Improvement of detection of small defects located near or far from welds of magnetic steam generator tubes using remote field eddy current

リモートフィールドECTによる蒸気発生器の磁性管の溶接部付近に存在する微小キズの検出性向上

Mihalache, O. ; 山口 智彦 ; 伊達 公司*; 上田 雅司 ; 山下 卓哉

Mihalache, O.; Yamaguchi, Toshihiko; Date, Koji*; Ueda, Masashi; Yamashita, Takuya

マルチコイル型リモートフィールド渦電流探傷法を用いた「もんじゅ」の強磁性体である蒸気発生器伝熱管の溶接部付近に存在する微小な欠陥の検出性能について報告する。筆者らが開発した3次元の渦電流解析コードを用いてマルチコイルを試作し、溶接部付近の微小な欠陥を従来式のボビン型より検出性が高いことがわかった。さらに伝熱管の外表面に存在する微小欠陥を鳥瞰図で表現できるようになった。

Using numerical software optimization, new remote field eddy current systems based on small multiple vertical and horizontal coils were build in laboratory to investigate smaller outer tube defect detection in ferromagnetic steam generator tubes of nuclear power plants. Small defects located on the outer tube surface as pinholes axial and circumferential notches are better visualized using the C-scan experimental data, even when these defects are located near weld zones and the inspection is done from the inside of the tube. Comparing with the classical system, based on Bobbin coils, the new system shows an improved detection and a better coping with the electromagnetic signal noise in the data arising from unknowns in the: weld structure (from electromagnetic point of view), probe wobbling during inspection, variation in the inner tube surface.