Abstract:
A modular pipeline pig provides scraping cup having holes therethrough, adapted to retain a plurality of scraper studs. Positioned a well-defined distance behind the scraping cup is a driving cup defined by a slightly larger diameter than the scraping cup. The studs in the scraping cup may be of any appropriate shape or material, depending in the particular job. The driving cup is preferably mounted on the forward end of a mandrel, and another driving cup mounted to the back end of the mandrel. The pig is modular, so that other scrapers and or cups may be mounted to suit the needs of a particular job.

Description:
FIELD OF THE INVENTION 
   The present invention relates generally to the field of pipeline pigs, and, more particularly, to pipeline pig for the removal of hard, tenacious deposits on the inside surface of a pipeline. 
   BACKGROUND OF THE INVENTION 
   Materials in crude oil, particularly paraffin, tend to build up in pipelines carrying such crude oil. Some of the materials originate in water used in secondary recovery efforts, but materials other than crude oil and gas exist in the crude in its natural state, and over time, the build up of precipitants on the interior surfaces of pipes degrades performance of the flow of fluids through the pipeline. 
   When crude oil is pumped from the ground and transported through pipelines, a large heavy material separates and comes out of solution. The main component of this residue is high molecular weight paraffin waxes. In some cases the wax represents as much as 90 percent of the deposited residues, and varies according to the origin of the crude oil. 
   Over the years, pipeline pigs have evolved to remove paraffin and other materials obstructing pipelines, and each step in the evolution of pigs has typically addressed a specifically identified need in the art. One need recognized in the art involves the removal of hard, solid, crystalline deposits within the pipe. In pipelines carrying crude oil, the deposits may originate from components in the crude, or elsewhere. In natural gas lines, the deposits commonly form at junctions of pipelines where dry and wet gas mix together. Typically, these deposits vary substantially in thickness throughout the pipe, so that a pig that can fit through the smallest diameter of the deposits is not particularly effective in removing the deposits, and larger pigs that effectively attack the deposits are likely to become plugged in the pipe. 
   To attack these hard, tenacious deposits, a known pipeline pig was developed which comprises a drive cup, a flexible coupling trailing behind the drive cup, and a set of one or more disks in which adjustable studs are molded into the disks. During a first pass of the pig through the pipe, a relatively small size disk is used, and the studs are adjusted to a relatively small diameter to run through the pipe, with relatively few studs installed on the disk(s). With subsequent runs of the pig through the pipe, more studs are added, and the studs are gradually adjusted to larger and larger diameters. Then, a larger size disk is installed on the trailing mount, and the process is repeated, adjusting the outside diameter of the studs and installing larger and larger disks, until the pipe is opened to an extent close to the inside diameter of the pipe. Often, this process may take up to one hundred runs of the pig through the pipe. It will be appreciated that the process is slow and labor intensive. 
   Thus, there remains a need for a pipeline pig that can aggressively attack such deposits. The present invention addresses this need in the art. 
   SUMMARY OF THE INVENTION 
   The present invention provides a modular pipeline pig defined by scraping cup having holes therethrough, adapted to retain a plurality of scraper studs. Positioned a well-defined distance behind the scraping cup is a driving cup defined by a slightly larger diameter than the scraping cup. The studs in the scraping cup may be of any appropriate shape or material, depending in the particular job. The driving cup is preferably mounted on the forward end of a mandrel, and another driving cup mounted to the back end of the mandrel. The pig is modular, so that other scrapers and or cups may be mounted to suit the needs of a particular job. 
   One distinct advantage in mounted the scraping studs to the cup is that, under pressure, the cup tends to balloon or vector outward, bringing the scraping studs into abrading contact with the target deposit layer. When smaller diameter deposit regions are reached, the polymeric material of the cup onto which the studs are mounted flexes inward to accommodate the reduced diameter region. 
   In another preferred embodiment of the invention, a plane, un-studded driving cup is mounted on the front end of the pig, and a studded cup is mounted on the back end. In this way, deposit material is scraped from the wall of the pipe at the tail end of the pig, and left behind in the pipe for a subsequent sweeping or flushing operation. 
   These and other features and advantages of this invention will be readily apparent to those skilled in the art. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     So that the manner in which the above recited features, advantages and objects of the present invention are attained and can be understood in detail, more particular description of the invention, briefly summarized above, may be had by reference to embodiments thereof which are illustrated in the appended drawings. 
       FIG. 1  is a side section view of a presently preferred embodiment of the pig of this invention. 
       FIG. 2  is an end view of the pig of  FIG. 1 . 
       FIGS. 3   a ,  3   b , and  3   c  depict the variety of shapes of a set of studs which may find application in this invention. 
       FIG. 4  is an exploded view of the pig of  FIG. 1 . 
       FIG. 5  is a side section view of another presently preferred embodiment, wherein the scraper element is mounted on the back end of the pig. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1  depicts a side section view of a pig  10  comprising primarily a front driving cup  12 , a back driving cup  14 , and an axially oriented mandrel  16  between them.  FIG. 2  illustrates the pig  10  as viewed along view lines  2 — 2 . The front and back driving cups  12  and  14  are preferably formed of a flexible, polymeric material, such as for example polyurethane. 
   Positioned forward of the front driving cup  12  is a scraper cup  18 . Holes  20  (see  FIG. 4 ) are drilled into the scraper cup  18  to receive a set of studs  22 . The outer profile of the studs may take a variety of shapes, as shown in  FIGS. 3   a ,  3   b , and  3   c .  FIG. 3   a  shows toothed stud  24 ,  FIG. 3   b  shows a domed button stud  26 , and  FIG. 3   c  shows a square-shaped stud  28 . One such stud  24 ,  26 ,  28  may be appropriate for a particular stage of performing pigging of a particular pipe, while any or all of them may be used at some point in the pigging evolution. 
   Returning to  FIG. 1 , the stud  22  is mounted from the outside of the cup  18  onto a washer  30 . An important feature of the invention provides that the stud  22  is accessible from the underside of the cup  18 , because the stud is mounted with a nut  32  to adjust the height of the stud extending above the cup. Also, and more importantly, the studs can be removed by removing the nut and the stud replaced with new, unworn studs. Thus, the pig can be quickly, easily, and inexpensively put back into the pipe for a pigging operation. 
   The driving cup  12  is placed onto a forward flange  34 , integrally formed as a part of the mandrel  16 . A cylindrical spacer  36  is then placed onto the top surface of the driving cup  12  to properly space the scraper cup  18  a distance in front of the driving cup so that the scraper cup does not collapse back on the driver cup. The scraper cup  18  is then placed on the spacer  36 , and finally a mounting plate  38  is place on the forward surface of the scraper cup. A set of bolts and washers  40  then mount the entire assembly to the mandrel  16 . 
   As shown in  FIG. 1 , the scraper cup  18  preferably defines a first angled or conical face  42  and a second angled or conical face  44  extending from the first angled face to a trailing edge  46 . The holes  20  are drilled or otherwise formed through the cup along the second angled face  44 . In  FIG. 1 , the second angled face  44  appears to be parallel to the interior surface of a tubular  48 , such as an oil and gas pipe, because the face  44  has been forced back through force of the contact of the studs with the interior surface of the tubular. The angle of the face  44  in its quiescent state is more clearly shown in  FIG. 5 , which shows the pig before entry into the tubular. 
   The back driving cup  14  is attached to the mandrel  16  at an after flange  50  by a plurality of bolts and nuts  52 . The cup  14  is further supported on the side opposite the flange by a support ring  54 . The back driving cup  14 , like the front driving cup  12 , is an incrementally larger size than the scraper cup  18  to provide motive force for the pig  10  through a pipeline. 
   As shown in  FIG. 1 , the mandrel  16  is hollow, thereby defining a through-channel  56 . The mandrel is preferably made of steel, and is substantially inflexible. A radially disposed hole  57  is formed in the mandrel so that fluid from behind the back driving cup  14  flows up through the channel  56 , out the hole, and into an annulus  58  between the mandrel and the tubular  48 . In this way, driving force is exerted behind both the front and back driving cups for axial force on the pig. This feature of the invention helps to keep the pig from getting cocked in the pipeline during use. 
     FIG. 4  illustrates the pig  10  in an exploded view to show the assembly of the pig and its various major components. Beginning with the forward end of the pig, the mounting plate  38  sits on the forward end of the scraper cup  18  which is separated from the front drive cup  12  by a spacer  36 . The length of the spacer  36  is determined by the diameter of the scraper cup  18 , in that the scraper cup and the drive cup  12  must be spaced apart such that when the pig moves through the narrowest portion of the pipeline, and the scraper cup is forced back toward the rear of the pig, the trailing edge  46  does not contact the front driver cup  12 . The front driver cup  12  mounts to the flange  34  of the mandrel  16  and the back driver cup  14  mounts to the flange  50 . The back driver cup  14  is secured to the flange  50  by the support ring  54 . Note also that the holes  20  penetrate all the way through the scraper cup, so that the mounting hardware for the studs is accessible from the back of the scraper cup. In this way, worn studs may be replaced or adjusted in the field to save time in operation of the pig. 
     FIG. 5  depicts another preferred embodiment of the invention. A pig  60  comprises a front drive cup  62 , a back drive cup  64 , and a scraper cup  66  behind the back drive cup  64 . In applications where the cuttings removed by a scraper cup at the forward end of the pig may present problems for the proper operation of the pig, it is desirable to leave the cuttings behind the pig. This feature of provided by the pig  60  by placing the scraping cup at the trailing end of the pig. 
   The front drive cup  62  is mounted to a flange  68  of a mandrel  70  and supported by a support ring  72 . The support ring  72  mounts the front drive cup  62  to the flange  68  with a set of bolts and nuts  74 . Similarly, the back drive cup  64  mounts to a flange  76  with a set of bolts and nuts  78 . The back drive cup  64  is separated from the scraper cup  66  with a spacer  80  so that the back drive cup does not come into contact with the scraper cup during travel through the narrowest region of the pipeline. The scraper cup  66  is mounted in abutting contact with the spacer by a support ring  82 . As before in respect of the pig  10 , a hole  84  through the hollow mandrel provides fluid between the front and back drive cups to balance the movement of the pig and to prevent the pig from getting cocked in the pipeline. 
   It should now be clear that the pig of this invention is modular, in that it is assembled from a plurality of interchangeable parts. More scraper cups and drive cups may be attached as required by a particular job, and other pig components may also be effectively used. 
   The principles, preferred embodiment, and mode of operation of the present invention have been described in the foregoing specification. This invention is not to be construed as limited to the particular forms disclosed, since these are regarded as illustrative rather than restrictive. Moreover, variations and changes may be made by those skilled in the art without departing from the spirit of the invention.