The turbine casing completely surrounds the rotor and provides the inlet and exhaust passages for the steam. the casings of turbine cylinders are of simple construction to minimize any distortion due to temperature changes. casings are usually split horizontally to permit easier access for inspection and repair. the flanges are accurately machined to ensure a steam-tight metal-to-metal fit, and the flanges are strongly bolted together. flange seals, except for corrective maintenance measures, are not normally used. in some (high temperature) units, both top and bottom casing halves are made of two vertical casings bolted together and seal-welded. the inlet end is made of alloy steel (cr-ni), while the exhaust end is made of carbon steel. the flanges in the casing are bolted together. one method of joining the top and bottom halves of the cylinder casing is by using flanges with machined holes. bolts or studs are insertion into these machined holes to hold the top and bottom halves together. to prevent leakage from the joint between the top flange and the bottom flange the joint faces are accurately machined. another method of joining the top and bottom cylinder flanges is by clamps bolted radially around the outer of the cylinder.