DEVICE FOR DETECTING DEFECTS ON METALS

Abstract

A stray flux measurement device for detection of defects near the surface and remote from the surface on ferromagnetic specimens (10) is characterized by at least one coil (20) or an equivalently acting core/coil combination that faces the specimen (24, 22) and at least one coil (30, 40) or an equivalently acting core/coil combination (34, 32; 44, 42) that faces at an angle relative to the surface of the specimen.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows a ferromagnetic specimen being moved past a device in accordance with the present invention in the practice of the process of the present invention;

FIG. 2 is a schematic side view of modified embodiment of the device and process of the present invention; and

FIG. 3 shows how the field lines run for a tubular specimen and use of the device of the invention for detection thereof.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 schematically shows a ferromagnetic specimen 10 with its direction of motion illustrated by the arrows “v”. The specimen is penetrated lengthwise by a constant field as is symbolized by the letters N and S; however, the polarity of the field is generally unimportant. A defect 12 near the surface causes displaced field lines 13 with relatively steep exit angles. A hidden defect 14 which lies under the surface causes displaced field lines 15 with relative flat exit angles. The field lines 13 are suited to producing a detectable signal in the coil or probe 20. The field lines 15 are suited to producing a detectable signal in the coil 30 or in the coil 40. The coils or probes 20, 30, 40 are shown in FIG. 1 schematically as coreless and single-layer coils with only one turn and are, in practice, are provided with additional turns.

FIG. 2 shows a similar arrangement in which the coils 22, 32, 34 are provided with cores 24, 34, 44. However, in this connection, the combination of a coil 22 and a core 24 is suited to producing a detectable signal in the presence of field lines 15 as are caused, for example, by a hidden defect 14 at a certain distance. The other coil/core combinations from FIG. 2 are designed to also, and preferably, detect field lines 13, optionally, with time storage of the assorted signals and their subsequent analysis by means of suitable electronics and a computer.

It goes without saying that the signal delivered by the coils 22, 32, 42 should be supplied to an amplifier and a following signal conditioning unit in order to obtain reliable indications of defects which are present. Likewise, it goes without saying that the coils must be suitably fastened relative to one another, and advantageously, are accommodated in a suitable housing which is spaced suitably away from the specimen.

FIG. 3 shows how the field lines run for a tubular specimen in a schematic appearance, in the case of a stray flux measurement arrangement. The defect 12 near the surface displaces the field lines which normally run roughly parallel to the surface, causing steeply emerging field lines 13 which are suited to producing a detectable signal in the coil 20. The hidden defect 14 displaces the normally parallel running field lines radially outward on the surface as field lines 15 which emerge relatively flat and which are suited to producing a detectable signal in the coil 40.

Claims

1. Stray flux measurement device for detection of faults or defects near and remote from a surface of a ferromagnetic specimen, comprising: at least one first coil or an equivalently acting core/coil combination disposed for facing the surface of the ferromagnetic specimen so as to be particularly suited for detecting surface faults or defects; andat least one second coil or an equivalently acting core/coil combination disposed for facing at an angle to the surface of the ferromagnetic specimen so as to be particularly suited for detecting subsurface faults or defects.

2. Stray flux measurement device according to claim 1, wherein the at least one second coil or equivalently acting core/coil combination is arranged perpendicular to the at least one first coil or equivalently acting core/coil combination.

3. Stray flux measurement device according to claim 1, wherein the at least one second coil or equivalently acting core/coil combination comprises two second coils or equivalently acting core/coil combinations, each of which is oppositely angled toward the other.

4. Process of detection of faults or defects near and remote from a surface of a ferromagnetic specimen, comprising the steps of: arranging at least one first coil or an equivalently acting core/coil combination disposed so that surface normals thereof are roughly parallel to the surface of the ferromagnetic specimen; andarranging at least one second coil or an equivalently acting core/coil combination disposed facing at an angle to the surface of the ferromagnetic specimen;moving the ferromagnetic specimen passed the first and second coil or an equivalently acting core/coil combinations;using the at least one first coil or equivalently acting core/coil combination for detecting surface faults and using that at least one second coil or equivalently acting core/coil combination defects for detecting subsurface faults or defects.

5. Process of detection of faults or defects according to claim 4, wherein the step of arranging at least one second coil or an equivalently acting core/coil combination is performed so that surface normals thereof are substantially perpendicular to the surface of the specimen and are oriented in a direction of movement of the specimen.

6. Process of detection of faults or defects according to claim 4, wherein the step of arranging at least one second coil or an equivalently acting core/coil combination is performed by arranging two second coils or an equivalently acting core/coil combinations is so that surface normals thereof are oriented at opposite angles relative to a direction of movement of the specimen.