This invention concerns a tool and a method for indicating when an external circumferential groove formed in a pipe has a desired outer diameter.
Mechanical pipe coupling systems which do not require welding, brazing or soldering for joining piping, find widespread use throughout industry, especially in petroleum and chemical applications where it may be hazardous and/or forbidden to use an open flame or an electrical arc. Such mechanical coupling systems are also more conveniently employable in the field or in remote locations where primitive environmental conditions and a lack of access to available services and supplies such as electricity or acetylene gas and oxygen inhibit traditional arc or gas welding techniques.
FIG. 1 shows an example of one mechanical pipe coupling system wherein pipe ends 20 and 22 are joined together by a coupling 24. Coupling 24 comprises segmented semi-circular collar segments 26 and 28 which are clamped together around the pipe ends. Each collar segment is roughly U-shaped in cross section as shown, the ends of the xe2x80x9cUxe2x80x9d forming a pair of flanges 30 and 32 which engage grooves 34 and 36 formed circumferentially in the pipe wall 38 on each pipe end. A pressure energized elastomeric seal 40 is positioned within the coupling to effect a fluid tight joint between the pipe ends.
In addition to providing a fluid tight joint, the mechanical coupling system shown in FIG. 1 also provides a strong connection between the pipe ends which allows the joint to withstand bending, axial and torsional loads on the pipes without joint separation or blowout.
To ensure a fluid tight and robust connection via the mechanical system, fairly tight tolerances must be maintained between the flanges 30 and 32 of the collar segments 26 and 28 and the grooves 34 and 36 in the pipe ends 20 and 22. Groove depth uniformity is also an important parameter affecting the connection. While the tolerances of the flanges are relatively easily controlled during manufacture of the collar segments, it is more difficult to control the outer diameter of the grooves, as well as the uniformity of the groove depth to within a desired tolerance. There are several factors which affect the accuracy of the grooves, such as the tolerance on the pipe outer diameter, the tolerance on the wall thickness and, for pipes having an outer diameter greater than 6 inches, the roundness of the pipe is also significant.
Groove 34 is formed by a cutting process which removes material from the pipe wall 38. This may be done, for example, on a lathe. The pipe is held in the lathe chuck and rotated about its longitudinal axis while a cutting tool engages the surface at the appropriate distance from the end of the pipe and cuts the wall 38 to the desired depth to form the groove 34 having a desired outer diameter appropriate for the particular pipe and coupling 24. Although lathes produce an accurate outer groove diameter, the groove often has non-uniform depth around the pipe circumference due to the inherent out of roundness of the pipe.
In contrast, groove 36 is formed by cold working the material comprising the pipe wall 38 beyond the yield point. Such grooves are most advantageously formed in the pipes by means of a grooving tool 21, shown in FIGS. 1A and 1B. Grooving tool 21 comprises a grooving roll 23 which cooperates with a backup roll 25 to permanently deform the pipe wall 38. The pipe wall is positioned between the grooving and backup rolls, and the rolls are forced toward each other while they are rotated around the pipe, either by rotating the tool 21 relatively to the pipe 20 or the pipe relatively to the tool. The grooving roll 23 has a hardened circumferential surface 27 which engages and permanently deforms the pipe wall 38 into a trough 29 positioned circumferentially around the backup roll 25 and in registration with the grooving roll 23. As the rolls rotate around the circumference of the pipe and pressure is applied to force them together, the groove 36 is deepened, making the outer diameter of the groove smaller. A hydraulic system may be used to force the grooving roll toward the backup roll, but other means, such as a manually turned jackscrew 31, are also feasible.
While the cold working process produces a groove of uniform depth, establishing the proper diameter of the groove 36 is usually a trial and error process. A variably adjustable depth gage 37 on the grooving tool 21 which limits the travel of the grooving roll toward the backup roll is used initially to form the groove 36 to a depth yielding a groove diameter near to, but short of, the desired diameter. The groove is then made progressively deeper in stages, and multiple hand measurements of the groove circumference or diameter are made between the stages until the groove is formed having a diameter within the allowable tolerance. However, this requires that the pipe being grooved must be removed and remounted on the tool between each stage, leading to significant inefficiencies in the formation of the grooves. These inefficiencies become especially costly when large numbers of pipes are required. Furthermore, the method using depth gages and hand measurements is prone to human error, leading to pipes in which the grooves are made too deep or too shallow. Grooves which are too deep allow the coupling 24 to reposition itself eccentrically on the pipe ends 20 and 22 when the pipe joint experiences bending loads. The coupling tends to move toward the side of the joint which is in tension, thus, reducing the engagement of flanges 30 and 32 on that side. This weakens the joint and may lead to joint separation. Conversely, grooves which are too shallow do not allow the coupling 24 to fully close around the pipe ends 20 and 22. Consequently, flanges 30 and 32 have less engagement with the side walls of the grooves 34 and 36. This reduces the load carrying capability of the joint which may also lead to joint separation, particularly blowout type failures. The seal 40 is also under less radial compression and is, therefore, more prone to leakage when the grooves are too shallow.
There is clearly a need for a more precise method and apparatus for forming grooves in pipe ends which avoids the time consuming trial and error procedure of multiple stages of alternating deformation and measurement and allows the grooves to be formed in one attempt efficiently, reliably and precisely at the proper diameter within the desired tolerances.
The invention concerns a tool for indicating that an external circumferential groove of a desired outer diameter has been formed in a pipe, for example, by cutting or cold forming. The pipe has an external surface into which the groove is cut or cold formed and a longitudinal axis arranged lengthwise along the pipe. In its preferred embodiment, the tool comprises a first arm pivotally mountable adjacent to the pipe for rotation about a pivot axis substantially parallel to the longitudinal axis. The pipe and the first arm are relatively rotatable to one another about the longitudinal axis. For example, for a cut groove the pipe may be mounted in the chuck of a lathe and the arm may be fixedly mounted on the lathe, the pipe turning relatively to the arm. For a cold formed groove, the arm may be mounted on a grooving tool which orbits around the pipe to form the groove.
A first feeler surface is mounted on the first arm and is engageable with the external surface of the pipe within the circumferential groove. The first feeler surface traverses the pipe circumference within the groove upon relative rotation of the pipe and the first arm. The first arm is pivotable to a predetermined angular position when the first feeler surface is engaged with the external surface of the pipe within the groove and the groove has the desired outer diameter.
The invention also concerns a tool for forming an external circumferential groove of a desired outer diameter in the wall of a pipe. The tool has a grooving roll rotatable about a first axis. The grooving roll has a circumferential surface which is engageable with the external surface of the pipe. The tool also has a backup roll rotatable about a second axis preferably located parallel with and in spaced relation to the first axis. The backup roll has a circumferential surface engageable with the internal surface of the pipe opposite the grooving roll. A circumferential trough is preferably positioned in registration with the grooving roll around the backup roll.
The tool also has means for rotating the pipe and the grooving and backup rolls relatively to one another to move the grooving roll and the backup roll circumferentially around the pipe. Preferably, the moving means comprises an electric motor which turns the backup roll. The backup roll in turn rotates the pipe and causes the pipe wall to move between the backup roll and the grooving roll.
Also included are means for moving the grooving roll and the backup roll relatively toward one another for yieldably deforming the wall between the circumferential surface of the grooving roll and the trough in the backup roll. The grooving roll and the backup roll cooperate to form the external circumferential groove in the wall upon relative motion between the pipe and the rolls circumferentially around the pipe.
The tool has an arm used to indicate when a groove of the desired diameter has been formed in the pipe. To accomplish this, the arm is pivotally mounted for rotation about a third axis parallel to and preferably coincident with the first axis. A feeler surface engageable with the external surface of the pipe within the circumferential groove is positioned on the arm. The arm is pivotable to a predetermined angular position relative to an arbitrary reference when the feeler surface is engaged with the external surface of the pipe within the groove and the groove has the desired outer diameter. The arbitrary reference may be, for example, an imaginary line passing between the first and second axes. The position of the feeler surface may be located at a predetermined distance from the circumferential surface of the grooving roll such that the predetermined angular position of the arm positions the feeler surface at a point on the pipe diametrically opposite to the grooving roll when the external circumferential groove is at the desired outer diameter.
The tool may have a second arm similarly pivotally mounted, the second arm also having a feeler surface. When two arms are present, they each have an indicator tang positioned distally to their pivot axes. The tangs face one another and are movable toward each other by moving the arms toward the pipe to place the feeler gages in contact with the external surface within the groove. The indicator tangs are in contact with one another when the external circumferential groove is at the desired outer diameter and the feeler surfaces are in contact with the external surface of the pipe within the groove.
Preferably, the tool is adaptable to form grooves in pipes of various diameters. This is accomplished by providing a plurality of predetermined positions along the arm or arms where the feeler surfaces may be mounted, each position being used in conjunction with a pipe having a particular diameter to form a groove having the outer diameter appropriate for the particular pipe.
The invention also includes a method of forming a circumferential groove of a desired outer diameter in the wall of a pipe. The method comprises the steps of providing the tool as described above and positioning the wall of the pipe between the grooving roll and the backup roll with the grooving roll engaging the external surface and the backup roll engaging the internal surface of the pipe. The grooving roll and the backup roll are rotated circumferentially around the pipe and the grooving roll and the backup roll are moved relatively toward one another to yieldably deform the wall between the rolls to form the groove. The arm is pivoted to bring the feeler surface into engagement with the external surface of the pipe within the groove. When the arm is at the predetermined angular position, the groove is at its desired diameter and the motion of the grooving roll and the backup roll toward each other is ceased. The pipe is then removed from the tool.
It is an object of the invention to provide a tool which can indicate when an external circumferential groove of a desired outer diameter has been formed in a pipe.
It is another object of the invention to provide a tool for forming grooves which eliminates the need for hand measurements of the groove diameter.
It is still another object of the invention to provide a tool which can form a groove in a pipe in one attempt without the need to repeatedly mount and remove the pipe from the tool.
It is again another object of the invention to provide a tool which can indicate when an external circumferential groove of a desired outer diameter has been formed in a pipe, the tool being adaptable to form grooves of various desired diameters in pipes of various sizes and wall thicknesses.
These and other objects and advantages of the invention will become apparent from a consideration of the following drawings and detailed description of the preferred embodiments.