Severe accidental water vapour explosions in a foundry in China in 2012

Abstract

On 20th February 2012 a severe water vapour explosion occurred in China. The site of the explosion was an in-door molding pit of the Steel Casting Plant of the Heavy Machinery Co. Ltd., a part of the Anshan Iron and Steel Group in the Liaoning Province in north–east China. The pit, located inside a large factory building, had been in use for a number of years. When the pit was first made years ago, a large hole of square cross section was dug out of the ground and lined with a whole-welded steel box of 10 mm wall thickness. Then the inside of the steel box was lined with a 0.7 m thick water-proof concrete layer. The completed pit was 4.5 m deep and the side-wall lengths were about 12 m. When the explosion occurred, a conical stainless-steel ring weighing about 90 tonnes and intended to be the foundation of a water turbine was being cast in a sand mold. The ground water level was about 2 m below the ground level at the location of the pit. Hence, the bottom of the pit was 2.5 m below the ground water level. Due to a holiday break during the preparation of the sand mold in the pit ground water sept into the sand at the bottom and corners of the pit via eroded holes in the steel lining and cracks in the concrete layer. When the completed sand mold received the molten stainless steel the sand was exposed to a substantial heat flux from the hot metal. The heat was conducted downwards and side-ways into to the regions of the sand in the pit containing water. The water evaporated and highly pressurized water vapour was gradually generated throughout the sand bed below the mold. Pouring of the molten stainless steel into the mold continued without any observable problems for about 30 min before the violent water vapour explosion occurred. Then the entire sand mold, with its content of molten stainless steel, was suddenly lifted at 5 m up in the air, just as by a piston, and shattered all around, killing 13 workers and injuring another 17.