Question 227Steam Plants - Assistant Engineer

The correct answer is D) The furnace brickwork has collapsed in that area. An external bulge or bowed area of the boiler furnace wall indicates that the furnace brickwork has collapsed in that particular area. This is because the boiler furnace walls are designed to withstand the high temperatures and pressures inside the furnace, and any collapse or deformation of the brickwork can lead to a visible bulge or bowed area on the external surface. The other options are incorrect because they do not directly explain the cause of the external bulge. Slagging of the brickwork or insulation block would not necessarily result in a visible bulge, and the failure of the corbels would not directly lead to a collapsed furnace brickwork area.