The present invention relates to a device for measuring residual stress and hardness. Residual stress remaining in a metallic material due to deformation, thermal stress, or the like is a cause of various problems including degradation of mechanical properties such as fatigue strength and fracture properties and difficulty in post-processing. It is very difficult to derive a calibration curve when measuring stress by an existing non-destructive Barkhausen noise measurement method. When cross points of Barkhausen noise measurements for three or more stresses are not at one position, calibrated curves can be easily found by scaling the Barkhausen noise measurements by using calibration equations of the present invention to collect the cross points at a unique position, thereby providing a practical method of easily measuring stress of a metal by a Barkhausen noise measurement method. Therefore, according to the present invention, it is found that the internal microstructure and surface residual stress of a metal cause crossing points not to be at a unique position in a conventional Barkhausen noise measurement experiment. In addition, basic physical properties and surface residual stress of a metallic material may be measured using the above-mentioned physical feature.

A device and method for weld root hardening determination compensated for variations in distance between sensor and sample are disclosed. A sensor is used to determine hardness of a weld for weld fabrication quality control. Because of irregular weld protrusion geometry, there may be variations in the tip of the sensor and the surface, resulting in inconsistent measurements. To compensate, one or both of a positional compensation or a software compensation are performed. Positional compensation mechanically moves the tip of the sensor to within a predetermined range of the surface. Software compensation may at least partly compensate for the variation by using one part of the generated sensor data (such as the 1.sup.st harmonic signal) in order to modify another part of the generated sensor data (such as the 3.sup.rd harmonic signal). In this way, the sensor determination of hardness of the weld may be less dependent on the variations.

A device and method for weld root hardening determination compensated for variations in distance between sensor and sample are disclosed. A sensor is used to determine hardness of a weld for weld fabrication quality control. Because of irregular weld protrusion geometry, there may be variations in the tip of the sensor and the surface, resulting in inconsistent measurements. To compensate, one or both of a positional compensation or a software compensation are performed. Positional compensation mechanically moves the tip of the sensor to within a predetermined range of the surface. Software compensation may at least partly compensate for the variation by using one part of the generated sensor data (such as the 1.sup.st harmonic signal) in order to modify another part of the generated sensor data (such as the 3.sup.rd harmonic signal). In this way, the sensor determination of hardness of the weld may be less dependent on the variations.

A method is disclosed for determining a mechanical-technological characteristic variable of ferromagnetic metals, preferably ferromagnetic steels, and in particular fine-grained steels, which are used in pipelines. A magnetization apparatus, which has at least one permanent magnet or solenoid, magnetizes the metal which is to be determined, and a sensor apparatus comprising a transmission coil generates a magnetic field which interacts with the magnetic field which is generated by the magnetization apparatus in the metal, and which generates an eddy current. The eddy current is generated in the magnetically at least substantially saturated metal, and the eddy current is measured by an eddy current sensor of the sensor apparatus. A magnetic field strength sensor measures the magnetic field of the metal at least close to the surface, and the electrical conductivity or the specific electrical resistance of the metal is ascertained from the data from the eddy current sensor on the basis of reference data by means of an evaluation apparatus. The characteristic variable of the metal is derived from the conductivity or the resistance, and also an inspection gauge for carrying out a method of this kind.

A method is disclosed for determining a mechanical-technological characteristic variable of ferromagnetic metals, preferably ferromagnetic steels, and in particular fine-grained steels, which are used in pipelines. A magnetization apparatus, which has at least one permanent magnet or solenoid, magnetizes the metal which is to be determined, and a sensor apparatus comprising a transmission coil generates a magnetic field which interacts with the magnetic field which is generated by the magnetization apparatus in the metal, and which generates an eddy current. The eddy current is generated in the magnetically at least substantially saturated metal, and the eddy current is measured by an eddy current sensor of the sensor apparatus. A magnetic field strength sensor measures the magnetic field of the metal at least close to the surface, and the electrical conductivity or the specific electrical resistance of the metal is ascertained from the data from the eddy current sensor on the basis of reference data by means of an evaluation apparatus. The characteristic variable of the metal is derived from the conductivity or the resistance, and also an inspection gauge for carrying out a method of this kind.

A device of detecting magnetic characteristic change for a long material includes: an exciting coil into which the long material is inserted and which magnetizes the long material in a longitudinal direction; a detecting coil into which the long material is inserted and which detects a magnetic flux generated in the long material due to magnetization by the exciting coil; and a yoke member which has a first opening portion which is positioned on one side of the long material in the longitudinal direction and into which the long material is inserted and a second opening portion which is positioned on the other side of the long material in the longitudinal direction and into which the long material is inserted, and has a shape which is substantially axially symmetrical about an axis passing the first opening portion and the second opening portion, and the exciting coil and the detecting coil are surrounded by the yoke member, the first opening portion, and the second opening portion.

A device of detecting magnetic characteristic change for a long material includes: an exciting coil into which the long material is inserted and which magnetizes the long material in a longitudinal direction; a detecting coil into which the long material is inserted and which detects a magnetic flux generated in the long material due to magnetization by the exciting coil; and a yoke member which has a first opening portion which is positioned on one side of the long material in the longitudinal direction and into which the long material is inserted and a second opening portion which is positioned on the other side of the long material in the longitudinal direction and into which the long material is inserted, and has a shape which is substantially axially symmetrical about an axis passing the first opening portion and the second opening portion, and the exciting coil and the detecting coil are surrounded by the yoke member, the first opening portion, and the second opening portion.

An embodiment identifies a cause of change in magnetic permeability of an object under inspection and evaluates the state of surface treatment(s) of the object under inspection with high accuracy. An embodiment of the method includes preparing a non-destructive inspection apparatus; placing the object under inspection; generating eddy current in the object under inspection; continuously changing the penetration depth of an AC magnetic field in the object under inspection; calculating the value of impedance at each penetration depth in the object under inspection; and evaluating the state of the surface treatment(s) by: calculating the ratio between the value of impedance at each penetration depth in the object under inspection and the value of impedance at a corresponding penetration depth in steel which has not been subjected to a surface treatment; and identifying a cause of a change in magnetic permeability of the object under inspection based upon the calculated ratio.

An embodiment identifies a cause of change in magnetic permeability of an object under inspection and evaluates the state of surface treatment(s) of the object under inspection with high accuracy. An embodiment of the method includes preparing a non-destructive inspection apparatus; placing the object under inspection; generating eddy current in the object under inspection; continuously changing the penetration depth of an AC magnetic field in the object under inspection; calculating the value of impedance at each penetration depth in the object under inspection; and evaluating the state of the surface treatment(s) by: calculating the ratio between the value of impedance at each penetration depth in the object under inspection and the value of impedance at a corresponding penetration depth in steel which has not been subjected to a surface treatment; and identifying a cause of a change in magnetic permeability of the object under inspection based upon the calculated ratio.

The invention relates to a method for observing a magnetic field of a material volume, in particular for determining properties of a workpiece under, in particular, magnetic, mechanical, thermal, and/or electrical excitation of a material volume of the workpiece, wherein the magnetic field of the material volume is sensed as a function of time and of frequency with high frequency resolution.