CARRYING CAPACITY” FIELD OF THE INVENTION

The present invention relates to casing connector. More particularly, the present invention relates to a weld-on casing connector with enhanced load carrying capacity as well as easy and smooth make-up, better sealing performance, over torque elimination, reduced stress levels, related cracking and corrosion.

BACKGROUND OF THE INVENTION

Casing strings or pipes or tubular members are the most important parts of well completion when oil wells are drilled for oil and gas production. The oil wells need to be cased with casing strings of sufficient strength and functionality. The casing strings are sent under the ground to get supply of liquid or gas and the casing strings are connected to each other in series using connectors such as threaded connectors, couplings and weld-on connectors etc.

In oil industry, there are various methods to connect tubular members. In first method, casings have individual male threads at one end while female thread at the other end and are threaded together. In second method, couplings have female threads and are used for joining tubings which have external threads at both ends. In third method, the threaded connectors have a box member and a pin member such that the box member has threads on its inner surface and the pin member has threads on its outer surface. The weld-on threaded connectors are connected with tubings and or casings by using suitable welding method.

Weld-on connectors are those connectors that are welded on the tubular members by using special processes such as TIG (tungsten inert gas) welding, submerged arc welding/ERW (electrical resistance welding), girth welding etc.

In oil and gas industry, strings of tubular elements like production tubing and couplings are used for joining threaded pipes of smaller diameter values. Casings and tubings of lower sizes have different type of thread structure for taking low pressure and in general need less strength connection. With existing technology for precision engineering hardware and components, industry is seeking for more efficient solutions and processes that help to quicken operations on well sites without compromising on performance parameters like tensile strength, burst pressure, collapse pressure etc. for the larger diameter casings as well.

In oil industry, great advances have been made and with passing years, deeper and deeper drilling is being done, and oil is being recovered from still deeper depths. With increasing depths, more challenges have to be met by the industry as the environment becomes more severe due to increase in both pressure and temperature at deeper depths. For weld-on connectors, more severe challenges are brought upon the threads as these have to provide sealing against both the internal and external fluid pressures, and have also to meet increased tensile stresses, threads must not jump out against increasing bending stresses because the trends are towards deviated drilling and horizontal drilling etc. As such, there have been continuous improvements in the thread profile used for these weld- on connectors and also more features are being added to the connector members to make these more useful for the industry. The industry over the years have progressed from using V- threads, square threads, ACME threads, buttress threads, modified buttress threads, and premium connections are also being used these days for special industrial requirements.

US4124229A discloses a pipe connector that has a pin initially stabbed into a box, the pin and box then being axially loaded together at confronting transverse surfaces while the pin and box are pressurized to expand the box and compress the pin, so that when the pressure is relieved a pressure energized shrink fit is provided and the connector is rendered rigid to enhance tensile, compressive and bending strength and provide a fluid tight joint useful in making up lengths of pipe such as tubing strings and pipelines. The main drawback of this invention is that it utilized an additional ring and a bolt assembly to ensure strength while in operation and hence involves increase cost.

Therefore, there is a need of casing connector which ensures strength and enhanced load carrying capacity along with reduced chances of field failure due to weak connection of the casings or mismatched threads.

OBJECT OF THE INVENTION The main object of the present invention is to provide a weld-on casing connector for casings of size 18.625” or higher.

Another object of the present invention is to provide a weld-on casing connector having modified buttress thread profile with a load flank angle of preferably 3° and stab flank angle of preferably 28°.

Yet another object of the present invention is to provide a weld-on casing connector that helps to get easy and smooth make-up, elimination of over torque condition and reduction in stress levels. This enables better avoidance of cracking due to stress induced corrosion.

Yet another object of the present invention is to provide a pin member of the weld-on casing connector with a stab guide near its free end and this stab guide helps in quick and affirmative alignment with a free end of the box member of other casing pipe, and a load shoulder that helps to provide visual indication of fully threaded connection.

Yet another object of the present invention is to provide a weld-on casing connector in which a clearance is maintained between an outer surface of the pin member and an inner surface of the box member just below the stab guide in the fully threaded connection.

Still another object of the present invention is to provide a box member of the weld-on casing connector with an elevated shoulder and a travelling block grip around the elevated shoulder that helps in lifting of the partly assembled or dis-assembled string of casing pipe.

SUMMARY OF THE INVENTION

The present invention provides a weld-on casing connector with enhanced load carrying capacity as well as easy and smooth make-up, better sealing performance, over torque elimination, reduced stress levels and related cracking and corrosion.

In an embodiment, the present invention provides a weld-on casing connector with enhanced load carrying capacity. Said weld-on connector comprises of a box member and a pin member welded on the casing, wherein the box member has threads on inner surface and the pin member has threads on outer surface for matching with the threads on the box member. Both the pin member and the box member are hollow to allow the flow of fluid through them. Said weld-on connector has a predefined thread profile that provides most optimal performance. Said predefined thread profile includes height, pitch, a load flank angle, a stab flank angle and a taper angle of the thread. Further, a clearance is provided between the outer surface of the pin member and mating inner surface of the box connector just below a stab guide provided on the pin member when the pin member is fully threaded into the box member. The box member and the pin member are made of a material selected from a group of materials such that the strength of the connector increases significantly.

In another embodiment, the present invention provides an improved box member of a weld-on connector. Said improved box member has a profiled seat that matches a protruding part near the free end of the pin member, and an elevator shoulder that helps in lifting of the partly assembled or dis-assembled string of casing pipe.

In another embodiment, the present invention provides an improved pin member of a weld-on connector. Said pin member has a stab guide referred as protruding part near the free end of the pin connector that helps in quick and affirmative assembly as the end of a casing pipe with pin member is inserted in another casing pipe having box member at its end. The improved pin member is provided with a load shoulder that aligns with the free end of the box connector when the two members are fully threaded, and provides a visual indication of the fully threaded connection.

Therefore, in the present invention the modified thread profile of the weld-on connector and features provided on the pin member and box member such as load shoulder, elevator shoulder, stab guide etc. strengthen the connector and help in achieving optimum results for load bearing capacity and ease of threading using minimum torque for quick fully threaded connection.

BRIEF DESCRIPTION OF THE DRAWINGS

An understanding of the device of the present invention may be obtained by reference to the following drawings:

Fig. 1(a) is a sectional view of the weld-on casing connector according to an embodiment of the present invention. Fig. 1(b) is a magnified sectional view of a portion of weld-on casing connector of Fig. 1(a), according to an embodiment of the present invention.

Fig. 1(c) is a sectional view of the modified thread profile of the weld-on casing connector Pin Member according to an embodiment of the present invention.

Fig. 2(a) is a sectional view of the improved box member welded to a tubular member according to an embodiment of the present invention.

Fig. 2(b) is a sectional view of the improved pin member welded to a tubular member according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will now be described hereinafter with reference to the accompanying drawings in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough, and will fully convey the scope of the invention to those skilled in the art.

Many aspects of the invention can be better understood with references made to the drawings below. The components in the drawings are not necessarily drawn to scale. Instead, emphasis is placed upon clearly illustrating the components of the present invention. Moreover, like reference numerals designate corresponding parts through the several views in the drawings. Before explaining at least one embodiment of the invention, it is to be understood that the embodiments of the invention are not limited in their application to the details of construction and to the arrangement of the components set forth in the following description or illustrated in the drawings. The embodiments of the invention are capable of being practiced and carried out in various ways. In addition, the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting.

The present invention provides an improved weld-on casing connector with enhanced load carrying capacity achieved using a modified thread profile of the weld-on connector and features provided on the pin member and box member such as load shoulder, elevated shoulder, stab guide etc. Said weld-on connector is strengthened and the chances of failure in the field are reduced. It helps in ensuring that the strength of the connector is more than that of casing pipes. In addition, the weld-on connector provides ease of threading using minimum torque for quick fully threaded connection.

In an embodiment, the present invention provides a weld-on casing connector with enhanced load carrying capacity. Said weld-on connector comprises of a box member and a pin member welded on the casing, wherein the box member has threads on inner surface and the pin member has threads on outer surface for matching with the threads on the box member. Both the pin member and the box member are hollow to allow the flow of fluid through them. Said weld-on connector has a predefined thread profile that provides most optimal performance. Dimensions of the said predefined thread profile include height, pitch, a load flank angle, a stab flank angle and a taper angle of the thread.

Further, the pin member includes a stab guide near its free end. Also, a clearance is provided between the outer surface of the pin member and the inner surface of the box connector just below the stab guide when the pin member is fully threaded into the box member. The box member and the pin member are made of a material selected from a group of materials such that the strength of the connector increases significantly. The material of the said pin and box members is selected from a material of grade such as but not limited to AISI 4130 or X70 (Material Grades as per API 5T). The yield strength of the material for the modified connector is in range of 70 ksi to 110 ksi.

Here, the predefined thread profile is modified buttress thread profile provided on both the members i.e. box member and pin member. The modified buttress thread profile has a load flank angle of preferably 3° and stab flank angle of preferably 28°. The thread profiles of the two members of the connector carry matching thread profiles so that the two members thread over each other. For casings of diameter 18.625” or larger, the predefined thread profile for most optimal performance includes height which is total height of the thread and lies in the range of 2.06-5.0 mm, typically 3.26 mm, pitch i.e. linear distance between two threads lying in the range of 5-10 mm, typically 6.6 mm. The load flank angle lies in the range of +2.0° to 3.0°, typically 3°. The stab flank angle lies in the range of +25° to +30°, typically 28°. Taper Angle 8° to 12°, typically 9.5°. The modified thread profile helps in achieving optimum values of different performance parameters such as tensile/compressive strength, burst and collapse pressure, bending yield etc.

In another embodiment, the present invention provides an improved box member of a weld-on connector. Said improved box member has a profiled seat that matches a protruding part near the free end of the pin member, an elevator shoulder that helps in lifting of the partly assembled or dis-assembled string of casing pipe.

In another embodiment, the present invention provides an improved pin member of a weld-on connector. Said pin member has a stab guide referred as protruding part near the free end of the pin connector that helps in quick and affirmative assembly as the end of a casing pipe with pin member is inserted in another casing pipe having box member at its end. Also, a clearance is maintained between the outer surface of the pin connector and the mating inner surface of the box member. The clearance is in the range of 0.75-2.0 mm. The improved pin member is provided with a load shoulder that aligns with the free end of the box connector when the two members are fully threaded, and provides a visual indication of the fully threaded connection. The box connector is provided with an elevator shoulder.

Fig. 1(a) shows a sectional view of the weld-on casing connector according to an embodiment of the present invention. Said weld-on connector (1) comprises a box member (2) and a pin member (3). Said weld-on connector includes a modified buttress thread profile with modified buttress threads (4). The box member (2) has an elevator shoulder (5). Further, the pin member (3) has a stab guide (6) at the free end (7) of the pin member (3). The pin member (3) further has a load shoulder (8) which provides a visual make up indicator (9) when the pin member (3) is fully threaded into the box member (2). An O-ring seal (10) is placed between the box member (2) and pin member (3) to ensure no leakage.

Fig. 1(b) is a magnified sectional view of a portion of weld-on casing connector according to an embodiment of the present invention. Said weld-on casing connector (1) has a box member (2) with an elevator shoulder (5) that helps in lifting of the partly assembled or dis-assembled string of casing pipe. The box member (2) has a welding portion (11) provided for welding to the casing string by using a welding method, preferably girth welding. The pin member (3) at the free end (7) has a stab guide (6). Between the pin member (3) and box member (2), there is a clearance (12) provided in the range of 0.75-2.0 mm.

Fig. 1(c) is a sectional view of the modified thread profile of the weld-on casing connector according to an embodiment of the present invention. The modified thread profile comprises linear dimensions including pitch PI and height HI. Pitch PI of the threads (4) is the linear distance between two threads. Height HI is the total height of the thread. The angle A is called load flank angle, angle B is called stab flank angle and angle C is called taper angle for the thread. For a 20” casing connector, load flank angle of 3° and stab flank angle of 28° provide the most optimal performance. The improved weld-on connector is enabled for all different connectors for different casing sizes 18.625” to 36”, typical casing sizes being 18.625 X 0.435, 20.0 X 0.625, 20 X 0.438, 30 X 1, and 36 X 1.5, all dimensions are in inches, the first number being the casing OD (outer diameter) and the second number being the wall thickness, thus 18.625 X 0.435 is a casing with nominal outer diameter of 18.625” and wall thickness of 0.435”.

Fig. 2(a) is a sectional view of the improved box member welded to a tubular member according to an embodiment of the present invention. Said box member (2) at one end forms a welding joint (13) to a casing pipe (14) while other end of the box member (2) is free end (16). Further, Fig. 2(b) is a sectional view of the improved pin member welded to a tubular member according to an embodiment of the present invention. Said pin member (3) at one end forms a welding joint (13) to a casing pipe (14) while the other end of the pin member is a free end (7). Outer surface of the pin member (3) has a groove (15) for adopting O-ring seal (10) and a load shoulder (8).

Therefore, the present invention shows improvement in strength of weld-on connector by changing the thread profile to a specified modified buttress thread. Said weld-on connector is more reliable and durable and the chances of field failures reduce significantly, resulting in no additional cost due to failures.

The foregoing description of embodiments of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of the invention. The embodiments were chosen and described in order to explain the principals of the invention and its practical application to enable one skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.