Assessing oxidation condition and lubricant refreshment in turbine oils
March 2023Maintenance, Test & Measurement, Calibration
In turbines, lubrication undergoes a hydrodynamic regimen in which wear arises only after very poor lubricant condition. Conversely, the main root cause of turbine failure is the formation of deposits. Deposits produce several detrimental effects on these systems, such as sticking valves, orifice obstruction, and inefficient heat exchange.
In the case of gas turbines, where the lubricant suffers mainly from thermal stress, deposits are usually associated with the formation of varnish. Varnish is commonly associated with oxidation processes. It is composed of sacrificed antioxidants and oxidation products that coalesce to form sticky soft matter. The cost of varnish is very high, both in downtime and in equipment replacement. For this reason, monitoring of the oxidation condition of turbine oils is of utter importance.
To protect the base oil from oxidation, turbine lubricants are supplemented with about 1% of antioxidants. These are sacrificed to protect the base oil from free radicals and thermal and oxidative stress.
It is usually accepted that turbine oils can be used until their remaining active antioxidants are 25% of the original formulation. In many cases, however, depending on the oil, varnish issues arise before this point. Both laboratory tests and turbine oil condition monitoring, show that varnish may start to build up even when remaining antioxidants are as high as 60%.
In order to keep the operation reliable, the oxidation condition of a turbine must be kept between safe boundaries. This implies keeping a high dose of antioxidants, and the varnish potential low, to predict a high oxidation resistance.
Oil refreshment is a viable option to keep turbines free of varnish. By integrating the outcomes of lubricant analytics, such as RULER (Remaining Useful Life Evaluation Routine), RPVOT (Rotating Pressure Vessel Oxidation Test), and MPC (Membrane Patch Colorimetry), it is possible to estimate the refreshment required to keep the turbine under lean operation.
The lubricant’s oxidation condition can be effectively monitored through RULER, MPC, and RPVOT tests. Besides the nominal ASTM (American Society for Testing and Materials) value for these tests, significant information can be gathered from digging into these tests and integrating their outcomes.
One major application for this integration is the estimation of the lubricant refreshment for lean operation. Through laboratory tests, this can be accurately estimated, planning ahead of the upcoming maintenance intervention. This method is shown, together with case studies.
Infrared thermometers for electrical, industrial and HVAC applications Comtest
Maintenance, Test & Measurement, Calibration
: Comtest, distributor of Fluke test and measurement equipment, explains how handheld infrared thermometers are transforming maintenance in electrical, industrial and HVAC environments, with three measurement strategies and a wide range of practical applications.
Read more...Reverse-engineering legacy industrial gearbox parts
Maintenance, Test & Measurement, Calibration
WEG Africa’s turbine workshop uses 3D scanning technology to reverse-engineer components for legacy gearboxes, turbines and compressors, enabling equipment to run for decades after OEM support and spare parts have dried up.
Read more...Unlocking ICCP remote monitoring Omniflex Remote Monitoring Specialists
Maintenance, Test & Measurement, Calibration
Cathodic protection keeps buried and submerged pipelines safe from corrosion, but verifying it traditionally means costly, hazardous manual site visits. Omniflex explains how a retrofit module brings remote monitoring to ageing transformer rectifiers without replacing functional infrastructure.
Read more...Microdieseling – the explosions you never hear
Maintenance, Test & Measurement, Calibration
Microdieseling is a pressure-induced thermal degradation mechanism in which entrained air bubbles are compressed so rapidly that the surrounding oil ignites, producing soot, varnish and sludge. WearCheck explains how it happens, why the damage varies, and how oil analysis detects it.
Read more...Electrostatic spark discharge – when static strikes back Wearcheck
Maintenance, Test & Measurement, Calibration
WearCheck technical manager, Steven Lumley explains how static electricity accumulates in modern low-conductivity lubricants, why compact system designs and fine filtration make ESD more likely, and how to recognise the degradation it leaves behind.
Read more...High-speed cameras for crash testing Horne Technologies
Maintenance, Test & Measurement, Calibration
Vision Research has expanded its Phantom C-series with two cameras optimised for crash and safety testing, offering 4 and 8 megapixel sensors rated to 170G, up to 1180 frames per second, and Phantom Academy application training planned for South Africa next year.
Read more...SKF extends remanufacturing expertise to bearing clearance modification SKF South Africa
Maintenance, Test & Measurement, Calibration
Using its clearance modification expertise, SKF helped a mining equipment OEM salvage spherical roller bearing inventory that would otherwise have been scrapped, confirming a new capability within its remanufacturing services and avoiding redundant procurement.
Read more...When maintenance-system compliance starts replacing plant reliability Wearcheck
Maintenance, Test & Measurement, Calibration
WearCheck ARC division manager, Annemie Willer argues that the greatest threat to effective maintenance is no longer a lack of technology, but the gradual replacement of technical judgement by CMMS compliance, leaving no one owning the machine.
Read more...Nitration: the acid you didn’t see coming Wearcheck
Maintenance, Test & Measurement, Calibration
Nitration is as destructive as oxidation in many engines but far less understood. WearCheck technical manager, Steven Lumley explains how nitrogen oxide gases degrade lubricants, why the process is difficult to detect, and what oil analysis can reveal before damage occurs.
While every effort has been made to ensure the accuracy of the information contained herein, the publisher and its agents cannot be held responsible for any errors contained, or any loss incurred as a result. Articles published do not necessarily reflect the views of the publishers. The editor reserves the right to alter or cut copy. Articles submitted are deemed to have been cleared for publication. Advertisements and company contact details are published as provided by the advertiser. Technews Publishing (Pty) Ltd cannot be held responsible for the accuracy or veracity of supplied material.
printer friendly version