Abstract:
A pipe element has a circumferential groove with a surface portion oriented at an angle with respect to its longitudinal axis. A surface portion of the groove adjacent to the angled surface portion is oriented perpendicular to the longitudinal axis. A mechanical coupling has projecting keys that engage the groove. The keys have mating surfaces that contact both the perpendicular and angled surface portions of the groove. When the pipe element and coupling are used in combination to form a pipe joint, axial load on the pipe, resisted by the mechanical coupling, is shared between the perpendicular and angled surface portions which results in a pipe joint that can withstand higher internal pressure than if the axial load were borne by the perpendicular surface portion alone.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is based upon and claims priority to U.S. Provisional Application No. 62/287,015, filed Jan. 26, 2016 and hereby incorporated by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention concerns improved groove shapes for pipe elements joined by mechanical couplings, and coupling key shapes compatible with improved groove shapes. 
       BACKGROUND 
       [0003]    As shown in  FIG. 1 , one type of prior art mechanical coupling  10  for joining pipe elements  12  and  14  end to end relies on arcuate projections, known as keys  16  that mechanically engage circumferential grooves  18  in the pipe elements. While these couplings have proved to be very effective and efficient, the prior art configuration is subject to certain limitations. For example, when such a joint is subjected to loads, especially loads arising from internal pressure induced end loads, axial tensile forces and bending, the joint may not be able to withstand such loads up to the full tensile strength of certain types of pipe. To realize a greater percentage of the potential strength of the pipe element and thereby increase the pressure capacity of a joint, external rings containing grooves may be welded to pipe elements to provide for mechanical engagement with the coupling&#39;s keys in a configuration that does not alter the pipe element&#39;s sidewall, either by removing material (machined grooves) or by deforming the sidewall (rolled grooves). 
         [0004]    While welded external rings may permit a larger percentage of the full pipe strength to be realized at a joint, the disadvantage of this solution is the need to weld rings onto the pipe elements. This procedure adds cost, time and requires skilled welders, complicating fabrication. There is clearly a need for a pipe design that improves the realization of pipe element strength and thereby increases the internal pressure performance and axial tensile loading limits achievable using mechanical couplings without the need for external welded rings. 
       SUMMARY 
       [0005]    The invention concerns a pipe element having first and second oppositely disposed ends. In one example embodiment the pipe element comprises a sidewall surrounding a longitudinal axis and defining a bore. The sidewall has an outer surface. A first groove is positioned in the outer surface. The first groove extends circumferentially around the bore and is positioned proximate to the first end. The first groove is defined by a first plurality of sub-surfaces of the outer surface including:
       a first sub-surface oriented at an angle with respect to the longitudinal axis and facing away from the first end;   a second sub-surface oriented at an angle with respect to the longitudinal axis, the second sub-surface being in spaced relation away from and facing toward the first sub-surface;   a third sub-surface contiguous with the first sub-surface, the third sub-surface oriented at an angle with respect to the longitudinal axis and sloping toward the second sub-surface; and   a fourth sub-surface contiguous with the third and second sub surfaces, the fourth sub-surface being oriented at an angle with respect to to the longitudinal axis.       
 
         [0010]    In a specific example embodiment the first sub-surface has an orientation angle from 80° to 90° with respect to the longitudinal axis. Further by way of example, the first sub-surface has an orientation angle of 89° with respect to the longitudinal axis. In another example, the third sub-surface has an orientation angle from 1° to 25° with respect to the longitudinal axis. In a further example, the third sub-surface has an orientation angle of 10° with respect to the longitudinal axis. In another example the second sub-surface has an orientation angle of 90° with respect to the longitudinal axis. Further by way of example, the second sub-surface has an orientation angle from 40° to 70° with respect to the longitudinal axis. In an example embodiment the second sub-surface has an orientation angle of 50° with respect to the longitudinal axis. In a further example embodiment the fourth sub-surface has an orientation angle from +5° to −5° with respect to the longitudinal axis. 
         [0011]    In an example embodiment the pipe element further comprises a second groove positioned in the outer surface. The second groove extends circumferentially around the bore and positioned proximate to the second end. The second groove is defined by a second plurality of sub-surfaces of the outer surface including:
       a fifth sub-surface oriented at an angle with respect to the longitudinal axis and facing away from the second end;   a sixth sub-surface oriented at an angle with respect to the longitudinal axis, the sixth sub-surface being in spaced relation away from and facing toward the fifth sub-surface;   a seventh sub-surface contiguous with the fifth sub-surface, the seventh sub-surface oriented at an angle with respect to the longitudinal axis and sloping toward the sixth sub-surface; and   an eighth sub-surface contiguous with the seventh and sixth sub surfaces, the eighth sub-surface oriented at an angle with respect to the longitudinal axis.       
 
         [0016]    In another example embodiment the first and fifth sub-surfaces have an orientation angle from 80° to 90° with respect to the longitudinal axis. Further by way of example, the first and fifth sub-surfaces have an orientation angle 89° with respect to the longitudinal axis. In another example, the third and seventh sub-surfaces have an orientation angle from 1° to 25° with respect to the longitudinal axis. By way of further example, the third and seventh sub-surfaces have an orientation angle of 10° with respect to the longitudinal axis. In another example, the second and sixth sub-surfaces have an orientation angle of 90° with respect to the longitudinal axis. In another example, the second and sixth sub-surfaces have an orientation angle from 40° to 70° with respect to the longitudinal axis. Further by way of example, the second and sixth sub-surfaces have an orientation angle of 50° with respect to the longitudinal axis. In another example, the fourth and eighth sub-surfaces have an orientation angle from +5° to −5° with respect to the longitudinal axis. 
         [0017]    The invention further encompasses, in combination, a pipe element as described above and a coupling. In one example embodiment the coupling comprises a plurality of segments attached to one another end to end surrounding the first end of the pipe element. Adjustable attachment members are positioned at each end of the segments for attaching the segments to one another. At least one arcuate projection is positioned on one side of each of the segments and engages with the first groove. The at least one arcuate projection comprises a plurality of mating surfaces including:
       a first mating surface oriented at an angle with respect to the longitudinal axis and in facing relation with the first sub-surface;   a second mating surface oriented at an angle with respect to the longitudinal axis and in facing relation with the second sub-surface;   a third mating surface oriented at an angle with respect to the longitudinal axis and contacting the third sub-surface; and   a fourth mating surface in facing relation with the fourth sub-surface.       
 
         [0022]    In an example embodiment a gap is positioned between the fourth mating surface and the fourth sub-surface. In a further example, the at least one arcuate projection comprises a recess therein forming the gap between fourth mating surface and the fourth sub-surface. 
         [0023]    A further example embodiment comprises, in combination, a pipe element as described above and a coupling. By way of example the coupling comprises a plurality of segments attached to one another end to end surrounding the first end of the pipe element. Adjustable attachment members are positioned at each end of the segments for attaching the segments to one another. At least one arcuate projection is positioned on one side of each of the segments and engages with the first groove. The at least one arcuate projection comprises a plurality of mating surfaces including:
       a first mating surface oriented perpendicular to the longitudinal axis and in facing relation with the first sub-surface;   a second mating surface oriented perpendicular to the longitudinal axis and in facing relation with the second sub-surface;   a third mating surface oriented at an angle with respect to the longitudinal axis and contacting the third sub-surface; and   a fourth mating surface in facing relation with the fourth sub-surface.       
 
         [0028]    By way of example, a gap is positioned between the fourth mating surface and the fourth sub-surface. In a further example the at least one arcuate projection comprises a recess therein forming the gap between the fourth mating surface and the fourth sub-surface. In an example embodiment the coupling comprises no more than two segments. 
         [0029]    The invention also encompasses a coupling for joining pipe elements. In an example embodiment the coupling comprises a plurality of segments attached to one another end to end surrounding a central space for receiving the pipe elements. Adjustable attachment members are positioned at each end of the segments for attaching the segments to one another. At least a first arcuate projection is positioned on a first side of each of the segments. The first arcuate projections comprise a plurality of mating surfaces including:
       a first mating surface oriented at an angle with respect to a longitudinal axis extending through the central space coaxially with the segments;   a second mating surface in spaced relation from the first mating surface and oriented at an angle with respect to the longitudinal axis;   a third mating surface contiguous with the first mating surface and oriented at an angle with respect to the longitudinal axis; and   a fourth mating surface between the third and second mating surfaces and oriented at an angle with respect to the longitudinal axis.       
 
         [0034]    In an example embodiment the pipe element further comprises a second arcuate projection positioned on a second side of each of the segments. The second arcuate projections comprise a plurality of mating surfaces including:
       a fifth mating surface oriented at an angle with respect to the longitudinal axis;   a sixth mating surface in spaced relation from the fifth mating surface and oriented at an angle with respect to the longitudinal axis;   a seventh mating surface contiguous with the fifth mating surface and oriented at an angle with respect to the longitudinal axis; and   an eighth mating surface between the sixth and seventh mating surfaces and oriented at an angle with respect to the longitudinal axis.       
 
         [0039]    In an example embodiment the first mating surface has an orientation angle from 80° to 90° with respect to the longitudinal axis. In another example embodiment the first mating surface has an orientation angle of 89° with respect to the longitudinal axis. By way of further example the third mating surface has an orientation angle from 1° to 25° relative to the longitudinal axis. In another example the third mating surface has an orientation angle of 10° relative to the longitudinal axis. In a further example the second mating surface has an orientation angle of 90° with respect to the longitudinal axis. In another example the second mating surface has an orientation angle from 40° to 70° relative to the longitudinal axis. Further by way of example the second mating surface has an orientation angle of 50° relative to the longitudinal axis. In another example the fourth mating surface has an orientation angle from +5° to −5° with respect to the longitudinal axis. In an example embodiment the first and fifth mating surfaces have an orientation angle from 80° to 90° with respect to the longitudinal axis. Further by way of example, the first and fifth mating surfaces have an orientation angle of 89° with respect to the longitudinal axis. In another example, the third and seventh mating surfaces have an orientation angle from 1° to 25° relative to the longitudinal axis. Further by way of example, the third and seventh mating surfaces have an orientation angle of 10° relative to the longitudinal axis. Also by way of example, the second and sixth mating surfaces have an orientation angle of 90° with respect to the longitudinal axis. In an example embodiment, the second and sixth mating surfaces have an orientation angle from 40° to 70° relative to the longitudinal axis. In a further example, the second and sixth mating surfaces have an orientation angle of 50° relative to the longitudinal axis. In another example, the fourth and eighth mating surfaces have an orientation angle from +5° to −5° with respect to the longitudinal axis. 
         [0040]    The invention also encompasses, in combination, a coupling as described above and a pipe element. In one example embodiment the pipe element comprises a sidewall surrounding the longitudinal axis and defining a bore. The sidewall has an outer surface. A first groove is positioned in the outer surface. The first groove extends circumferentially around the bore and is positioned proximate to the first end. The first groove is defined by a first plurality of sub-surfaces of the outer surface including:
       a first sub-surface oriented at an angle with respect to the longitudinal axis and in facing relation with the first mating surface;   a second sub-surface oriented at an angle with respect to the longitudinal axis and in facing relation with the second mating surface;   a third sub-surface oriented at an angle with respect to the longitudinal axis and contacting the third mating surface; and   a fourth sub-surface in facing relation with the fourth mating surface.       
 
         [0045]    In an example embodiment a gap is positioned between the fourth mating surface and the fourth sub-surface. In an example embodiment the first arcuate projection comprises a recess therein forming the gap between the fourth mating surface and the fourth sub-surface. 
         [0046]    Another example embodiment comprises, in combination, a coupling as described above and a pipe element. By way of example the pipe element comprises:
       a sidewall surrounding the longitudinal axis and defining a bore, the sidewall having an outer surface;   a first groove positioned in the outer surface, the first groove extending circumferentially around the bore and positioned proximate to the first end, the first groove being defined by a first plurality of sub-surfaces of the outer surface including:   a first sub-surface oriented perpendicular to the longitudinal axis and in facing relation with the first mating surface;   a second sub-surface oriented perpendicular to the longitudinal axis and in facing relation with the second mating surface;   a third sub-surface oriented at an angle with respect to the longitudinal axis and contacting the third mating surface; and   a fourth sub-surface in facing relation with the fourth mating surface.       
 
         [0053]    By way of example a gap is positioned between the fourth mating surface and the fourth sub-surface. In an example embodiment the first arcuate projection comprises a recess therein forming the gap between the fourth mating surface and the fourth sub-surface. 
         [0054]    In an example embodiment the coupling comprises no more than two segments. 
         [0055]    The invention also encompasses a method of assembling a coupling having an arcuate projection with a pipe element. In one example embodiment the method comprises:
       contacting the third sub-surface of the groove with a portion of the arcuate projection;   contacting the second sub-surface of the groove with another portion of the arcuate projection.       
 
         [0058]    The invention also encompasses a method of using a coupling having an arcuate projection engaged with a groove of a pipe element. In one example the method comprises:
       applying a tensile force between the pipe element and the coupling, thereby causing a portion of the arcuate projection to engage the first sub-surface and another portion of the arcuate projection to engage the third sub-surface.       
 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0060]      FIG. 1  is a longitudinal sectional view of a pipe joint according to the prior art; 
           [0061]      FIG. 2  is an isometric view of an example combination coupling and pipe elements according to the invention; 
           [0062]      FIG. 3  is a longitudinal sectional view of a portion of an example coupling and pipe elements according to the invention shown initially upon assembly; 
           [0063]      FIG. 3A  is a longitudinal sectional view of a portion of another example coupling and pipe elements according to the invention; 
           [0064]      FIG. 3B  is a longitudinal sectional view of the portion of the example coupling and pipe elements shown in  FIG. 3  in the fully loaded condition; 
           [0065]      FIG. 4  is a partial longitudinal sectional view of an example pipe element according to the invention; and 
           [0066]      FIG. 5  is a partial longitudinal sectional view illustrating a device and a method for forming pipe elements according to the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0067]      FIG. 2  shows an example mechanical pipe coupling  20  according to the invention joining example pipe elements  22  and  24  according to the invention. Coupling  20  comprises segments  26  and  28  attached end to end to surround a central space  30  which receives the pipe elements  22  and  24 . Attachment of the segments to one another is effected by adjustable attachment members  32  and  34  which, in this example, comprise lugs  36  and  38  that respectively project from opposite ends of each segment  26  and  28 . Lugs  36  and  38  in this example have reinforcing gussets  40  and openings  42  that receive fasteners  44 , in this example studs  46  and nuts  48 . 
         [0068]    As shown in the sectional view of  FIG. 3 , each segment ( 26  being shown in section) has two arcuate projections, also known as keys  50  and  52  positioned on opposite sides of each segment. Keys  52  and  50  project toward the central space  30  and mechanically engage respective circumferential grooves  54  and  88  in each pipe element. A fluid tight joint is ensured by a ring seal  56  captured and compressed between the segments  26  and  28  and the pipe elements  22  and  24  when fasteners  44  (see  FIG. 2 ) are adjustably tightened to draw the segments  26  and  28  toward one another and into engagement with the pipe elements to form the joint. 
         [0069]      FIG. 4  shows pipe element  24  and its groove  54  in detail. In this example pipe element  24  comprises a sidewall  58  surrounding a longitudinal axis  60  and defining a bore  62 . Groove  54  is positioned in an outer surface  64  of the sidewall  58 . Groove  54  extends circumferentially about the bore  62  and is positioned proximate to an end  66  of the pipe element  24 . As shown in  FIG. 3 , the position of the groove  54  with respect to the pipe end  66  is coordinated with the coupling  20  so as to provide lands  70  for sealing engagement with the glands  72  of the ring seal  56 . 
         [0070]    As shown in  FIG. 4 , groove  54  comprises a first sub-surface  74  shown oriented perpendicular (90°) relative to the longitudinal axis  60 . The orientation angle  73  of first sub-surface  74  may range from 80° to 90° with respect to the longitudinal axis  60 , with an orientation angle of about 89° being advantageous. First sub-surface  74  faces away from the end  66  of the pipe element  24 . A second sub-surface  76  is oriented at an angle with respect to the longitudinal axis  60 . Second sub-surface  76  is positioned in spaced relation away from the first sub-surface  74  and faces the end  66  of the pipe element  24 . A third sub-surface  78  is contiguous with the first sub-surface  74 , is oriented at an angle with respect to the longitudinal axis  60  and slopes toward the second sub-surface  76 . A fourth sub-surface  80  is contiguous with both the second and third sub-surfaces. The fourth sub-surface  80  is shown oriented parallel (0° angle) to the longitudinal axis  60 , but its orientation angle  79  may range from +5° to −5° for a practical design. The terms “perpendicular”, “parallel” and “oriented at an angle” mean perpendicular or parallel or oriented at an angle with respect to a reference axis within normal manufacturing tolerances for the pipe element in question. 
         [0071]    In a practical design, second sub-surface  76  may have an orientation angle  82  from about 40° to about 70° relative to the longitudinal axis  60 ; an orientation angle  82  of about 50° is considered advantageous for certain applications. Similarly, the third sub-surface  78  may have an orientation angle  84  from about 1° to about 25° relative to the longitudinal axis  60 , and an orientation angle  84  of about 10° is considered advantageous for certain applications. 
         [0072]    As further shown in  FIG. 4 , pipe element  24  may have a second end  86  oppositely disposed from the end  66  (which may thus be considered the “first” end), the second end  86  having a second groove  88  with a groove configuration similar to the first groove  54 . In this example embodiment second groove  88  comprises a fifth sub-surface  90  shown oriented perpendicular (90°) to the longitudinal axis  60 . The orientation angle  91  of fifth sub-surface  90  may range from 80° to 90° with respect to the longitudinal axis  60 , with an orientation angle of about 89° being advantageous. Fifth sub-surface  90  faces away from the second end  86  of the pipe element  24 . A sixth sub-surface  92  is oriented at an angle with respect to the longitudinal axis  60 . Sixth sub-surface  92  is positioned in spaced relation away from the fifth sub-surface  90  and faces the second end  86  of the pipe element  24 . A seventh sub-surface  94  is contiguous with the fifth sub-surface  90 , is oriented at an angle with respect to the longitudinal axis  60  and slopes toward the sixth sub-surface  92 . An eighth sub-surface  96  is contiguous with both the sixth and seventh sub-surfaces. The eighth sub-surface  96  is shown oriented parallel (0° angle) to the longitudinal axis  60 , but its orientation angle  97  may range from about +5° to about −5° for a practical design. 
         [0073]    In a practical design, sixth sub-surface  92  may have an orientation angle  98  from about 40° to about 70° relative to the longitudinal axis  60 ; an orientation angle  98  of about 50° is considered advantageous for certain applications. Similarly, the seventh sub-surface  94  may have an orientation angle  100  from about 1° to about 25° relative to the longitudinal axis  60 , and an orientation angle  100  of about 10° is considered advantageous for certain applications. 
         [0074]    Grooves  54 ,  88  may be formed in pipe elements  22  and  24  by roll grooving, as shown in  FIG. 5 . As shown by way of example for groove  54  in pipe element  24 , the pipe element is cold worked while being rotated between an inner roller  101  that contacts the inside surface  103  of the pipe element, and an outer roller  105  that contacts the pipe element outer surface  107 . Typically, the inner roller  101  is driven (rotated about an axis  109  parallel to the longitudinal axis  60  of the pipe element  24 ). The driven inner roller  101  rotates the pipe element, which, in turn rotates the outer roller  105  about an axis  111  as a result of contact friction between the rollers and the pipe element. The outer roller  105 , being an idler, is usually forced toward the inner roller  101  with a hydraulic ram  113 , deforming the pipe element and forming the groove  54  having a shape dictated by the shapes of the inner and outer rollers  101  and  105 . Grooves  54  and  88  may also be formed by machining operations. 
         [0075]      FIGS. 2 and 3  show a combination pipe element ( 22  and/or  24 ) and coupling  20  connecting the pipe elements end to end.  FIG. 3  shows in detail, the cross sectional geometry of the arcuate projections or keys  50  and  52  effecting mechanical engagement with circumferential grooves  88  and  54  in each pipe element  22  and  24  initially upon assembly of the joint, i.e. prior to the application of internal pressure induced end loads, axial tensile forces and bending loads. 
         [0076]    In this example embodiment, key  52  comprises a plurality of mating surfaces including a first mating surface  102  shown oriented perpendicular to the longitudinal axis  60  and in facing relation with the first sub-surface  74 . Note initially upon assembly there usually will be a gap between first mating surface  102  and first sub-surface  74  because the angular relationship between sub-surface  78  and sub-surface  80  tends to bias the location of key  52  away from sub-surface  74 . A second mating surface  104  is oriented at an angle with respect to the longitudinal axis  60 , is spaced away from the first mating surface  102 , and contacts the second sub-surface  76  initially upon assembly. A third mating surface  106  is oriented at an angle with respect to the longitudinal axis  60  and is contiguous with the first mating surface  102 . Third mating surface  106  contacts third sub-surface  78  initially upon assembly. A fourth mating surface  108  is between the second and third mating surfaces  104  and  106 , is in facing relation with the fourth sub-surface  80  and in spaced apart relation therefrom thereby forming a gap  115 . The gap  115  is ensured by the fourth mating surface  108  comprising a recess in the arcuate projection (key)  52 . Similarly, key  50  also comprises a plurality of mating surfaces including a fifth mating surface  110  shown oriented perpendicular to the longitudinal axis  60  and in facing relation with the fifth sub-surface  90 . A gap is typically present between the fifth mating surface  110  and the fifth sub-surface  90  initially upon assembly because the angular relationship between sub-surface  94  and sub-surface  96  tends to bias the location of key  50  away from sub-surface  90 . A sixth mating surface  112  is oriented at an angle with respect to the longitudinal axis  60 , is spaced away from the fifth mating surface  110 , and contacts the sixth sub-surface  92  initially upon assembly. A seventh mating surface  114  is oriented at an angle with respect to the longitudinal axis  60  and is contiguous with the fifth mating surface  110 . Seventh mating surface  114  contacts seventh sub-surface  94  initially upon assembly. An eighth mating surface  116  is between the sixth and seventh mating surfaces  112  and  114 , is in facing relation with the eighth sub-surface  96  and in spaced apart relation therefrom thereby forming a gap  117 . The gap  117  is ensured by the eighth mating surface  116  comprising a recess in the arcuate projection (key)  50 . 
         [0077]    In a practical design, the mating surfaces will have orientation angles matched to the respective sub-surfaces they contact. Thus the first mating surface  102  may have an orientation angle  119  from about 80° to about 90° with respect to the longitudinal axis  60 , with an orientation angle of about 89° being advantageous. The second mating surface  104  may have an orientation angle  118  from about 40° to about 70° with respect to the longitudinal axis  60 . An orientation angle  118  of about 50° is considered advantageous for certain applications. The third mating surface  106  may have an orientation angle  120  from about 1° to about 25° with respect to the longitudinal axis  60 . An orientation angle  120  of about 10° is considered advantageous for certain applications. The orientation angle  121  of the fourth mating surface  108  may range from about +5° to about −5° with respect to the longitudinal axis  60 . 
         [0078]    Similarly, the fifth mating surface  110  may have an orientation angle  123  from about 80° to about 90° with respect to the longitudinal axis  60 , with an orientation angle of about 89° being advantageous. The sixth mating surface  112  may have an orientation angle  122  from about 40° to about 70° with respect to the longitudinal axis  60 . An orientation angle  122  of about 50° is considered advantageous for certain applications. The seventh mating surface  114  may have an orientation angle  124  from about 1° to about 25° with respect to the longitudinal axis  60 . An orientation angle  124  of about 10° is considered advantageous for certain applications. The orientation angle  125  of the eighth mating surface  116  may range from about +5° to about −5° with respect to the longitudinal axis  60 . 
         [0079]      FIG. 3A  illustrates another example embodiment wherein coupling  20   a  joins pipe elements  22   a  and  24   a . In this example embodiment the sub-surface  92   a  on pipe element  22   a  and its mating surface  112   a  on key  50   a  of coupling  20   a  are oriented at about 90° to the longitudinal axis  60 . Similarly, sub-surface  76   a  on pipe element  24   a  and its mating surface  104   a  on key  52   a  of coupling  20   a  are oriented at about 90° to the longitudinal axis  60 . As evidenced by the absence of gaps between mating surface  110  and sub-surface  90  and mating surface  102  and sub-surface  74 , the joint is shown subjected to internal pressure induced end loads and/or axial tensile forces, as explained in detail below. 
         [0080]    Example pipe elements  22  and  24  (or  22   a  and  24   a ), when used in combination with the example coupling  20  (or coupling  20   a , respectively) provide a marked improvement over prior art direct mechanical roll groove or machined groove coupling systems. The improved performance is due to a better axial load distribution, which, unlike prior art couplings, is not borne entirely at the first and fifth sub-surfaces  74  and  90 . Rather, a portion of the axial load is borne by the sub-surfaces  74  and  90  as a result of contact between the third mating surface  106  and the third sub-surface  78  and the seventh mating surface  114  and the seventh sub-surface  94 . These mating surfaces on the coupling and sub-surfaces on the pipe elements are oriented at an angle with respect to the longitudinal axis  60 . Thus, when, as shown in  FIG. 3B , the pipe joint is subjected to internal pressure induced end loads and/or axial tensile forces, the pipe elements  22  and  24  (or  22   a  and  24   a ) move axially away from one another, the aforementioned mating surfaces  106  and  114  ride up angled sub-surfaces  78  and  94  to come into greater wedging, clamping contact with the mating surfaces  106  and  114  respectively, until mating surfaces  102  and  110  firmly contact the first and fifth sub-surfaces  74  and  90  of the pipe element  24  and  22  (or  24   a  and  22   a ). The internal pressure induced end loads and/or axial tensile forces are thus resisted not only by contact between mating surfaces  102  and  110  of the coupling and sub-surfaces  74  and  90  of the pipe elements, but also by the wedging, clamping contact of mating surfaces  106  and  114  with angled sub-surfaces  78  and  94 . Keys  50  and  52  (also  50   a  and  52   a ) are designed so that they do not completely fill their respective grooves  88  and  54 . Rather, as the pipe joint is loaded, pipe elements  22  and  24  push away from one another until sub-surfaces  74  and  90  come into contact with mating surfaces  102  and  110  respectively. This will open a gap between sub-surfaces  92  and  76  and their respective mating surfaces  112  and  114 . The spaced relation of the fourth mating surface  108  from the fourth sub-surface  80  and the spaced relation of the eighth mating surface  116  from the eighth sub-surface  96  provide the needed space to ensure that contact is achieved between sub-surface  78  and mating surface  106  as well as between sub-surface  94  and mating surface  114 . 
         [0081]    The load sharing which provides improved performance is effected by the geometries of the keys  50  and  52  and the respective grooves  88  ad  54  which they engage as well as the method of assembling and using the coupling and pipe elements according to the invention. In an example embodiment of one method of assembly, described for pipe element  24  and coupling  20  with reference to  FIG. 3 , comprises contacting the third sub-surface  78  of groove  54  with a portion (third mating surface  106 ) of the arcuate projection (key)  52 , and contacting the second sub-surface  76  of groove  54  with another portion (second mating surface  104 ) of the arcuate projection (key)  52 . When the combination includes the second pipe element  22  the assembly proceeds similarly; contacting the seventh sub-surface  94  of groove  88  with a portion (seventh mating surface  114 ) of the arcuate projection (key)  50 , and contacting the sixth sub-surface  92  of groove  88  with another portion (sixth mating surface  112 ) of the arcuate projection (key)  52 . 
         [0082]    An example method of using the coupling  20  having arcuate projections  50 ,  52  engaged with grooves  88 ,  54  of the pipe elements  22  and  24  is illustrated with reference to  FIGS. 3 and 3B  and comprises assembling coupling segments  26  and  28  about pipe elements  22  and  24 , such that keys  50  and  52  are located within grooves  88  and  54 , respectively ( FIG. 3 ). Fasteners  44  are then installed and tightened to connect attachment members  32  and  34  and ensure that at least mating surfaces  106  and  114  come into contact with sub-surfaces  78  and  94  respectively. As shown in  FIG. 3B , forces are applied to the coupling (arising from system pressure, gravitational or other end loads) which create a tensile force between the pipe elements and the coupling, thereby causing respective portions of the arcuate projections (first and fifth mating surfaces  102 ,  110 ) to engage respective first and fifth sub-surfaces  74  and  90  of grooves  54  and  88 , and other portions (third and seventh mating surfaces  106  and  114 ) of the arcuate projections  52  and  50  to respectively engage the third and seventh sub-surfaces  78  and  94 . 
         [0083]    Pipe elements and their associated couplings according to the invention have demonstrated a marked improvement in the goal of realizing a greater portion of the potential strength of the pipe element when compared to prior art pipe elements and couplings.