A MOBILE, MULTI-MODE APPARATUS AND METHOD FOR NONDESTRUCTIVELY INSPECTING COMPONENTS OF AN OPERATING SYSTEM

Abstract: A mobile apparatus for and a method of non-contacting, nondestructive, on-line inspection of installed components of plants, facilities or other systems using penetrating radiation sources and detectors mounted on a ring assembly which can be placed about the component while it remains in place and in use. The ring assembly is held in place by a yoke assembly in a manner that allows the ring to be rotated relative to the yoke assembly so that multiple scans of the same cross-section of it can be performed from different angles. The apparatus is also capable of sub-positioning the detectos relative to the source while the ring assembly is stationary to increase the number of scans that can be taken from different angles. The yoke assembly, in turn, is mounted to a beam assembly in a manner that allows the yoke assembly to move relative to the beam assembly. The apparatus can operate in multiple scanning modes and the resulting data collected can be processed using both application specific real time data analysis techniques and computerized axial tomographic (CAT) scanning techniques many available data processing algorithms.

Description: A MOBILE, MULTI-MODE APPARATUS AND METHOD FOR NONDESTRUCTIVELY INSPECTING COMPONENTS OF AN OPERATING SYSTEM BACKGROUND OF THE INVENTION 1. FIELD OF THE INVENTION The present invention relates generally to a method o and apparatus for, non-contact nondestructive inspection o objects using penetrating radiation and in particular, relate to a mobile scanning apparatus and method for nondestructiv measurements and inspection of stationary components, such a piping, elbows, pumps and defuzers of an operating facility plant or system while the components are in use and determin use degradation. 2. DESCRIPTION OF PRIOR ART In the past many attempts have been made to develo methods of nondestructive inspection of structural or tubula fluid transmission components of plants and facilities a exemplified by U.S. Patent Nos. 4,415,980 and 4,425,505. Man of these inspection methods required that the facility be shu down and at least partially disassembled in order to ge useful data. Nevertheless some prior art methods attempte to perform nondestructive testing on such components while th components were in use, such as U.S. Patent Nos. 3,006,251 4,352,065; 4,467,654; and 4,680,470. Of these, U.S. Paten Nos. 3,006,251 and 4,680,470 disclose use of penetratin radiation. United States Patent No. 3,006,251 discloses a devic that scans pipe, using both penetrating radiation an electromagnetic fields, while being translated along th length of oil and gas field pipes. However the disclose device has serious disadvantages. The scanning was no performed in a non-contacting manner and, therefore, was inoperable on hot insulated pipe. The device was also dependant on maintaining a concentric position around the pipe so that the radiation gauge would not be off center. The radiation gauge also gave only one thickness measurement rather that a complete ulti angle and multiple detect cross-sectional measurements. No method is disclosed f monitoring the position of the gauge either longitudinally rotationally about the object as it scanned the pipe. Additionally, the disclosed device could not be open and closed about the pipe under examination, thereby virtual requiring that the system would have to be shut down a partially disassembled in order to position the device abo in-place pipe to begin its inspection. U.S. Patent No. 4,680,470, discloses another prior a apparatus and method which uses penetrating radiation detect flaws in installed objects. However, the disclos method was passive in that it relied on background radiati for the radiation source, thereby restricting its use detecting major defects or flaws. In particular, the prima system disclosed is only operable on objects that conta radiation sources inside the object. An alternative system disclosed where a radioactive liquid is placed on the out surface of the object, however the usefulness of this meth is limited to showing flaws on the outer surface of the obje and is impracticable to use in non-nuclear facilities due safety and public health concerns. Since the strength of t radiation is unknown, the system is only capable of detecti flaws such as cracks and pits which manifest immediate chang in a localized area. More gradual flaws are much mo difficult to detect with a passive system. Additionally, t disclosed system only contemplates translating the disclos radiation detector along the length of a pipe but fails disclose any particular means for accomplishing such movemen SUMMARY OF THE INVENTION Briefly, the present invention provides a new method and mobile apparatus for, nondestructively inspecti installed stationary objects or components, such as insulat and non-insulated piping, pumps, elbows and defuzers of facility. The mobile apparatus comprises a scanning unit have ring assembly for encircling the component to be scanned, beam, a yoke assembly positioned on the beam for support the ring assembly about the component wherein the y assembly is movable relative to the beam. A penetrati radiation source for transmitting radiation through t component and a detector array for detecting the transmitt radiation are mounted opposite each other on the ri assembly. Stepping motors mounted on the yoke assembly a used to rotate the ring assembly relative to the yoke assemb about the component to obtain multiple scans of a cros section of the component. Motors mounted on the beam are us to translate the yoke assembly relative to the beam assemb along the length of the component to be scanned. The operat transmits predetermined signals stored in a computer control the motors. An encoder on the beam motor monitors the longitudin position of the ring and yoke assembly relative to the be assembly and an encoder on the yoke motor is used to monit the rotational position of the ring assembly relative to t yoke assembly. The position monitors are used to accurate determine the position of the portion of the component und examination. A data processing system sends control signa to the apparatus for controlling the translational a rotational movements of the source and detector, receiv position signals from the monitors and receives signals fr the detector array. The apparatus may be operated in gauging mode and/or an analytical mode. During the gaugi mode, the apparatus initially scans a limited number of cros sections of the components along the longitudinal length the component at a limited number of rotational position The data processing system using limited angle collection a analysis method to determine the dimensions of the compone and to locate flaws which need further investigation. Durin the analytical mode, the apparatus scans at least one cross section of the component at the location of the previousl detected flaw at a larger number of rotational positions. Th data processing means is programmed with computer tomographi methods to analyze the resulting signals generated during eac scan to reconstruct image of the detected flaw in order t better identify the characteristics of the flaw. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a simplified diagrammatic illustration of steam power generating facility in which the present inventio may be employed. Fig. 2 is an illustrative drawing of the overal apparatus of the present invention. Fig. 3 is an illustrative drawing of the gantry system o the present invention with emphasis on the longitudina translation components Fig. 4a is an illustrative drawing of the yoke and rin assembly components of the gantry system of the presen invention with emphasis on the rotational translatio components. Fig. 4b is an illustrative drawing of the ring driv subsystem in a side view. Fig. 5 is an illustrative drawing of a cross-section o the ring assembly showing the tracks of the recirculatin bearings in each half of the ring assembly. Fig. 6a is an illustrative drawing of the encoder whee of an absolute position optical encoder. Fig. 6b is an illustrative drawing showing severa rotational positions of the wheel and their respective code encoded. Fig. 7 is an illustrative drawing showing the sourc assembly and two penetrating radiation sources. Fig. 8a is an illustrative drawing showing the component within the detector housing as seen from the source. Fig. 8b is and illustrative drawing of the detector arra as seen from the top of the detector housing. Fig. 9a is an illustrative drawing of an open individua detector showing the tungsten shielding strips, scintillatin plastic and photomultiplier tube. Fig. 9b is an illustrative drawing of a cross-section o a detector showing the housing and its various layers. Fig. 10a is an illustrative drawing of an air drive ratchet and pawl sub-positioning actuator system. Fig. 10b is an illustrative drawing of a electric moto driven sub-positioning actuator system. Fig. 11 is an illustrative drawing of the geometry of th detector array about the ring center and the sub-positionin guide-rail about the source. Figs. 12a and b is an illustrative drawing of a scannin pattern along a section of pipe used by the present inventio in a gauging mode. Fig. 13 is an illustrative drawing of the dimensional gauge scanning mode longitudinally scan results of a pipe's outside diameter inside diameter and wall thickness. Fig. 14 is an illustrative drawing of a model pipe profile based on average data of outside diameter, inside diameter and wall thickness. Fig. 15a is an illustrative waterfall display drawing of actual measured pipe profiles. Fig. 15b is an illustrative waterfall display drawing of the difference resulting from subtracting the model pipe profile in Fig. 14 from each profile in Fig. 15a. Fig. 16 is an illustrative drawing of how density length paths can be used to triangulate on the location of an anomaly. DESCRIPTION OF THE PREFERRED EMBODIMENT Fig. 1 is a diagrammatic illustration of a typical steam powered electrical generating facility to which the present invention is well suited for inspection purposes. An energy source 10 generates heat which heats the boiler 12. As the water 14 in the boiler 12 begins to boil it lets off steam 16. The steam 16 travels through steam pipe 18 to the turbines 20 of an electrical power generator 22. The steam pipe 18 is covered by a sheath of insulating material 24 to prevent energy losses. The steam that is exhausted 26 from the generator 22 passes through a condenser 28 which condenses the steam into water. The condensed water then returns to the boiler 12 for another cycle. The apparatus (Fig. 2) and method of the present invention is ideally suited to inspect steam pipe 18 and othe components in such electric power plants while such pipe o other components are in place and in use. In order to perfor such inspections using the apparatus it is not necessary t disassemble the steam pipe 18 into sections, to shut down th facility, or remove insulation 24. The use of the present invention, however, is not limite to steam transportation systems in steam driven electrica power generation facilities. The invention is also useful i chemical plants and refineries or in any facility o structural system utilizing installed components about whic the Apparatus A can be positioned and are made of material that can be scanned by penetrating radiation. The preferre embodiment disclosed herein, however, is particularly adapte to inspecting steam pipe in a steam driven electrical powe generating facility. Fig. 2 is a diagrammatic illustration of the mobil apparatus embodying the invention which has been particularl adapted to inspect pipe in steam driven electrical powe plant. The apparatus A is transported to the power plant i a trailer 50. The scanning Unit S and data collectio subsystem 64 are taken out of the trailer 56 and the scannin unit s positioned about the pipe 18 to be inspected. Th scanning unit S includes a gantry 52 and a ring assembly 54 The gantry system 52 includes a beam 80, one or more linea rod and ball bearing arrangements 86, a threaded rod an bearing arrangement 89 and an actuation system shown in Fig 3 and described below, is placed parallel to the axis of pip 18 so that once in place the ring assembly 54 will fit aroun the pipe 18 and can travel along the length of the pipe 18 The ring assembly 54 is composed of two inner ring halves 11 and 120 and two outer ring halves 110 and 112. A penetrating radiation source 58 is mounted on one hal of the inner ring 118. Mounted onto the other side of t ring assembly 54 on the other inner ring half 120 is t detector array housing 60. It is mounted to face t radiation source 58. While the source 58 and detector arr housing 60 are translated along and rotated about the st pipe 18, the source 58 emits gamma or x-ray penetrat radiation in the direction of the detector array housing The presence of pipe 18 between the source 58 and detec array housing 60 causes the radiation to be attenuated. attenuated radiation is converted into electrical sign within the detector array housing 60 as described below. electrical signals generated within the detector array hous 60 are transmitted through wiring in the umbilical cord 62 a data collection subsystem 64. The subsystem 64 collects signals transmitted from the detector array housing 60 prepares them for transmission to the remote trailer via fiber optic transmission system 66 or other suitab transmission system. The signals transmitted by the fib optic transmission system is received by the main computer and its peripherals 70 in the trailer. The data collectio preparation, transmission, and processing is described greater detail below. GANTRY SYSTEM Fig. 3 is an illustrative drawing of the gantry syst 52. the gantry system 52 is built around a beam 80. Althou the figure shows a C-shaped beam, other structures may also used. Mounted to the sides of the beam 80 are smooth rods 8 The yoke assembly 84 is connected to the smooth rods mounted to the outside of the beam 80 by ball bearings 8 creating a linear rod and ball bearing arrangement 86. T linear rod and ball bearing arrangement 86 allows the yo assembly 84 to travel along the length of the beam 80 wi ease. A threaded rod 88 is mounted within the C-shaped beam in such a manner that it can be rotated while it is held place. The threaded rod 88 is also fitted into a fema threaded coupling 90 which is mounted on the yoke assembly 8 In this manner when the threaded rod 88 is rotated the yo assembly 84 is translated along the length of the beam 8 The direction of translation is determined by the direction which the threaded rod 88 is rotated. The threaded rod 88 is rotated with a electrical mot 92. The shaft 94. of the electrical motor 92 is connected the threaded rod 88 via the shaft 94. A motor controller conditions control signals it receives from the comput system 68 via the fiber optic cable 66, data collecti subsystem 64, and umbilical cord 62. Fig. 3 also shows how the translational position of t yoke assembly 84 is monitored. Since the position of the yo assembly 84 is directly dependant on the rotation of t threaded rod 88, the present invention monitors the positi of the yoke 84 by optically encoding the rotation of t threaded rod 88. Gears 102 and 104 are mounted to the sha 94 of the motor 92 and optical encoder 106. Thereby as t threaded rod 88 rotates the gear 102 and 104 also rotate a optical encoder 106 monitors this rotation. The manner which the rotation is encoded is described in greater deta below. YOKE AND RING ASSEMBLY While fig. 3 shows the gantry mechanism by which the ri assembly 54 is translated along the length of the steam pi 18, figures 4a, 4b, and 5 show the ring assembly mechanisms which the source 58 and detector array housing 60 apparatus are rotated about the axis of the steam pipe 54. One half the outer ring 110 of the ring assembly 54 is mounted to t yoke 84 and is held in a fixed position while the other ha of the outer ring 112 is free to open and close about a hin 114 and be locked in a fixed closed position via a locki bracket 116. When the outer ring halves 110 & 112 are clos in a locked position, the inner ring halves 118 & 120 can released to rotate freely. When the ring assembly 54 is to opened the inner ring halves 118 & 120 are aligned with t outer ring halves 110 & 112 and held in place by pins (n shown) . These pins prevent the movement of the inner ri halves 118 & 120 relative to the outer ring halves 110 & 1 when the ring assembly 54 is opened. In an alternative embodiment of the present invention t two ring halves can be joined together with two mounti brackets 116; a hinge 114 is not necessary. Fig. 5 is an illustrative drawing showing how the inn and outer rings 122 & 124 act as a large recirculating ba bearing when the ring assembly 54 is locked in a clos position and the inner rings halves 118 & 120 are release The outer ring 124 is held in a fixed position by the yoke while the inner ring 122 is free to rotate on ball bearin 126. The ball bearings 126 on which the inner ring 1 rotates roll in two recirculating tracks 128 & 130. The tracks 128 & 130 are seated in the outer ring halves 110 & 1 and remain fixed relative to the outer ring halves 110 & 112 The use of two independent recycling tracks 128 & 130 and pi (not shown) to hold the inner half rings in place enables t ring assembly 54 to be opened without loss of ball bearin 126. Returning to figure 4a and 4b, the inner ring 122 bear a toothed surface 140 about its periphery by which th rotation of the inner ring 122 is controlled. The rotation o the inner ring 122 is actuated by an electric motor 142. Th motor 142 rotates a pulley 144. The pulley 144 drives a bel 146 which turns a second pulley 148 of larger diameter tha the pulley 144 attached to the motor 142. The ratio of th diameters of these pulleys 144 & 148 is known. Tension i maintained in the belt 146 by a tensioning pulley 150. sprocket 152 is mounted on the same axil 154 as the large pulley 148 as shown in fig. 4b. This sprocket 152 drives chain 156 which in turn drives two additional sprockets 158 160 of the same diameter as the first sprocket 152. On sprocket 158 is positioned proximate to the toothed surfac 140 of the inner ring 122 maintaining contact between th chain 156 and the inner ring's toothed surface 140 so that th chain 156 drives the rotation of the inner ring 122 when th sprockets 152, 158 & 160] rotate. The other sprockets 160 i attached to an optical encoder 162 which encodes the rotatio of the sprocket 160. The method used to optically encode th rotation of the sprocket 160 is described in greater detai below. Since the circumference of the inner ring's toothe surface 140 and the circumference of the sprocket 160 is known, monitoring the rotational position of the sprocket 160 enables the calculation of the position of the inner ring 122 Tension in the chain 156 is also maintained by a tensioning wheel 164. OPTICAL ENCODING As was described above, the rotation of the threaded rod 88 and the rotation of the sprockets 152, 158 & 160 that rotate the inner ring 122 of the ring assembly 122 are both optically encoded. Nevertheless, other methods of monitoring the longitudinal position of the ring assembly 54 and the rotational position of the inner ring 122, other than optical systems are possible. There are two general types of optical encoders: incremental encoders and absolute position encoders. Although an incremental optical encoder is suitable, an absolute optical encoder is preferable since it can be used to determine not only rotation but also direction of rotation and precise angular position rather than simply a change in position. An absolute optical encoder disk 172 is shown in Fig. 6a. The disk 172 has multiple tracks 174 with slots 176 cut out. The .disk 172 rotates between light emitting sources (not shown) and light sensors (also not shown) . One pair of light emitting sources and light sensors are positioned along each track of the absolute optical encoder disk 172. As the disk 172 rotates the slot patterns on each track 174 of the disk 172 pass by the tracks 174 corresponding light source/sensor pair. When a slot 176 is positioned between the source/sensor pairing, the light sensor senses light. When no slot 176 is present, the sensor does not sense light. Thereby, each source sensor pair generates a digital signal. Fig. 6b shows an example of a typical slot pattern 178 as seen by four sensors [not shown]. In the disk's 172 current position 180, the code 182 generated by the sensors in the four tracks 184, 186, 188 & 190 is "1011". each position 180 around the disk 172 has a unique code 182. The number of position 180 is determined by the number of tracks 174 on the encoder disk 172. The coded signals generated by the sensors in the optical encoder 162 are transmitted via hardwire 107 to an a decoder 108 which converts the encoded signal into meaningful positional data. The decoders 108 (Fig. 3) decode the signal and transmit it along the optical fiber transmission system 66 to the computer 68. Since the codes 182 are unique for each position 180 of the encoder disk 172, the direction of rotation can be determined by comparing one position 180 reading with the previous position reading. For the present invention, a conventional, multiturn absolute optical encoder and accompanying decoder with a rotational resolution of 1024 positions per 360 degrees, and 512 turns is suitable. THE SOURCE Fig. 7 is a more detailed depiction of the penetrating radiation source assembly 58. As shown in Fig. 2, the source assembly 58 is mounted on inner ring half 118 of the ring assembly 54. The source assembly 58 preferably contains two radioactive source pellets 202 and 204. Since the material which is being scanned may not have uniform density throughout, it is useful to be able to scan the component with radiation from different sources. One example of the importance of the ability to scan components of non-uniform density is pipe welds. The density of the material around and in a pipe weld is not uniform with the rest of the pipe. Cobalt and iridium radioactive sources emit suitably different radiation for the described purposes, although other radiation sources may also be suitable. The source pellets 202 and 204 are mounted on a tungsten rod 206. This tungsten rod 206 can be moved in order to position one of the source pellets 202 and 204 into the beam port 208. Fig. 7 shows the cobalt source pellet 204 in the beam port 208. The steel rod 206 is driven by an air solenoid 210. The controller 212, which controls the movement of th tungsten rod 206 and source pellets 202 and 204, provides th system operator with three setting choices for operating th source 58: Off, Manual and Automatic. In the Off setting th tungsten rod 206 can not be moved. In the Manual settin either source pellet 202 or 204 can be chosen to be in th beam port 208. In the Automatic setting, the movement of th tungsten rod 206 is controlled by the system computer 68. THE DETECTOR ARRAY Fig. 8a and 8b show the contents of the detector arra housing 60: the base plate 232, the sub-positionin components 234, the detector guide plate 236 the individua detectors 238 and the signal conditioning electronics 240. The detector array 242 consists of a plurality o individual radiation detectors 238. The detector guide plat 236 has a plurality of slots 244 into which the individua detector units 238 are fitted. These detectors 238 are sli into these slots 244 in the detector guide plate 236 and ar held in place by a ball/detent locking mechanisms (not shown) Each of the individual detectors 238 shown in Figs. 9a 9b is composed of an aluminum housing 246 which holds section of scintillating plastic 248 wrapped in aluminum foi 250, sandwiched between two tungsten strips 252. Thi assembly is positioned by two wave springs 254 which appl positive pressure between the aluminum casing 246 and it contents. The tungsten strips 252 are longer than th scintillating plastic 248 and act as radiation precollimators which limit the radiation which enters the frontal end 256 o the scintillating plastic 248 to those entering the detecto 238 perpendicular to the frontal end 256 of the detector 23 in a straight line from the source 58. The tungsten strip 252 also decrease the amount of interdetector scatterin radiation which is absorbed by the scintillating plastic 248 The aluminum foil 250 which is wrapped around th scintillating plastic 248 serves as a reflector which prevent light from escaping the plastic strip 248. The scintillating plastic 248 converts the radiatio signal into a light signal. The distal end 258 of the scintillating plastic 248 has a forty-five degree angle 260 which reflects light down to a photomultiplier tube 262 which is also encased in the aluminum casing 246 perpendicular to the tungsten strip 252 and scintillating plastic 248 portion of the detector 238. The photomultiplier tube 262 transduces the light signal into an electric signal, which is transmitted to the detector conditioning electronics boards 240 described in greater detail below via hardwire. The signal conditioning electronics boards 240 are mounted on top of the detector guide plate 236. The detector electronics are substantially the same as those disclosed in U.S. Patent Application Serial No. 531,454 t filed in the name of Morgan, et al., entitled "An Automated system for Controlling the Quality of Geometrically Regular- Shaped Products during Their Manufacture," except that the stability of the system has been improved by using a programmable high voltage source (not shown) instead of a set high voltage source (also not shown) to the photomultiplier tube 262. Since the high voltage affects the gain of the system, a programmable voltage source allows for programmable gain thereby allowing the sensitivity of all detectors to be adjusted similarly, this increasing the stability of the system. The detector guide plate 236 is mounted on top of the detector housing base plate 232 through a sub-positioning guide rail 270 and. three v-grooved rollers 272. The sub- positioning guide rail 270 is mounted to the bottom surface 273 of the detector guide plate 236, while the three v- grooved rollers 272 are mounted to the detector housing base plate 232. The detector array housing cover (not shown) is mounted on top of the detector array base plate 232 in such manner as to cover the contents of the detector array 242, sub-positioning mechanism 234, and detector conditioning electronics 240. The back wall (not shown) of the detector array housing 60 is lined with a lead or tungsten shield (not shown) to block stray radiation that is not attenuated by the detectors 238. SUB-POSITIONING OF THE DETECTOR APPARATUS In addition to scanning the components 18 by translati along its length, and rotating around the components via t gantry 52, yoke 84 and ring assembly 54 described above, t present invention also shifts the detector array subassemb 242 relative to the source 58 and detector base plate 232 order to increase the density of scanning data collected a to cover blind spots caused between the scintilating plast of the detectors 238. This technique is called su positioning. The sub-positioning guide rail 270 and grooved rollers 272 mentioned above are key to su positioning of the detector array 242. The v-grooved rolle 272 which are fixed to the detector housing base plate 2 allow the sub-positioning guide rail 270 to move relative the base plate 232. Since the detector guide plate 236 fixed to the sub-positioning guide rail 270 the detector gui plate 236 moves along with the sub-positioning guide rail 2 and the whole detector array 242 moves relative to t detector base plate 232. Since the detector base plate 232 in a fixed position relative to the source 58, the detect array 242 also moves relative to the source 58 when the su positioning guide rail 270 moves. Fig. 10a shows one actuation system for moving the su positioning guide rail 270. A controller 274 receives contr data from the computer system 68 and sends a signal to a val 276 which allows pressurized air to flow into or out of pneumatic cylinder 278 which is mounted to the detect housing base plate 232. The extension of the rod 280 in t pneumatic cylinder 278 rotates an eccentric cam 282 which also mounted to the detector housing base plate 232. As t eccentric cam 282 rotates, two rollers 284 & 286 attached the sub-positioning guide rail 270 move to remain tangenti to the outer surface 288 of the cam 282. Since the cam 282 eccentric it forces the sub-positioning guide rail 270 to mo relative to the detector housing base plate 232 to which t cam 282 is attached. Fig. 10b shows an alternative actuation system 289 f moving the sub-positioning guide rail 270. In this embodime the sub-positioning guide rail 270 is caused to move by motor 290 which receives signals from a controller 292. Th motor 290 cause a screw rod 294 to turn through transmission system 296 and thereby extend out of its housin 298. The end of the screw rod 294 is attached to the sub positioning guide rail 270 is such a manner so as to allo movement when the threaded rod 294 extends from its casin 298. The motor and screw rod sub-positioning actuation syste 289 must be mounted to the detector housing base plate 232 i such manner as to allow the assembly 289 to freely rotat enough to account for the nonlinear path the portion of th rod screw 294 attached to the sub-positioning rail 270 mus travel. SYSTEM GEOMETRY Fig. 11 illustrates the geometry of the source 5 /detector array 242 /sub-positioning 234 systems. Th detector array 242 positions the detectors 238 in an arc of circle centered at the center of the ring assembly 300 Although this structure complicates the calculations require to use the data collected from scanning an component 18, a object-centered detector array system can be constructed wit an overall smaller system diameter 302 than a source-centere detector array system. In applications where the scannin apparatus must maneuver between support structures around th component scanned, the size of the system can be o significant importance. However, while the detector arra 242 is centered around the center of the ring assembly 300, each individual detector 238 is oriented at different angle as though the source 58 is the center of the system. Likewise the sub-positioning guide rail 270 is structured to move along an arc of a circle centered at the source 58. THE SAFETY AND ENVIRONMENTAL CONTROL SYSTEM The disclosed apparatus is also equipped with safety and environmental control equipment and safeguards. The trailer, shown in Fig.2, which holds the computer 68 and all its periphery 70, has a separate thermostat and heating and air conditioning system (not shown) . This keeps the temperature inside the trailer 50 fairly consistent and comfortable for the system operators. The rest of the safety and environmental control system is controlled by the computer 68 which receives signals from temperature and radiation sensors (not shown) and sends control signals to various components of the system. The data collection subsystem 64 contains an air conditioner (not shown) and temperature and radiation sensors (also not shown) . The air conditioner keeps the inside of the data collection subsystem housing 64 cool and maintains positive air pressure inside the housing 64 to help prevent dust and debris from entering the housing 64. The temperature sensor provides feed back to the air conditioning system. Both the temperature and radiation sensors transmit data to the computer system 68 in the trailer 50. If the temperature or radiation levels rise to a predetermined level and the computer system 68 transmits a warning message to an annunciator peripheral 70 inside the trailer 50 and out in the facility where the scanner is being used. The data collection subsystem 64 also contains a second air conditioning system (not shown) . This air conditioning system sends cold air to the detector array housing 60 via the umbilical cord 62. Positive air pressure is also maintained in the detector array housing 60 to help keep out dirt and other debris. Temperature and radiation sensors (not shown) are also placed in and around the detector array housing 60. These sensors transmit information to the computer system 68 which will also activate annunciators peripheral 70 if temperature and/or radiation levels rise to predetermined levels. DATA ACQUISITION A suitable data collection system 64 for use with the Apparatus herein may be constructed by a person of ordinary skill in the art by adapting the data collection system disclosed in pending U.S. Patent Application Serial No. 531,454 , filed in the name of Morgan, et al., entitled "A Automated System for Controlling the Quality of Geometricall Regular-Shaped Products During Their Manufacture." SCANNING MODES The present invention can be operated in two categorie of scanning modes: gauging modes and analytical modes. Th distinguishing characteristics between these two categories o scanning modes is the number of actual scans made and th methods used to analyze the data collected. For the gaugin mode, the computer 68 is programmed to employ limited angl data collection and analysis methods described in pending U.S. Application Serial No. 531,454 , filed in the name o Morgan et al., entitled "An Automated System for Controllin the Quality of Geometrically Regular-Shaped Products Durin Their Manufacture." except that the programming must b adapted to an object-centered detector array system geometr as described above rather than a source-centered detecto array system geometry. The programming must be adapted to this new geometry because the intensity of the gamma ray signal entering each individual detector is a function of the distance from the source to the detector. In a source-centered detector array system geometry, this distance is equal for all detectors; while, in a object- centered detector array system geometry this distance varies. The intensity of the gamma ray signal as detected by the detector is a function of the following ratio: 1/r 2 where "r" is the distance from the source to the detector. For the analytical mode, the computer 68 is programed to employ conventional computer tomographic principles summarized in U.S. Patent 4,284,895 except that the programming must also be adapted to an object-centered detector array system geometry as described above rather than a source-centered detector array system geometry as described above. Preferably, the computer 68 is programmed to employ a Radon- based analytic reconstruction technique, such as those based on the Fourier or Convolution reconstruction theorems, to form a first estimate of the linear attenuation coefficient of each pixel or element of the component. Then iterative reconstruction techniques can be employed to refine the estimate to obtain a final estimate of the attenuation coefficient. Although the methods used to analyze the data collected in the analytical mode generate results with high resolution and precision, they require much more data and a great deal more time to complete. In comparison, the methods used in the gauging mode are less accurate; however, they require substantially less data and require substantially less time for completion. Another characteristic that distinguishes the scanning modes is the type of movement required of the mechanical system. The gauging mode type scans only require that the mechanical system rotate the source 58 and detector array housing 60 to a limited number of rotational positions 308 or angles. An example of a set of rotational positions used in a gauging mode scan is shown in Fig. 12a. Fig. 12a shows 5 macro-steps 306 and 3 micro steps 304 per macro-step 306. The density of data per cross-section of the component depends on the number of macro 306 and micro 304 steps taken. Another characteristic distinguishing the gauging mode from the analytic mode is the option to translate along a given length of the component for each rotational position 308 shown in Fig. 12a. The use of the translational scan option is shown in Fig. 12b. This figure shows a series of translational scans for two macro-steps 306 with three micro-steps 304 each. The increasing numerals indicate the positional sequence of the source as the component is being scanned. The source 58 and detector array 242 are held in a rotationally fixed position and the ring assembly 54 is translated along the length of the component 18 taking scans at predetermined intervals. Once the ring assembly 54 has been translated the length of the component 18, it is rotated a few degrees if a macro-step contemplated or a portion of a degree if a micro-step i contemplated and then is translated back along the same lengt of the component 18. After the ring assembly 54 has returne to its original position the ring assembly 54 is again rotate and translated along the length of the component 18. Afte a series of these small rotational scans 304, the rin assembly 54 makes a larger rotation 306, . - degrees fo example. The operator of the system specifies the number an size (in degrees) for macro-steps 306, micro-steps 304, th number of translational steps and the size (in units o length) . The degree of resolution in the gauging mode i determined by the number and size of macro-steps 306 an micro-steps 304 steps and also the number of translationa steps per unit length. The larger the number of macro 306 an micro-304 and translational steps the greater the resolutio but the slower the total scan time. Another option in the gauging mode is to take sub positional measurements for each rotational position of th ring assembly. While micro-steps.typically range from a fe degrees to a fraction of a degree, sub-positioning changes th angular positions of the detector array housing 60 by fraction of a degree to a very small fraction of a degree 1/30 of a degree, for example. Although sub-positionin increases the data density and therefor the resolution of th results it also substantially increases the time required t collect the data. In the analytical mode the large number of rotationa positions of the ring assembly 54 around the component scanne blurs the distinction between macro-steps 306 and micro-step 304, rather there are simply a large number of micro steps 304 for each cross-section of the component 18 scanned by using a analytical mode. The analytical mode also allows the option of using sub- positioning for each rotational position to increase the data density of the scan. However, unlike the gauging mode in the analytical mode, the scanning apparatus S does not typically translate longitudinally along the length of the component 18 for each rotational position 308 as shown in Fig. 12b. Rather in the analytical mode since localized cross-sections are the focus of the scan, the scans for one cross-section are completed before beginning a new cross-section. Prior to scanning the component 18 the operator of the system inputs the scanning mode parameters. If a gauging mode scan is desired the operator must define the number of macro- steps 306, additionally if the operator wishes to define the scanning mode to include micro-steps, sub-positioning and or translational movement these parameters must also be entered. On the other hand, if an analytical mode scan is desired, the operator must define the number of rotational positions for each cross-section and the number of sub-positions per rotational position if any. In the preferred embodiment of this invention the operator has the option and flexibility to define a number of scanning modes and use them separately or. together to inspect a component 18. An example of using several differently defined scanning modes to scan a section of pipe in a steam power generating facility is described in the operation below. OPERATION In a steam power generating facility environment shown in Fig. 2, the present invention is implemented by positioning the beam 80 of the gantry assembly 52 in parallel with the axis of the component 18 to be examined. The gantry 52 should be at a distance from the component 18 to be scanned so that when the ring assembly 54 is closed about the component 18, the center of the component 18 and the center of the ring assembly 52 are approximately concentric. The invention is now capable of traveling along the length of the component 18 and rotating about the component 18 through the gantry 52, yoke 84 and ring assembly 54 means described above. As the invention moves, it can scan cross-sections of the component 18 with penetrating radiation through use of the source 58 and detector array 242 described above. The description of a preferred operation of the present invention uses several differently defined scanning modes depending on the type of flaws detected. The first scanning mode is a gauging mode scan with typically seven macro-steps 306, one micro-step 304 per macro-step 306, no sub- positioning, and longitudinal coverage of 10 feet of pipe. The scanning apparatus S quickly scans the length of the pipe 18 at one rotational position then rotates a micro-step 304 and travels back along the same length of pipe. The scanning apparatus S then takes a macro-step 306 and again travels the length of the pipe 18. This proces repeats itself until the all of the rotational steps 306 & 304 have been taken and the entire length of the pipe is scanned for each rotational position 308. This scanning mode is called the dimensional gauge scanning mode since as it travels along the length of the pipe it can use the limited angle data collection and analysis techniques disclosed in U.S. Patent Application Serial No. 531,454 filed in the name of Morgan, et al., entitled "An Automated System for Controlling the Quality of Geometrically Regular-Shaped Products During Their Manufacture," calculates the pipe's inside diameter, outside diameter and wall thickness. After the scan is complete, the computer 68 calculates eccentricity, and ovality using the limited angle data analysis techniques disclosed in said pending application, the description of which is incorporated herein. The outputs from this part of the dimensional gauge scanning mode analysis can be graphically displayed as shown in Fig. 13. The computer 68 then calculates an overall average OD, ID, and wall thickness, this information is used to generate a computer model of [an ideal] section of the pipe scanned. Fig. 14 is an illustration of the computer profile model of an [ideal] section of pipe as determined by the pipe averages calculated above. The computer 68 then subtracts the calculated ideal model profile from the actually measured profiles. The difference is a representation of how each profile deviates from ideal. Fig. 15a illustrates a series of actual pipe profiles from a dimensional gauge scanning mode as described above. Fig. 15b illustrates the results when the ideal pipe profile model is subtracted from the actual profile. If these deviations exceed a threshold previously set by the operator, the computer 68 will store the associated longitudinal and angular positions and identify the deviation as a particular class of anomaly. If the anomaly is a narrower wall thickness, then wall thinning is identified as the type of flaw. If the OD is larger than average, then creep is identified as the flaw. If the OD is only larger on a portion of the outer surface of the pipe, then plastic deformation is identified as the type of flaw. If the anomaly is small and localized, its longitudinal position along the length of the pipe is marked for further investigation. The computer 68 is also able to identify weld locations, plugs and attachments beneath the insulation because of their unique effects on the component profile at various angular views. After the computer 68 has completed the above described calculations, the apparatus begins a higher resolution gauge scanning mode in longitudinal positions where anomalies were identified by the dimensional gauge scanning mode. In this scanning mode, the apparatus typically scans the localized area at 15 macro-step locations 306 and 8 micro-steps 304 per macro-step 306 about the component. No sub-positioning is called for and the longitudinal length of each scan is determined by the results of the dimensional gauge scanning mode. The scanning sequence is essentially the same as was previously described in the dimensional gauge scanning mode description except for the increased number of scans. As its name indicates the higher resolution gauge scanning mode generates higher data densities sufficient to make more accurate measurements of the dimensions determined in the dimensional gauge scanning mode and also more accurately analyze the magnitude and location of the anomalies. The location of flaws can also be determined by the computer 68 from data taken in a high resolution gauge mode by triangulation. As shown in Fig. 16, triangulation is performed by calculating the intersection of all the path lengths in which the flaw was detected. The type of flaw (corrosion wear, erosion wear, pitting, cavitation, gouges, voids, and cracks) can be identified by the shape by comparison to the flaw shape previously determined to empirical shape characteristics of typical flaws. If a weld or crack or any other anomaly for which more detailed information would be useful was identified in either of the gauging mode scans, the apparatus may be moved to the longitudinal location of these anomalies to perform a low resolution analytical mode scan. The low resolution analytical mode scan typically has approximately 360 rotational positions and one sub-position for each rotational position. In the analytical mode one cross-section of the component is typically completely scanned before being longitudinally translating to a second cross-section. Once the low resolution analytical mode scan is complete the computer 68 utilizes conventional tomographic algorithms as described above to generate a three dimensional tomographic image of the flaw. These high resolution results allow for the characterization of anomalies not inspectable by the apparatus during the gauge modes, for example, smaller lugs, attachments, plugs, cracks indications and welds where a resolution of greater than 0.5% is needed. In the case of welds or other areas where the density of the component is not consistent, the scan can be run twice, once with each source 202 & 204. The path-lengths from these two scans can be used to calculate the density of the component using available algorithms. If the detail obtained form the low resolution analytical mode scan is not enough, a high resolution analytical mode scan can be run. Typically, the scanning apparatus during a high resolution scan made will move to 1080 rotational positions and S sub-positions per rotational position. Using the data collected in this scan, the computer 68 utilizes the same CT algorithms described above. The foregoing disclosure and description of the invention are illustrative and explanatory thereof, and various changes in the details of its construction or mode of operation of the inspection and analys may be made without departing from the spirit of the invention.

Claims: We Claim: 1. A mobile apparatus for nondestructively inspectin stationary components, such as piping, of a facility comprising: a) ring means encircling the component to be scanned; b) source means mounted on the ring means fo transmitting penetrating radiation through a cross section of the component; c) detector means for detecting penetrating radiatio which passes through the component from said sourc means and for converting the detected radiation into electrical signals representative of the density length of the component material along a path between the source and the detector; d) beam means positioned along the length of the component; e) yoke means for supporting the ring means about the component wherein the yoke means is movable relative to the beam means; f) means for rotating the ring means relative to the yoke means about a cross-section of the component to be scanned; g) means for translating the yoke means relative to the beam along the length of the component to be scanned; h) means for monitoring the longitudinal position of the ring means relative to the yoke means; and i) means for monitoring the rotational position of the ring means relative to the yoke means. 2. The apparatus of Claim 1, which further comprises: processing means for sending control signals to the translating and rotating means for translating and rotating the source means and detector means, for receiving both longitudinal and rotational positional data from the monitoring means for receiving density length signals from the detector means for a plurality of translated and rotational positions. 3. The apparatus of Claim 2, wherein: a) the processing means further comprises a comput model of the component scanned; and b) the processing means processes the density leng signals using the computer model in order to dete flaws in the component scanned. 4. The apparatus of Claim 3, wherein: the computer model of the component is generated by sa processing means from density length signals generated the apparatus scanning the component at a plurality longitudinal and rotational positions during dimensional gauging mode. 5. The apparatus of Claim 4 wherein said computer mod comprises: a) stored data representative of an average profile a plurality of cross-sections of the compone scanned; and b) said processing means compares the average and re profiles of the component to find differenc representative of flaws in the component scanned. 6. The apparatus of Claim 6, further comprising: program means for generating a plurality of contr signals for operating the apparatus during a hi resolution gauging mode wherein during such hi resolution scanning mode the apparatus rescans t portion of the component having the detected flaw from larger number of longitudinal and rotational positio than the positions scanned in the dimensional gaugi mode in order to more accurately determine the volumetr and dimensions and characteristics of the flaw. 7. The apparatus of Claim 5, wherein said processing mea further comprises: program means for operating the apparatus during analytical mode wherein the apparatus scans the portio of the component containing the previously detected fl from many rotational positions about the components a use the resulting signals to generate a tomograph reconstruction of the portion of the component containing the previously detected flaw. 8. The apparatus of Claim 3, further comprising: a) pyrometer and pressure gauge means for measuring the temperature and pressure of the component scanned; and b) program means for adjusting the calculated dimensions of the component to account for variations in temperature and pressure. 9. A mobile apparatus for nondestructively scanning stationary insulated components of a facility, such as piping, while the facility is in operation, without removing the insulation from the component under examination, comprising: a) ring means encircling the insulated component to be scanned; b) source means mounted on the ring means for transmitting penetrating radiation through a cross- section of the insulated component; c) detector means for detecting penetrating radiation which passes through the component and for converting the detected radiation into electrical signals representative of the density length of the component material along a path between the source and the detector; d) beam means positioned along the length of the component; e) yoke means for supporting the ring means about the component wherein the yoke means is movable relative to the beam means; f) means for rotating the ring means relative to the yoke means about a cross-section of the component to be scanned; g) means for translating the yoke means relative to the beam means along the length of the component to be scanned; h) means for monitoring the longitudinal position of the ring means relative to the yoke means; and i) means for monitoring the rotational position of the yoke means relative to the beam means. 10. The apparatus of Claim 9, further comprising: processing means for receiving positional data from the monitoring means, for sending control signals to the translating and rotating means for translating and rotating the source means and detector means, and for receiving density length signals from the detector means for each of a plurality of translated and rotational positions. 11. The apparatus of Claim 10, wherein said processing means further comprises: a computer model of the component scanned and the processing means processes the density length signals using the computer model in order to detect flaws in the component scanned. 12. The apparatus of Claim 11, wherein: the computer model of the component is generated by said processing means from density length signals generated during the apparatus scanning the component at a plurality of longitudinal and rotational positions during a dimensional gauging mode. 13. The apparatus of Claim 10, which further comprises: a) stored data representative of an average profile of a plurality of cross-sections of the component scanned; and b) said processing means compares the average and real profiles of the component to find differences representative of flaws in the component scanned. 14. The apparatus of Claim 10, which further comprises: program means for generating a plurality of control signals for operating the apparatus during a high resolution gauging mode wherein during such high resolution scanning mode the apparatus rescans the portion of the component having the detected flaw from a larger number of longitudinal and rotational positions than the positions scanned in the dimensional gaugi mode in order to more accurately determine the volumetr and dimensions and characteristics of the flaw in ord to correlate to historical changes producing similar fl characteristics related to creep, deformation, corrosio wear, and pitting, errosion, cavitation and stres cracking. 15. The apparatus of Claim 11, which further comprises: program means for operating the apparatus during o analytical mode wherein the apparatus scans the portion of the component containing the previously detected fla from many rotational positions about the components an use the resulting signals to generate a tomographi reconstruction of the portion of the component containin the previously detected flaw. 16. The apparatus of Claim 3, wherein: a) pyrometer and pressure guage means for measuring th temperature and pressure of the component scanned and b) program means for adjusting the calculate dimensions of the component to account fo variations in temperature and pressure. 17. A method of nondestructively inspecting components of a operating facility while the components are in use comprising: a) positioning a penetrating radiation scannin apparatus having a source and a detector about th component to be scanned; b) scanning a cross-section of the component wit penetrating radiation along a plurality of paths; c) generating signals representative of the radiatio attenuation along each of a plurality of paths; d) converting the attenuation signals to densit /length signals and storing the density lengt signal in a computer accessible memory; e) monitoring the longitudinal and rotational positio associated with the density length signals generated by the scan and storing the signals in a computer; f) translating the scanning apparatus to another longitudinal position along the component; g) repeating steps (a) through (f) until the length of the component has been scanned; h) rotating the scanning apparatus about the axis of the component; i) repeating steps (a) through (f) ; and j) processing the density length signals from the plurality of scans to generate a computer model of the component wherein the calculated dimensions of the component are representative of the average of the dimensions computed for different cross sections of the component. 18. A method for nondestructively inspecting components, such as piping, of an operating facility while the components are in use: a) positioning a scanning apparatus about the component to be scanned; b) scanning with penetrating radiation a plurality of cross-sections of the component along the longitudinal length of the component from a plurality of different rotational positions about each of such cross sections; c) monitoring the longitudinal and rotational positions associated with each scan; d) generating signals representative of the radiation attenuation along each of a plurality of paths at each longitudinal and rotational position; e) associating the position of each scan with the signals generated by each scan; and f) processing the density length signal and associated position signals from the plurality of scanning to generate dimensional measurements of the component and detect flaws in the component. 19. The method of Claim 19, wherein the attenuation signals are converted into density length signals. 20. The method of Claim 19, wherein: the step of scanning comprises selecting a dimension gauging mode and scanning the component at a relative small number of longitudinal and rotational position and

Inventors: BOLGER JOSEPH E, CRANE BOB, MORGAN IRA L, RICE ROBERT H, BOLGER, JOSEPH, E., CRANE, BOB, MORGAN, IRA, L., RICE, ROBERT, H.
Applicants: INT DIGITAL MODELING CORP, INTERNATIONAL DIGITAL MODELING CORPORATION
Application year: 1991
Main classification: G01N23
IPC codes: G01N23