In the paper, a methodology, a cycle program and a software system for gas turbine on-condition monitoring and diagnostics are described. The cycle program allows:
the validation of the measurements that are acquired;
the determination of gas turbine measurement normalized values and characteristic parameters, which are indices of the machine health state;
the determination of a production index;
the calculation of statistical indices to assess plant availability.
Moreover, the software system that was set up allows the prompt visualization of the required information by means of a user-friendly interface, so allowing gas turbine health state analysis and supporting the decision for maintenance actions. The first results of the application of the methodology to the gas compression plant of ENI E&P Division in Casalborsetti (RA - Italy) are presented.