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25. Should oil systems of turbines fitted with oil filtration systems be cleaned and washed?

The cleaning and washing of turbines' oil systems (and other machinery and equipment) is the most important operation before commissioning new machinery, and when making general overhauls after longer periods of intensive operation, no matter if machines are equipped with oil filtration systems or not.

Protective filters (full-flow) are usually installed much farther from bearings, hydrogen seals, adjustment system actuators and other abrasion nodes. Contaminants may also occur between a filter and protected bearings:

• in new machines - after production and assembly;
• in extensively operated machines - deposits generated from ageing products, products of machine parts wearing, rust and corrosion products and contaminants penetrating into oil systems from the environment with oil when adding oil, as well as post-assembly contaminants.

In addition, protective filters in oil systems of high-capacity machines, for constructional reasons (large flow capacity, low difference in pressures before and after filters, high hydraulic resistance) have low filtration accuracy - they protect bearings against destruction from large contaminants, but do not eliminate smaller particles, which are "polishing" shaft necks and bearings.

Working (by-pass) filters, installed usually within the area of the main tank of a turbine set, they clean turbine oil of particles that escape from an oil system and organic products produced in the oil ageing process. Moreover, the capacity of by-pass filters is generally very low compared with the capacity of oil system pumps. For this reason, the majority of contaminants suspended in the flowing oil stream "circulate" in the oil system, and are depositing slowly on its surface (especially in coolers, compensators and tanks). After more than ten years of operation (and in the event of poor operating culture - already after several years), deposits become a source of secondary oil contamination and are very dangerous for oil (by catalysing ageing processes) and for lubricated machine parts (causing wear-and-tear processes and damages). Contaminant particles deposited on surfaces of pipelines, tanks and in oil coolers are carried away from the surface and reintroduced into the stream of oil during interruptions in a turbine's work that bring about temporary turbulences of flowing oil. It is always taking place during start-up, lowering power, shutting a turbine and any other machine downtime.

Without a cleaning process, contaminants cannot be flaked off from internal surfaces of the oil system, without washing the oil system with high-flow speeds - the flaked dirt cannot be removed from oil, and contaminants in oil entail the high wear of filter elements and unforeseen costs of repairs and downtime losses for turbines and other machines (more information in guide_1 and presentation).