Electricity: measuring and testing – Magnetic – With means to create magnetic field to test material
Patent
1981-11-16
1985-03-26
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
With means to create magnetic field to test material
G01B 710, G01R 3312
Patent
active
045076090
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to nondestructive testing of metals and in particular to the thickness measurement of a magnetic flux conductive base material that has been applied over a magnetic flux conductive base material of a permeability different from the permeability of the clad material.
Vessels, piping and other parts used in the nuclear, petrochemical, and other industries that require corrosion or heat protection are often fabricated of a clad material, chosen for its particular properties, over a base material. The clad construction is more economical than fabricating the entire vessel, pipe or other part entirely from the clad material. The clad material is often applied to the base material of the vessel, pipe or other part by a welding process after which the clad material is machined or ground to form the final surface. Although the original clad thickness can be estimated from the particular welding process used to apply the clad material, it is difficult to estimate the thickness of clad material remaining after machining or grinding.
Ultrasonic methods have been used to measure the thickness of clad material by detecting the interface between the clad material and the base material. Ultrasonic methods detect the interface better when the clad material is not applied well to the base material than when the clad material is applied well to the base material. The more desirable condition where the clad material is applied well to the base material does not result in reliable ultrasonic determination of the thickness of the clad material.
A method of determining clad thickness by pulling a magnet resting on the surface normal to the surface of a clad material that has been applied over a base material has also been used. This method measures the break-away force and correlates that force to clad thickness. This method of determining clad thickness is limited to applications where the permeability of the clad material is low and the permeability of the base material is high.
Therefore, a need exists for a nondestructive method and apparatus for determining the thickness of a magnetic flux conductive clad material that has been applied over a magnetic flux conductive base material of a permeability different from the permeability of the clad material.
SUMMARY OF THE INVENTION
The present invention uses a core-type transformer to nondestructively determine the thickness of a magnetic flux conductive clad material. The invention has application where the magnetic flux conductive clad material has been applied over a magnetic flux conductive base material and the permeability of the clad material is different from the permeability of the base material. The primary and secondary windings of the core-type transformer are interlinked by a mutual magnetic field conducted through an incomplete core and the material being clad-thickness measured. The three legs of the incomplete core are ferromagnetic and form a U-shape with an air gap between the ends of two legs. The flux path is completed by placing the magnetic flux conductive material being clad-thickness measured across the air gap.
An alternating voltage is applied to the primary winding of the core-type transformer. The primary and secondary windings of the core-type transformer are interlinked by a mutual magnetic field conducted through an incomplete core and the material being clad-thickness measured. The magnitude of the voltage induced in the secondary winding is dependent on the magnitude of the voltage applied to the primary winding, the ratio of the number of turns in the secondary winding to the number of turns in the primary winding and the reluctance of the flux path.
A ratio of the magnitude of voltage induced in the secondary winding to the magnitude of voltage applied to the primary winding is a nondestructive measurement of the thickness of the clad material. The turns ratio remains constant. Normalizing the voltage induced in the secondary winding by the magnitude of the voltage applied to the primary wi
REFERENCES:
patent: 2226275 (1940-12-01), Abbott et al.
patent: 2320761 (1943-06-01), Tait et al.
patent: 2595380 (1952-05-01), Hudson
patent: 3747085 (1973-07-01), Bala et al.
Hole, J. E., Magnetic Reluctance, Film Thickness Gauge, IBM Tech. Discl. Bull., vol. 13, No. 10, Mar. 1971, pp. 3048, 3049.
Combustion Engineering Inc.
Smith David L.
Strecker Gerard R.
LandOfFree
Apparatus for nondestructively measuring the thickness of a magn does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Apparatus for nondestructively measuring the thickness of a magn, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Apparatus for nondestructively measuring the thickness of a magn will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1296284