Abstract:
A pipeline includes a pair of pipe sections with ends ( 20, 22 ), connected together by thread the pipe ends having axial and radial abutments lying beyond the ends of the thread, The abutments ere located to stabilize a nib sealing arrangement and to enhance the capacity to resist bending while using a shorter thread length. The shorter threads ( 24, 26 ) enable pipe ends of smaller wall thicknesses to be used. At the abutments, each pipe end has a nib ( 40 A,  40 B) that is deflected to enter a groove as the pipe ends mate.

Description:
CROSS-REFERENCE 
       [0001]    Applicant claims priority from U.S. provisional patent application Ser. No. 61/850,292 filed May 22, 2012. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    Pipelines are commonly constructed by connecting together pipe sections, each of about 40 feet length, by turning one pipe section to connect its tapered thread to a tapered thread of the other pipe section. It is well known in thread design that most of the loads applied to the threads are applied over the first few threads. Beyond the opposite ends of the threads, the pipe sections are sealed together by abutments where axially-facing surfaces or radially-facing surfaces of the pipe sections abut each other to help seal the pipe joint. Further sealing is obtained by forming each pipe end with a nib that projects beyond the axial facing abutment and into a groove formed in the other pipe section. To obtain good sealing, the nibs have to fit very closely into the grooves. A strong pipeline with mating pipe sections of small wall thickness, and with good sealing at the pipe section ends, would be of value. 
       SUMMARY OF THE INVENTION 
       [0003]    In accordance with one embodiment of the invention, pipe sections are provided for threadable connection, which are of small wall thickness, which have high axial and bending resistance, and which provide good fluid sealing. The pipe sections each have a thread of small axial length with long gaps between the thread ends and the abutments at the ends of the pipe sections. 
         [0004]    The pipe sections are sealed together by nibs that are each formed at the end of one pipe section and that lie in a groove formed at the end of the mating pipe section. Each nib extends 360° about a circle, and each groove extends in a circle, about the pipe axis. For good sealing, the nibs fit with an interference fit into the grooves. Each nib is sequentially deflected into alignment with a groove by a tapered pipe internal wall leading to a radial abutment surface, so as the pipe sections become fully mated, the radial interference abutments deflect the nibs and grooves into accurate alignment. 
         [0005]    The novel feature of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0006]      FIG. 1  is a sectional side view of the mated end portions of pipe sections of a pipeline, showing only one side of the cross-section as taken along the pipeline axle. 
           [0007]      FIGS. 2-5  are sectional views of a portion of the pipeline of  FIG. 1 , showing how a nib is aligned with a groove during mating of pipe sections. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0008]      FIG. 1  shows a pipe line  10  that includes two pipe sections  12 , 14  having pipe ends  20 ,  22  that are fully mated in a pipe connection  51 . The pipe ends include a radially outer (with respect to pipe axis  16 ) pipe end, or box  20 , and a radially inner pipe end, or pin  22 , that are connected in series along the pipeline axis  16 . The pipe sections have short pipe threads  24 ,  26  of conical (tapered) shape. A common NPT (national tapered thread) thread has a taper angle A of about 3° (1.6° to 4°). 
         [0009]    The mated ends of each pipe section have abutments where radial and axial surfaces of two pipe ends abut.  FIG. 1  shows axial-facing, or axial abutments  32 ,  36  near the outside, and axial abutments  34 ,  30  near the inside of the pipe sections. The pair of pipe ends are mated by forcing one pipe section&#39;s threads to load the threads of that pipe section into the threads of the other mating pipe section, as by turning one pipe section, so the axial faces at abutments  32 ,  36  and  30 ,  34  are forced to abut one another. The pipe connection  51  has opposite ends  63 ,  55  at the axially-facing abutments such as  32 ,  36 . 
         [0010]    Each pipe section also has nibs  40 A,  40 B (small pipe projections that include surface  68 ) that have ends that fit into grooves  42 , to seal against the leakage of fluids. The nib  40 A lies at the right side of  FIG. 1 , where the pipeline radially outer side is of smallest thickness R. The nib  40 B lies at the left side of  FIG. 1 , where the pipeline radially inner side is of smallest thickness W. Each nib extends in a circle by 360° around the axis  16  and seals against the 360° walls of the groove. Radially-facing radial interference shoulders such as  68 ,  69  and  66 ,  67 , which lie adjacent to the nib-in-grooves, both align and stabilize these interfering nib surfaces and also help each end of a pipe section to take loads in bending of the pipeline, to increase the strength in bending without significant axial loading of the threads. The radially-facing shoulders  66 - 67 ,  68 - 69  are each cylindrical and extend 360° about the pipe axis. 
         [0011]    A long axial distance M between the axially-facing abutments such as  32 ,  36  and  30 ,  34  is desirable to resist bending of the pipe line and to improve the axial abutment. The longer distance M improves resistance to bending as it provides a longer moment arm for the radial abutments ( 68 ,  69  and  66 ,  67 ) in pipe sections  12 ,  14 , which enhances the pipe bending resistance. The axial abutment is improved as the longer distance M increases the distance E and F between the ends of the threads and the axial abutments. This longer distance allows for slight imperfections in the dimensions E, F of the pipe ends to minimize the effect on the variation of the desired axial abutment load. This axial abutment load variation is improved by longer E and F dimensions as the opposing E and F dimensions in the pin and box go into tension and compression when achieving the axial abutment load. The E and F sections are like springs defined by their cross-sectional area, elastic modulus and length. The longer the length, the better these “springs” adjust to any axial imperfection in their length dimensions. By having longer lengths it is thus easier to obtain at least some minimum of the desired interference with reasonable machining tolerances. 
         [0012]    The threads  24 ,  26  that connect the pipe section ends, are each of a short length L compared to the length M between the axial abutment surfaces. Axially-elongated spaces  50 ,  52  of lengths E and F are left between each end of a thread and an adjacent abutment at the connection end. Each axially-elongated space E and F Includes a wide gap part  62 ,  64  between the inner and outer pipe sections, and also includes interference shoulders at  66 ,  67  and  68 ,  69  which form radially-facing abutments. The lengths E and F are each at least 25% of the length M between abutments at opposite ends of the connection. 
         [0013]    The use of connecting threads  24 ,  26  of short length (in a direction parallel to the pipeline axis  16 ) has the advantage that it results in pipe section walls of small radial thickness. Along the tapered thread length L, the thickness grows from the thickness at B to the thickness at C. The increase in thickness (C-B) equals the sine of the thread taper angle A such as 3°, times the thread length L. In one example, the minimum outer pipe wall thickness B is 0.5 inch, and the thread length L is 6 inches. The sine of 3° (0.05) times 6 inches is 0.3 inch. Therefore, the pipe wall thickness grows by 0.3 inch along the thread length L. If the threads  24 ,  26  each extended the full length of the distance M, which is 2.6 times the short thread length L then the wall thickness would increase by 0.8 inch instead of 0.3 inch. A decrease in maximum wall thickness of 0.5 inch, from 1.3 inches to 0.8 inch, saves considerable cost by reducing the amount of steel to be used and the weight of the pipe to be supported. 
         [0014]    Applicant prefers to use threads  24 ,  26  of a length L no more than 60%, and preferably no more than 50%, of the distance M. The distance M is the distance between axial abutments such as  30 ,  34  and  32 ,  36  of the pipe connection  51 . 
         [0015]      FIGS. 2-5  show how applicant installs a nib  40 A of one pipe section end into a groove  42  of another pipe section end. After installation there is a radial interference fit between the nib and groove wails that is preferably 0.002 to 0.008 inch (50 to 200 microns), between the uncompressed thickness D of each nib such as  40 A and the radial width G of the groove such as  42 . The interference fit results in a metal-to-metal fluid seal. 
         [0016]    The make-up of these pipe sections depends on the type of thread used, in a first procedure, a tapered helical thread at  24  ( FIG. 1 ), threadably engages another thread at  26  when one pipe end is turned into the other. In a second procedure there are tapered concentric threads that are engaged by axially forcing the threads over one another into a predetermined fit. U.S. Pat. Nos. 5,954,374 by Gallagher, et al. and 5,964,486 by Sinclair show such concentric threads. When using tapered helical threads, the sections come together moving one end in the direction J ( FIG. 2 ) until the threads  24 ,  26  engage. In this arrangement the nib  40 A is positioned to clear interference surface  69 . As shown in  FIG. 3 , the turning of the threads forces taper  73  against taper  72  to start to deflect the nib walls. This causes interference surfaces  68 ,  69  and  66 ,  67  ( FIG. 1 ) to slide on one another at ends of the pipe sections. Further sliding of the nib in the direction J ( FIG. 4 ) moves the nib  40 A along an interfering taper  75 . This interference causes the pipe end  22  to move radially inward (toward the pipeline axis) and the pipe end  20  to expand radially, thereby bringing the nib  40 A and groove  42  at opposing sides into alignment for a proper entry. The turning continues and forces the nibs into grooves  42  until the axial abutments  32 ,  36  ( FIG. 4) and 34 ,  30  ( FIG. 1 ) abut one another. 
         [0017]    When using a second procedure that involves using “concentric threads”, the pipe sections are inserted into one another, advancing one end in direction J ( FIG. 2 ). The make-up of the tapered concentric vs. helical connector is largely the same, however with the concentric thread the radial thread height is smaller than the helical thread and thus the threads are not the first interference contact between the pin  22  and box  20 . The first interference contact between the pin  22  and box  20  would be between the taper at  72  ( FIG. 3 ) of surface  69  with the taper  73 . The surfaces  68  and  69  are forced onto each other by applying external axial forces. The sections now slide further onto each other and the conical threads begin to make contact. 
         [0018]    Conical threads have a unique arrangement of wide and narrow threads that do not engage until they are at their made up position (their fully mated position). A considerable force would be required to advance the threads at  24 ,  26  and to advance interference surfaces such as  68 ,  69  at both ends of the sections over one another. Additionally the nibs must be forced into their grooves while the conical threads move to their final locked engagement. When the threads finally mate the axial abutment surfaces will preload against the opposing thread slopes. When using a concentric thread arrangement it is possible to significantly reduce the axial force required to overcome the radial interference between threads by injecting pressurized fluid between the inner and outer pipe sections once the interferences between surface  68 ,  69  allow for pressurizatson. When the nibs  40  finally start to enter the grooves  42  this pressure can be increased to effectively force the threads over one another. 
         [0019]    When installing the nib by sliding it in direction J ( FIG. 2 ). It is desirable that the nib enters the groove with good alignment between them. The radial dimensions of the nib and mating groove are machined so they will become aligned during make-up when deflected by the interference surfaces such as  68 ,  69  ( FIG. 1 ). The nib of box  20  will therefore deflect outward during make-up while the nib of the pin  22  will deflect inward. Applicant constructs a guide wall  69  ( FIG. 2 ) with tapers at  72  and  75  that deflect the nib surface  68  radially outward until the nib  40 A enters the deflected groove  42  ( FIG. 5 ). When the nib enters the groove, the walls of the groove and nib deflect and compress the nib until the nib presses against both the radially inner side  80  and radially outer side  82  of the groove. 
         [0020]    The first nib  40 A ( FIG. 1 ) and the corresponding pipe end at  68  ( FIG. 1 ) lie closer to the outside  14   a  than the inside of the pipe inside the right side groove  42  the pipe end thickness of part  90  is T, where T is at least 1.5 times, and usually two times the distance R. R is the pipe end thickness of part  92  outside the right side groove  42 . The nib ends of the pipe ends are always thinner than the groove ends. When they are forced to interfere by the radial interference sections  68 ,  69 ,  67 ,  66 , the deformation or strain will always be larger on the thin end, and therefor the nibs always deform more than the groove walls. Due to this, the groove wall is deflected by much less than half the radial deflection of the nib. 
         [0021]    In the initial nib position, shown in  FIG. 2 , before the nib  40 A is deflected radially outward and the groove wall ( 82 ) is deflected inward, axial movement of the nib  40 A would move the nib so its outer surface  84  would not firmly contact the groove outer surface  82 . Only when the nib  40 A is deflected radially outward and groove inward, by the inclined surfaces  72 ,  75  will the nib  40 A contact the groove outer surface  82 . 
         [0022]    The nib  40 B and groove  42  at the second end  56  of the pipe connection  51  are virtually mirror images of the construction at the first end  53 . That is, at the second end  53  the nib  40 B lies on the inner pipe end  22  which is of smaller radial thickness than the outer pipe end  20 . The nib is deflected radially inward into the groove. 
         [0023]    Thus, the invention provides a pipeline with threadably connected ends, that avoids extra pipe wall thickness and that allows the pipe ends to be joined in a good fluid tight seal. The pipe ends have pipe threads that join the two pipe ends, the pipe ends have engaging racial and axial abutments, and the pipe ends have nibs that enter grooves, when full assembly is reached. The tapered threads that join the pipe ends are of short length, which is made possible by the radial and axial abutment surfaces at axially opposite ends, thereby freeing the threads of considerable bending loads. By minimising the thread tapered length, applicant minimizes the maximum pipe wall thickness. Depending on which end of the pipe section, each nib and groove has a larger or smaller initial diameter (from the pipeline axes) than that of their final made-up diameter. The pipe end from which the nib projects, has guiding walls that deflect the nib so it enters the groove with a gentle deflection. 
         [0024]    Although particular embodiments of the invention have been described and illustrated herein, it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.