Liquid Metal Embrittlement of Austenitic Stainless Steel Fitting Caused by Copper Contamination

Abstract

A failure was observed in an 1800 long radius elbow of ASTM A403 WP 304-WX grade, during site fabrication and erection activities. All the welded fittings used were manufactured from SS 304 plates by the Monaka process [1], which involves cold forming of plates and subsequent welding of the formed halves. The fabrication sequence followed by the fitting manufacturer is shown in Fig. 1. The cracked fitting was an 1800 Sch. 10 90 long radius elbow. This elbow was welded to a pipe and radiographic testing (RT) was carried out for this joint to ensure soundness of the weld. A crack was seen in the RT film, away from the circumferential weld seam and perpendicular to the same. The location of the crack with respect to the circumferential weld seam, as seen from the RT film, is provided in Fig. 2. On careful visual inspection of the component, it was observed that the crack was present on the inside diameter of the fitting, perpendicular to the circumferential weld, the orientation on cross section being 90 to the two longitudinal weld seams of the fitting. The image of cracked portion after dye penetrant testing (DPT) is shown in Fig. 3. Assuming this was a superficial crack, an attempt was made to grind it off. However, the crack found on the ID was not removed completely, even after grinding up to a depth of 3 mm. To ascertain the exact root cause of the failure, the defective piece from the component was sectioned and analyzed thoroughly. Analysis