BACKGROUND OF THE INVENTION

Under ordinary use, flow pipes may develop cracks which can result in failure. For example, unintended cyclic loading of the sub ends of certain flow pipes typically generates local stresses that can initiate and propagate

circumferential cracks, sometimes to fatigue failure. When the cracks are detected in time, the failure can be prevented. However, if a failure of a flow pipe occurs in the field, damage to the environment and ancillary equipment and injury to personnel may occur.

Flow pipes are routinely inspected and pressure tested to determine whether they meet certain criteria established by end users and/ or suppliers which indicate that they are suitable for return to field service. A key challenge in the inspection process is the identification of cracked samples, particularly those that include circumferential cracks resulting from unintended cyclic loading. The cracks are generally closed cracks and occur in areas that make visual detection very difficult. Without the aid of dye penetrant testing (PT) or magnetic particle inspection (MPI), the cracks are generally impossible to detect visually. MPI and PT generally require a significant time investment and ongoing expenses to train and qualify inspectors to ensure that they have the skills necessary to conduct the inspections. Also, some of the common crack locations lead to MPI and PT results that are difficult to interpret conclusively. This is particularly true in the threaded areas of the nut and female sub ends of union connectors.

The detection of cracks in union sub ends has been a challenge for many years. Although MPI has been used for many years it has never been highly effective and is often avoided by end users due to the high associated costs. PT is as effective as MPI but is even more time consuming. Other inspection methods such as radiographic inspection and eddy current inspection are typically not used because they are more time consuming than MPI and PT and only provide equivalent or marginally better results.

Acoustic emissions monitoring has been utilized for many years in conjunction with hydrostatic pressure testing to identify and locate defects in pressure containing equipment. In the known applications of acoustic emissions monitoring, the applied load is similar to the load seen by the test item during service. However, in some cases the magnitude of the load is increased slightly, for example by 10%, to ensure that any defects in the test item produce an acoustic emission (AE) event. An AE event occurs when a crack tip grows, dislocations move, or load distribution shifts suddenly. The change in stress distribution generates a vibration that travels throughout the defective part.

Acoustic emissions sensors and associated software recognize these vibrations and record them. However, the increased load placed on the test item during acoustic emission monitoring creates an undesirable risk of initiating a crack or defect in a piece that would otherwise be undamaged prior to testing.

SUMMARY OF THE INVENTION

In accordance with the present invention, these limitations in the prior art are addressed by providing an apparatus for detecting cracks in a flow pipe which comprises a first support member, a bending member which is positioned adjacent the first support member, a second support member which is fixed in position relative to the first support member, means connected between the first support member and the bending member for generating a load on the bending member, and a number of sensors for detecting acoustic emissions generated by cracks in the flow pipe. A first end of the flow pipe is connectable to the bending member and a second end of the flow pipe is connectable to the second support member. In operation of the apparatus, the flow pipe is connected between the bending member and the second support member and the load generating means is activated to thereby generate a load on the bending plate which in turn generates a bending load on the flow pipe. In this manner, the bending load causes cracks in the flow pipe to generate acoustic emissions which are detected by the sensors.

In accordance with an embodiment of the invention, the load generating means is activated to effectively rotate the bending load substantially 360° around the central axis of the flow pipe.

In accordance with another embodiment of the invention, the apparatus further comprises a computer for comparing the detected acoustic emissions with baseline acoustic emissions obtained from a corresponding undamaged flow pipe. The computer may be configured to sum the magnitudes of the detected acoustic emissions and compare the result with an acceptable magnitude determined from the baseline acoustic emissions.

The load generating means may comprise a plurality of hydraulic cylinders which are mounted between the first support member and the bending member. In addition, the apparatus may comprise a computer for selectively activating the hydraulic cylinders in order to generate a desired bending load on the flow pipe. In this regard, the computer may be configured to selectively activate the hydraulic cylinders in order to effectively rotate the bending load substantially 360° around the central axis of the flow pipe.

Also, the apparatus may comprise a plurality of electronic valves, each of which is connected between a source of hydraulic fluid and a corresponding hydraulic cylinder and is operated by the computer to thereby selectively activate the hydraulic cylinder. The apparatus may also comprise a plurality of pressure sensors, each of which is connected to the computer and is operable to detect the pressure in a corresponding hydraulic cylinder. In this embodiment, the computer may be configured to activate the hydraulic cylinders in accordance with a predetermined pressure profile in order to generate the desired bending load on the flow pipe.

In accordance with another embodiment of the invention, the apparatus comprises a support rail to which the first and second support members are connected. At least one of the first and second support members may be rotatably connected to the support rail. In addition, at least one of the first and second support members may be slidably connected to the support rail.

In accordance with yet another embodiment of the invention, the apparatus may comprise a first adapter which is connected between the bending member and the first end of the flow pipe. The first adapter may comprise a first end connection which is configured to releasably engage a corresponding second end connection provided on the first end of the flow pipe. The apparatus may further comprise a second adapter which is connected between the second support member and the second end of the flow pipe. The second adapter may comprise a third end connection which is configured to releasably engage a corresponding fourth end connection provided on the second end of the flow pipe. In one exemplary embodiment of the invention, the apparatus for detecting cracks in a flow pipe comprises a first support member, a bending member which is positioned adjacent the first support member, a second support member which is fixed in position relative to the first support member, a plurality of hydraulic cylinders which are mounted between the first support member and the bending member, a number of sensors for detecting acoustic emissions generated by cracks in the flow pipe, and a computer for selectively activating the hydraulic cylinders and for receiving signals representative of the acoustic emissions detected by the sensors. A first end of the flow pipe is connectable to the bending member and a second end of the flow pipe is connectable to the second support member. In operation, the flow pipe is connected between the bending member and the second support member and the hydraulic cylinders are activated to thereby generate a load on the bending plate which in turn generates a bending toad on the flow pipe which causes cracks in the flow pipe to generate acoustic emissions that are detected by the sensors. The computer then compares the detected acoustic emissions to baseline acoustic emissions obtained from a corresponding undamaged flow pipe.

In accordance with one aspect of this embodiment, the hydraulic cylinders are selectively activated to effectively rotate the bending toad substantially 360° around the central axis of the flow pipe.

In accordance with another aspect of this embodiment, the apparatus comprises a plurality of electronic valves, each of which is connected between a source of hydraulic fluid and a corresponding hydraulic cylinder and is operated by the computer to thereby selectively activate the hydraulic cylinder. The apparatus may also comprise a plurality of pressure sensors, each of which is connected to the computer and is operable to detect the pressure in a

corresponding hydraulic cylinder. In addition, the computer may be configured to activate the hydraulic cylinders in accordance with a predetermined pressure profile in order to generate a desired bending load on the flow pipe.

In accordance with a further aspect of the exemplary embodiment, the apparatus comprises a support rail to which the first and second support members are connected. In this embodiment, at least one of the first and second support members may be rotatabry connected to the support rail. Also, at least one of the first and second support members may be slidaWy connected to the support rail.

In accordance with yet another aspect of the exemplary embodiment, the apparatus comprises a first adapter which is connected between the bending member and the first end of the flow pipe. The first adapter may comprise a first end connection which is configured to releasably engage a corresponding second end connection provided on the first end of the flow pipe. Also, the apparatus may comprise a second adapter which is connected between the second support member and the second end of the flow pipe,. The second may comprise a third end connection which is configured to releasably engage a corresponding fourth end connection provided on the second end of the flow pipe.

The present invention is also directed to a method for detecting cracks in a flow pipe which comprises generating a bending load on the flow pipe, rotating the bending load 360° around the central axis of the flow pipe, and detecting acoustic emissions generated by cracks in the flow pipe as the flow pipe is subjected to the bending load.

In accordance with an embodiment of the invention, the bending load is generated on the flow pipe by axially loading an end of the flow pipe.

In accordance with another embodiment of the invention, the flow pipe is removably connected between a bending member and a support member and the bending load is generated on the flow pipe by generating a load on the bending member.

In accordance with a further embodiment of the invention, the method also comprises the step of comparing the detected acoustic emissions to baseline acoustic emissions obtained from a corresponding undamaged flow pipe. In this embodiment, the method may also comprise the step of removing the flow pipe from service if the detected acoustic emissions exceed the baseline acoustic emissions.

Thus, the crack detection apparatus and method of the present invention use bending to focus stresses in the areas of the flow pipe where cracks most commonly occur. When cracks or other defects are stressed enough to grow or release energy, such as in the form of dislocation movement, an acoustic event occurs which is captured by sensors. During the process, acoustic events of various quantity and magnitude are captured. The summation of the acoustic events (energy released) is compared against a baseline result for a comparable new or undamaged flow pipe. When the summation of the acoustic events exceeds an empirically determined threshold, the flow pipe is considered to be too damaged to return to service. When the summation is below the threshold, the flow pipe is considered safe and may be returned to service pending other routine tests.

Thus, the crack detection apparatus and method of the present invention take a different approach to loading the test item than do the AE test methods of the prior art. The loading is applied in a specific manner to open or close cracks that are commonly the cause of failure or inspection rejection. In contrast to the prior art, the present invention uses bending which focuses the stresses in the areas that are most likely to contain cracks. The bending stresses can be locally higher than the previous load without damaging a previously undamaged specimen. The high local stresses will produce AE events in a cracked specimen because the presence of the cracks amplifies the local stress that creates the acoustic event.

In one embodiment, the bend test apparatus of the present invention includes three double-acting hydraulic cylinders. These cylinders are each independently controlled to produce loads parallel to the flow axis of the test piece. Balancing these loads allows for the neutral axis of bending to be cycled through the full 360 degrees to ensure that all sections of the test piece have been loaded through a fully reversed pure bending cycle. No net tension or compression is applied because the sum of the loads from all three cylinders is maintained at zero. Each end of the test piece is essentially fixed, and the pure bending load therefore translates through the full length of the test piece.

The hydraulic cylinders may be controlled by proportional control valves. In this embodiment, electronic signals from differential pressure transducers provide the feedback for the system, and a PC based software program provides goal signals for the proportional control valves to match.

In another embodiment of the invention, each end of the bend test apparatus may be adjusted for angle and position to accommodate virtually any test piece geometry which is essentially planar. Each end may also be fitted to interchangeable adapters to suit the specific test specimen connection. In this embodiment, the acoustic emission sensors are attached to the adapters and are interfaced with a PC based software package to filter out signals which are not crack-related AE events. The software processes the full acoustic emission response of the test piece and determines if the test piece contains significant circumferential cracks.

In addition to being able to perform the bending test, the bend test apparatus allows for hydrostatic pressure testing of the test piece during the same setup. The AE equipment can be used during the pressure test to identify other cracks or defects that may not be oriented properly to cause an AE event during the bending test.

Although AE testing has been used in the prior art to search for cracks, the preset invention is unique. The invention is designed to identify the most common crack found in flow pipes and the like, that is, cracks which result from unintended loading of the flow pipe in the field, and the bending process is specifically selected to highlight these cracks. This represents a significant difference in how AE testing has been used in the past.

In addition, the invention produces a simple go or no-go result that does not require interpretation by a test technician. In contrast, MPI and PT require interpretation by the inspector to determine the validity and severity of the defect indication. The invention will not eliminate all field failures but will identify many cracked specimens that currently go undetected. These identified samples may then be removed from service before they can result in a field failure.

These and other objects and advantages of the present invention will now be described with reference to the accompanying drawings. In the drawings, the same reference numbers may be used to denote similar components in the various embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is front-side perspective view of one embodiment of a bend test apparatus which is suitable for use in the crack detection method of the present invention with a representative flow pipe component mounted therein;

Figure 2 is an enlarged view of the left hand portion of the bend test apparatus shown in Figure 1;

Figure 3 is an enlarged rear-side perspective view of the left hand portion of the bed test apparatus shown in Figure 1 ; Figure 4 is a longitudinal partial cross sectional view of the bend test apparatus shown in Figure 1 with the hydraulic cylinder control and acoustic detection components of the invention shown schematically;

Figure 5 is an enlarged partial cross sectional view of illustrative embodiments of the turntable and clamp components of the invention;

Figure 6 is an enlarged cross sectional view of an embodiment of a mounting adapter component of the invention; and

Figure 7 is a perspective view of the bend test apparatus shown in Figure 1 but with a different flow pipe component mounted therein.

DETAILED DESCRIPTION OF THE INVENTION

The crack detection method described herein can be performed with any suitable apparatus which is capable of imparting a desired bending load on a flow pipe of interest. An embodiment of one such apparatus is shown in Figures 1 - 4. The bend test apparatus of this embodiment, which is referred to generally by reference number 10, is shown with a sample flow pipe 12 installed thereon. In this example, the flow pipe 12 comprises a conventional pup joint having first and second ends 14, 16 which are joined by a length of tubing 18. The first end 14 comprises a threaded end connection and the second end 16 is provided with a wing union nut 20 for connecting to, e.g., the threaded end of another flow pipe. As shown in Figures 1 and 2, the pup joint is supported between a bending unit 22 which is connectable to the first end 14 and a support stand 24 which is connectable to the second end 16.

The bending unit 22 includes a support member 26, a bending plate 28 which is connectable to the first end 14 of the pup joint 12, and a number of hydraulic cylinders 30 (Figure 4) which are operatively connected between the support member and the bending plate. In the illustrated embodiment, the bending unit 22 comprises three hydraulic cylinders 30 which are spaced equidistantly around the central axis 32 of the bending plate 28. In operation of the bend test apparatus 10, the first end 14 of the pup joint 12 is connected to the bending plate 28, the second end 16 is fixed in position relative to the support member 26 and the hydraulic cylinders 30 are selectively activated to load the bending plate 28 in a predetermined fashion in order to generate a desired bending load on the pup joint, as will be explained in greater detail hereafter. In the exemplary embodiment of the invention shown in drawings, the support member 26 is configured as a generally cylindrical housing 34 having a reaction ring 36 connected to one end thereof, and the hydraulic cylinders 30 extend axially through the housing and are connected between the reaction ring and the bending plate 28. In addition, the housing 34 is connected to a turntable 38 which in turn is movably secured to a support rail 40 by suitable means, such as a pair of clamps 42.

Referring also to Figure 5, the turntable 38 may comprise, for example, a rotatable part 44 which is connected to the housing 34 by a stub bracket 46, a non-rotatable part 48 which is connected to the clamps 42, a top ring 50 which is positioned over a radially outer portion of the rotatable part, and a number of bolts 52 which extend through corresponding arcuate grooves 54 in the rotatable part and into corresponding threaded holes 56 in the non-rotatable part. When the bolts 52 are tightened, the top ring 50 forcibly engages the rotatable part 44 and prevents the rotatable part from turning relative to the non-rotatable part 48, but when the bolts are loosened the top ring permits the rotatable part to turn relative to the non-rotatable part. In this manner, the turntable 38 allows the housing 34 to be oriented at a desired angle relative to the support rail 40.

Each clamp 42 includes an upper jaw 58 which is connected to the non- rotatable part 48 and a lower jaw 60 which is connected to the upper jaw by a pair of screws 62. Each of the upper and lower jaws 58, 60 comprises a cutout 64 (Figure 3) which is configured to correspond to the profile of the support rail 40. In the embodiment of the invention shown in the drawings, for example, the support rail 40 is made of a length of square stock turned forty-five degrees to horizontal and the cutouts 64 accordingly comprise a V-shaped configuration. With the jaws 58, 60 positioned on the support rail 40 as shown in the drawings and tightened together by the screws 62, the turntable 38 and thus the housing 34 are fixed in position relative to the support rail. However, when the screws 62 are loosened, the housing 34 may be moved along the support rail 40 to any desired position. In order to accommodate this arrangement for the clamps 42, the support rail 40 is preferably elevated slightly above a supporting surface by a pair of feet 66.

Referring also to Figure 6, the first end 14 of the pup joint 12 is preferably connected to the bending plate 28 by one of a plurality of interchangeable adapters 68. Each adapter 68 includes a flange 70 which is bolted to the bending plate 28, a nipple 72 which is connected to the flange and an end connection 74 which is connected to the distal end of the nipple. Although not required, the flange 70 may be connected to the bending plate 28 such that the central axis 76 of the adapter 68, and thus of the pup joint 12, is offset vertically from the central axis 32 of the bending plate (Figure 4). The end connection 68 is designed to connect to the end connection provided on the first end 14. In the embodiment shown in the drawings, wherein the first end 14 is provided with a threaded end connection, the appropriate end connection 74 may comprise a corresponding wing union nut. For other flow pipes with other end connections, a different adapter 68 having a corresponding end connection may be bolted to the bending plate 28.

The support stand 24 maintains the second end 16 of the pup joint 12 fixed in position relative to the support rail 40, and thus the support member 26, of the bending unit 22. The support stand 24 includes a support column 78 which is preferably rotatably and movably connected to the support rail 40 by a turntable 38 and a pair of clamps 42 similar to those described above. In this manner, and in conjunction with the turntable 38 and clamps 42 of the bending unit 22, the bend test apparatus 10 may be configured to accommodate any of a number of different flow pipes and pipe components. For example, Figure 7 illustrates the bend test apparatus 10 being used to test an L-shaped flow pipe 12\

Referring again to Figure 3, the second end 16 of the pup joint 12 is ideally connected to the support column 78 by an adapter 68 which comprises an appropriate end connection. For example, where as shown in the drawings the second end 16 is provided with a wing union nut 20, the end connection may comprise a corresponding threaded end connection.

In accordance with the method of the present invention, a predetermined bending toad is imparted on the pup joint 12 to cause any cracks in the pup joint to generate one or more AE events. The AE events are then detected and compared to an empirically-determined AE event profile of an undamaged pup joint to determine if the pup joint is damaged to an extent which would require its removal from service. The crack detection apparatus 10 imparts the predetermined bending load on the pup joint 12 by selectively actuating the hydraulic cylinders 30 in a manner which will now be described. Referring to Figure 4, each hydraulic cylinder 30 is connected via a corresponding hydraulic line 80 to a source of hydraulic fluid 82. Each line 80 includes an electronic valve 84 for controlling the supply of hydraulic fluid to the hydraulic cylinder 30 and a pressure sensor, such as a differential pressure transducer 86, for monitoring the pressure in the hydraulic cylinder. The valves 84 are controlled by a computer 88 or other such controller to which the pressure sensors 86 are also connected.

In a preferred embodiment of the invention the valves 84 are proportional control valves and the pressure sensors 86 provide feedback which enables the computer 88 to operate the valves to generate the pressures in the hydraulic cylinders 30 which are required to produce the desired predetermined bending load on the pup joint 12. In this regard, the computer 88 may comprise a PC based software program which is designed using ordinary skill in the art to execute an appropriate feedback control system using the information obtained from the pressure sensors 86.

In accordance with one embodiment of the invention, the hydraulic cylinders 30 are operated to generate a bending load which is cycled through 360 degrees to ensure that all sections of the pup joint 12 have been loaded through a fully reversed pure bending cycle. Such loading may be illustrated by reference to Figure 2, in which a three dimensional coordinate system is shown with the X- axis positioned on the central axis 76 of the pup joint 12 and the Y- and Z-axes positioned in the plane of the bending plate 28. In operation of the bending unit 22, the hydraulic cylinders 30 generate a force on the bending plate 28 which is parallel to but offset from the X-axis. This force results in the generation of a bending moment on the pup joint 12. This bending moment is represented by the double-headed vector M in the Y-Z plane. In accordance with this embodiment of the invention, the computer 88 controls the operation of the hydraulic cylinders 30 in accordance with a predetermined pressure profile to rotate the bending moment M 360 degrees about the X-axis. This will ensure that the full

circumference of the pup joint 12, including the first and second ends 14, 16, will be subject to the bending load. As the pup joint 12 is being subjected to the bending loads described above, the bend test apparatus 10 employs AE detection means to detect any resulting AE events which could indicate the presence of unacceptable cracks or other defects in the pup joint. Referring still to Figure 4, the AE detection means includes a number of AE sensors 90 which are connected to the computer 88. While the AE sensors 90 may be mounted on the bend test apparatus 10 or the pup joint 12, or both, in the exemplary embodiment of the invention shown in Figure 4, the AE detection means employs four AE sensors, two of which are mounted on the adapter 68 connected to the bending plate 28 and two of which are mounted on the adapter 68 connected to the column 78. In addition, the AE sensors 90 mounted on each adapter 68 are ideally positioned 180 degrees apart, with the AE sensors on one adapter rotated 90 degrees relative to the AE sensors on the other adapter.

The computer 88 is provided with a preferably PC based software program to process the signals detected by the AE sensors 90 and to filter out any extraneous signals. A suitable such program and its associate hardware is the MICRO II PCI-2 Acoustic Emission System sold by Mistras Group, Inc. of

Princeton Junction, New Jersey, U.S.A. This system may be used with model R15I-AST sensors, also sold my Mistras Group, Inc. During the bend test, AE events of various quantity and magnitude are detected. The computer 88 sums these AE events and compares this summation against a baseline result for an undamaged pup joint of the same configuration. If the computer 88 determines that the summation exceeds an empirically determined threshold, the test specimen is considered too damaged to return to service. If the computer determines that the summation is below the threshold, the specimen is

considered safe for service, pending other routine tests. Thus, the method provides a simple go-no go result which leaves no room for error.

It should be recognized that, while the present invention has been described in relation to the preferred embodiments thereof, those skilled in the art may develop a wide variation of structural and operational details without departing from the principles of the invention. For example, the various elements shown in the different embodiments may be combined in a manner not illustrated above. Therefore, the appended claims are to be construed to cover all equivalents falling within the true scope and spirit of the invention.