Recently one of our Gas Turbines (300MW) in our 450MW CCGT Power Plant, underwent a major upgrade involving complete replacement of all stator vanes, all rotor blades of the Gas Turbine and the rotor blades of the Axial compressor. Besides the manufacturer replaced of the complete set of combustors, transition pieces, cross fire tubes etc.

The Power Station was in service for over eighteen months following commissioning and PG Test done in March 2014 as per ASME PTC 46. However there was a major breakdown following a first stage nozzle failure in the Gas Turbine. The machine has been repaired and ready for re-commissioning now.

Considering that the EPC contractor today is contractually liable for an extended guarantee of the plant heat rate for the entire CCGT plant, we are suggesting a repeat of the PG Test as per ASME PTC46 to arrive at the station benchmark parameters.

However the EPC Contractor is advising that since the steam turbine and HRSG were not touched we should use a Computerized Heat Balance Method using DCS data to arrive at the plant heat rate and use degradation curves to compare whether there has been any losses or not.

We have seen a few references that under such conditions we may only conduct a PG Test on the GT as per ASME PTC22 and calculate the heat rate of the steam cycle obtained from the exhaust flow of the GT and the other parameters using DCS data from permanently mounted gauges, and instruments to arrive at the Plant Heat Rate.

Can any one of our esteemed experts throw some light as to what may be done and the methodology or standard to be followed for the PG Test under such conditions as after a major overhaul or upgrade.

 

hiemvanezi,

Based on the information provided, the answer to your question is whatever the two parties can agree--or agree to disagree--to use.

If there was no performance test before the "upgrade", then how can performance after the "upgrade" be determined?

Unless this is all spelled out in a contract document (and it almost never is!), it's completely subjective and open to interpretation and negotiation.

And, if the performance test criteria/method used after the plant has been running is different from that used when the plant was commissioned and accepted from the builder/supplier, how can a performance comparison be made?

It happens all too frequently that different testing criteria/methods are used--and that just leads to more legal fees and profits for the lawyers. And, it happens all too frequently that such testing and criteria/methods are not written into any contract, so, it's subjective and open to interpretation/negotiation.

But, if an apples-to-apples (like-to-like) comparison is to be made, then like criteria and methods must be used.

Even new instruments used in later tests using similar criteria/methodology as prior tests can introduce "differences" that lead to further profits for lawyers.