DETACHMENT PREVENTIVE METAL FITTING

PROBLEM TO BE SOLVED: To eliminate a possibility of damage to a socket pipe and generation of a crack due to fatigue and to improve durability of a pipe. SOLUTION: When thrust load due to water pressure and external force due to ground displacement such as an earthquake are applied as extracting force to a pipe coupling part, an insertion pipe 16 is drawn from the socket pipe 12. When an insertion pipe 16 is drawn by a prescribed length, an insertion saddle 26 is locked by an arm 28 and the arm 28 is pulled in an extracting direction. Since the arm 28 is locked by the socket saddle 24, force displaced in the extracting direction is applied to the socket saddle 24 and the socket saddle 24 is locked by a tapered external surface 18 of the socket pipe 12. At this time, force is applied from the socket saddle 24 to the tapered external surface 18 and the force is mitigated by a buffer material 34 provided on a tapered internal surface 32 of the socket saddle 24. Therefore, stress concentration is not generated on the tapered external surface 18 of socket pipe 15.