Piping inspection instrument carriage with precise and repeatable position control and location determination

An instrument carriage for inspection of piping comprises front and rear leg assemblies for engaging the interior of the piping and supporting and centering the carriage therein, and an instrumentation arm carried by a shaft system running from the front to rear leg assemblies. The shaft system has a screw shaft for moving the arm axially and a spline gear for moving the arm azimuthally. The arm has a pair of air cylinders that raise and lower a plate in the radial direction. On the plate are probes including an eddy current probe and an ultrasonic testing probe. The ultrasonic testing probe is capable of spinning 360.degree. about its axis. The instrument carriage uses servo motors and pressurized air cylinders for precise actuation of instrument components and precise, repeatable actuation of position control mechanisms.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to apparatus for inspecting the interior of 
piping. In particular the present invention relates to piping inspection, 
instrumentation-carrying apparatus having the capability of locating and 
scanning a specific feature along the interior of the piping. 
2. Discussion of Background 
Throughout industry, piping is used to convey fluids of every kind over 
short distances and long. Because of the adverse effects of stress, 
temperature, and fluids flowing through pipes, both the effects of 
specific fluids (corrosion) and the effects of fluid flow in pipes 
generally (erosion), the piping will eventually degrade and may fail 
completely or may cease to be serviceable or may simply begin to leak. 
Flaws frequently begin to form at welded joints. However, even newly 
welded pipe joints can also have flaws that will cause leaks or pipe 
failure. 
The integrity of piping is an important industrial concern and can become 
crucial depending on a number of factors, including the volume of material 
transported by the piping per day, the hazardous nature of the material, 
the cost of the fluid transported, and the impact of a loss of the fluid 
on the user's operation at the fluid's destination. 
Pipe inspection can prove very useful in avoiding pipe failure by 
determining the condition of piping and how that condition changes over 
time. Welds can be inspected visually, ultrasonically and using eddy 
currents. Not only is periodic pipe inspection useful during operation, 
but pipe inspection prior to use may be especially important. For example, 
it is prudent to conduct a pre-service inspection of piping that will 
carry hazardous or radioactive fluids to verify the condition of welds or 
to fix flaws before the interior of the piping becomes contaminated. 
There are a number of piping inspection devices. Some of these are 
self-propelled and others are pulled or pushed by pipe crawlers or other 
means. See for example the pipe inspection devices described by Wentzell 
in U.S. Pat. No. 4,581,938, Takagi, et al. in U.S. Pat. No. 4,621,532 and 
Weber, et al. in U.S. Pat. No. 4,460,920. Pipe inspection can be done by 
ultrasonic transducers, eddy current sensors and visual devices. See 
Metala, et al. (U.S. Pat. No. 4,856,337), Krieg, et al. (U.S. Pat. No. 
4,769,598) and Weber, et al. Weber includes a television camera with his 
pipe inspection device. Metala, et al. and Krieg, et al. carry both 
ultrasonic and eddy current measuring equipment. A companion application, 
commonly assigned, titled "Pipe Crawler With Extendable Legs", Ser. No. 
679,497 filed Apr. 2, 1991, now U.S. Pat. No. 5,121,694 is incorporated by 
reference and describes a system for distribution of air via manifolds and 
solenoid switches. Also, see issued U.S. Pat. No. 5,018,451, commonly 
assigned, for a description of another pipe crawler such as could be used 
to move a pipe inspection apparatus. 
Inspecting the interior of piping must be coupled with a fairly accurate 
system for knowing where the inspection device is and how it is oriented. 
Sometimes only distance in one direction is needed, distance that can be 
obtained from a simple odometer or from the length of the tether, for 
carrying power cables, air hoses, and the like, that trails from the 
inspection device to the entrance of the pipe. If the pipe has a number of 
bends and variations in diameter, and especially if the area to be 
inspected is relatively small, more precise locational information may be 
needed, sometimes, in fact, full coordinate information. The device as 
described by Thome in U.S. Pat. No. 4,506,549 provides position 
information in four dimensions: axial, radial, azimuthal and rotational 
about itself. 
However, there remains a need for a pipe inspection device that is capable 
of making minute inspections and of knowing the precise location of the 
inspected areas for comparison to previously inspected areas. Fine 
inspections can enable pipe flaws and changes in those flaws to be 
detected, analyzed and corrected sooner rather than later. 
SUMMARY OF THE INVENTION 
According to its major aspects, the present invention is an instrument 
carriage for inspecting a feature on an interior surface of piping. The 
carriage has a frame carrying front and rear sets of radially extendable 
legs that engage the interior surface of the pipe and straddling the 
feature, means for finding the feature, and means for systematically 
scanning the feature and associating position information with the feature 
so that flaws, once found, can be located repeatedly with accuracy. The 
scanning means is an instrumentation arm that moves axially, radially and 
azimuthally and can, in a horizontal pipe, determine absolute orientation 
of the carriage. The arm moves along two mutually orthogonal coordinates, 
oscillating back and forth in an axial coordinate with respect to the pipe 
while moving steadily along an azimuthal coordinate. Probes for ultrasonic 
and eddy current testing are carried by the arm. A camera assists in 
finding the features but is not required. If so desired, the ultrasonic 
testing probe or the eddy current probe may be extended to the pipe wall 
to perform a quick scan and check to see if the desired feature is 
present. At least one television camera is carried by the arm for finding 
features on the interior surfaces of the piping. 
An important feature of the present invention is the combination of 
position control mechanisms that permit accurate and repeatable axial, 
radial and azimuthal movement of the probes. Because of this combination, 
features that were found to have small cracks or signs of stress can be 
located on a second pass through the piping. Scanning results of more than 
one examination can be aligned within a few hundredths of an inch for 
analysis. 
Another important feature of the present invention is the location of the 
instrumentation arm between the front and rear leg assemblies. This 
position requires the carriage leg assemblies to straddle the feature to 
be examined, resulting in improved stability for measurement. The 
importance of stability cannot be too strongly emphasized because of the 
need for fine measurements. 
Another feature of the present invention is the method for scanning a 
feature. In particular, the center of a feature is located and scanned 
systematically along two mutually orthogonal coordinates. The arm 
oscillates in one direction while traversing in a second direction. 
The stiffened, double air cylinders used for radial extension of the probes 
is another feature of the invention. It provides more stability for the 
plate that carries the probes than a single air cylinder. 
The wire guide for carrying wiring and air hoses from one leg assembly to 
another and its location are another feature of the present invention. 
Since the instrumentation arm rotates at least 360 degrees azimuthally and 
engages the inside surface of the piping, the wire guide must be radially 
inside the arm and preferably carried by a part that does not rotate so 
that the wires do not become twisted. The wire guide is a hollow tube that 
runs from front to rear leg assembly, running axially and located radially 
within the ring gear that is rotated by a spline gear to rotate 
instrumentation arm. Thus the wiring and air hoses are protected and kept 
from fouling on the rotating and advancing instrumentation arm. 
Other features and advantages of the present invention will be apparent to 
those skilled in the art from a careful reading of the Detailed 
Description of a Preferred Embodiment presented below and accompanied by 
the drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring now to FIG. 1, there is illustrated a section of piping 20 in 
cross section. Moving within piping 20 is a pipe inspection carriage 24, 
in accordance with a preferred embodiment of the present invention, being 
pushed by a pipe crawler 28. Pipe inspection carriage 24 is connected to 
pipe crawler 28 by a flexible coupling 32 that enables carriage 24 to be 
pushed through bends in piping 20. Flexible coupling 32 is preferably a 
cylinder with a spiral groove cut through it. 
Pipe crawler 28, which is not part of the present invention can be any type 
capable of providing pushing or pulling power to carriage 24. 
Specifically, there are pipe crawlers that move in "inchworm" fashion, as 
in the case of crawler 28, with a front leg assembly 36 and a rear leg 
assembly 40 each having a plurality of leg cylinders 44. Front and rear 
leg assemblies 36 and 40 are connected by one or more air cylinders 48. 
Each leg cylinder has a foot 52 for frictionally engaging piping 20. The 
movement of crawler 28 is then achieved by the following sequence: leg 
cylinders 44 of rear leg assembly 40 radially extend feet 52 to engage the 
interior wall of piping 20; front leg assembly 36 is moved forward by air 
cylinders 48 along piping 20; then leg cylinders 44 of front leg assembly 
36 extend feet 52 to engage the wall of piping 20; leg cylinders 44 of 
rear leg assembly 40 retract; and rear leg assembly 40 is pulled toward 
front leg assembly 36 by air cylinders 48. As crawler 28 moves forward, it 
pushes carriage 24. 
Carriage 24 has a frame 54 to which is attached a front leg assembly 56 and 
a rear leg assembly 60. Front and rear leg assemblies 56, 60 are spaced 
apart and their spacing is rigidly maintained, as will be further 
described below. Each leg assembly has a plurality of leg cylinders 64 
that extend radially to engage the interior surface of piping 20; each leg 
64 has a ball transfer 68 or other wall-engaging device on the end thereof 
to facilitate low-frictional engagement and movement of carriage 24. Axial 
movement of carriage 24 through piping 20 is controlled by crawler 28. 
Front and rear leg assemblies 56, 60, by engaging the interior surface of 
piping 20, stabilize and center carriage 24 radially with respect to the 
axis of piping 20. Electrical wiring and air hoses for leg cylinders are 
not shown for simplification. A preferred method for delivery of air to 
air cylinders via manifolds and solenoid switches is described in a 
companion application titled Pipe Crawler With Extendable Legs, recently 
filed application Ser. No. 679,497, now U.S. Pat. No. 5,121,694, 
incorporated herein by reference. 
Carriage 24 has shaft system 72 for, among other purposes, maintaining the 
spacing between front and rear leg assemblies 56, 60 of carriage 24. Shaft 
system 72 carries an instrumentation arm 76 for scanning features on the 
interior surface of piping 20 and at least one television camera (not 
shown on FIG. 1) for assistance in finding such features. Additional 
cameras may be used for viewing in the direction carriage 24 is moving. 
FIG. 2 shows a side view of carriage 24. Front and rear leg assemblies 56, 
60 operate by air cylinders 80 or other means such as hydraulic cylinders 
or electromechanical cylinders. Preferably at least three legs 64 and most 
preferably four legs 64, as shown in FIG. 2 (three of which are visible in 
the figure), all at right angles with respect to adjacent legs 64 are 
provided to center and support carriage 24 in piping. Each leg 64 has ball 
transfer 68 on its end that provides low-friction movement when the legs 
64 of carriage 24 engage the interior surface of piping 20. Between front 
and rear leg assemblies 56, 60 are two splined shafts 84 and 88, deployed 
in parallel with each other and parallel to the axis of carriage 24. In 
addition to shafts 84 and 88, there is a ball screw shaft 92 and a wire 
tube 96 (see also FIG. 3). Tube 96 simply serves as a conduit for running 
wiring and air hoses from front leg assembly 56 to rear leg assembly 60, 
keeping the wiring and air hoses from being caught on instrumentation arm 
76. Spline shaft 84 assists in the rotation of instrumentation arm 76 
about the axis of carriage 24, as will be described below. Spine shaft 88 
is used for guiding linear travel. It also provides stability, or 
rigidness, to the carriage acting as a third brace, along with spline 
shaft 84 and ball screw shaft 92. 
At the rear of rear leg assembly 60 are two electrical motors. Motor 104 is 
for producing linear motion of instrumentation arm 76; motor 100 is for 
producing rotational, or azimuthal, motion of instrumentation arm 76. As 
motor 104 turns screw shaft 92, as illustrated in FIG. 6, instrumentation 
arm 76 is moved linearly in one direction or another depending on whether 
screw shaft is being turned clockwise or counter-clockwise. 
Motor 100 turns spline shaft 84 which, as best seen in FIGS. 3 and 5, turns 
gear 108 which drives ring gear 112 so that instrumentation arm 76 
rotates, azimuthally, about the axis of carriage 24. In FIGS. 4 and 5, 
radial movement from the axis of carriage 24 outwardly to the interior 
surface of piping 20 is achieved through two air cylinders 116, 120 
mounted in parallel and on opposing sides of instrumentation arm 76 that 
move instrumentation plate 124 radially in and out. Each air cylinder 116, 
120 has a shaft 128, 130, respectively, for stiffening sliding motion in 
stiffening blocks 132, 134, respectively, that move in bearings 136 (FIG. 
4). 
Plate 124 carries an ultrasonic testing probe 140 and an eddy current probe 
144. Ultrasonic probe 140 is mounted on a gimbal 148 so that the face 152 
of probe 140 engages the interior surface of piping 20 fully regardless of 
the angle of approach. Probe 140 is rotated through one complete 
revolution by a motor 156 connected via miter gears 160 to a shaft 164 
running through the center of probe 140. Control of the degree of 
revolution is imposed by a sprocket 168 also mounted to shaft 164 which 
sprocket rotates a chain 170 through a portion of its length. On face 152 
of probe 140 is a small hole 172 (FIG. 7) through which a fluid may be 
dispensed onto face 152. The fluid serves as both a lubricant and 
dielectric for good ultrasonic measurements. 
Eddy current probe 144 is mounted near but to the side of ultrasonic 
testing probe 140 on an eddy current mount 176 (FIG. 4) that is held to 
instrumentation arm 76 by a bracket 178. 
Ultrasonic probe 140 is preferably of the type that produces both a 
45.degree. shear wave to look for intergranual stress corrosion cracking 
and a 90.degree. "straight-through" wave for laminate flaws. Eddy current 
probe tests magnetic properties, looking for a change in those properties 
present due to welding or other instigators. 
Also mounted to instrumentation arm 76 is a electronic level potentiometer 
180 mounted in a bracket 184. Potentiometer 180 has a pendulum-like 
electronic contact that hangs "down" in response to gravity as long as 
carriage is in a generally horizontal pipe, to indicate the direction of 
"down" in any section of piping 20, that is, potentiometer 180 indicates a 
gravitational "down" for establishing an absolute orientation for 
referencing all other directions and orientations of pipe carriage 24. In 
a vertical pipe, only relative position is known. 
Mounted to either front or rear leg assembly 56, 60 is at least one camera 
188. A single camera 188, as shown will be directed to the interior 
surface of piping 20 and the end of instrumentation arm 76 so that it can 
help to find surface features and observe engagement of ultrasonic testing 
probe with the wall of piping 20. Preferably equipped with a wide angle 
lens 192, camera 188 can determine if pipe crawler 24 has moved to within 
range of a reature on the inside surface of piping 20 and can observe the 
scanning of the feature by instrumentation arm 76. If a second camera is 
included with pipe crawler 24, it would be aimed in the direction of 
carriage travel. 
FIG. 8 is a schematic diagram of the control system of carriage 24. The 
device may be controlled with a joystick 200 or other manual or automatic 
device. The output of joystick 200 is input to a computer 204. Computer 
204 receives data as input from ultrasonic testing probe 208 and eddy 
current probe 212 and limit switches 216 from the extreme axial, 
azimuthal, and spin movements of instrumentation arm 76. These are 
compared with reference inputs 200 to verify position information, as will 
be described in more detail below. 
Computer 204 directs an air supply 224 that sends air through a regulator 
228 and an air pressure gauge 232 to the air cylinders 236 of front and 
rear leg assemblies 56, 60 to control the extension of ball transfers 68 
to engage the piping wall. Computer 204 also directs three servo 
amplifiers 240, 244, 248 that drive motors for linear motion 252, 
instrumentation arm rotational motion 256 and probe rotational motion 260. 
Each motor produces velocity feedback while potentiometers 264, 268 and 
272, respectively, driven by motors 240, 244, 248, provide position 
feedback to computer 204. Ultrasonic testing probe 208, eddy current 
testing probe 212, limit switches 216, cylinders 236, motors 252, 256, 
260, and potentiometers 264, 268, 272 are carried by instrumentation 
carriage 24. Joystick 200, computer 204, reference inputs 220, air supply 
224, regulator 228, gauge 232, servo amplifiers 240, 244, 248, are remote 
from carriage 24 as is a display 276 of position information and the 
output of at least one on-board camera 280. These components are connected 
to carriage 24 by a tether. 
In use, pipe crawler 28 pushes (or pulls) pipe carriage 24 along piping 20, 
ball transfers 68 in rolling engagement with piping 20 and camera 188 
being trained on the inside surface of piping 20, until a surface feature 
such as a weld is found. Usually the length of the umbilical cord plus 
piping diagrams determines approximately where crawler 28 is in the piping 
system. Camera 188 is used to find the specific location of feature once 
the approximate location has been reached. Crawler 28 maneuvers carriage 
24 so that carriage 24 straddles the feature, front leg assembly 56 on one 
side and rear leg assembly 60 on the other side of the feature. The arm is 
then extended radially and moves in the axial direction as the eddy 
current probe or ultrasonic testing probe is used to determine the center 
of the weld. Scanning the heat-affected-zone (HAZ) about a weld is done to 
look for signs of stress corrosion cracking and or other defects. 
Routinely every few years or so, piping is inspected. A crack that might 
be just forming is checked in the next inspection. Because of the 
importance of finding the same crack in two or more successive inspections 
several years apart, reliable position information, confirmed to some 
extent with visual correlation, is essential in any inspection program. 
Instrumentation arm 76 extends ultrasonic testing probe 140 via air 
cylinders 132 and 140 to engage wall surface in the proximity of the 
surface feature. If the pipe has axial and circumferential welds, then the 
centerpoint of the intersection is found by the same process. The 
centerpoint of a weld can be found to within a few hundredths of an inch. 
Then rotating instrumentation arm 76 azimuthally, arm 76 moves back and 
forth axially by the alternate clockwise, counterclockwise turning of ball 
screw 92, to systematically scan the feature along two mutually orthogonal 
coordinates, in a circumferential weld, by oscillating in the axial 
direction and traversing in the azimuthal direction and producing outputs 
that reflect the results of the probes' measurements. Scanning is done 
with ultrasonic testing probe 140 and eddy current probe 144. Ultrasonic 
testing probe 140 rotates about its own axis. Position information 
regarding axial, radial, azimuthal locations is fed back to computer 204 
so that the position of any flaw or crack in the feature can be 
established and located on a second trip into piping 20. Detailed visual 
inspection is by the television camera mounted on the arm. Any ultrasonic 
or eddy current image taken in a scan is aligned with an image from one or 
more previous scans. 
Clearly, instruments other than eddy current probes and ultrasonic 
detectors could be carried by carriage 24 when needed to be brought to a 
particular location. For example, gripping devices can be carried for 
retrieval of objects or placement of sources for radiography; water 
nozzles and steam hoses, materials for coating and grinding tools can also 
be carried to a location for operating on the inside surfaces of piping. 
It will be apparent to those skilled in the art that many changes and 
substitutions can be made to the preferred embodiment herein described 
without departing from the spirit and scope of the present invention which 
is defined by the appended claims.