Metal lined composite risers in offshore applications

Abstract

The present invention provides a metal lined composite riser section for use in offshore applications featuring a traplock metal-to-composite interface to secure a plurality of structural composite overwrap layers about a metal liner assembly. Each traplock is formed with at least one annular groove or channel which has been made in the exterior surface of the metal liner assembly. The annular trap grooves may be of various geometries and may be arranged adjacent to each other to form a traplock having 2 to 8 or any number of grooves required to ensure proper adhesion between the composite overwrap layers and the metal liner assembly. A number of structural composite overwrap layers are secured about the assembly by building up alternating combinations of helical and hoop fiber windings to form a composite material. The present invention also provides a method of making composite riser sections using either a mandrel or counterweights to facilitate the composite fiber winding process.

What we claim as our invention is:  
     
         1 . A composite riser section for offshore applications comprising: 
 a metal liner assembly including a traplock MCI having at least one trap groove on an outer surface proximate to each end of the metal liner assembly;    a plurality of structural composite overwrap layers disposed about the metal liner assembly; and    wherein the plurality of structural composite overwrap layers further composes alternating helical plys and hoop plys.    
     
     
         2 . The composite riser section of  claim 1  wherein at least one helical ply is a 0° prepreg ply.  
     
     
         3 . The composite riser section of  claim 1  wherein each helical ply is compressed by an overlying hoop ply to fit snugly into the at least one trap groove at each end of the metal liner assembly.  
     
     
         4 . The composite riser section of  claim 2  wherein each trap groove holds  3  pairs of alternating helical and hoop plys.  
     
     
         5 . The composite riser section of  claim 1  wherein the at least one trap groove is a trapezoidal channel.  
     
     
         6 . The composite riser section of  claim 1  wherein the at least one trap groove is a rectangular channel.  
     
     
         7 . The composite riser section of  claim 1  wherein the traplock MCI has at least 3 trap grooves on an outer surface proximate to each end of the metal liner assembly.  
     
     
         8 . The composite riser section of  claim 1  wherein the metal liner assembly is formed of metal selected from the group consisting of titanium, steel, stainless steel and combinations thereof.  
     
     
         9 . The composite riser section of  claim 1  wherein the metal liner assembly further comprises a welded transition ring.  
     
     
         10 . A method of making a composite riser section for offshore applications comprising the steps of: 
 providing a metal liner assembly including a traplock MCI having at least one trap groove on an outer surface proximate to each end of the metal liner assembly; and    winding resin impregnated fibers about the metal liner assembly to form a structural composite overwrap; and    wherein the step of winding resin impregnated fibers about the metal liner assembly further comprises the step of winding helical plys and hoop plys in an alternating manner.    
     
     
         11 . The method of  claim 10  wherein the step of winding helical plys and hoop plys in an alternating manner further comprises the step of compressing each helical ply into the traplock MCI with an overlying hoop ply.  
     
     
         12 . The method of  claim 11  wherein the traplock MCI has at least one trap groove and the step of compressing each helical ply further comprises filling each trap groove with at least three pairs of alternating helical and hoop plys.  
     
     
         13 . The method of  claim 10  further comprising the step of laying-up strips of uncured rubber material to form an elastomeric shear ply about the metal liner assembly prior to winding resin impregnated fibers.  
     
     
         14 . The method of  claim 13  further comprising the step of coating the traplock MCI with mold release prior to laying-up strips of uncured rubber to form an elastomeric shear ply.  
     
     
         15 . The method of  claim 13  further comprising the step of applying sufficient heat to cure the elastomeric shear ply and the structural composite overwrap.  
     
     
         16 . The method of  claim 15  wherein the step of applying sufficient heat to cure the elastomeric shear ply and the structural composite overwrap further comprises the steps of holding the part at a temperature of about 150° F. to about 175° F. for from about 12 to about 13 hours, and then holding the part at a temperature of about 290° F. to about 310° F. for from about 8 to about 9 hours.  
     
     
         17 . The method of  claim 15  further comprising the steps of: 
 laying-up strips of uncured rubber material to completely enclose the structural composite overwrap in an external jacket;  
 winding resin impregnated fibers over the external jacket to form a scuff-resistant protective layer; and  
 applying sufficient heat to cure the external jacket and the scuff-resistant protective layer.  
 
     
     
         18 . The method of  claim 17  wherein the step of applying sufficient heat to cure the external jacket and the scuff-resistant protective layer further comprises the step of holding the part at a temperature of about 290° F. to about 310° F. for from about 4.5 to about 5.5 hours.  
     
     
         19 . The method of  claim 10  further comprising the step of mounting the metal liner assembly on a mandrel prior to winding resin impregnated fibers.  
     
     
         20 . The method of  claim 10  further comprising the step of holding the metal liner assembly between at least two counterweighted supports to minimize deflection prior to winding resin impregnated fibers.  
     
     
         21 . The method of  claim 20  further comprising the step of positioning the at least two counterweighted supports such that the metal liner assembly is bowed slightly upward prior to winding resin impregnated fibers.  
     
     
         22 . The method of  claim 20  wherein the counter weighted supports further comprises rollers to permit rotation of the metal liner assembly during the winding resin impregnated fibers.  
     
     
         23 . The method of  claim 10  further comprising the step of bowing the metal liner assembly slightly upward prior to winding resin impregnated fibers.  
     
     
         24 . The method of  claim 10  further comprising the step of laying up at least one 0° prepreg ply during the step of winding resin impregnated fibers.  
     
     
         25 . The method of  claim 12  further comprising the step of laying up a 0° prepreg ply following the second and third helical plys and prior to winding the second and third hoop plys during the step of winding resin impregnated fibers.  
     
     
         26 . The method of  claim 10  further comprising the step of laying up at least one 90° prepreg ply during the step of winding resin impregnated fibers.  
     
     
         27 . A composite riser section manufactured according to the method of  claim 10.