Device for adjustable mounting of magnetic sensing coils used in pipe inspection

An adjustable mounting shoe 10 for sensing coils 31 of a pipe inspection apparatus. The mounting shoe 10 comprises a base member 12 with a recess 14 in a surface thereof in which the magnetic sensing coils 31 are mounted. A thin shim 40 of magnetically transparent material is removably supported on the base member 12 in covering relationship to the sensing coils 31 whereby the coils are protected from abrasive contact with the exterior surface of a pipe to be inspected. A pair of adjustable contact members 51 are mounted on opposite sides of the recess 14 and provided with contact surfaces 51b positioned to engage the exterior surface of a pipe while supporting the magnetic sensing coils protected by the shim in an optimum sensing range from the surface of the pipe. Means (21,22,23,60) are provided for adjustably mounting each contact member 51 for selected movement towards or away from the recess 14 for accommodating use of the sensor shoe with pipes of different diameters while maintaining the sensing coils in optimum sensing distance. The shim 40 is also replaceable if it becomes worn down by abrasive contact through extensive use or if it is desired to use a shim of different thickness if a different coil sensing range is appropriate.

FIELD OF THE INVENTION 
This invention relates to magnetic pipe inspection apparatus, and more 
particularly to sensor shoes for mounting magnetic sensing coils which are 
used for sensing variations in a magnetic field in a tubular pipe member. 
BACKGROUND ART 
Inspection of metal pipe or tubular members by magnetic means 
conventionally involves magnetizing the member to create a magnetic field 
which extends circumferentially and is characterized by lines of magnetic 
flux which extend either axially of the tubular member or generally 
perpendicular to its axis, dependent on the manner by which magnetism is 
induced. In many of the present systems, current flow through a wire coil 
positioned about the tubular member forms magnetic lines of flux through 
the opening of the coil which extend axially of the member under 
inspection. In other systems, current flows axially of the tubular member 
within the wall thereof so as to create a magnetic field, the lines of 
flux of which extend circumferentially about the tubular member in an 
orientation substantially perpendicular to the tubular member. The 
presence of structural flaws or anomalies in the wall of the tubular 
member, such as surface nicks or pits, cracks, voids, or various 
crystalline discontinuities, disturbs the uniformity of a magnetic field 
in the wall of the tubular member. Accordingly, the structural integrity 
of the tubular member and its relative freedom of such flaws may be 
inspected by sensing and detecting the magnetic field variations with 
sensors disposed closely adjacent the surface of the tubular member. 
The sensing of variations in a magnetic field in a pipe wall is customarily 
achieved by passing or moving an induction coil or similar device through 
the magnetic field and any magnetic field variations to induce voltages in 
the coil indicative of the magnetic field variations. The voltages or 
voltage signals may then be transmitted to appropriate recording and 
processing equipment. For optimum detection sensitivity and for detection 
of very small cracks in a pipe wall which can be a few thousandths of an 
inch in depth, it is necessary that the detecting or sensor coil be placed 
closely adjacent the exterior surface of the tubular member. Normally the 
adjacent coil is disposed from 0.002 inches (0.051 mm) to 0.020 inches 
(0.51 mm) relative the surface of the tubular member with the axis of the 
coil substantially perpendicular to the surface. The sensor coils are 
mounted in a support, conventionally referred to as a sensor shoe, which 
is provided with contact surfaces adapted to contact with the surface of 
the tubular member in a manner so that the sensing coil is supported 
closely adjacent the surface of the tubular member at an optimum distance 
or spacing. Normally, the coil is protected from direct contact with the 
surface of the pipe by means of a thin shim of magnetically transparent 
material. 
Inspecting the surface of the tubular members requires that the inspection 
sensor be moved along the surface in a predetermined inspection path. In 
one widely used pipe inspection apparatus, a plurality of sensor shoes are 
applied to the surface of the pipe in circumferential spacing thereabout 
and each of the sensor shoes is moved relatively to the pipe in a 
circumferential helical path whereby the plurality of sensors provide more 
than 100 percent coverage of the pipe surface. The relative movement may 
be effected by moving the sensors longitudinally while rotating the sensor 
shoes around a stationary pipe or the pipe can be moved longitudinally 
while the sensors are rotated about the pipe. In any event, there is 
relative sliding movement between the sensor shoes and the pipe surface, 
which causes wear of the contact surfaces of a sensor shoe by extensive 
use. The shim also can come into contact with the pipe and can be 
similarly eroded. The wearing down of the contact surfaces and shim 
results in the coils being supported from the pipe surface inside the 
optimum spacing range or possibly being damaged by eventual contact with 
the pipe. When either event occurs, a new sensor shoe is required. 
Furthermore, sensor shoes are customarily designed for use with a specific 
diameter of pipe, and the contact surfaces of a sensor shoe are fixed in a 
permanent orientation such that when placed in contact with the surface of 
the pipe, the sensing coil is positioned for optimum detection 
sensitivity. Accordingly, a given sensor shoe is designed for inspection 
of only one diameter of pipe and is inappropriate for use as an inspection 
sensor for pipes of a different diameter since for such pipe diameters the 
sensing coil is supported at other than an optimum distance from the 
surface to be inspected. 
SUMMARY OF THE INVENTION 
The invention relates to an adjustable mounting shoe for mounting magnetic 
sensing coils of a pipe inspection apparatus. The mounting shoe comprises 
a base member with a recess in a surface thereof in which the magnetic 
sensing coils are mounted. The mounting shoe includes a thin shim of 
magnetically transparent material which is removably supported on the base 
member in covering relationship to the magnetic sensing coils whereby the 
coils are protected from abrasive contact with the exterior surface of a 
pipe to be inspected. The mounting shoe is also provided with a pair of 
adjustable contact members mounted on opposite sides of the recess and 
provided with contact surfaces positioned to engage the exterior surface 
of a pipe while supporting the magnetic sensing coils protected by the 
shim in an optimum sensing range from the surface of the pipe. Further 
included are means for adjustably mounting each said contact member for 
selected movement towards or away from the recess and sensing coils for 
accommodating use of the sensor shoe with pipes of different diameters 
while maintaining the sensing coils in optimum sensing distance from the 
pipe. The protective shim is also readily removable and replaceable when 
it becomes desirable to replace the shim if it becomes worn down by 
abrasive contact through extensive use or to use a shim of different 
thickness if a different coil sensing range is appropriate.

DETAILED DESCRIPTION OF THE INVENTION 
Referring more particularly to the drawings, there is shown in FIG. 1 an 
adjustable sensor mounting shoe 10 which illustrates a preferred 
embodiment of the invention. The reusable sensor shoe 10 comprises a base 
member 12 of nonmagnetic material, such as brass or the like. The base 
member 12 is preferably of elongate form with rectangular planar surfaces. 
As shown in FIG. 2, one of the faces 12a of the base member is provided 
with a recess 14 extending the length of the base member 12 along the 
mid-line thereof and a transverse groove 16 which extends from a narrow 
side 12b of the base 12 to communicate with the recess 14. The base member 
12 is also provided with three pairs of elongate slots 21, 22, 23 
extending through the base member 12 from the face 12a to a bottom face 
12c. As best seen in FIG. 2, the slots extend in a transverse direction 
with respect to the elongate recess 14 with the slots of each pair located 
on opposite sides of the recess 14 in axially aligned relationship with 
respect to one another. 
A plurality of inductance coils 31 are fitted in the recess 14, positioned 
adjacent to one another throughout the length of the recess 14. Each coil 
is comprised of axially aligned wire turns with the coil axes disposed 
perpendicular to the plane of the surface 12a. For purposes relating to 
signal strength, sensitivity and the like, the number of coils located in 
the recess 14 may be a selected number and their particular positional 
relationship to one another may vary from the arrangement shown in FIG. 2. 
For example, some of the coils may be positioned in superimposed 
overlapping relationship to others. In addition the leads from the several 
coils 31 are brought together in the form of a cable 36 which is run 
through the transverse groove 16 and provided with a multi-pronged 
connector 37 for accommodating connection of the individual sensing coils 
to appropriate circuitry and equipment for recording and processing 
voltage signals from the coils. The cable 36 is also tightly clamped in 
the groove 16 by a suitable clamp means 38 which precludes damage to the 
coils 31 and the coil leads by inadvertent tension forces applied to the 
cable 36. The clamp 38 could be in the form of an insert in the face 12a 
or a screw. 
For fixing the coils 31 in the recess 14, the recess 14 is filled with a 
magnetically transparent potting material 15, of epoxy or the like, which 
encases each of the coils and secures it in place. For further protecting 
the coils 31, the sensor shoe 10 is also provided with a thin metallic 
shim 40 of magnetically transparent material, such as stainless steel (see 
FIG. 3). The shim 40 is typically of a thickness in the range of 0.002 
inches (0.051 mm) to 0.02 inches (0.51 mm) and is of a configuration 
conforming to that of the base surface 12a over which it is superposed in 
flush engagement. The shim 40 is also provided with three pairs of 
elongate slots 41, 42, 44 which are respectively disposed in registry with 
the slot pairs 21, 22, 23 of the base member 12. 
Seated atop the flat surface of the shim 40 are a pair of elongate contact 
members 51 (see FIG. 4), each of triangular cross-section and provided 
with a flat surface 51a disposed in flush engagement with the surface of 
the shim 40 and a planar contact surface 51b angularly disposed and 
convergent therewith. Each of the contact members 51 is mounted on the 
shim 40 by three screws 60, the threaded shanks 61 of which extend through 
slots 41, 42, 43 of the shim 40 and slots 21, 22, 23 in the base member 12 
which are in registry therewith and disposed on the same side of the 
recess 14. As shown in FIG. 4, each of the contact members 51 is provided 
with threaded blind bores 64 for accommodating connection with the screws 
60 and each of the screws 60 is provided with a screw head 63 for clamping 
against the base member 12 on both sides of a slot 21, 22, or 23 in which 
it is disposed. By positioning the shank 61 of a screw 60 at a select 
location along the length of a slot 21, 22, or 23, a contact member 51 is 
adjustably mounted for movement in a transverse direction towards or away 
from the axis of the recess 14. 
As shown in FIG. 5, the contact members 51 are symmetrically positioned on 
opposite sides of the longitudinal axis of the recess 14 at equal 
distances from the center of the recess 14. The particular distance 
selected is chosen to provide an optimum configuration of the sensor shoe 
10 for use in inspecting a pipe of specific diameter. Preferably, the 
contact members 51 are of identical cross-section and similar 
configuration. The angle of convergence of the contact surface 51b with 
the bottom surface 51a is identical in each contact member and may be 
selected as desired. Typically, a large convergence angle requires a 
greater extension of the slots 21, 22, 23 and a wider base member 12. 
As seen in FIG. 5, which shows a sensor shoe 10 in operational engagement 
with a pipe 70 about which a magnetic field has been created, the contact 
members 51 are positioned to provide two parallel lines of contact between 
the sensor shoe 10 and the pipe 70 (indicated by the points 71,72) such 
that the shim 40 is closely adjacent the exterior surface 70a of the pipe 
70, typically 0.002 inches (0.057 mm) therefrom at the center line of the 
coils. Since the coils 31 are generally in abutting relation with the shim 
40, a very thin shim allows placement of the sensing coils in very close 
proximity to the surface of the pipe where it is possible to detection 
variations in magnetic flux caused by very small surface cracks with 
dimensions of a few thousandths of an inch. 
In a configuration of the sensor shoe 10, as shown in FIG. 5, the sensor 
coils 31 are shown spaced at an optimum sensing range from the pipe 70. 
However, with extensive use, the contact surface of the contact members 51 
(at points 70,71) can be worn down and the shim 40 could come to contact 
the pipe and become abraded by frictional contact as the sensor shoe 10 
moves relatively over the pipe in a magnetic inspection procedure. At this 
point of operation, replacement of the shim 40 and an adjustment of the 
contact members 51 to maintain optimum sensing range is therefore very 
desirable and is easy to accomplish. The shoe is reusable, only the shim 
and possibly the contact members 51 need be replaced. 
It is also to be noted that if the sensor shoe 10 of FIG. 5 is applied to a 
pipe of different diameter, the shim 40 and the sensing coils are likely 
to be at an inappropriate distance from the pipe for magnetic inspection 
purposes. In FIG. 6, the sensor shoe 10 is shown applied to a much larger 
diameter pipe 80. In order that the sensing coils in the recess 14 are in 
the optimum sensing range and the shim 40 spaced from the pipe surface by 
approximately 0.002 inches (0.051 mm), the contact members 51 are adjusted 
outwardly from the recess 14, establishing lines of contact 81, 82 with 
the pipe 80. 
It will therefore be seen that a new and improved sensor mounting shoe for 
magnetic pipe inspection apparatus is disclosed herein. The sensor shoe is 
provided with pipe contacting members which may be adjustably positioned 
for accommodating the use of the sensor shoe for inspecting pipes of 
different sizes and a wide range of diameters. In addition, the parts of 
the sensor shoe which are likely to be worn down by extensive use, such as 
the contact members 51 and the shim 40 may be readily replaced, thereby 
effecting considerable economies in the conduct of magnetic pipe 
inspection operations. To minimize wear, the contact members 51 are made 
of hard material, such as tungsten carbide or beryllium-copper alloy. 
It will therefore be seen that a new and improved sensor mounting shoe for 
application to the exterior surface of a pipe or tubular member of 
ferromagnetic material is disclosed herein. The shoe, which typically 
includes sensors for detecting variations in a magnetic field produced by 
direct or alternating current, can be readily adjusted for use with pipes 
or tubular members of a wide range of diameters. In addition, the parts 
thereof, which are normally disposed in contact with the pipe and are 
susceptible to wear with extensive use, and the protective shim, should it 
also become abraded, can be readily replaced. 
It is also to be understood that the foregoing description of a preferred 
embodiment of the invention has been presented for purposes of 
illustration and explanation and is not intended to limit the invention to 
the precise form disclosed. For example, the base member could have a 
configuration, other than rectangular cross-section, and it is not 
essential that the contact members have planar contact surfaces for making 
contact with the curved exterior of the pipe. It is only essential that 
the contact members be adjustable so that contact can be made which will 
accommodate pipes of different diameter while maintaining an optimum 
sensing range for the sensing coils and optimum spacing for the protective 
shim. 
It is to be appreciated therefore that various material and structural 
changes, many of which are suggested herein, may be made by those skilled 
in the art without departing from the spirit of the invention.