Each of two exhaust pipes has a flared flange with the flange on one pipe spaced from the pipe's end edge forming a corner with the pipe's end segment. A triangular seal between the two flanges abuts the pipe segment and corner. One flange has an outer convex spherical surface and a concave inner spherical surface which engages the outer convex spherical surface of the seal at a contact point. Two depending conical legs of a U shaped in section band clamp engage and force the flanges and pipe corner and end segment against the seal. A clamp leg engages the outer convex spherical surface of the one flange at a tangential contact point. The one clamp leg, the one flange and the seal exhibit two tangential respective contact points defining a plane normal to that flange providing enhanced stress concentration on the seal and flanges.