Shrink connection modelling of the steam turbine rotor

• Too small contact pressure of the shrink connection leads to unstable operation.
• An additional butt-weld joining two rotor parts causes a local increase in contact stress.
• Too small contact pressure may cause the weld to break.
• A properly made interference connection can be effective even without a weld.

The paper analyzes the causes of improper operation of the interference connection between two members of the 34 MW turbine rotor. Diagnostic signals, especially in the form of vibrations arising at some operation stages of the machine, pointed to a possible malfunction of the interference connection. After dismantling, a visual inspection and material testing confirmed these predictions. Numerical thermal and strength simulations of the rotor operation showed a loss of the capacity to transfer load on part of the interference connection between the rotor components in some phases of the turbine start-up. The repair involved an increase in values of interference stress and an additional protection in the form of a circumferential weld between the linked parts of the rotor, which removed the problem and ensured a further safe and reliable operation of the turbine under analysis.