Abstract:
A self-draining composite plastic and steel thread protector for both the pin and box ends of oil field tubulars. The protector completely seals and prevents pressure differentials across the threads as well as provides openings for draining any moisture that may enter the tubular.

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to pipe thread protectors and particularly to thread protectors which are designed to protect the sealing surfaces of threads on tubular joints used in drilling and producing oil, water and gas wells. 
     Thread protectors have been traditionally used to protect threads on the ends of tubular goods during shipment and handling. Most protectors are in the form of cup-shaped members which thread over the end of the pipe to protect the threads. In addition, some thread protectors have been designed with completely closed ends to exclude water and foreign material from the interior of the pipe or completely open ends to provide maximum air circulation. Typically, thread protectors have been formed of metal or plastic or a combination of the two materials. 
     A typical thread protector is shown in U.S. Pat. No. 4,210,179 and comprises a cup-shaped plastic member which fits over the end of the pipe and is secured in position by a steel band. The steel band engages wedge-shaped projections formed on the exterior of the protector to force the protector into firm engagement with the threads of the pipe. In addition, the plastic portion of the protector is provided with a groove for containing an O-ring that seals the threads from moisture or water while the bottom wall of the protector effectively seals the interior of the pipe from moisture or water. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved thread protector which is especially adapted for use with threaded connections having corrosion sensitive metal-to-metal sealing surfaces. These threads have sealing surfaces on both the pin and box ends which contact when the two joints of pipe are assembled. The sealing surfaces function both to prevent leakage of fluids or gas through the threaded joint and the contact between the surfaces allows the torque of the rotary table to be transmitted through the tubular pipe to the rotary bit at the bottom of the well. The improved thread protector comprises a cup-shaped member which is molded from suitable plastic materials and surrounded on one surface by a second cup-shaped member formed of metal such as steel. The combination of the two materials provides a thread protector which will not damage the threads, yet has sufficient mechanical strength to absorb the abuse to which the tubular joint may be subjected during shipment and handling. 
     The molded plastic member is provided with sealing rings which effectively isolate the threads and the faces of the pipe joint from water, vapor or other materials. In addition, the thread protector is provided with drain holes which allow the interior of the pipe to drain so that no liquid or water vapor will accumulate within the pipe joint. While the drain holes provide a means for draining the interior of the pipe, they are so positioned that rain will not penetrate into the interior of the pipe, thus subjecting the inside of the pipe to corrosion or similar conditions, unlike open-ended thread protectors. The drain holes also prevent air pressure differentials from occurring across the threads during seasonal and day to night temperature cycles; which effect has been observed to pull corrosive, moisture containing air across the corrosion sensitive threads of tubulars equipped with closed-end thread protectors. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more easily understood from the following detailed description when taken in conjunction with the attached drawings in which: 
     FIG. 1 is a longitudinal section of a pipe protector for use with the pin end of a tubular joint. 
     FIG. 2 is a cross section of a thread protector for use with the box end of a tubular joint. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, there is shown a thread protector constructed according to this invention for use with the pin end 11 of a tubular joint 10. The thread protector comprises a first plastic cup-shaped member 20 which is surrounded on its outside by a second cup-shaped member 21 formed of steel or similar metal. The inner plastic cup-shaped member is secured to the outer steel cup-shaped member by a series of bosses 22 which project outwardly into openings 23 formed in the cylindrical wall of the steel member 21. The bosses should project into the steel member a sufficient distance to firmly secure the two members together and allow the plastic member to be threaded onto the pin end of the tubular joint by rotating the steel member 21. The inner cylindrical wall of the plastic member is provided with threads 24 which mate with the threads on the pin member of the joint. The inner plastic member is provided with a bottom wall portion which has a raised annular flanged section 25 adjacent the inner wall of the inner cylindrical wall of the member. The raised portion 25 is shaped so that it corresponds to the seal end 26 of the tubular joint. In addition, the raised portion is provided with a raised angular ring section 30 which with grease effectively seals the seal end 26 of the tubular joint from any fluids or other foreign matter which may be in the interior of the tubular joint. A similar raised annular ring section 31 is formed at the end of the cylindrical wall of the plastic member 20 to form an effective seal between the plastic member and the outer surface of the tubular joint adjacent the ends of the threads. 
     From the above description it is seen that the plastic member effectively seals the seal surface 26 of the tubular joint as well as the threads from water or other foreign materials. 
     The plastic member is provided with a series of openings or drain holes 40 around the periphery of the bottom wall. The openings 40 are aligned with the inner diameter of the tubular joint as shown in FIG. 1. Thus, any water of other foreign material in the interior of the tubular joint will flow along the path indicated by the arrows 45 and exit from the tubular joint. Drain holes 40 align with radial passageways 41 formed in the end of the plastic member 20. The passageway 41 is aligned with drain openings 42 formed in the bottom wall of the steel outer member 21. A similar drain hole 43 is provided in the center of the bottom wall of the plastic member while radial passageways 44 allow the bottom of the plastic member to drain into the passageways 41. 
     A square shaped hole 50 is provided in the bottom wall of the steel outer member to provide a means for threading the protector onto and off of a pin end of a tubular joint. The square opening may be closed by a plastic button 51. 
     As explained above, the inner cup-shaped member 20 is formed from an easily moldable plastic such as polyethylene or polypropylene. In addition, other types of plastic materials or natural or synthetic rubber type materials that are easily molded may be used. The main requirement for the material is that it be readily moldable, withstand the temperatures to which it may be subjected and provide good sealing contact between the surfaces of the tubular joint and the plastic member. The outer cup-shaped member 21 may be formed of any type of material which will provide a hard surface which can withstand the abuse to which the thread protector is subjected. Since low cost is a desirable feature of any thread protector, the member 21 is preferably formed of thin steel which can be readily drawn into the cup-shaped configuration shown in the drawings. 
     Referring to FIG. 2, there is shown a thread protector constructed according to the present invention for use with the box end of a tubular joint. The thread protector in FIG. 2 includes a cup-shaped plastic member 61 and an inner cup-shaped member 62 formed of suitable metal such as steel. The inner cup-shaped member 62 is retained in the plastic cup-shaped member by a series of projecting bosses 63 formed on the plastic member which engage a series of holes 64 formed in the metal member. The cup-shaped plastic member is provided with a surface 71 at its inner end which conforms to the seal surface of the box end 60 of the tubular joint. The surface 71 is also provided with a raised sealing ring 72 for effectively sealing the seal surface of the box end from the interior of the tubular joint. The bottom wall of the plastic member is provided with a series of drain holes 80 along its outer periphery that align with the inner surface of the tubular joint. Similar drain holes 81 are provided in the bottom wall of the cup-shaped metal member 62 to provide drainage for the interior of the tubular joint. The plastic member is provided with an outwardly projecting radial flange 74 which seals the end of the tubular joint. The seal is effected by a raised seal ring 73 which projects from the bottom of the flange 74 and a coating of grease is applied to the surface of the tubular joint and the plastic member. A square opening 83 is formed in the bottom wall of the metal cup-shaped member and may be closed by a sealing button 84. This square hole provides a means for threading the protector on and off a boxed end of the tubular joint. 
     The thread protector shown in FIG. 2 is constructed in exactly the same manner and from the same materials as the protector shown in FIG. 1. The thread protector also provides means for sealing both the seal surfaces of the tubular joint using a grease coating and the raised seal rings having a semicircular cross section that is formed integrally with the plastic cup-shaped member. 
     The plastic cup-shaped member may be molded in the steel cup-shaped member or the two may be formed separately and then assembled. The two members must be securely fastened together so that the steel member can be used to thread the plastic member on the tubular joint. The drain holes must be accurately located to eliminate the possibility of small amounts of water collecting in the tubular joints. A different size of protector may be required for each weight of tubular joint even though the joints may all have the same thread diameter.