Varnish and Deposit Problems

RULER as Part of Proactive Oil Analysis Programs to Avoid Varnish and Deposit Problems With Turbine Oils–

Varnishing and deposit formation is becoming a day-to-day problem for a wide variety of industries. With modern oil Condition Monitoring strategies, as part of root cause failure analysis strategies, these problems can be addressed by applying the correct lubricant analytical techniques.

The reliability management is the central driver, where many field-operating failures are a direct consequence of extreme antioxidant additive depletion failure, as load factors can be extremely high.

Root cause failure analysis consists of 3 steps: analyze/monitor the oil’s parameter, define the condemning limits , and select the appropriate corrective actions to avoid the root cause failure. If we keep us to the first step, analyzing the oil’s parameters, with the RULER we will be able to predict varnish formation.

What is varnish, and how do they get formed?
Lubricant varnish products are better knows as insoluble oil degradation products, where we all know, the antioxidants play a major role in avoiding the formation of these by-products.

Temperature – local overheating on
the bearing surfaces

Water (mainly from condensates)

Particle contamination (especially the fine particulates less than
2µm),

Antioxidants will perform their job by neutralizing these oxidation products. Once a lack of these antioxidants will start to occur, the oxidation products (polar oil degradation species) are very active compounds, and continuously inter(re)act with each other.

But at the same time, as a combination of these polar products, with the degraded/depleted antioxidants, they become insoluble compounds and depose on internal metallic surfaces of the turbine lubricating system.

It will be key to a lubricating professional to keep the antioxidant concentration above their condemning limits, and avoid accelerated varnish and deposit formation.
Several oil laboratories on the market are offering their oil analysis services, including RULER to be able to predict the varnishing problems with turbine and compressor lubricants.
The figure below shows a typical graph from a 450 MW gas turbine lubricant, after 38 months of operating time and show significant depletion of phenols (AO at 15 seconds), and moderate depletion of he aromatic amines(45% RUL) resulting in the first formation and appearance of varnishes.

Figure 1 industrial gas turbine lubricant -450 MW GT - after 38 months lifetime

Once the RULER instrument was purchased the following improvements to the on-site condition-monitoring program were established:

Quality control of all incoming oil batches for RUL estimation
Used oil analysis for all turbine lubricants (and some cases greases and hydraulic fluids)
Oil analysis frequency was adapted in function of the RUL% (higher than 50% RUL / every 4 month sampling – for RUL% between 25 – 50 % every 1-2 months – critical limit at 25% RUL).
Data were correlated with particle counting and water monitoring, and the plant operators were able to trend life of the oil.

The savings from this can be significant:
Lubricant savings => on-site oil analysis achieved significant savings in oil life extension – with the price of 2 to 3 Euro per liter of synthetic lubricant
Maintenance savings => by detecting proactively potential equipment problems (trend analysis ) figures not included, but on-site condition monitoring program allowed to plan maintenance = significant cost reduction – downtime costs. Especially with the combined cycle power plants, which operate from peak-to-peak conditions.