Hydrogen explosion in a foundry.

The event occurred in the continuous casting of hot metallic melt of the plant.
Cooling water leaked through a crack in the cooling water inlet pipe of a secondary cooling line and directly into the hot melt (temperature > 1500 °C). This resulted in the formation of hydrogen which ignited on the hot surface.

The INITIATING cause was the leaking of cooling water onto the melted metal, which produced hydrogen by thermolysis, followed by its ignition.
The pipe in question had been in operation for a prolonged period. The material analyses of the component showed that the rupture occurred because of mechanical fatigue. The annual visual inspection had revealed no signs of imminent failure.

Lack of protection against direct contact between water and hot surfaces suggest that part of the ROOT CAUSES regarded an inadequate risk assessment based on worst case scenario, resulting in a design deficit. Moreover, accelerated material ageing could be an indication of a design deficit. The failure to detect it during inspection could be the consequence of the use inadequate tools for inspection.

casting unit, water cooling pipe

The annual visual inspection had revealed no signs of imminent failure.

In order to effectively avoid such an event in future, the DECHEMA report identified the the following critical points:
(1) The discussion of potential hazard sources should include a sufficiently wide range of possibilities to ensure the safe management of the process.
(2) Cooling water connection points should be fitted with a splash protector, if hazardous conditions can be created by escaping leakage water.
(3) In presence of fatigue stress, it should be critically evaluated whether components are suitably designed and monitored.
(4) Fatigue-affected components should be inspected for fatigue damage by means of dye penetration method or ultrasound.