Detection of corrosion fatigue in boiler tubes using a spike EMAT pulser
First Claim
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1. A method for detecting damage in a ferromagnetic workpiece, comprising the steps of:
- positioning a pair of EMAT coils adjacent to an outer surface of the workpiece at a non-zero angle with respect to one another;
applying a spike pulse to one of the EMAT coils for a period of time which is less than the time required to generate a toneburst signal in the one of the EMAT coils in order to magnetostrictively generate a shear horizontal polarized wave in the workpiece, wherein the shear wave is capable of being reflected by a flaw in the workpiece;
receiving a reflected wave from a flaw in the workpiece at the other EMAT coil; and
analyzing the received reflected wave and comparing an amplitude thereof to an amplitude of a reflected wave produced by a known calibration standard flaw and producing an indication that a flaw has been detected in the workpiece when the amplitude of the received reflected wave exceeds a predetermined percent of the amplitude of the reflected wave produced by the known calibration standard flaw.
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Abstract
A method of detecting damage in a ferromagnetic workpiece such as a boiler tube positions a pair of EMAT coils adjacent to the workpiece at a non-zero angle with respect to one another. A spike pulse is applied to one of the EMAT coils for generating a horizontally polarized shear wave in the workpiece which is capable of being reflected by a flaw, and the amplitude of a reflected wave from any flaw is received at the other EMAT coil and analyzed and compared to a predetermined percent of an amplitude of a calibration standard flaw to establish the presence of the flaw.
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Citations
11 Claims
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1. A method for detecting damage in a ferromagnetic workpiece, comprising the steps of:
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positioning a pair of EMAT coils adjacent to an outer surface of the workpiece at a non-zero angle with respect to one another; applying a spike pulse to one of the EMAT coils for a period of time which is less than the time required to generate a toneburst signal in the one of the EMAT coils in order to magnetostrictively generate a shear horizontal polarized wave in the workpiece, wherein the shear wave is capable of being reflected by a flaw in the workpiece; receiving a reflected wave from a flaw in the workpiece at the other EMAT coil; and analyzing the received reflected wave and comparing an amplitude thereof to an amplitude of a reflected wave produced by a known calibration standard flaw and producing an indication that a flaw has been detected in the workpiece when the amplitude of the received reflected wave exceeds a predetermined percent of the amplitude of the reflected wave produced by the known calibration standard flaw. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for detecting corrosion fatigue damage in a ferromagnetic boiler tube, comprising the steps of:
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positioning a pair of EMAT coils adjacent to an outer surface of the ferromagnetic boiler tube at a non-zero angle with respect to one another; applying a spike pulse to one of the EMAT coils for a period of time which is less than the time required to generate a toneburst signal in the one of the EMAT coils in order to magnetostrictively generate a shear horizontal polarized wave in the ferromagnetic boiler tube, wherein the shear wave is capable of being reflected by a corrosion fatigue flaw therein; receiving a reflected wave from a corrosion fatigue flaw in the ferromagnetic boiler tube at the other EMAT coil; and analyzing the received reflected wave and comparing an amplitude thereof to an amplitude of a reflected wave produced by a known calibration standard flaw and producing an indication that a corrosion fatigue flaw has been detected in the ferromagnetic boiler tube when the amplitude of the received reflected wave exceeds a predetermined percent of the amplitude of the reflected wave produced by the known calibration standard flaw.
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11. A method for detecting a flaw in a ferromagnetic boiler tube, comprising the steps of:
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positioning a pair of EMAT coils adjacent to an outer surface of the ferromagnetic boiler tube at a non-zero angle with respect to one another; applying a spike pulse to one of the EMAT coils for a period of time which is less than the time required to generate a toneburst signal in the one of the EMAT coils in order to magnetostrictively generate a shear horizontal polarized wave in the ferromagnetic boiler tube, wherein the shear wave is capable of being reflected by a flaw therein; receiving a reflected wave from a flaw in the ferromagnetic boiler tube at the other EMAT coil; and analyzing the received reflected wave and comparing an amplitude thereof to an amplitude of a reflected wave produced by a known calibration standard flaw and producing an indication that a flaw has been detected in the ferromagnetic boiler tube when the amplitude of the received reflected wave exceeds a predetermined percent of the amplitude of the reflected wave produced by the known calibration standard flaw.
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Specification