GT26 gas turbine: varnish figure from 52 to 8.4 in three months
The varnish potential in a GT26 gas turbine had risen from 24 to 52 in one year. Three months after an offline filter was installed, the figure was 8.4, and the cleanliness code had fallen from ISO 18/17/12 to 15/13/10.
MPC (varnish potential)
The lubricating oil in the power station’s GT26 gas turbine was monitored with regular oil samples. Over one year the varnish potential (MPC) rose from 24 in July 2023 to 38, 30 and finally 52 in May 2024. Varnish settles as a lacquer on valves and bearings, and in a turbine with 28,000 litres of oil an oil change is a major cost item.
On 7 May 2024 a Delta Xero DX1006-T was installed in a side loop on the turbine’s oil tank.
The samples over the following months showed MPC 21.3, then 16.8 and, on 1 August 2024, 8.4. The cleanliness code fell from ISO 18/17/12 to 15/13/10, and the ferrography, which had previously shown varnish particles of 1 to 6 µm, showed none.
The figures come from laboratory reports reproduced in the manufacturer’s case material; the laboratory is not named.
The figures before and after
| Measurement | Before | After |
|---|---|---|
| MPC (varnish potential) | 52 | 8.4 |
| ISO 4406 cleanliness code | 18/17/12 | 15/13/10 |
| Varnish by ferrography | 1 to 6 µm | not detected |
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