Thermal Effects
The turbine casing distorts due to the heat differential.
The pressure within the casing distorts casing halves shape to a more cylindrical one, with the high temperature creep results
Hence when the casing cools
The flanges become warped . This can be checked by laying a straight edge across the casing, measuring with a feeler gauge and keeping a log of the results.
No action should be taken unless absolutely necessary.
The casing may leak during warming through as the bolts fail to close the inner faces of the flange. If the leakage stops when the turbine is up to temperature then this is considered satisfactory.
However, if leakage still occurs the some machining must take place. If the leakage is allowed to remain then at high power output damage can ensue.
A temporary repair is with the use of Phurmanite, this is a goo which is pumped into the flange, under pressure through a tapped hole.
The use of shouldered bolts
