6.2 Horizontal joints
Horizontal joints in turbine casings are essential for the construction and maintenance of the turbines, but cause several problems. The flanges have to be substantially thicker than the rest of the casing to allow room for the bolts and bearing surfaces for the nuts (Fig 1.97).
Because of the extra thickness, the flanges warm up less quickly than the rest of the casing, setting up thermal stresses and distortion. These can be minimised by a flange warming system which passes steam through passage ways or holes drilled in the flanges, warming them up at a rate similar to the rest of the casing. The bolt holes themselves may be used for this, with small interconnecting passages drilled diagonally between them.