Abstract
This paper presents an algorithm that estimates the presence, location, shape, and depth of flaws using a bobbin-type magnetic camera consisting of bobbin probes and a bobbin-type integrated giant magnetoresistance (GMR) sensor array (BIGiS). The presence of the flaws is determined by the lobe path of the Lissajous curves obtained from bobbin coil with respect to the applied frequency. The location of the flaw, i.e., whether it is an inner diameter (ID) or outer diameter (OD) flaw, can be determined from the rotational direction of the lobe with respect to the frequency change. The shape of the flaw is then determined from the area of the lobe and the BIGiS image. At this stage, multi-site damage can be determined from the BIGiS image. The effectiveness of the flaw classification algorithm was evaluated using various types of artificial flaws introduced into small-bore tube test specimens made of austenitic stainless steel.
Highlights
Nuclear power plants consist of many heat ex-changers (HXs), such as a steam generator (SG), moisture separator and reheater (MSR), condenser (CDS), and feedwater heat exchanger (FWH)
This study proposed an algorithm that can evaluate the presence, location, shape, and depth of the flaws in high pressure (HP) FWH tubes using a bobbin type magnetic camera composed of a differential-type bobbin coil and a giant magnetoresistance (GMR) sensor array
The characteristics of the output signal of the differential-type bobbin coils and the GMR sensor array according to the presence, location, and shape of the defects were investigated using various types of artificial flaws introduced to small-bore tubes made of austenitic stainless steel
Summary
Nuclear power plants consist of many heat ex-changers (HXs), such as a steam generator (SG), moisture separator and reheater (MSR), condenser (CDS), and feedwater heat exchanger (FWH). The high pressure (HP) FWH is made of welded austenitic stainless steel tubes (ASTM A688-TP304L). A unit of HP FWH contains three heaters and consists of more than. The tubes have small bores and significant length, with an outer diameter (OD) and thickness of 15.87 mm (0.625 in) and 1.27 mm (0.05 in), respectively. Few nondestructive testing (NDT) methods exist which can quickly assess the integrity of this material and its structure, namely paramagnetic, narrow, long, and large number of tube bundles. Eddy current testing (ECT) can be applied to small-bore tubes, does not require a couplant between the sensor and the specimen, and can inspect a large number of HX tubes within a short time
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