to contain the debris and vapor caused by the explosion.