GB2035571A - Improvements in flaw detection - Google Patents

Abstract

A coreless flaw detection head 1, for detecting a flaw or flaws which may be present on the inner surface of a non-magnetic metal pipe and variation in the wall thickness of the pipe, comprises a cylindrical main body 2 having first annular grooves 5 adjacent to one end and a second annular groove 7 adjacent to the other end. Differential system detection coils 6 are received in said first annular grooves 5, and an absolute value system detection coil 8 in the second annular groove 7. A sheath 4 surrounds a substantial portion of the length of said main body 2 and a substantially hollow cylindrical cover member 3 is provided at said other end of the main body 2, protection rings 16, 18 being provided on said one end of the main body 2 and on the end of said cover member 3 opposite to said main body 2. <IMAGE>

Description

SPECIFICATION Improvements in flaw detection This invention relates to a coreless flaw detection head for detecting a flaw or flaws which may be present on the inner surface of a non-magnetic metal pipe of small diameter and concerns a coreless flaw detection head for detecting a flaw or flaws which may be present on the inner surface of a nonmagnetic metal pipe of small diameter such as 20-25 mm, for example, by the impedance metal flaw detection method whereby two different types of flaw wave forms are simultaneously indicated and recorded for comparison.

The prior art coreless flaw detection heads of the type referred to above are generally designed to perform detection by the differential system and the absolute value system.

The former type detection system is designed to numerically detect a flaw of flaws on the inner surface of a non-magnetic metal pipe and indicate the sum of the detection results. However, the differential type detection system has the disadvantage that the system is applicable to detect only flaws positioned adjacent to each other and flaws having shallow depths and large areas which may be present on the inner surface of a metal pipe, but not to the detection of variation in the wall thickness of the pipe. Furthermore, this type of detection system requires a difficult discrimination procedure in detecting flaws on the pipe such as those due to ammonia attack or inlet attack.The latter or absolute value type flaw detection system has excellent electromagnetic wave permeability and exhibits satisfactory detection characteristic in detecting variation in the wall thickness of a pipe to be detected, but can not finely detect a flaw or flaws which may be present on the inner surface of the pipe.

Any of the prior art flaw detection heads for nonmagnetic metal pipes is designed to perform the two different flaw detection procedures by switching the electrical circuit of a probe coil and therefore, requires to perform the detection operation two times. Thus, the prior art flaw detection head referred to above has the disadvantages that the flaw detection takes rather much time and labor and the detection results obtained by the differential and absolute value detection systems frequently do not coincide with each other.

Therefore, the purpose of the present invention is to provide a coreless flaw detection head which incorporates the differential and absolute value detection systems therein in such a manner that two different detection results by the two different detection systems are simultaneously indicated and recorded by two different types of wave forms representing a flaw or flaws present on the inner surface of a non-magnetic metal pipe and variation in the wall thickness of the pipe, respectively, for comparison.

In order to attain the purpose, according to the present invention, the outer surface of the solid cylindrical main body of the coreless detection head is provided adjacent to one end thereof with two longitudinally spaced annular grooves and two differential system detection coils are received in the annular grooves for detecting flaws having small sizes and/or shallow depths and large areas which may present on the inner surface of a non-magnetic metal pipe which is to be detected. The outer surface of the solid cylindrical main body is further provided adjacent to the other end thereof with a single annular groove and an absolute value system detection coil is received in the single annular groove for detecting variation in the wall thickness of the nonmagnetic metal pipe.A sheath formed of a material having a hardness higher than that of the material of which the main body is formed surrounds a substantial portion of the length of the main body and inter nallythreaded stainless rings are screwed on the externally threaded opposite ends of the main body.

By the use of the flaw detection head of the invention, the detection results obtained by both the differential and absolute value detection systems are simultaneously indicated and recorded on recording means in vertically aligned positions for comparison whereby the provision of a rather large number of parts or components and troublesome operation such as that to be performed by a shift switch as required in the prior art coreless flaw detection heads can be eliminated. Furthermore,the hard sheath which surrounds a substantial portion of the length of the cylindrical main body protects the detection coils against possible wear and damage to ensure a long service life of the detection coils.In addition, the stainless steel rings screwed on the opposite ends of the main body protects the main body against possible wear and damage to ensure a long service life of the main body.

The present invention will be more readily apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawings which show one preferred embodiment of the invention for illustration purpose only, but not for limiting the scope of the same in any way.

Fig. lisa side elevational view of the preferred embodiment of the coreless pipe flaw detection head of the present invention; Fig. 2 is a longitudinally sectional view of said pipe flaw detection head as shown in Fig. 1; Fig. 3 is a partially exploded perspective view of said pipe flaw detection head as shown in Fig. 1 with the sheath thereof removed therefrom; Fig. 4 is a perfectly exploded perspective view of said pipe flaw detection head as shown in Fig. 1; Fig. 5 is a cross-sectional view taken along substantially the line A-A of Fig. 2; Fig. 6 is a cross-sectional view taken along subs tantiallythe line B-B of Fig. 2;; Fig. 7 is a longitudinally sectional view on a reduced scale of said pipe flaw detection head as shown in Fig. 1 showing the head as being electrically connected to a standard for the so-called absolute value detection; and Figs. 8A and 8B are charts showing the results of detection by said pipe flaw detection head.

The present invention will be now described referring to the accompanying drawings and more par ticularly, to Figs. 1 through 7 in which one preferred embodiment of the pipe flaw detection head cons tructed in accordance with the present invention is shown. The pipe flaw detection head is generally shown with reference numeral 1 and generally com prises a solid cylindrical main body 2 formed of a suitable electrically insulative material such as synthetic resin, a substantially hollow cylindrical cover member 3 in threaded engagement with the main body and formed of the same material as the latter and a sheath 4 surrounding a substantial por tion of the length of the main body 2 and formed of a synthetic resin having a hardness higher than that of the material of the main body and cover member.

The main body 2 is reduced in diameter at the oppo site ends 9, 9a which are externally threaded and the cover member 3 has a stepped bore 10 including a larger diameter bore portion which is internally threaded for threaded engagement with one or the inner reduced diameter end 9 of the main body 2 and a smaller diameter bore portion. The outer end of the cover member 3 is reduced in diameter and externally threaded for the purpose to be described hereinafter.

The main body 2 is provided adjacent to the reduced diameter leading end 9a with two longitudinally spaced annular recesses 5, 5 in which differential system detection coils 6, 6 are received for detecting pipe flaws of shallow depths and large areas. The main body 2 is also provided adjacent to the reduced diameter rear end 9 with an annular recess 7 in which an absolute value system detection coil 8 is received for detecting variation in the wall thickness of a non-magnetic metal pipe to be detected for its flaw or flaws and variation in the pipe wall thickness.

A plurality of cord anchoring pins 13 (five anchoring pins in the illustrated embodiment) project from the rear end face of the main body inner end 9 and each of the five cores or lead wires 12 of a five-core electrical cord 11 extending through the stepped bore 10 in the cover member is soldered at one end to the corresponding anchoring pin 13. Three of the five lead wires 12 are electrically connected to the differential system detection coils 6, 6 and the remaining two leads wires are electrically connected to the absolute value system detection coil 8. One leading wire in each of the two groups of lead wires 12 associated with the differential system detection coils 6, 6 and absolute value system detection coils 8, 8, respectively, serves as the earth line.In Fig. 7, the earth lines are shown with refference numeral 24 and the remaining lead wires are shown with reference numeral 28, respectively. The cover member 3 is provided with a plurality of through threaded bores 14 extending radially to communicate with the smal ler diameter bore portion in the cover member 3 (fourthreaded bores are provided in an equally cir cumferentially spaced relationship in the illustrated embodiment) and set screws 15 are screwed in the respectively corresponding threaded bores 14to hold the five-core electrical cord 11 in position.

As more clearly shown in Fig. 4, an internally threaded first or leading ring 16 is in threaded engagementwiththethreaded leading end 9a of the main body 2 and a similarly threaded second or rear ring 18 is in threaded engagement with the reduced diameter threaded outer end 21 of the cover member 3. The first and second rings 16 and 18 are formed of a wear-resistance material such as stainless steel Referring again to Fig. 7, a standard 25 for the absolute value detection system is electrically con nected to the absolute value detection coil 8 through thelead wire 28 and earth line 24 associated with the coil and-a calibration coil 27 is wound about the reduced diameter portion of the standard 25. A control pipe 26 is disposed about the standard 25 surrounding the reference or calibration coil 27.The control pipe 26 is identical with a metal pipe (not shown) which is to be detected for its flaws and variation in the wall thickness, but free of defects such as flaws and/or variation in the wall thickness. Any variation in the wall thickness of the metal pipe to be detected for its flaws and variation in the wall thickness is detected by comparing electromagnetic waves provided by the reference or calibration coil 27 with electromagnetic waves provided by the lead wire 28 associated with the absolute value detection system coil 8.

The operation of the flaw detection head of the present invention will be now described. The flaw detection head is inserted into a non-magnetic pipe the inner surface of which is to be detected for flaws and variation in the wall thickness at one end of the pipe and moved along the pipe inner surface to the other end of the pipe. When the detection head has reached the other end of the pipe, a measuring and recording device (not shown) electrically connected to the detection head through the five-core cord 11 and a bridge circuit (not shown) is actuated to energize the differential and absolute value detection coil systems and the detection head is then moved back along the pipe inner surface towards the firstmentioned end of the pipe.When A.C. electromagnetic waves generated by the differential detection system coils 6, 6 and/or electromagnetic waves generated by the absolute value detection system coil 8 encounter or detect flaws on the inner surface and/or variation in the wall thickness of the pipe, the electromagnetic waves provide impedances which vary depending upon the shape and size of the flaws and/or the amount of variation in the wall thickness and which are indicated and recorded on the recording device which is connected to the cord 11 through the bridge circuit to thereby provide positive detection results representing the defects on the pipe such asflaws and/or variation in the wall thickness.

Figs. 8A and 8B are charts on which the wave forms representing the detection results obtained by the differential and absolute value detection systems are plotted. Fig. 8A shows the wave forms of the absolute valuedetection system deflecting in one direction with respect to the reference line and Fig.

8B showsthewaveforms of the differential detection system deflecting in the opposite directions with respect to the reference line.

As mentioned hereinabove, according to the coreless detection head of the present invention, both the differential detection system in which wave forms deflecting in the opposite directions with res peck to the reference line are provided and the abso lute value detection system in which wave forms def lecting in one direction with respect to the reference line are provided are incorporated in one coreless detection head to thereby make it possible to simultaneously detect a flaw or flaws on the inner surface of a non-magnetic metal pipe and variation in the wall thickness of the pipe by passing the detection head through the pipe to be detected once.Therefore, the present invention provides practical and excellent effects that detail adjacent small size flaws, flaws of shallow depths and large areas on the inner surface of the pipe to be detected and defects within the material of the pipe as well as variation in the wall thickness of the pipe can be positively and simultaneously detected and recorded.

Since the coreless detection coils are employed in the detection head, the detection head is highly responsive to a reaction from a pipe to be detected for flaws on the inner surface thereof and/or variation in the wall thickness of the pipe and in despite of the fact that both the differential and absolute value detection systems are incorporated in the single detection head, there will be no mutual interference between the actions of the two systems.

Since the outer surface of the cylindrical main body is provided adjacent to one end with two longitudinally spaced annular grooves and differential detection system coils are received in the annular grooves for detecting small size flaws and flaws having shallow depths and large areas, the detection head is quite responsive to the presence of defects on the inner surface of a pipe to be detected to thereby detect even small flaws of pitching shape.

Electromagnetic waves generated from one of the absolute value system coils are caused to permeate into the material of a non-magnetic metal pipe to be detected to thereby precisely detect variation in the wall thickness of the pipe.

Furthermore, since the hard synthetic resin sheath is placed on the cylindrical main body to cover the detection coils wound about the main body, the sheath can positively hold the coils under stabilized conditions to thereby substantially improve the sensitivity of the detection head in response to any defect on the inner surface of a non-magnetic metal pipe.As compared with the prior art detection head having detection coils wound aboutthe main body of the head which are not covered by any cover member such as a sheath and easily subjected to wear and damage as the detection head is passed through the interior of a non-magnetic metal pipe to be detected for flaws on the inner surface thereof and variation in the wall thickness thereof, the detection head of the invention having the detection coils wound about the main body are protected by the sheath against possible wear and damage and not subjected to wear and damage as the detection head is passed through the interior of such pipe whereby the detection head can enjoy a long service life.

Furthermore, since the stainless steel rings are placed on the opposite ends thereof, the detection head can be positively protected against possible wear and. damage at the ends to thereby ensure a long service life to the detection head.

While only one embodiment of the invention has been shown and described in detail, it will be understood that the same is for illustration purpose only and not to be taken as a definition of the invention, reference being had for this purpose to the appended claims.

Claims (10)

1. A coreless flaw detection head for detecting flaws on the inner surface of a non-magnetic metal pipe and variation in the wall thickness of said pipe, comprising an electrically insulative solid cylindrical main body having the reduced diameter opposite ends, first longitudinally spaced annular grooves near or adjacent to one of said opposite ends and a second annular groove near or adjacent to the other end; differential system detection coils received in said first annular grooves; and absolute value system detection coil received in said second annular groove; a substantially hollow electrically insulative cylindrical cover member on the other end of said main body and reduced in diameter and externally threaded at the end opposite to the other end of the main body; a five-core electric cord extending axially through said cover member and electrically connected to said differential and absolute value system detection coils; and an outer sheath surrounding a substantial portion of the length of said main body to protect said detection coils against wear and damage.

2. A coreless flaw detection head as set forth in Claim 1, in which said main body and cover member are formed of the same synthetic resin and said outer sheath is formed of a synthetic resin having a hardness higher than that of the synthetic resin of the main body and cover member.

3. A coreless flaw detection head as set forth in Claims 1 or 2, in which said reduced diameter opposite ends of the main body are externally threaded and the interior of said cover member is threaded at the end opposite to said reduced diameter end for threaded engagement with said externally threaded other end of the main body.

4. A coreless flaw detection head as set forth in Claim 3, in which a first protection ring is screwed on the reduced diameter and threaded end of said main body opposite to said cover member and a second protection ring is screwed on said reduced diameter and externally threaded end of the cover member.

5. A coreless flaw detection head as set forth in any one of the preceding Claims, in which three of the five lead wires of said electric cord are electrically connected to said differential system detection coils and the remaining two lead wires of the electric cord are electrically connected to said absolute value system detection coil.

6. A coreless flaw detection head as set forth in Claim 5, in which one of said lead wires associated with said differential system detection coils is an earth line and one of said lead wires associated with said absolute value system detection coils is an earth line.

7. A coreless flaw detection head as set forth in any one of the preceding Claims, in which a plurality of radially extending threaded bores are formed in said cover member to communicate with the interior or the cover member and a corresponding number of set screws are screwed in said radially extending threaded bores to hold said electric cord in position.

8. A coreless flaw detection head as set forth in Claim 4, or any one of Claims 5 to 7 as dependent upon Claim 4 in which said first and second protection rings are formed of stainless steel.

9. A coreless flaw detection head substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. The features as herein disclosed, or their equivalents, in any novel selection.