構造要素熱過渡き裂進展試験-試験中き裂計測結果-

Crack propagation tests on the fundamental structure under cyclic thermal transients; Results of nondestructive inspection for cracks

小林 澄男; 堀切 守人

not registered; not registered

本データ集は、空気冷却熱過渡試験施設(AGS)で実施した構造要素熱過渡き裂進展試験のうち、円筒構造内面から進展させたき裂を非破壊検査手法によって計測した結果に関するものである。本試験では、全長1500mm,外径130mm,内径70mmのSUSF304型ステンレス鋼の内面に軸方向及び周方向の半楕円形状の初期切欠きを施工した試験体を使用し、その試験体を内外面より650に加熱した後、内面側を圧縮空気で一気に90秒間冷却することにより、板厚内に等二軸曲げ荷重の負荷を繰り返し、初期切欠きからき裂を進展させた。試験は数年間にわたって行われた。環状き裂と軸・周の表面き裂を進展させたCPTT-103試験は10,000サイクル、軸・周方向の異なる長さの表面き裂を進展させたCPTT-103試験は5,000サイクルの試験を実施した。これらの試験においては、試験途中のき裂進展状況を把握するため、超音波探傷法、直流電位差位法、表面観察法によるき裂の非破壊計測を実施した。超音波探傷法はパルス反射法を適用した。直流電位差位法は、一定の直流電流を局部的にき裂を跨いて流す方法を適用した。内表面観察は、試験途中における内表面のき裂発生状況をボアスコープにより写真撮影する方法を行った。これらの計測の結果、超音波探傷法は、き裂破面の開放後の計測結果と良く一致しており、き裂進展中の形状を計測できることが確認できた。直流電位差法は、き裂破面の計測結果を基準に校正した結果、き裂深さとのよい一致を示した。また、パソコン上でつなぎ合わせた内表面の写真により、亀甲状き裂と主き裂の接続状況が確認できた。

This report shows the results of crack inspection in crack propagation tests that were carried out at the Air-cooling Thermal Transient Test Facility (ATTF), Test specimens were made of 304 type austenitic stainless steel, and they were the same cylindrical shape, 1,500 mm in height, 130 mm in outer diameter and 30 mm in thickness. And they had initial slits machined on inner surfaces. Firstly the specimens were heated up to 650 C in a furnace, then cooled by pressurized air blowing through the specimen for 90 seconds. These cyclic changes of temperature gradients in the wall of specimens were loaded. Specimens were tested for several years. The specimen No. CPTT-102 with machined two circumferential slits and two semi-elliptical slits was tested up to 10,000 cycles. And the specimen No. CPTT-103 with machined six semi-elliptical slits of different length respectively was tested up to 5,000 cycles. Cracks of specimens were inspected nondestructively fbr a giving cycle in these tests. Applied inspection methods were ultra-sonic testing, potential-drop method and inner surface observation. Ultra-sonic testing was carried out by applying the pulse-echo method. Potential-drop testing was carried out by measurement of localized constant direct current beyond cracks. Photographs of the inner surface of specimens were taken using a bore-scope. The results of ultra-sonic testing have been close to destructive test results. The depth of crack by the potential-drop method was almost corresponding to destructive test results, too. Photographs of the inner surface were synthesized by the computer, and connection between main crack and hair crack was observed.