Welding repair of cracks on spherical tank for ethylene storage

Abstract

The spherical pressure vessel, with a 3000 m³ working volume, where ethylene is placed, is made of microalloyed steel Nioval 47 P460NL1 (EN 10028: 3), with a wall thickness of 18 mm and welded on 12 supporting pillars. Regular tests were performed by nondestructive methods (visual, magnetic particle testing, and ultrasonic testing), and the indications included undercuts, groups of pores, the lack of weld, and craters formed during vessel manufacturing. What is very important but has not been paid enough attention to over the past fifteen years is the visual inspection of the base material of the spherical storage tank, where the indications such as cracks with a total length of over 6000 mm and a depth of 6 to 12 mm (examined by ultrasound) were observed, which were not observed during previous inspection. This paper presents the technological process of repairing a tank using the 111 welding process, as well as testing of welded joints after repair. The tank is successfully repaired and tested. Results of this work indicate the need for more detailed testing of base metal in the future.