Abstract:
Several embodiments of an end cap are provided for use with a spreader bar system for distributing the lift force of a load across multiple points. The end cap comprises at least one lifting lug with the shackles positioned therethrough, along with at least one visual indicium for keeping a minimum of a 45 degree lift angle. Additionally, the end cap is provided with a pinch bolt system for easy assembly as well as a flat, horizontal foot plate located beneath the end cap for quick alignment. A four-point embodiment duplicates these features and positions two end caps at a 90 degree perpendicular angle atop a support plate. Additionally, a method of use is provided for pre-calculating maximum load so as to reduce the computation to a single chart.

Description:
FIELD 
     Embodiments within the scope of this disclosure relate, generally, to apparatuses, systems, and methods for fitting tubulars or pipes as spreader bars onto a shackle or lifting sling. This is accomplished through the use of an “end cap” fitting, which keeps the tubular in a compressive state and allows the tubular to be quickly and easily attached and disconnected from the lifting system without material alteration. 
     BACKGROUND 
     The use of spreader bar systems for lifting tubulars is well-known in the art. Examples of such spreader bar systems include, e.g., U.S. Pat. No. 4,397,493 to Khachaturian, et al., and U.S. Pat. No. 5,603,544 to Bishop, et al. The advantage of these systems is that they allow the force of a single-point lifting system, such as a shackle or hook, to be divided into multiple lifting points, thus avoiding the material stress and safety concerns associated with lifting a heavy load by a single point. 
     In order to adapt the shackle and spreader bar systems for various dimensions and weights, it is common to utilize an “end cap” system (also known as a compression cap system) for attaching spreader bars to the shackle. In this system, the spreader bar is fitted between two “end caps,” which contain multiple orifices for connecting to both the lifting mechanism above and the load below. This allows for quick swapping of various sizes and weights of spreader bar as necessitated by the lift. 
     However, there are still several drawbacks to the state of the art in spreader bar lifting. Assembly of the end cap requires precise alignment of the end cap with the spreader bar, and often requires a tubular spreader bar to be physically altered (e.g., through spot welds or attachment holes) which can weaken the spreader bar&#39;s tolerance for metallurgical stresses. 
     Additionally, the process of determining the correct end cap fitting for use with a given load and span of weight to be lifted can often be time-consuming and prone to error when calculated by workers in the field. This can lead to an increased stress on the equipment and the risk of lift failure. 
     A need therefore exists for an end cap system in which both the method of selecting a properly rated and sized end cap and the physical method of fixing the end cap to a selected spreader bar are simplified to allow field personnel to more quickly and reliably rig-up lifting systems. Embodiments disclosed in the present invention meet these needs. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the detailed description of various, example embodiments within the scope of the present disclosure, reference is made to the accompanying drawings, in which: 
         FIG. 1  depicts the overall layout of an embodiment of the end cap system in the context of connections to a single-point lift and a load to be lifted. 
         FIG. 2  depicts an embodiment of the end cap described in the present invention in perspective view. 
         FIG. 3  depicts an embodiment of the end cap described in the present invention in an exploded view. 
         FIG. 4A  depicts an embodiment of the end cap described in the present invention in an outward-facing longitudinal view. 
         FIG. 4B  depicts an embodiment of the end cap described in the present invention in a plan (overhead) view. 
         FIG. 4C  depicts an embodiment of the end cap described in the present invention in a side view. 
         FIG. 4D  depicts an embodiment of the end cap described in the present invention in an inward-facing longitudinal view. 
         FIG. 5  depicts the overall layout of an embodiment of the end cap system in the context of connections to a multi-point lift and a load to be lifted. 
         FIG. 6  depicts an embodiment of the end cap described in the present invention in perspective view. 
         FIG. 7  depicts an embodiment of the end cap described in the present invention in an exploded view. 
         FIG. 8A  depicts an embodiment of the end cap described in the present invention in a plan (overhead) view. 
         FIG. 8B  depicts an embodiment of the end cap described in the present invention in a outward-facing longitudinal view. 
         FIG. 8C  depicts an embodiment of the end cap described in the present invention in a side view. 
         FIG. 8D  depicts an embodiment of the end cap described in the present invention in an inward-facing longitudinal view. 
         FIG. 9  depicts a series of equations used to derive pre-calculated tolerances for the end cap described in the present invention 
     
    
    
     One or more embodiments are described below with reference to the above-listed Figures. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Before describing selected, example embodiments of the present disclosure in detail, it is to be understood that the present invention is not limited to the particular embodiments described herein. The disclosure and description herein is illustrative and explanatory of one or more example embodiments and variations thereof, and it will be appreciated by those skilled in the art that various changes in the design, organization, order of operation, means of operation, equipment structures and location, methodology, and use of mechanical equivalents may be made without departing from the spirit of the invention. 
     As well, it should be understood the drawings are intended to illustrate and disclose presently example embodiments to one of skill in the art, but are not intended to be manufacturing level drawings or renditions of final products, and may include simplified conceptual views as desired for easier and quicker understanding or explanation. As well, the relative size and arrangement of the components may differ from that shown and still operate within the spirit of the invention. 
     Moreover, it will be understood that various directions such as “upper,” “lower,” “bottom,” “top,” “left,” “right,” and so forth are made only with respect to explanation in conjunction with the drawings, and that the components may be oriented differently, for instance, during transportation and manufacturing as well as operation. Because many varying and different embodiments may be made within the scope of the concept(s) herein taught, and because many modifications may be made in the embodiments described herein, it is to be understood that the details herein are to be interpreted as illustrative and non-limiting. 
     Referring now to  FIG. 1 , a lifting assembly  1  utilizing an embodiment of two end caps  10 ,  11  is illustrated. Lifting assembly  1  comprises spreader bar  2 , lift point  4 , and four shackles  6 ,  7 ,  8 ,  9 . Shackles  6 ,  8  are connected by slings  12 ,  14  to lift point  4 , while shackles  7 ,  9  are connected by slings  12 ,  14  to a weight to be lifted (not shown). Optimally, the relationship between the slings  12 ,  14  and the spreader bar  2  are defined by a minimum angle (also known as a fleet angle), shown as a, so as to keep the compressive force exerted on the spreader bar  2  within a maximum tolerance. 
     Referring now to  FIG. 2 , the embodiment of the end cap  10  illustrated in  FIG. 1  is shown in greater detail. End cap  10  comprises a load lug  20  extending longitudinally from a load plate  30 . Load lug  20  in turn comprises two apertures  22 ,  24 , which accommodate the shackles  6 ,  7  (not shown, illustrated in  FIG. 1 ). To reinforce the strength of the material, apertures  22 ,  24  are reinforced through pairs of cheek plates  23 A,  23 B, and  25 A,  25 B, respectively (B plates not visible). 
     Load plate  30  faces a first end of spreader bar  2 , which is compressed against load plate  30  and extends through a pipe retainer, also known as receptacle,  40 , which extends from load plate  30  in the opposite longitudinal direction from load lug, also known as lifting lug,  20 . In this embodiment, pipe retainer  40  is a hollow cylinder through which spreader bar  2  can be fitted. Pipe retainer  40  also comprises two apertures  42 ,  44  (not visible) through which two retaining bolts, also known as pinch bolts,  43 ,  45  ( 45  not visible) extend to compress against spreader bar  2 . Retaining bolts  43 ,  45 , allow the use of intact pipe for spreader bar  2 , rather than pipe which has had holes torched through it, thereby compromising the material stress properties thereof. 
     Extending downward from pipe retainer  40  and normally to load plate  30  is leg plate  46 , which terminates at foot plate  50 . Leg plate  46  and foot plate  50  allow the end cap  10  to be easily mounted to spreader bar  2  in parallel with another end cap  11  (see  FIG. 1 ). 
     Additionally, end cap  10  comprises two alignment references. Alignment aperture  35  is located through load plate  30  and serves to align two end caps (e.g., end caps  10  and  11  as depicted in  FIG. 1 ) when in use. Angle reference  37 , meanwhile, is located on load lug  20  and serves as a visual safety reference to keep the angle of the shackles  6 ,  8  and slings  13 ,  15  (depicted in  FIG. 1 ) at a minimum effective angle. 
     In the present embodiment, angle reference  37  is depicted as a second aperture, however, it may be appreciated that other embodiments may include a simple surface reference (e.g., a reflector), or alternatively, a protruding physical stop. Any feature which serves to visually or physically mark the minimum effective angle (depicted as α in  FIG. 1 ) between slings  13 ,  15  and spreader bar  2  may be utilized without departing from the scope of this invention. In an example embodiment, the minimum effective angle is a 45 degree angle, which is specifically referenced in the associated chart for this specific system but may differ in other embodiments. 
     Referring now to  FIG. 3 , the embodiment of the end cap  10  illustrated in  FIGS. 1-2  is shown in an exploded view. Retaining bolt  45 , aperture  42 , and cheek plates  23 B,  25 B are visible in this view. Additionally, braces  32 ,  34  are also illustrated, which brace load plate  30  against load lug  20 . 
       FIG. 4A-4D  show the embodiment of the end cap  10  illustrated in  FIGS. 1-3  in an overhead view ( FIG. 4A ), left side view ( FIG. 4B ), side-on view ( FIG. 4C ), and right side view ( FIG. 4D ). Significantly, the side views in  FIGS. 4B and 4D  illustrate how alignment aperture  35 , which is located on load plate  30 , may ensure that two end caps are properly aligned when mounted onto a spreader bar, as one end cap  10  will be in the position illustrated by  FIG. 4B  and the other in the position illustrated by  FIG. 4D . Aperture  35  can also be used for a connection or “tag” line used with an adjoining rope or line to allow the spreader bar system to be guided from a safe distance from the load that is being lifted. 
     While all of the embodiments thus shown are directed to two-point lifts, it can be appreciated that the principles of the invention can also apply to more elaborate lifting systems.  FIG. 5  illustrates a perspective view of another embodiment of the invention: an end cap system directed to four-point lifts rather than two-point lifts. 
     Continuing with  FIG. 5 , the depicted embodiment comprises a plurality of end caps  110   a - d , connected by a plurality of spreader bars  112   a - d , wherein each end cap  110   a - d  is connected by an upper sling  114   a - d  ( 114   c  not visible) connecting to a common lift point  105 , and a lower sling  116   a - d  ( 116   c  not visible) connected to a load to be lifted (not visible). 
     Turning now to  FIG. 6  and  FIG. 7 , these drawings depict a perspective view and exploded view, respectively, of an embodiment of the four-point end cap  110 . End cap  110  comprises mounting plate  120 , and similar to the embodiment shown in  FIG. 1-4 , additionally comprises load plates  130   a    130   b , pipe retainers  140   a ,  140   b , and feet plate  150   a ,  150   b  ( 150   a  not visible in  FIG. 6 ). Pipe retainers  140   a ,  140   b  enclose spreader bars  112   a ,  112   b , respectively. Pipe retainers  140   a ,  140   b  are supported in place by load plates  130   a ,  130   b , as well as support braces  132   a ,  132   b  inside braces  134   a - b  ( 134   b  not visible in  FIG. 6 ), outside braces  136   a - b  ( 136   a  not visible in FIG.  6 ), and mounts  138   a ,  138   b . In addition to compression forces, pipe is fixed in place through retaining pinch bolts  143   a ,  143   b  and  145   a ,  145   b  ( 145   a  not visible in  FIG. 6 ). 
     In this embodiment, upper and lower shackles  106  and  108  are connected to mounting plate  120  via two different means. Upper shackle  106  is connected to swivel ring  126 , which is connected to mounting plate  120  via a ring bushing  128  seated in an aperture  127 . Lower shackle  108  is connected to lifting lug  121 , a structure that partially duplicates the structure depicted in the embodiment of  FIGS. 1-4 , with an aperture  122  through which shackle  108  can be attached and reinforced by cheek plates  123   a ,  123   b.    
     Additionally, as with the embodiment depicted in  FIGS. 1-4 , this embodiment comprises two horizontal foot plates  150   a ,  150   b , which, in turn, are connected to mounting plate  120  via two vertical leg plates  146   a ,  146   b.    
     Turning now to  FIGS. 8A-8D , the embodiment shown in  FIGS. 5-7  is depicted in overhead, front, side, and rear views, similar to those of  FIG. 4A-4D  for the previous embodiment. (Note that  FIGS. 8B and 8C  can be distinguished by the position of lower shackle  108  with respect to the face-on foot plate  150   a  or  150   b .) 
     Turning now to  FIG. 9 , a method of calculation is disclosed whereby the design parameters of various embodiments of the present invention can be pre-calculated from the load and span required in a lifting job. In this method, the load is purely compressive, i.e., the horizontal resultant is aligned with the pipe centerline. The exemplar calculations shown are for a load of 30 tons having a span of 20 ft to be lifted using a spreader bar of cylindrical pipe, made of standard ASTM A53B carbon steel. 
     The material parameters used in the calculation are as follows: Minimum yield (F y , 35 ksi), density (p, 0.284 lbf/in3), modulus of elasticity (E, 29,000 ksi), outside diameter (OD, 6.625 in), wall thickness (t w , schedule 40). Additionally, the spreaders in this calculation are presumed to be 9.75 inches in length, making the unbraced insert length (L sprd ) 220.5 in (span minus two spreaders). 
     From the above material parameters, several secondary parameters can be deduced, such as inside diameter (ID), area of section (A sect ), MOI (I p ), section modulus (S p ), radius of gyration (r), and linear weight (ω p ), using the formulas at the top of  FIG. 9 . Additionally, a design parameter (N d ) is given in ASME BTH-1 2005, which for the purposes of the exemplar calculation is 3.0 (Category B). 
     Box 1, two compression load factors are calculated: a slenderness ratio, and a column slenderness ratio separating elastic and inelastic buckling, using the formulas given in Box 1. Depending on which of the two results is greater, the allowable column stress can be calculated using the formulas in Box 2A and Box 2B, while the actual column stress can be calculated using the formula in Box 3. 
     Meanwhile, the allowable and actual bending load stresses can be calculated using the formulas in Box 4. Then, the allowable and actual combined (Euler) stresses can be calculated utilizing the formulas in Box 5. 
     Finally, a two-part unity check is performed utilizing the values derived in Box 3, Box 4, and Box 5, and plugging them into the equations of Box 6. 
     While the exemplar calculations are given for a load of 30 tons having a span of 20 ft, it should be appreciated that these calculations may be performed in advance for any number of specific weights and spans. In addition, other parameters such as diameter, thickness, and weight of the end caps may also vary while still remaining within the scope of the present disclosure. In a method embodiment, the maximum tolerance for a given weights and span is pre-calculated and placed in a chart having weights and spans corresponding to different scales of end cap (e.g., diameter, thickness), for field workers to quickly and reliably select an embodiment of the present invention having dimensions which tolerate the lift stresses of a given task. 
     While various embodiments usable within the scope of the present disclosure have been described with emphasis, it should be understood that within the scope of the appended claims, the present invention may be practiced other than as specifically described herein.