Boiler Tube Failure due to Opening a Drain Valve

We had just erected and commissioned a circulating fluidized bed boiler for an industrial plant in Southeast Asia. The boiler was a state of the art CFBC and almost the largest boiler in the region at that time. It was capable of producing nearly 400 tons per hour of steam for power generation and utility purposes, firing coal and biomass with superheated steam at a pressure of 140 bar and temperature of 540°C.