Abstract
A metallurgical investigation was performed on a sample of cracked ring header cross material from the Grand Gulf Unit No. 1 Nuclear Power Station. The cracks were located in a 6–7 in (15–17·5 cm) width band running circumferentially below the cross to cap weld with a similar band above the cross to discharger pipe weld. The indications were up to 19 mm in length and 6·0 mm in depth. This particular sample was cut from a cross which had not seen actual service but which had been used to qualify the induction heating stress improvement (IHSI) technique for the Grand Gulf units. The base material was SA 182 material manufactured to SA 403-type WP 304 stainless steel. The investigation consisted of visual/dye penetrant examination, chemical analysis, hardness testing, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. The evaluated cracks were intergranular and initiated on the forging's exterior surface. The grain size of the material was larger than ASTM 00 and no definitive corrosive species were found by Energy Dispersive Spectroscopy (EDS). The cracking is considered to be the result of the forging having been overheated/burned during manufacture.
Published Version
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