EP1877767A2

EP1877767A2 - Near fieldtm and combination near fieldtm - remote field electromagnetic testing (et) probes for inspecting ferromagnetic pipes and tubes such as those used in heat exchangers

Info

Publication number: EP1877767A2
Application number: EP06758357A
Authority: EP
Inventors: Henry Moncrieff O'connor
Original assignee: Individual
Current assignee: Individual
Priority date: 2005-04-14
Filing date: 2006-04-14
Publication date: 2008-01-16
Also published as: WO2006113504A3; WO2006113504A2

Abstract

Ferromagnetic pipes and tubes are inspected for flaws by inserting probes having a near field sensor comprising at least one send coil (50) and at least one receive coil (52) which are located directly adjacent one another. According to various configurations, the send and receive coils (50,52) are of the same or different diameters or are positioned axially adjacent one another. Configurations of the near field sensor include arrangements wherein there are pluralities of send coils (50) as well as pluralities of receive coils (52). The near field sensor is in one embodiment in combination with remote field sensor coils and in another embodiment in combination with a remote field sensor and a remote field receive coil.

Description

NEAR FIELDTM AND COMBINATION NEAR FIELD_TM - REMOTE FIELD ELECTROMAGNETIC TESTING (ET) PROBES FOR INSPECTING FERROMAGNETIC PIPES AND TUBES SUCH AS THOSE USED IN HEAT EXCHANGERS

Related Application:

This application claims priority from United States Provisional Application No.

60/671,106, filed April 14, 2005, incorporated herein its entirety.

Background of the Invention:

Three techniques are used for detecting defects in ferromagnetic heat exchanger tubes on the inside surface as well as the outside surface of a tube.

With the flux leakage method, a permanent magnet, electro magnet, or both, are used

in the probe to apply a magnetic field to the tube as the probe is passed through the tube. If

there are no flaws in the tube, the flux field is constant. Variations in the flux field as the probe travels through the tube are taken to be flaws, support structure, or both. No alternating

magnetic field is applied to the test object with this method.

. Partial saturation eddy current testing of magnetic heat exchanger tubes is carried out

by applying a strong, magnetic field, usually using a permanent magnet to the tube. This field magnetically saturates or almost magnetically saturates the material, reducing its permeability

close to 1, enabling eddy current testing very similar to testing a non-magnetic tube.

Remote Field Eddy current Testing (RFET) has separate send and receive coils in the

probe, spaced a significant distance apart, approximately 2-1/2 to 3 tube diameters. An alternately electromagnetic field is developed in the send coil by energizing it with an AJC

current. The field travels outside of the tube wall some distance down the tube towards the

send coils, where the field re-enters the tube. The receive signals are processed much like that in a regular eddy current application to inspect non-magnetic tubes and defects are detected

and measured in a similar way.

AU three of these techniques have the disadvantage high sensitivity (i.e., large signals

are generated) to support structures, such as baffle plates, support plates, and tube sheets. In partial saturation and flux leakage measurements, this external magnetic structure significantly

changes the magnetic field, resulting in large signals. For RFET techniques, support structure blocks the flux that travels from the send to the receive coils on the outside of the tube. As a

result, all of these three methods have significantly reduced defect signals and signals that are

very difficult to analyze at support structure. Many types of defects occur at the support structure, due to the support structure, so this is a very important inspection site.

RFET and flux leakage techniques are unable to distinguish between inside and outside defects.

In both the partial saturation and magnetic flux leakage methods the strong magnetic fields applied to the tube result in the probes sticking to the tube, increasing significantly the

force required to push the probe down the tube, and causing the probe to wear out quickly.

RFET results in more than one response from small defects. There is a response when

the probes send coils pass a defect, and a separate response, when the probes receive coils pass a defect. This complicates analysis. RPET further suffers from significantly different signals from long defects and short

defects. If the defect is long enough that both the send and the receive coils are under the

defect simultaneously, then the signal amplitude and angle, both of which are used to measure the defect, are significantly altered. This adds complexity to analysis of RPET signals.

Summary of the Invention:

A near field sensor assembly for inspecting ferromagnetic metal tubes for flaws comprises a probe for insertion of the near field sensor into a metal tube. The probe has near field sensors

having at least one send coil and at least one receive coil, wherein the coils are located directly

adjacent to one another.

In other aspects of the invention, there are pluralities of send coils and receive coils in

close proximity to one another.

In still a further aspect of the invention, near field sensors are in combination with remote

field send coils and remote field receiving coil(s).

Brief Description of the Drawings:

Various other features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood when considered in conjunction with the

accompanying drawings, in which like reference characters designate the same or similar parts

throughout the several views, and wherein:

Fig 1 is a schematic view of prior art eddy current testing arrangement over which the present inventor is an improvement. Fig. 2A-2D are elevations of send and receive coils in perspective, configured in

accordance with a first example of the present invention;

Fig. 3A-3D are elevations of send and receive coils in perspective, configured in

accordance with a second example of the present invention;

Figs 4A-4D are elevations of send and receive coils, in perspective, configured in accordance with a third example of the present invention;

Figs. 5A-5D are elevations of send and receive coils, in perspective, according to a fourth

example of the invention;

Figs . 6 A-6F are side elevations of send and receive coils in perspective according to a fifth example of the present invention;

Fig. V is a perspective view of a first alternate configuration for the receive coils of Figs. 1 -

6;

Fig. 8 is a perspective view of a second alternate configuration for the receive coils of Figs. 1-6;

Fig. 9 is a perspective view of a combination of a near field sensor and a pair of remote field send coils using the near field sensors of Figs. 2-7, and

Fig. 10 is a perspective view of a combination near field-remote field sensor with shared send coils using the near field sensor of Figs. 2-7.

Detailed Description:

Referring now to Fig. 1, there is shown schematic of a basic prior art arrangement for testing a ferromagnetic alloy tube 10 to detect in the wall 11 thereof anomalies such as

through-holes 12, interior pits 14, exterior pits 16 and dents 18 using the aforementioned RFET technique. Also illustrated is an inclusion or deposit 20 and an outside circular groove

21 superimposed on an inside circular groove 22 indicative of an anomaly formed by a roll stop. These last two anomalies are, in almost all instances, harmless. Differentiating of these

anomalies and of harmful defects is of utmost importance in ensuring the integrity of ferromagnetic tubes 10, which may be used, for example, as the heat exchanger tubes in

nuclear power plants, such tubes typically have an outside diameter in a range of about lcm to about 10cm and an inside diameter.

A typical arrangement for detecting the presence of the anomalies 12-22 the tube 10

utilizes a probe 25. The probe 25 is a cylindrical device comprising a cylindrical housing 26

having therein send coil 29 and receiving coils 30. The send coils 29 are spaced a distance from the receive coil of 21/2 to 3 diameters of the tube 10. As the probe 25 is advanced through the tube 10 with the excitation or send coils 29 generating eddy currents in the wall of

the tube 11, the receiving coils 30 detect the voltage and phase of the eddy current fields induced in the wall 11 of the tube 10.

If the arrangement for displaying the data from the probe 25 is similar to that of U.S.

Patent Application No. 09/740,042, then a cable 32 connects the probe 25 to an eddy current testing circuit 34 which includes an oscillator 35 which connected via the cable 32 to the

excitation coil 29 to apply sine wave (or other wave shape) signals 36 to the excitation coil.

The receiving coils 30a and 30b detect the voltage and phase of the eddy current in the wall 11 of the tube 10 and transmits via the cable 32 the voltage and phase of the eddy current in the

form of an analog sinusoidal signal 37 to an eddy current detection circuit 38. Basically, the

eddy current detection circuit 38 converts the sinusoidal signals 37 to lissajous waveforms 39 which are displayed on a display 40. In current day eddy current instruments, it is more common that two or more oscillators (often four) generate two or more simultaneous sine (or other wave shape) waves, which are applied simultaneously to the excitation coil. The

receiving coils 30a and 30b detect the voltage and phase of all of these signals, and the eddy

current detection circuit 38 convert each original signal into two time variant signals, which are each displayed as lissajous wave forms. Another form of the multi-frequency eddy current

instruments emulates multiple, simultaneous sine (or other shape wave) form by rapidly switching the frequency of an oscillator in time. This is referred to as a multi-frequency eddy

current instrument that uses time domain multiplexing. The display 40 is either a cathode ray tube or, preferably the monitor of a computer which has the display capabilities of a cathode

ray tube.

The current invention set forth in Figs. 2-10 is similar to RFET in that there are both

send coils 50 and receive coils 52; however, unlike RFET, the send coils are placed very close to or directly adjacent to the receive coils. There may be a very narrow separation but that

separation is only to facilitate manufacture and is only measurable in hundredths of an inch.

The separation is so small, the coils may touch and is orders of magnitude less than the 21/2 to 3 diameters of tube 10 of current RFET arrangements. The send coils 50 send an alternating

magnetic flux through the tube wall 11 of Fig. 1. The signal comes back to the receive coils

52 without having to travel outside of the tube 10. As a result, the support structure has very

little influence on the test result. It makes no difference whether the defects 12, 14, 16, 18 and 20-22 are long or short. Moreover, there is only one signal response to a defect when the group of send and receive coils 50 and 52 pass the defect.

With reference to Fig. 2A-2D, a coil portion 45 of Near Fieldi_M sensor is shown which has several alternate configurations. In first configuration, a send coil 50 is placed between two receive coils 52 (Fig. 2A); in a second configuration, a receive coil 52 is placed between

two send coils 50 (Fig. 2B); in a third configuration, two receive coils 52 are placed between

two send coils 50 (Fig. 2C) and, in a fourth configuration, send coils 50 are separated by receive coils 52 (Fig. 2D). In each configuration, the send coil or coils 50 are axially proximate the receive coils 52 with the send and receive coils having substantially the same

diameter.

With reference to Figure 3A-3B, a coil portion 45' of a Near Field_TM sensor has several alternative configurations, a send coil 50 is placed outside of one receive coil 52 (Fig. 3A); in

a second configuration, a send coil 50 is placed outside of two receive coils 52 (Fig. 3B); in a third configuration, a receive coil 52 is placed outside of a send coil 50 (Fig. 3C), and in a

fourth configuration, a pair of axially spaced receive coils 52 are placed around send coil 50 (Fig. 3D). In each configuration there are send and receive coils 50 and 52 of different diameters.

With reference to Figs. 4A-4D, a coil portion 45" of a Near Fieldt_M sensor is shown which has several alternative configurations. In a first configuration, send coils 50 are placed

on either side of a receive coil 52 and inside of the receive coil (Fig. 4A); in a second configuration, a send coil 50 is placed between two receive coils 52 and an additional send

coil 50 is placed inside of the receive coils 52 (Fig. 4B); in a third configuration, send coils 50

are placed on either side of a pair of receive coils 52 and an additional send coil 50 is placed

inside of the receive coils 52 (Fig. 4C), and in a fourth configuration, two receive coils 52 are placed between three send coils 50 and an additional send coil is placed inside of the receive coils 52 (Fig. 4D). Figs. 5A-5D, include all of the configurations of Figs. 4A-4D except that in each Fig.

additional send coils 50 are placed outside of and around the receive coils 52.

Figs. 6A-6F, include all of the configurations of Figs 5A-5D except that in each Fig. an additional send coil 50 is placed inside of the receive coils 52.

With reference to Figs. 7 and 8, a Near Fieldi_M probe 60 is provided with the configurations listed in Figs. 2A-2D through Fig. 6A-6F in which the receive coil or coils 52 are configured with multiple receive coils 52 A in which the axis 61 of each receive coil 52 is

parallel to (Fig. 7) or coils 52B perpendicular to (Fig. 8) the axis 13 of the tube 11.

With reference to Fig. 9, a combination Near Fieldi_M Remote Field probe 70 is shown with shared receive coils 52 which would be any of the configurations of Figs. 2-8, except that

one or two additional send coils 5OA and 5OB are placed in front of and/or after the Near

FieldτM configuration of coils, and spaced a distance 72 and 74 from the Near FieldxM receive coils 52 so as to be appropriate for RFET.

With reference to Figure 10, a combination Near Field_tM Remote Field portion of a sensor 80 is shown, with shared send coils 50 which would be any of the configurations of

Figs. 2-8, except that one or two remote field receive coils 82 are placed in front of and/or

after the Near Fieldi_M configuration of coils 80, and spaced a distance from the Near Fieldj_M coils 50 so as to be appropriate for RFET.

Claims

I Claim:

1. In a near field sensor assembly for inspecting ferromagnetic metal tubes for flaws, the

probe assembly comprising:

a probe for insertion of the near field sensor into the metal tube, the probe having near field sensors having at least one send coil and at least one receive coil, wherein the coils are located directly adjacent to one another.

2. The near field sensor of claim 1 wherein the send and receive coils are in direct abutment with one another.

3. The near field sensor of claim 1 wherein the send coil and receive coil are of substantially the same diameter.

4. The near field sensor of claim 3 wherein there are a plurality of send coils with at least one receive coil therebetween.

5. The near field sensor of claim 3 wherein there are a plurality of receive coils and at least one send coil therebetween.

6. The near field sensor of claim 1 wherein the at least one send coil has a different diameter

than the at least one receive coil and wherein the send and receive coils are directly adjacent one another in a radial direction.

7. The near field sensor of claim 6 wherein the send coil has an axial length greater than the

receive coil.

8. The near field sensor of claim 7 wherein there is more than one receive coil, the receive

coils being axial spaced from one another and disposed radially adjacent the send coil.

9. The near field sensor of claim 8 wherein there are send coils of a smaller diameter and send coils of a larger diameter juxtaposed radially with respect to one another and wherein there

are receive coils of disposed around the send coils of a smaller diameter, the receive coils of the

larger diameter being disposed adjacent to the send coils of smaller diameter.

10. The near field sensor of claim 8 wherein there are send coils of still a larger diameter disposed around the receive coils and smaller diameter send coils.

11. The near field sensor of claim 1 in further combination with at least one remote field send coil in spaced relation with the near field sensor.

12. The near field sensor of claim 11 wherein the near field sensor is disposed between two remote field send coils.

13. The near field sensor of claim 1 wherein the near field sensor is in combination with a

remote field sensor with shared send coils in the near field sensor and with additional of remote field receive coils.