Spiral magnetic field apparatus and method for pipeline inspection

1. A pipeline inspection method comprising:

identifying a pipeline defining a circumferential direction and an axial direction and containing an in-line inspection tool comprising

a first end,

a second end opposite the first end, and

a primary sensor section positioned between the first and second ends, the primary sensor section comprising at least one magnet and at least one sensor, the at least one magnet producing a first magnetic field having an orientation, the orientation being directed obliquely with respect to each of the circumferential and axial directions and pointed more toward the first end than toward the second end;

producing relative motion between the at least one magnet and the pipeline, the relative motion comprising substantially exclusively translation in the axial direction of the at least one magnet with respect to the pipeline;

generating, by the in-line inspection tool during the producing, one or more oblique magnetic fields each having the orientation, the one or more oblique magnetic fields comprising the first magnetic field and all other magnetic fields that emanate from the in-line inspection tool and are oriented obliquely with respect to each of the circumferential and axial directions; and

collecting, by the at least one sensor during the generating, data characterizing one or more physical characteristics of the pipeline.

2. The method of claim 1 , wherein the producing comprises producing, by a fluid traveling within the pipeline, relative motion between the at least one magnet and the pipeline.

3. The method of claim 2 , wherein the magnetic field is oriented with respect to the circumferential direction at an angle between ten and sixty degrees.

4. The method of claim 3 , wherein the primary sensor section further comprises a transmitter positioned between two opposite magnetic poles generated by the least one magnet.

5. The method of claim 4 , wherein the transmitter cooperates with the two opposite magnetic poles to form an electromagnetic acoustic transducer.

6. The method of claim 5 , wherein the generating comprises generating, by the electromagnetic acoustic transducer, a transverse shear wave traveling in the circumferential direction within a wall of the pipeline.

7. The method of claim 6 , wherein the collecting comprises receiving, by the at least one sensor, the transverse shear wave from the wall.

8. The method of claim 7 , wherein:

the at least one sensor comprises the first transmitter in a non-transmitting mode;

the first end of the in-line inspection tool comprises one of a leading end and a trailing end; and

the second end of the in-line inspection tool comprises the other of the leading end and the trailing end.

9. The method of claim 7 , wherein the primary sensor section further comprises:

a frame extending in the axial direction; and

an armature independently suspended from the frame.

10. The method of claim 9 , wherein:

the armature supports two magnets of the at least one magnet spaced apart a distance to form the two opposite magnetic poles; and

the armature supports the transmitter between the two magnets.

11. A pipeline inspection method comprising:

identifying a pipeline defining a circumferential direction and an axial direction and containing an in-line inspection tool comprising

a first end,

a second end opposite the first end, and

a primary sensor section, the primary sensor section comprising a magnet dipole and at least one sensor, the magnet dipole producing a first magnetic field having an orientation, the orientation being directed obliquely with respect to each of the circumferential and axial directions and pointed more toward the first end than toward the second end;

producing relative motion between the magnet dipole and the pipeline, the relative motion comprising substantially exclusively translation in the axial direction of the magnet dipole with respect to the pipeline;

generating, by in-line inspection tool during the producing, one or more oblique magnetic fields each having the orientation, the one or more oblique magnetic fields comprising the first magnetic field and all other magnetic fields that emanate from the in-line inspection tool and are oriented obliquely with respect to each of the circumferential and axial directions; and

collecting, by the at least one sensor during the generating, data characterizing one or more physical characteristics of the pipeline.

12. The method of claim 11 , wherein the primary sensor section further comprises a frame extending in the axial direction.

13. The method of claim 12 , wherein the primary sensor section further comprises a plurality of armatures, each being independently suspended from the frame and comprising a first end and a second end, opposite the first end.

14. The method of claim 13 , wherein the primary sensor section further comprises a plurality of first magnets, each connected to the first end of a different armature of the plurality of armatures to form a first pole.

15. The method of claim 14 , wherein the primary sensor section further comprises a plurality of second magnets, each connected to the second end of a different armature of the plurality of armatures to form a second, opposite pole.

16. The method of claim 15 , wherein a distance between the first and second poles corresponding to a first armature of the plurality of armatures is less than a distance between the first pole corresponding to the first armature and the second pole corresponding to an adjacent armature of the plurality of armatures.

17. The method of claim 16 , wherein the first and second magnets corresponding to each armature of the plurality of armatures generate a magnetic field orientated obliquely with respect to the circumferential direction.

18. The method of claim 17 , wherein:

the plurality of armatures are distributed spirally with respect to the frame;

the first end of the in-line inspection tool comprises one of a leading end and a trailing end; and

the second end of the in-line inspection tool comprises the other of the leading end and the trailing end.

19. A pipeline inspection method comprising:

identifying a pipeline defining a circumferential direction and an axial direction and containing an in-line inspection tool comprising

a first end,

a second end opposite the first end, and

a primary sensor section, the primary sensor section comprising a substantially rigid frame, at least two continuous magnetic poles spiraling about the substantially rigid frame, and at least one sensor, the at least two continuous magnetic poles producing a first magnetic field having an orientation, the orientation being directed obliquely with respect to each of the circumferential and axial directions and pointed more toward the first end than toward the second end;

producing relative motion between the at least two continuous magnetic poles and the pipeline, the relative motion comprising substantially exclusively translation in the axial direction of the at least two continuous magnetic poles with respect to the pipeline;

generating, by the in-line inspection tool during the producing, one or more oblique magnetic fields each having the orientation, the one or more oblique magnetic fields comprising the first magnetic field and all other magnetic fields that emanate from the in-line inspection tool and are oriented obliquely with respect to each of the circumferential and axial directions; and

collecting, by the at least one sensor during the generating, data characterizing one or more physical characteristics of the pipeline.

20. The method of claim 19 , wherein the primary sensor section further comprises at least one brush contact extending radially outward from each continuous magnetic pole of the at least two continuous magnetic poles.