Explosion enhancement through a 90° curved bend

Abstract Junctions and bends are commonly incorporated in pipeline systems conveying potentially explosive mixtures. Very little data exists on how these affect the development and transmission of an accidental explosion. There is therefore great uncertainty when designing explosion protection measures for such systems. A 3 m long, 162 mm diameter tube, closed at both ends and incorporating a 90° curved bend was used to investigate the influence of the bend on the development of gaseous explosions. Methane/air mixtures of 10% and 5.7% by volume were used. The mixture was ignited at one end of the tube at 5 mm or 53 mm from the flange. It was found that for all explosions, the flame moved faster around the inner wall of the bend than the outer and hence it was elongated. This gave rise to an overall acceleration of the flame and a significant increase in the rate of pressure rise. The enhancement factor due to the bend ranged from 4 to 6 for the 10% mixture and it was equivalent to the effect of an orifice plate with a 20% blockage in the path of the flame. These findings highlight the need for more work on bends of different shapes and in different layouts.