Oil analysis - a condition based monitoring tool
Hydraulic and lubricating oil is a very important factor in the better functioning of machinery. It performs tasks such as load transfer, heat dissipation and reduction in wear. The changes in the physical and chemical parameters of the oil can adversely affect the performance of the machine. So it is important to monitor the parameters of the oil to help maximise the life of the equipment .
PARAMETERS OF OIL
The life of the oil and the proper functioning of the system depend on many critical parameters of the oil. Oil has numerous parameters out of which there are critical parameters which determine the proper functioning of the system and also the life of the oil. Oil has a particular working life which can be extended by maintaining the oil clean, dry and cool. EKS has capabilities of testing lot more parameters but only some critical physio – chemical parameters are mentioned below.
1) Kinematic viscosity
This is the parameter of the oil which determines the film thickness which will be maintained between two moving parts. It is the resistance to flow which is termed as viscosity.
2) Viscosity index
This parameter gives the correlation of the viscosity and the temperature. Change in Viscosity Index can cause adverse problems as the change in Kinematic Viscosity.
How change in Kinematic viscosity and Viscosity Index affects the machine:
- The change in viscosity usually increases the friction losses in the machine.
- This increases the power consumption in the particular machine.
- It causes a reduction in oil film thickness causing metal to metal wear
3) Total Acid Number
This parameter of the oil determines the oxidation level in the oil and also the general chemical condition of the oil. As the oil ages and oxidizes small amounts of acidic by products are formed in the oil causing the TAN to increase.
How increased TAN number affects the oil
- One of the common reasons for Increased TAN is the depletion of some additives.
- It indicates higher oxidation rate of the oil. A high TAN number usually indicates that the oil’s useful life has expired and it needs to be changed.
How increased TAN number affects the machine
- High TAN number increases the corrosive potential of the oil.
4) Moisture Content
This parameter of the oil is often called the scourge of hydraulic and lubricating machines. Water contamination is the second most destructive contamination after particulate contamination that affects the hydraulic system. Since in a hydraulic system the typical clearance is between 2 to 40 microns, the particles of such size can cause extensive wear on the surface of the sliding or mating parts.
How Moisture content affects the oil:
- Water reacts with some additives to form precipitant and some chemically aggressive by products.
- Water acts as a catalyst to promote oxidation especially in the presence of reactive metals.
How water contamination affects the machine
- Water in the emulsified or free state interfere with lubrication by weakening the strength of the lubricant film
- Water rusts iron and steel surfaces and increase the corrosive potential of acids that attacks bearing metals
This is the most popularly known devil to the hydraulic system. Since in a hydraulic system the typical clearance is between 2 to 40 microns, the particles of such size can cause extensive wear on the surface of the sliding or mating parts.
How particulate contamination affect the oil
- The catalytic metal particles like copper, iron and lead increase the rate at which oxidation occurs.
- Particles strip the oil of its polar additives such as anti wear additives, rust inhibitors
- Numerous particles in stable suspension can cause an increase in viscosity
How Particulate contamination affects the machine
- Abrasive particles are responsible for much of the wear leading to premature machine failure.
- Particulate contamination causes filter clogging
- Under sliding condition clearance sized particles enter the oil film and cuts away material
- Under rolling contact particles transfer concentration load leading to pitting.
6) Wear Debris Analysis
This is otherwise called Wear Metal Analysis where the oil sample is analysed for the various elemental particles (21 Elements) which reveals the level of the degradation in the machine. The wear debris analysis is also capable of analyzing additive elements in the oil and the amount of reduction in the same in order to understand the level of degradation of the the quality of the oil.
WHY OIL ANALYSIS
Like blood in the human body, the oil carries important clues about the health of the machine. Oil analysis turns these clues into valuable information which supports operations and maintenance decisions. The various reasons why hydraulic oil is equated to blood is that it is not used to do just one thing but does many which are
- Friction and wear reduction
- Heat control
- Contamination control
- Transfer of energy
- Prevent chemical attack
It is important to ensure that this oil is kept healthy, clean and dry. Oil analysis checks if we have accomplished this goal. In order to make sure that all the above operations are performed to its full efficiency it is critical to check whether all the key parameters are being maintained.
As long as hydraulic oil is considered as the blood of the machine the benefits derived from it are of numerous folds. Starting from increase in machine life to doubling the life of the fluid to reduction in power consumption.
Oil analysis is a three stage process with each stage having their own process and procedures
- Oil sampling
- Oil testing
- Data interpretation
Oil sampling is a process and not just a single action. Oil samples are meant to be taken from the most turbulent area in the power pack or directly from one of the return lines. The Oil testing and data interpretation is done in accordance with the ASTM procedures which are known world wide. We are also in the process of getting our laboratory accredited by NABL.