Conduits are used to transport a variety of liquid and gaseous products, such as crude oil, liquid propane, ethanol, water, etc., such products encounter friction against the interior surface of the conduit. The friction between the product being conveyed and the interior surface of the conduit is greater in curved conduit sections than over linear conduit sections because of the changes in direction of the product imposed by the curved conduit and because of swirling of the product as the change in direction is undertaken. In some situations, the liquid is used as a medium to convey particulate material in suspension within the product, such as with mining slurries and sludge. Such particulate material can be extremely abrasive and magnify the wear cause by friction within the conduit.
To minimize the effects of friction on the interior surface of conduits, the conduits, particularly on curved conduit segments, can be coated with a wear surface, such as a carbide metal coating, that can be applied to the interior surface of the conduit. The application of a wear coating on the interior surface of conduits is called hard surfacing. The hard facing of conduits can be applied to new conduit or as a refurbishing of old conduit to replace the wear surface that has been eroded through the use of the conduit. The application of hard surfacing can be accomplished via a number of techniques, including spraying and plasma, but is most typically by applying a series of weld beads along the interior surface of the conduit with each successive weld bead building on the adjacent weld bead.
The application of a wear resistant coating material by the placement of welding material on the interior surface of curved conduits is disclosed in U.S. Pat. No. 4,514,443, issued to Gene Kostecki on Apr. 30, 1985. In the Kostecki patent, a guide member is installed through the center of the curved conduit section and the weld placement apparatus is mounted to follow the guide member in the laying of weld beads along the length of the curved conduit segment. Similarly, Canadian Published Application No. 2,302,083, of Donald Hannu published on Mar. 27, 2000, discloses a track member on which a welding head is mounted to move along the track while depositing weld material along the interior surface of the conduit. In Canadian Published Patent Application No. 2,578,308 of Barry Kossowan, a three-axis robot arm is disclosed to provide for a radial and angular adjustment of the welding; however, the movement of the welding head through the conduit is also guided by a track extending longitudinally through the conduit.
Accordingly, it would be desirable to provide an apparatus that is operable to apply successive longitudinal weld beads along a curved conduit section without requiring the placement of a longitudinal guide track on which the welding head is carried while moving longitudinally through the conduit.