The 5AT boiler will therefore be approximately 1,4 metric tons lighter than that of the BR 5MT using either type A or type E superheater elements. This reduction in mass, despite an increase in pressure from 1551 kPa to 2130 kPa, is due primarily to the welded construction eliminating butt straps and all lap joints, a smaller volume of water in the barrel due to a larger tube bundle, thinner inner firebox plates due to the use of steel rather than copper, and to the use of a U-section foundation ring instead of the solid type.