PROTECTION STRUCTURE OF PROPULSION PIPE COUPLING PART

PROBLEM TO BE SOLVED: To provide the protection structure of the coupling part of a propulsion pipe. SOLUTION: A protection layer is prevented from damage due to contact with soil and sand and gravel in earth through the improvement of hardness of synthetic resin and by forming an adhesion end face part in a taper-form state, the change of a peripheral length owing to tolerance is regulatable. By point-symmetrically forming adhesion end faces on both the right and left sides, a two-division protection layer is formed by one and the same forms. A protection layer 1 is formed in a cylindrical shape and the coupling protection layer is longitudinally divided into half-sections and divided into 1a and 1b and formed of synthetic resin of which forms are molded by using a norbornene monomer having Shore hardness (D) of approximate 80 and a reaction solution containing a metathesis and an activated agent catalyst. Adhesion end face parts 11a-11d with the two division protection layers 1a and 1b have respective tip part formed in a taper shape having width gradually decreased toward the tip. Adhesion end faces 4a and 4b on both the left and right sides are formed point- symmetrically about the center of a propulsion pipe 2.