Helically wound pipe and related method

A method of manufacturing helically ribbed pipe, the method comprising:

• using an elongate composite plastic strip having a base portion having an upper surface and a lower surface, a plurality of ribs extending upward from the upper surface of the base portion, each rib formed by a reinforcement strip within plastic material, the composite plastic strip having a first side and a second side;
• helically wrapping the composite plastic strip into a tubular pipe form with the upper surface and the ribs at an exterior of the tubular pipe form and with a first portion of the first side overlapping a first portion of the second side at a helical joint, and, during the wrapping, applying a plastic seam weld between the overlapping first portions for bonding the overlapping first portions;
• applying pressure to the overlapping first portions of the first side and the second side to compress the plastic seam weld;
• after the application of the pressure, applying a plastic overweld that extends over the overlapping first portions of the first side and the second side and over both a second portion of the first side and a second portion of the second side, wherein the second portion of the first side is adjacent to the first portion of the first side and does not overlap with any part of the second side, and wherein the second portion of the second side is adjacent to the first portion of the second side and does not overlap any part of the first side.