Lubricating oil Testing, Analysis and Review

On Board Testing Procedure and scope, Shore Analysis review with Onboard action,Shore testing procedures overview.

On board testing kits

1.Water content

Water content is tested by a reaction of hydride to water – resulting in formation of steam and the pressure exerted by released Hydrogen is calibrated as water content in a given sample.The results are usually expressed as percentage.

Oil has dissolved water in the form of emulsions/ suspension

.

 1. Solvent (20ml- 50ml as per test kits),often referred to as the first reagent, dissolves oil and has more adhesion to the polar molecular contents(semi emulsion) when mixed with a certain quantity of oil(5ml). It separates water from the mixture- makes it easily accessible for reaction.

2.Calcium Hydride (CaH₂ ) is added to the solution(either in dissolved form or sachets), vessel is closed and agitated

CaH₂ + 2H₂O ----à Ca(OH)₂ + H₂

 

2.Comparative viscosity test

This test is done by an incline – comparing oil sample with fresh oil.In this clinometer , the lines indicate, weather oil can be used or not- This is only a guide line for action. This has to be

checked with Shore analysis for reasons and further action. 

 3. Total Base Number  test 

This test is done by mixing a certain quantity of oil – 10ml (basic in nature)in a reagent 50ml (Acid), and the resultant reaction exerts pressure on the cell, due to an exothermic reaction – by the formation of Vapours, as a result of neutralization reaction - which is calibrated to read out base number in the sample.

This test cell needs to be calibrated for Fresh oil and then sample is to be tested – to get accurate results. This test has to be set up everytime  before the test. Reaction cell test is given here under , working on the same principle.

4.Insolubles

This test is known as

Pentane/ toluene / N-heptane insoluble test.

Lub oil sample is mixed with a solvent(pentane/ toluene) , which will discolor oil and keep insoluble in suspension. The resultant color is compared in a comparator  and equated to insoluble. Insolubles are basically soot and other matter related to oil or additive degradation which are not souble in oil and kept as suspension.

Pentane insoluble are finely suspended paricles- partly removed by good centrifugation , but are not fully removable

Toluene insolubles are soot and water , which can be removed by centrifugation.

N-heptane insoubles test : To determine the asphaltenes in oil

5.Salt in oil test

Indicative test is described as under,

 but in the absence of test equipment , the best method is to dilute the oil  in a solvent with 1:4 ratio (10ml oil to 40 ml solvent), and the resultant mixed with 50 ml distlled water. The solution is agitated properly and titrated for chlorides.

Percentage water as determined : X

For a chloride dilution with distil water : 1:5

Chloride in water : 5 x calculated chloride.

But this is misleading, as Fresh water on board limit of chloride is 50 ppm , and  cooling system (FW or SW for engines), where ingress can happen.

If shore based fresh water is used , ppm ranges up to 1100 ppm as per source of water. Hence Judgement is to be exercised in ascertaining the source of leaks and further action.

Shore based Analysis program

Shore based oil analysis is carried out in addition to ship board analysis to study further the deterioration.

This is expressed as a trend and has to be compared with previous readings.

Techniques overview used at shore 

Category	Key analysis	Analytical techniques
Machine Wear	Fine wear metals	Rotating Disc Electrode (RDE) Spectroscopy*, Inductive Coupling Plasma (ICP) Spectroscopy
	Large wear metal elements	Rotode Filtration Spectroscopy (RFS)*
	Partice count and distribution	Particle count, Laser Net Fine (LNF)*
	Wear particle shape analysis	LNF*, Ferrography, Wear Debris Analysis (WDA)
Contamination	Sand and Dirt	Particle count, Laser Net Fines (LNF)*
	Fuel Dilution	Fuel Sniffer*, Gas Chromatography (GC)
	Water/Moisture	Infrared (IR)*, Karl Fischer Titration (KF)
	Glycol/Coolant	IR*
	Soot	Soot meter, IR*
	Alien Fluid	IR*
Degradation	Oxidation, Nitration, Sulfation	IR*
	Viscosity	Viscosity*
	Acid number (AN), or Base Number (BN)	Titration, IR*

Shore Analysis data with Onboard action.

Water (vol%)   :  Percent water found in the oil sample. Could be from cooling system leaks,

                       Condensation due to to frequent shutdowns, low-temperature operations, poor

                        sump ventilation, or outside. Water contamination. in oil decreases lubricity,

                         prevents additives from working  and furthers oxidation.

Limit is 0.5% before considering removal of sources and increased Centrifugation at 95 degrees.In case of oils with EP additives like gear cases , they have to be replaced.

Viscosity (SAE) :    Less/ more  viscosity indicates Fuel contamination (Gas oil/ HFO) – to be                   

                                 Ad judged by increase in Vanadium, and Sodium. Operating conditions and

                                abnormalities in machinery needs to be addressed and rectified , before

                                further action . This is adjudged by the contaminants from fuel or gasoil

                                 contamination .

Consider partial/ full  renewal of oil depending on the contamination  within 20% of normal  values, after addressing sources of leaks

Soot Index (Weight%) : Indicates the insoluble matter as a result of burning residues(carbon

                                       and ash), usually in trunk piston engines. (max allowed :1.5% mass)

Partial renewal with Proper purification needs to be considered, if associated with TBN change.

TBN (mg KOH/gm)   : To be checked with actual oil value-

                                     -Decrease of more than  30% necessitate oil change partial or full  and                       

                                       investigate the cause-  blow past- indicated by increase in soot and

                                        contaminants.

                                    Specific LO consumption needs to be checked , if  very                 

                                     less(sometimes experienced by use of Tribopack piston kits), then Part replenishment of oil needs to be done to maintain , if other parameters like soot and insoluble are less

Increase Purification if soot is observed, and re-test on board , before considering replenishment of oil .

Increase more than 30% – cross contamination – ex: cylinder oil to main engine sump.To check efficacy of stuffing boxes. Indicated by increase in additives like Ca and increase in wear elements, which can stratify and abrade the bearings.or Fuel contamination to be checked.

Partial or full replenishment with microfiltration can be considered

Insolubles   (% mass)  :Efficacy of separation (Toluene insoubles), Asphaltenes from fuel (n-

                                        Heptane) , Suspended particles (Pentane insoluble) (max :1.0%)

Particle size is the indicator for debris on hydraulic oils(filtration up to 100microns, Magnetic plugs above 100 micrn sizes)

Increased centrifugation with less throughput , Micro filtration, with monitoring on-board, followed by oil replacement as necessary

Oxidation Test (RBOT)   :Related to degradation. If RBOT results for the new oil are known,

                                           these can be compared with the values for the used oil to determine

                                           the oxidation stability reserve of the used oil. Changes in the RBOT   

       and TAN(max variation 2.0%) of the oils are the best indication

       of the remaining useful life of the lubricating oil.This is mainly

        important for  Hydraulic oils.

Oxidation index also is followed by higher oil operating temperatures.

The caution is determined by manufacturer/ testing facility, as they have the ranges for this change.

Oil with proper additives / replacement of oil needs to be considered.

Particle Quantifier Index(PQ): This test determines metal fatgue by analyzing wear particles,

                                                   ferrous , as well as non-ferrous. Debris is an indication of wear

                                                   has to be checked with previous readings to analyze any

                                                  abnormalities in wear and action to be taken.

Micro filtration needs to be considered , with installation of magnetic plugs to separate ferrous particles

Trend analysis of wear metals , additives (increased due to separation) needs to be considered from previous readings , and a high count  has to be investigated , by the sources and through operational parameters.                                     

Wear Elements – with sources - measured in ppm(mg/kg)

Silver(Ag)               :  Bearings ,bushings, platings

Aluminum(Al)         : Pistons, bearings, pumps, blowers,rotors,thrust-washers

Chromium(Cr)        : Rings, roller/taperbearing,rods, platings

Copper(Cu)            :Bushings,bearings,thrust-washers,frictionplates, oilcooler, additive in oil

Iron(Fe)                  :Cylinders,gears,rings,crankshafts,liners,bearings,housings,rust

Molybdenum (Mo)  : Anti-wear additive

.

Nickel(Ni)                :Valves, Residual Fuel.

Lead(Pb)                 : Bearing overlays,additive in gear oil and gasoline

Tin (Sn)                   :Bearings, bushings ,pistons, platings

Titanium(Ti)             :Trace element

Contaminants with Sources- measured in ppm(mg/kg)

Boron (B)                :Present in most permanent antifreeze systems and cooling system

                                 Inhibitors (sometimes used as an additive).

Potassium (K)         :Present in most permanent antifreeze,systems and cooling system

                                 Inhibitors(sometimes used as an additive in gear oil).salt water ingress.

Sodium (Na)           :Present in most permanent antifreeze systems and cooling system  

                                 inhibitors ( sometimes used as an additive), salt water ingress.

Silicon (Si)               : Airborne dirt and abrasives in the oil (sometimes used as an anti-foam

                                   agent)., antifreeze or gasket material.

Vanadium (V)         : As ash / soot in oil.

Additive Elements in oil - measured in ppm(mg/kg)

Barium (Ba)             : Detergent oil additive.

Calcium (Ca)           :Oil additives usually used for detergents or dispersants.

Magnesium (Mg)     :Lightweight housings or casings, or oil additive as a detergent or

                                  dispersant.

Phosphorus (P)       :Anti-wear or antioxidant oil additive.

Zinc (Zn)                 : Anti-wear additive.

A brief overview of Shore tests

Rotating Disc Electrode Optical Emission Spectroscopy (RDEOES)

optical emission spectrometers consist of three main components, these components are

1. Excitation Source - introduces energy to the sample.

2.  Optical System - separates and resolves the resulting emission from that excitation into its component wavelengths.

3.  Readout System - detects and measures the light that has been separated into its component wavelengths by the optical system and presents this information to the operator in a usable fashion. 

Spectral signature of Iron shown

The readout system of a spectrometer is typically controlled by an industrial grade processor and software. A clocking circuit and amplifier periodically reads the charge on a Photo Multiplier Tube or CCD chip and converts it from an analog to digital (ADC) signal to measure the light that has fallen on a pixel. The charge accumulated on a pixel is converted to an arbitrary number defined as “intensity” units. At the end of the analysis, the total intensities for each element are compared to calibration curves stored in

memory and are converted to the concentration of the element present in the sample. Concentration is usually expressed in parts per million (ppm).

 Infrared Spectroscopy 

The infrared spectroscopy of lubricants relies on a very simple method. You observe how much infrared radiation the lubricant absorbs as a function of frequency of that radiation. Figure  shows such spectra for typical lubricants.

                                                         Oil Vs Used oil  or mix of oils Finger printing

 

This relies on  a systematic process involves three key pieces:

 (1) creating calibrations for known lubricant families,

(2) providing an upfront statistical analysis methodology to identify whether an unknown lubricant belongs to a particular family (done by using well-established statistical classifiers

(3) identifying lubricants which don’t belong to a particular identified family, and creating new families for these lubricants. 
If we keep working at these three steps, we can exponentially expand the applicability of infrared analysis to each and every oil that proves to belong to a given family

 The spectrum of all fluids in each family changes in a similar way with a given amount of degradation or contamination. Family-specific algorithms are assigned that accurately quantify these amounts. These algorithms yield quantitative results for the

most critical properties for the most common oil types. Multivariate calibrations are applied so that quantitative readings can be obtained even with complex contaminated sample Most laboratories report lubricant condition parameters using a combination of benchtop FTIR (Fourier Transform Infrared Spectroscopy) spectrometers and wet chemistry titrators.
Infrared spectroscopy is a recommended tool for detecting lubricant mix ups because it allows analysts to compare the molecular fingerprint of the unknown sample to a known reference


 

LNF Technology

Oil Analysis Including Particle Count and Particle Shape Classification

all particles larger than 20 μm in major dimension are automatically classified into the following categories:

• Cutting  • Severe sliding  • Fatigue

• Nonmetallic  • Fibers  • Water droplets

1.  A representative oil sample is drawn from the lubricating system and brought to the unit.

2.  The oil is drawn through a patented viewing cell that is back-illuminated with a pulsed laser diode to freeze the particle motion.

3.  The coherent light is transmitted through the fluid and imaged onto an electronic camera.

4.  Each resulting image is analyzed for particles.

For wear particles in lubricating oil, the instrument displays particle size in terms of maximum chord. For particles in hydraulics, it displays the size in equivalent circular diameter for compatibility with ISO

cleanliness codes. In either fluid, shape characteristics are calculated for particles greater than 20μm, and the particle is classified into either a wear category or contaminant category.

Classification is performed with an artificial neural network developed specifically for the LNF system. Shape features were chosen to provide optimal distinction between the assigned classes of fatigue, cutting, severe sliding, non-metallic particles, fibers, water bubbles, and air bubbles

  Gas Chromatography Test for Fuel Dilution

Gas chromatography (GC) is a separation technique used to analyze used engine oils for evidence of fuel dilution. The technique as applied to fuel dilution measurements is used to separate and measure two volatile fractions of specified boiling ranges from used engine oil samples. The first volatile fraction of interest has a boiling range similar to that specified for gasoline, while the second fraction has a boiling range similar to diesel. The instrument is calibrated and measurements are reported as a percentage contamination by mass.

The fuel dilution test is typically performed either when a significant drop in sample viscosity is measured, or when the flash-point test has failed. It is important that the oil brand and grade are correctly described to your laboratory if problematic samples are to be detected. Special care is necessary in interpreting results because many factors can influence their interpretation. Fuels are complex mixtures of organic compounds that are classified into products based largely on distillation ranges rather than specific chemical data. There are also significant overlaps between various product specifications, making it sometimes difficult to accurately separate and quantify fuel mixtures.   
Another method used is called a Fuel Sniffer method.

The Fuel Sniffer employs a Surface Acoustic Wave (SAW) Vapor Microsensor to measure the concentration of fuel in used lubricating oil samples by sampling the “headspace” in the sample bottle. The instrument assumes (based on Henry’s Law) that the fuel vapor concentration is directly related to the fuel present in the oil sample. A pump inside the instrument draws headspace vapors across the SAW sensor which detects absorbed hydrocarbons by a change in frequency of a surface acoustic wave.

A SAW sensor consists of a piezoelectric substrate that has an interdigital electrode lithographically patterned on its surface. The surface of the SAW sensor has a polymer coating that offers solubility to fuel vapors. The mechanism of detection is a reversible absorption of the fuel component into the polymer. When this device is excited by external RF (Radio Frequency) voltage, a Rayleigh wave (waves perpendicular to the surface) generates on the surface of the device. When fuel contamination comes in contact with the SAW sensor surface it will absorb into the polymer coating.

This absorption into the polymer causes a mass change, producing a corresponding change in the amplitude and velocity of the surface wave. When used in a self-resonant oscillator circuit, the change in Rayleigh wave velocity resulting from vapor absorption into the polymer coating causes a corresponding change in oscillator frequency. This change in frequency is the basis of the Fuel Sniffer’s detection. The absorption is semi-selective based on the properties of the polymer coating and the partition coefficient (solubility of the chemical and polymer) of the chemical of interest.