Abstract:
A riser assembly and method of forming where the riser assembly is made up of tubular members joined together. A metal spray process applies a layer of cladding onto ends of the tubular members and the ends are threaded to form respective box and pin configurations. Grooves are provided onto the surface of the tubular members beneath where the metal spray is applied for enhancing adhesion of the cladding and tubular members. The layer of cladding provides sufficient material so that threads may be selectively formed on the outer or the inner surface of the tubular members.

Description:
BACKGROUND 
     1. Field of Invention 
     The invention relates generally to a riser assembly. More specifically, the invention relates to a string of tubular members and method of making, where a substrate is deposited onto the ends of the members after grooves have been formed in the ends, the ends are threaded, and the members are threaded together. 
     2. Description of Prior Art 
     Offshore drilling operations are typically performed through a drilling riser that extends between a subsea wellhead assembly at the seafloor and a drilling vessel. Drilling risers are usually made up of a number of individual tubulars attached to each other end to end to form a string. Ends of the tubulars are often threaded so that adjacent tubulars can be attached by engaging their respective threaded ends, where a smaller diameter pin end threadingly inserts into a larger diameter box end. Typically, the box ends diameters are increased by a separate upset forging process to provide material for machining threads thereon. 
     SUMMARY OF THE INVENTION 
     Provided herein is an example of a riser string and a method of forming a riser string. In one example described herein is a riser string having a first tubular with a box end and grooves on an outer surface proximate the box end. A metal cladding is on the grooves, and threads are on an inner surface of the box end. Also included is a second tubular with a pin end that is inserted into the box end with grooves on an outer surface proximate the pin end and cladding over the grooves. Threads on the outer surface of the pin end are engaged with the threads on the inner surface of the box end. The grooves on the first tubular may optionally each have a height that decreases with distance from a terminal end of the box end and a width that increases with distance from a terminal end of the box end. Grooves on the second tubular may each have a height that decreases with distance from a terminal end of the pin end and a width that increases with distance from a terminal end of the pin end. In an example, the grooves on the first tubular are shaped like a trapezoid with a bottom end distal from the outer surface of the box end, an opening at the outer surface of the box end having a length greater than the bottom end, and converging sides that extend from the opening to the bottom end. Optionally, the grooves on the second tubular are shaped like a trapezoid with a bottom end distal from the outer surface of the pin end, an opening at the outer surface of the pin end having a length greater than the bottom end, and converging sides that extend from the opening to the bottom end. Adjacent grooves on the first tubular may be separated by a space that increases with distance from a terminal end of the box end. In an alternative, adjacent grooves on the first tubular are separated by a space that decreases with distance from a terminal end of the box end. 
     Also described herein is a method of forming a riser string that includes forming grooves onto end portions of tubulars and depositing a layer of metal cladding onto the end portions of the tubulars and over the grooves. Threads are provided on an inner surface of an end of a tubular to form a box end along with threads on an outer surface of an end of a tubular to form a pin end. Threads on the pin end are engaged with threads on the box end to define a connection. In one example, the steps of forming the grooves, threads, and engaging the threads are repeated with additional tubulars. In an example, the step of forming the grooves involves forming a helical groove proximate an end of the tubular, the groove having a triangular shaped cross section. Optionally, the grooves are formed by forming a helical groove proximate an end of the tubular, the groove having a castellated shaped cross section. Forming the grooves may alternatively involve forming a series of trapezoidal shaped grooves that have a successively decreasing depth with distance from a terminal end of the tubular. The step of depositing a layer of metal cladding onto the end portions of the tubulars and over the grooves may use cuttings taken from one of the tubulars. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side partial sectional view of an example of applying a metal spray to a tubular in accordance with the present invention. 
         FIG. 2  is a side sectional view of an example of the tubular of  FIG. 1  and having a metal spray substrate in accordance with the present disclosure. 
         FIG. 3A  is a side sectional view of an embodiment of tubulars having a metal spray substrate and threaded ends in accordance with the present invention. 
         FIG. 3B  is a side sectional view of the tubulars of  FIG. 3A  in threaded engagement in accordance with the present invention. 
         FIG. 4  is a side sectional view of tubulars having profiled surfaces with the metal spray applied over the profiled surfaces in accordance with the present invention. 
         FIG. 5  is a side view of an alternate embodiment of a profiled surface on a tubular in accordance with the present invention. 
         FIG. 6  is a side view of an example of a riser connected between a subsea wellhead and a platform in accordance with the present invention. 
     
    
    
     While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF INVENTION 
     The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. 
     It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation. Accordingly, the improvements herein described are therefore to be limited only by the scope of the appended claims. 
     Shown in side view in  FIG. 1  is an example of applying a cladding material to a tubular  20  where a spray  22  is directed from a spray gun  24  onto an outer surface of the tubular  20 . In the example of  FIG. 1 , the tubular  20  is rotated while applying the spray  22  thereby forming a spray deposit  26  on the tubular  20  and in a designated location on the tubular  20 . In an embodiment, the spray deposit  26  onto the tubular  20  is applied using a metal spray process. One example of a metal spray process is found in Carter, U.S. Patent Application Publication No. US 2011/0193338, having application Ser. No. 12/702,340, which is assigned to the assignee of the present application and incorporated by reference herein in its entirety for all purposes. The spray  22  may be a metal spray, and in an example the metal spray can include cuttings or other debris removed from the tubular  20  during its machining. 
       FIG. 2  is a side sectional view of an example of the tubular  20  having a spray deposit  26  on the outer surface of the tubular  20  and adjacent an end  28  of the tubular  20 . Embodiments exist however, wherein the spray deposit  26  extends substantially the length of the outer surface of the tubular  20 . Referring now to  FIG. 3A , tubulars  20   1,2  are shown each with spray deposits  26   1,2  formed on their respective ends  28   1,2 . Further illustrated in  FIG. 3A  are threads  30   1  formed on the outer surface of the spray deposit  26   1  thereby forming a pin end on the tubular  20   1 . Similarly, threads  30   2  are shown formed on an inner surface of the tubular  20   2  thereby forming a box end in tubular  20   2 . In the example of  FIG. 3A , the machining forming the threads  30   1,2  may cut entirely through the spray deposits  26   1,2  in a radial direction and into the tubulars  20   1,2  along a portion of the length of the spray deposits  26   1,2 . As shown in the example of  FIG. 3B , an advantage of the spray deposit method described herein is that tubulars  20   1,2  having substantially the same inner and outer diameters may be threaded together by interlocking threads  30   1,2  formed on the spray deposits  26   1,2 . This is an advantage over coaxially connecting tubulars with unions on an outer surface and/or an upset forging process. 
     In an optional embodiment as shown in side sectional view in  FIG. 4 , outer surfaces of tubulars  20 A,  20 B are treated with grooves  32 A,  32 B so that when a spray  22  is deposited over the grooves  32 A,  32 B, the spray deposits  26 A,  26 B have increased adhesion properties over that with a surface of a tubular having little or no profile. More specifically, grooves  32 A are made up of a repeating series of adjacently positioned upwardly pointed teeth that resemble a saw tooth-like configuration. When the spray  22  ( FIG. 1 ) is deposited over the grooves  32 A, the lower portions of the spray deposit  26 A reside between adjacent teeth of the grooves  32 A. Grooves  32 B, which are shown as a repeating castellated configuration, may or may not have a consistent lengthwise distance between successive or adjacent teeth within the grooves  32 B. In one example embodiment, after initially applying spray  22  ( FIG. 1 ), an axial cross section of the spray deposit  26  is semi-elliptically shaped and can be machined to have a general planar upper surface with forward and aft surfaces extending generally perpendicular from an axis A X  of tubular  20 A. 
     Referring now to  FIG. 5 , a side sectional view of an example of grooves  32 C is shown wherein the groove members  34   1-n  have a trapezoidal-like cross-section. In the example of  FIG. 5 , the groove members  34   1-n  are formed into an outer surface of the tubular  20 C and may each have a height and width that changes with respect to adjacent groove members. In the specific example of  FIG. 5 , groove member  34   1  has a height greater than other groove members  34   2-n  making up the grooves  32 C. The sequentially reduced heights between the groove members  34   1-n  may follow a generally linear function, or may optionally be nonlinear as well. In the example of  FIG. 5 , the groove members  34   1-n  having the larger height and width are located proximate an end  28 C of the tubular  20 C. However, the order may be reversed so that groove members  34   1-n  adjacent or more proximate the end  28 C may have a height exceeded by other groove members in the grooves  32 C. The shape of the grooves  32 C can be set with a more obtuse angle to improve density and adhesion of the metal spray, and also so that the metal spray contacts as much surface area as possible to prevent shadowing. 
     Referring now to  FIG. 6 , an example of a riser  36  is shown deployed subsea, wherein the riser  36  is made up of a series of tubulars  20   1-n  that extend from a wellhead assembly  38  subsea and up to a platform  40 . In the example of  FIG. 6 , the wellhead assembly  38  is shown mounted on a sea floor  42  wherein the platform  40  is above sea surface, and may be floating or may have legs (not shown) mounted on the sea floor  42 . 
     The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims.