Magnetic testing device for internal surfaces of pipe using a magnetizing means and expandable magnetizable material within the pipe

A magnetic testing device is provided in which a magnetic recording tape or paper is wrapped around the outside of a tubular pressure member of elastomeric material which is disposed between two circular end plates which form pole portions of a yoke having a central core extending between the end plates and having a coil wound thereon with a copper shield being disposed around the outside of the coil. The device is disposed in a pipe or the like and compressed air is supplied to inflate the pressure member and press the magnetic tape paper into intimate contact with the interior surface of the pipe while an AC current is supplied to the coil to apply a magnetic field to the pipe and to record a magnetic field pattern on the magnetic tape or paper.

This invention relates to a magnetic testing device and more particularly 
to a device capable of inspecting internal surfaces of pipes or the like 
for defects. Testing can be performed readily and rapidly with the device 
and it is highly sensitive to provide indications which can be easily 
interpreted to provide accurate knowledge as to the character of the part 
tested. 
BACKGROUND OF THE PRIOR ART 
In prior proposed systems for the magnetic testing of parts for defects 
therein, difficulties have been experienced in testing of surface portions 
of a part which are irregular in contour or which are inside of a part to 
present difficulties with respect to access thereto. An example is drill 
pipe in which transverse fatigue cracks and corrosion pitting are 
oftentimes developed on the internal surface of the type especially in the 
end regions in which the pipe is formed with coupling portions to permit 
the end of one pipe section to be joined to the end of another. Prior art 
systems for testing of drill pipe and the like have been quite 
complicated, expensive, difficult to operate and not always reliable. 
Systems have been proposed for optical scanning which is not capable of 
detecting some types of serious defects, especially when the surface of 
the pipe is rusted or corroded. Systems have also been proposed using 
probes moved around on the inside of the pipe to scan the internal surface 
for defects, presenting problems especially with respect to obtaining the 
required scanning movement of the probe while maintaining the proper 
spacing relationship between the probe and the internal surface of the 
part. 
There also have been prior art systems using a magnetic tape or other 
magnetizable material placed in contact with the surface of a part. 
Generally such systems have been designed for the testing of external or 
otherwise readily accessible surfaces. However, in the De Forest U.S. Pat. 
No. 2,764,733 issued Sept. 25, 1956, there is a suggestion in FIG. 6 of 
placing a tube inside a pipe, the tube being of an elastomeric material 
such as rubber with magnetizable particles such as iron or iron oxide 
particles dispersed therein and being inflated by compressed air to 
contact the internal surface of the part. The manner of magnetizing the 
part is not specifically disclosed. 
SUMMARY OF THE INVENTION 
This invention was evolved with the general object of overcoming the 
disadvantages of prior art systems and of providing a device for detection 
of inhomogeneities in parts which can be readily applied to testing of 
surfaces which are irregular in contour and not readily accessible. 
Another object of the invention is to provide a device which is easy to 
operate and inexpensive to manufacture while providing an indication of 
inhomogeneities which can be readily and accurately interpreted. 
A specific object of the invention is to provide a device for ready and 
accurate inspection of the interior surfaces of drill pipe and similar 
parts. 
This invention is based, in part, upon the recognition of the problems 
involved with prior art systems and in the recognition that an arrangement 
similar to that shown in FIG. 6 of the aformentioned De Forest patent 
might be used for the testing of drill pipe or similar objects, with 
suitable additions thereto. An important feature of the invention is in 
the provision of a unitary device including a support structure which 
carries a pressure member to support the member with one surface of a 
flexible wall thereof opposite a surface portion of the part and with 
means for applying pressure against the opposite surface of the wall to 
press magnetizable material on the wall into intimate contact with the 
surface portion of the part. The support structure may also carry 
magnetizing means for developing a magnetic field in the surface portion 
of the part and to thereby develop in the magnetizable material localized 
magnetized portions corresponding to inhomogeneities in the portion of the 
part engaged thereby. 
With this arrangement, a unitary device is provided which can be readily 
positioned in proper relationship to a part to perfor the testing thereof. 
The magnetizable material, preferably separate from the pressure member, 
can be removed and magnetic particles can be dispersed thereon to develop 
a visible pattern corresponding to the recorded flux pattern. 
Alternatively, a magnetic recording paper may be used to directly develop 
a visible pattern corresponding to the flux pattern. In either case, a 
record is obtained which can be inspected for an accurate and readily 
interpretable indication of the character of the part, after which the 
flux pattern may be erased, if desired, to permit re-use of the material. 
Preferably and in accordance with a specific feature, compressed air or 
other pressurized fluid is used to press against the flexible wall of the 
pressure member to obtain the intimate contact between the magnetizable 
material and the surface of the part. 
In accordance with another important feature, the device is arranged for 
testing an internal generally cylindrical surface portion of a part such 
as an end section of drill pipe. The flexible wall of the pressure member 
is preferably of tubular form and the support structure is adapted for 
insertion within the part to position the pressure member within the outer 
surface thereof opposite the generally cylindrical surface portion of the 
part to be tested. 
In accordance with another feature, the magnetizing means includes a yoke 
of magnetic material having opposite pole portions positioned in proximity 
to spaced internal surface portions of the part on opposite sides of the 
surface portions engageable by the magnetic material, and a core portion 
is provided extending axially between the pole portions with a magnetizing 
coil wound thereon. 
Another feature is in the provision of a generally cylindrical shield of 
conductive metal surrounding the magnetizing coil and extending between 
the pole portions. 
A further feature is that in the alternative, or in addition, the 
magnetizing means includes a coil around the outside of the member tested, 
energized from a DC source.

This invention contemplates other objects, advantages and features which 
will become more fully apparent from the following detailed description 
taken in conjunction with the accompanying drawings. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 is a side elevational view of a device constructed in accordance 
with the invention, auxiliary equipment being shown diagrammatically; 
FIG. 2 is a longitudinal sectional view of the device of FIG. 1, also 
showing the device in operation, positioned within an end portion of a 
section of drill pipe; and 
FIG. 3 is a sectional view taken substantially along line IIII--III of FIG. 
2. 
DESCRIPTION OF A PREFERRED EMBODIMENT 
Reference numeral 10 generally designates a testing device constructed in 
accordance with the principles of this invention. The device 10 is 
arranged to be disposed within a part to be tested such as an end portion 
of a section of drill pipe and includes a pair of circular end plates 11 
and 12 which form pole portions of a yoke structure as hereinafter 
described with a handle 13 being connected to the end plate 12 through a 
rigid rod 14, the end of rod 14 being threaded into the end plate 12 or 
otherwise secured thereto. A cable 15 projects from the end plate 12 for 
connection to an AC source 16 and a tubular fitting 17 projecting from the 
end plate 12 is arranged for connection through a flexible tubing 18 to a 
valve 19 which is connected to a compressed air source 20, as 
diagrammatically illustrated. 
A pressure member in the form of a sleeve 22 is provided having opposite 
ends sealingly secured to reduced-diameter portions of the end plates 11 
and 12 by clamps 23 and 24. The member 22 is of an elastomeric material 
providing a flexible generally cylindrical wall. 
In operation, a sheet of magnetizable tape or paper is wrapped around the 
outside of the member 22 and may be loosely held thereon by rubber bands 
or the like. Then the device is inserted into the end of a part to be 
tested, and the valve 19 is opened to supply compressed air into a space 
within the member 22 which is then inflated to press the magnetizable 
material into intimate contact with an internal surface portion of the 
pipe. Then a magnetizing current is applied from the source 16 and a 
magnetic field is developed extending longitudinally through the pipe 
between the end plate 11 and 12. As a result, a magnetic flux pattern is 
produced in the magnetizable material, which corresponds to the character 
of the internal surface portion of the pipe. Any cracks or other 
inhomogeneities will produce strongly magnetized localized portions. Then 
after cutting off the supply of current from the source 16, the valve 19 
is moved to a position to release the pressure within the member 22 and 
the device is removed from the pipe. The magnetizable material is then 
removed and magnetic particles may be dispersed thereon to make the flux 
pattern visible or if the material is in the form of a magnetic recording 
paper, the pattern may be immediately viewed. It will be appreciated that 
the inspection can be performed quite easily and quite rapidly and a 
highly accurate indication of the character of the part is obtained. 
Referring to FIG. 2, the end plates 11 and 12 include reduced diameter 
portions 25 and 26 to which the ends of the member 22 are secured by the 
clamps 23 and 24 and may further include sockets 27 and 28 which receive 
the opposite ends of a central magnetic core structure 30. A coil 31 is 
wound on the core structure 30 and is connected through the cable 15 to 
the AC source 16. A split tube 32 of highly conductive metal, preferably 
copper, is disposed around the coil 31 between the end plates 11 and 12, 
in order to contain the magnetic flux lines and to minimize magnetic 
bridging. The provision of the tube 32 greatly increases the length of the 
section in which good inspection results are obtained. 
The device is shown in FIG. 2 in an operative condition disposed within an 
end portion of a drill pipe section 34, which includes an externally 
threaded portion 35, an enlarged outside diameter portion 36 and a portion 
37 between the portion 36 and a main portion 38 of the pipe section 34. 
The portions 34, 36 and 37 have the same internal diameter which is less 
than that of the main portion 38. The region depicted and a similar region 
at the opposite end of the pipe section are termed the "up-set" end 
regions of the drill pipe and it is in these regions that pipe failures 
occur. Stress reversals are a routine factor while drilling and the 
highest stress reversals are apparently localized near the up-set regions. 
As shown, when compressed air is supplied into the space within the member 
22, it is inflated to press a magnetizable member 40 thereon into intimate 
contact with the facing internal surface portions of the pipe section 34. 
It is noted that because of the flexibility of the member 22, the device 
can accommodate irregular contours in the surface which it engages. 
When current is applied to the magnetizing coil 31, magnetic flux passes 
from one of the end plates 11 and 12 to the other and longitudinally 
through the portion of the pipe in which the device is disposed. A flux 
pattern is thereby recorded by the magnetizable material corresponding to 
the character of the internal surface portion of the pipe. 
A practical construction for the central core 30 is illustrated in the 
cross-sectional view of FIG. 3. A tube 42 is provided which may be of an 
insulating material and a stack of rectangular laminations 43 is disposed 
within the tube 42 with small rods 44 being inserted to fill in the spaces 
between the outer faces of the stack of laminations 43 and the internal 
cylindrical surface of the tube 42. Other core constructions might be used 
but a construction similar to that illustrated is preferred. It produces 
results superior to those obtained with a solid core or a core consisting 
of rods only. 
Excellent results can be obtained with a device constructed in accordance 
with the invention. For example, a device has been tested having a 
construction as shown in the drawings with an overall length of 213/8 
inches from the outer face of one end plate to the outer end face of the 
other, the components having substantially the same proportionate 
dimensions as shown in the drawing. The end plates 11 and 12 were of hot 
rolled steel. The core included 0.023 inches by 1 inch by 20 inch 
laminations 43, rods 44 having a diameter of 1/16 inches and a length of 
20 inches, disposed in a tube having an internal diameter of 1.407 inches 
and an external diameter of 1.876 inches, also with a length of 20 inches. 
The coil consisted of 620 turns in two layers of No. 16 copper wire. 
Excellent results were obtained using alternating current excitation such 
as to provide 5500 ampere turns. Slots milled into the internal surface of 
the pipe for test purposes and having a depth of 0.02 inches produced 
strong indications on a magnetic tape material and comparable results can 
be obtained on a magnetic paper material. 
The provision of the conductive tube or shield 32 is important. Without the 
shield, good inspection results were confined to approximately plus or 
minus 3 inches each side of the core center. With the addition of the 
copper shield, good inspection coverage was extended to within 2 inches 
from either of the end plates. 
Close fitting between the end plates and the internal pipe surfaces does 
not appear to be critical. Good inspection results were obtained using 
gaps as large as 0.25 inches. If desired, ring collars can be slipped over 
the end plates to accommodate pipe having a larger internal diameter. 
The alternating current excitation with the magnetizing means on the inside 
of the pipe results in a concentration of the magnetic flux in the 
internal surface of the pipe and is preferable, especially when the pipe 
has a relatively thick wall. It is possible, however, to use DC excitation 
of the coil 31 or a combination of DC and AC excitation. In addition, a 
coil 45 may be placed around the pipe, as shown in FIGS. 2 and 3, coil 45 
being connected to a DC source 46. Coil 45 may be connected to the handle 
13 through a rod 47 to be moved with the assembly, it being important that 
the coil extend for at least the full length of the portion of the pipe 
with which the magnetizable material is engaged. 
The coil 45 is especially advantageous in the testing of thin-walled 
members and in devices especially designed for such purpose, the internal 
coil 31 and associated core 30 and shield 32 may be eliminated it being 
then only necessary to provide supporting structure for the member 22. 
It will be understood that modifications and variations may be effected 
without departing from the spirit and scope of the novel concepts of this 
invention.