Riser sections and methods for making same

Abstract

A riser section for joining to another riser section to form a drilling riser includes a weld region generated by welding a first riser tube to a second riser tube. The weld region includes a fusion zone in which material of the first riser tube coalesces with material of the second riser tube, and a heat-affected zone adjacent the fusion zone. The riser section also includes a cover positioned over the weld region and welded to the first riser tube and to the second riser tube such that the cover covers the fusion zone and the heat-affected zone to protect the zones. The cover may be a solid piece of material that is welded to the riser tubes, or the cover may be a bead of weld filler material that is welded (melted and deposited) onto the weld region of each of the riser tubes.

What is claimed is: 
     
         1 . A riser section for joining to another riser section to form a drilling riser, the riser section comprising:
 a weld region generated by welding a first riser tube to a second riser tube, the weld region including:
 a fusion zone in which material of the first riser tube coalesces with material of the second riser tube, and 
 a heat-affected zone adjacent the fusion zone; and 
   a cover positioned over the weld region and welded to the first riser tube and to the second riser tube such that the cover covers the fusion zone and the heat-affected zone to protect the zones.   
     
     
         2 . The riser section of  claim 1  wherein the cover is weld filler material that is melted and deposited onto the fusion zone and the heat-affected zone. 
     
     
         3 . The riser section of  claim 1  wherein the first riser tube and the second riser tube, each includes an exterior surface, and the cover is welded to the exterior surface of the first riser tube and to the exterior surface of the second riser tube. 
     
     
         4 . The riser section of  claim 1  wherein the first riser tube and the second riser tube, each includes an interior surface, and the cover is welded to the interior surface of the first riser tube and to the interior surface of the second riser tube. 
     
     
         5 . The riser section of  claim 1  wherein the weld region is generated by friction stir welding the first riser tube to the second riser tube. 
     
     
         6 . The riser section of  claim 1  further comprising:
 a longitudinal axis; and 
 a relief zone that spans both the fusion zone and the heat-affected zone, the relief zone having an interior surface disposed a distance away from the longitudinal axis in a direction perpendicular to the axis that is greater than the distance of a second interior surface adjacent the relief zone's interior surface from the longitudinal axis in a direction perpendicular to the axis. 
 
     
     
         7 . The riser section of  claim 1  further comprising:
 a longitudinal axis; 
 a relief zone that spans both the fusion zone and the heat-affected zone, the relief zone having an interior surface disposed a distance away from the longitudinal axis in a direction perpendicular to the axis that is greater than the distance of a second interior surface adjacent the relief zone's interior surface from the longitudinal axis in a direction perpendicular to the axis; and 
 a second cover positioned over the weld region in the relief zone and welded to the first riser tube and to the second riser tube such that the second cover covers the fusion zone and the heat-affected zone to protect the zones. 
 
     
     
         8 . The riser section of  claim 1  wherein the first riser tube includes a material, and the second riser tube and the cover, each includes material that is the same as the first riser tube's material. 
     
     
         9 . The riser section of  claim 1  wherein the cover includes an aluminum alloy. 
     
     
         10 . The riser section of  claim 1  wherein the cover includes an iron alloy. 
     
     
         11 . The riser section of  claim 1  wherein the shape of the cover mimics the contour of the weld region. 
     
     
         12 . The riser section of  claim 1  wherein the cover has a thickness that is 0.1 inches. 
     
     
         13 . A method for forming a riser section that may be coupled with other riser sections to form a drilling riser, the method comprising:
 welding a first riser tube to a second riser tube;   positioning a cover over a weld region generated by welding the first riser tube to the second riser tube, such that the cover covers the fusion zone of the weld region and the heat-affected zone of the weld region; and   welding the cover to the first riser tube and to the second riser tube.   
     
     
         14 . The method of  claim 13  wherein welding the first riser tube to the second riser tube includes friction stir welding. 
     
     
         15 . The method of  claim 13  wherein welding the cover to the first riser tube and to the second riser tube includes gas tungsten arc welding. 
     
     
         16 . The method of  claim 13  wherein:
 positioning the cover over the weld region includes positioning the cover over an exterior surface of the first riser tube and over an exterior surface of the second riser tube, 
 welding the cover to the first riser tube includes welding the cover to the exterior surface of the first riser tube, and 
 welding the cover to the second riser tube includes welding the cover to the exterior surface of the second riser tube. 
 
     
     
         17 . The method of  claim 13  wherein:
 positioning the cover over the weld region includes positioning the cover over an interior surface of the first riser tube and over an interior surface of the second riser tube, 
 welding the cover to the first riser tube includes welding the cover to the interior surface of the first riser tube, and 
 welding the cover to the second riser tube includes welding the cover to the interior surface of the second riser tube. 
 
     
     
         18 . The method of  claim 13 :
 wherein:
 welding the cover to the first riser tube includes welding the cover to an exterior surface of the first riser tube, and 
 welding the cover to the second riser tube includes welding the cover to an exterior surface of the second riser tube; and 
   further comprising:
 positioning a second cover over the weld region, an interior surface of the first riser tube, and an interior surface of the second riser tube, such that the second cover covers the fusion zone and the heat-affected zone of the weld region, 
 welding the second cover to the interior surface of the first riser tube, and 
 welding the second cover to the interior surface of the second riser tube. 
   
     
     
         19 . The method of  claim 13  further comprising forming a relief zone that spans the fusion zone and the heat-affected zone of the weld region. 
     
     
         20 . The method of  claim 13  further comprising:
 forming a relief zone that spans the fusion zone and the heat-affected zone of the weld region, 
 positioning a second cover over the weld region in the relief zone, 
 welding the second cover to an interior surface of the first riser tube, and 
 welding the second cover to an interior surface of the second riser tube. 
 
     
     
         21 . The method of  claim 13  wherein positioning and welding the cover includes melting weld filler material and depositing the molten filler material onto the fusion zone and the heat-affected zone.