report interpretation understanding wear metal...
TRANSCRIPT
Report Interpretation: Understanding Wear Metal Results
Elemental Spectroscopy (ASTM D5185)
• Scope– Covers the determination of additive elements, wear metals and contaminants in used and unused lubricating oil by inductively coupled plasma atomic emission spectrometry (ICP‐AES)
• Significance– Difference in additive concentrations may indicate incorrect fluid
– Increase in wear metals can be indicative of abnormal wear
– Can be used to monitor equipment condition to define when corrective action are needed
Ref: ASTM D5185‐13e1, Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP‐AES), ASTM International, West Conshohocken, PA, 2013.
Elemental Spectroscopy
• Principle– Sample is diluted with solvent and injected into a plasma where it is ionized (“burned”) at 10,000 K
– Each element produces a unique spectra of light, intensity determines elemental concentration
Atomic Emission Spectrum Examples
• Aluminum
• Tin
• Lead
Elemental Spectroscopy
• Limitations– Measures 0‐5 µm particles accurately, essentially blind beyond 8‐12 µm range*• Supplemental testing is available for larger particle analysis
• Interferences– Samples must dissolve in solvent for accurate measurement
– High water content samples may require different preparation
*Various sources in general agreement that spectrometers lose their ability to detect particles in the 5‐10 micron range.
0.001 0.01 0.1 1 10 100 1,000
Particle Size, µm
Detection Efficiency, %
100
50
0
Spectrometry Large Particle Detection Methods
e.g. AF, WPC, Patch
Particle Detection Efficiency in Used Oil
Courtesy Spectro Inc.
Repeatability versus Reproducibility
• Repeatability Conditions– the same method
– on identical test items
– in the same laboratory
– by the same operator
– using the same equipment
– within short intervals of time
• “As close as possible”
• Reproducibility Conditions– the same method
– on identical test items
– in different laboratories
– with different operators
– using different equipment
• “Real World” comparison
Ref: ASTM E177‐14, Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods, ASTM International, West Conshohocken, PA, 2014
These values will only be exceeded 1 case in 20 (i.e. 95% confidence)
Precision and Bias
Ref: ASTM D5185‐13e1, Standard Test Method for Multielement Determination of Used and Unused Lubricating Oils and Base Oils by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP‐AES), ASTM International, West Conshohocken, PA, 2013.
Measured Elements
• Wear Metals– Iron
– Copper
– Lead
– Aluminum
– Tin
– Nickel
– Chromium
– Titanium
– Vanadium
– Silver
• Additives
– Calcium
– Magnesium
– Phosphorus
– Zinc
– Barium
– Molybdenum
• Contaminants
– Silicon
– Boron
– Lithium
– Sodium
– Potassium
Iron – Common Cause
• Wear metal
– All steel is composed of iron and carbon, alloy steels contain one or more other elements, such as chromium, copper, manganese, nickel, silicon, or vanadium
• Proportional increase of iron and other metals often indicate alloy steel wear
• Disproportional increase of iron and other metals may indicate coated steel parts, or sacrificial parts like bearings or brass parts
Iron – Exceptions
• Clay‐based absorbents
– Common oil absorbents are made from Fuller’s Earth (a.k.a. kitty litter), as are some acid scavenging filters
• Contains a magnesium‐ and calcium‐based clay, with iron contaminant; generally increases particle count
Iron – Pitfalls
• Some wear is corrosion– Iron may also be present due to elevated water content and/or air entrainment causing corrosion (rust)
Copper – Common Cause
• Wear metal
– Copper is a common alloy in journal bearings, and is also a component of brass and bronze alloys, but may be found on its own in bearing cage, thrust and wear plates, bushings and guides
• Proportional increase of copper and other metals often indicate brass and bronze alloys
• Disproportional increase of copper and other metals may indicate exposing of the copper layer in a Babbitt bearing or copper overlaid part
Copper – Exceptions
• Coolers– The tubing in many coolers is copper‐based, which needs to form a protective oxidative layer• Increase in copper levels only during the first ~1500 hours of service, with no recurrence after oil change
• Anti‐seize products– Some thread anti‐seize products contain high amounts of copper• Increase in copper, and often particle count
Copper – Exceptions
• Reactive EP additive chemistry
– Some EP additive chemistries employ active sulfur, which is aggressive towards copper and copper alloys
• Increase in copper in conjunction with presence of phosphorus– If using R&O oil, phosphorus is usually not present
– If using AW oil, phosphorus and zinc will be relatively equal
Copper – Pitfalls
• Wear particle size– Severe wear, such as wear from overloaded gears, may produce particles too large for detection
• Decreases viewed too positively– Without a maintenance activity, such as fluid change or <5 µm filtration, lower than typical values may indicate particle size has increased, suggesting worsening of problem
Lead – Common Cause
• Wear metal– Lead is a common overlay in journal bearings• Proportional increase of lead, tin and copper often indicate Babbitt wear, or wear from brass or bronze parts
Lead – Exceptions
• Solder– Lead is commonly mixed with tin for solder• Increase in both lead and tin, often with an increase in Acid Number
• Anti‐seize products– Some thread anti‐seize products contain high amounts of lead and molybdenum• Increase in lead and molybdenum, and often particle count
Lead – Pitfalls
• Lead is not always from mechanical wear
– Lead due to leaching of solder requires a fluid change to restore the acidity to lower levels
– Lead due to anti‐seize products is typically not harmful and will be removed at the next fluid change
Aluminum – Common Cause
• Wear metal
– Though aluminum is used in the manufacture of many different parts, it is not often used in an oil‐wetted and wearing surface (e.g. aluminum pistons use chromium or molybdenum rings, aluminum‐blocked engines are lined with steel sleeves)
– Thrust washers and bushings are legitimate sources of aluminum as a wear metal
Aluminum – Exceptions
• Dirt– Dirt is aluminum silicate
• Proportional increase of silicon and aluminum is an ~3:1 ratio is indicative of dirt
• May not correlate with particle depending on manner ingested and system filtration
• Activated Alumina– Some acid scavenging media, e.g. Selexsorb®, is alumina based• Proportional increase of sodium and aluminum
• May not correlate with particle depending on system filtration
Aluminum – Pitfalls
• Cause, not symptom– Aluminum from dirt often suggests increased wear will occur, but the true problem is the point of entry• Check for damaged or loose caps and breathers
• Many OEM breathers are not suitable for optimal exclusion
Tin – Common Cause
• Wear metal
– Tin is a common overlay in journal bearings
• Proportional increase of lead, tin and copper often indicate Babbitt wear, or wear from brass or bronze parts (bearing cage, bushings, thrust plates)
• Tin by itself could be piston overlay (break‐in coating)
Tin – Exceptions
• Solder– Lead is commonly mixed with tin for solder• Increase in both lead and tin, often with an increase in Acid Number
• Polyol Esters– Certain polyol ester fluids contain 200‐300 ppm tin as a leftover catalyst from their manufacture• Confirm with baseline from new oil sample
Tin – Pitfalls
• Tin is not always from mechanical wear– Tin due to leaching of solder requires a fluid change to restore the acidity to lower levels
• Wear particle size– Severe wear, such as wear from overloaded gears, may produce particles too large for detection
Nickel – Common Cause
• Wear metal– Nickel is a common layer in journal bearings, between the intermediate layer and the overlay, but may also be used as flashing• Increase in nickel with decrease in other metals, or high nickel during break‐in period (~1500 h)
Courtesy ACL Performance
Nickel – Exceptions
• Anti‐seize products– Some thread anti‐seize products contain high amounts of nickel• Increase in nickel, and often particle count
Nickel – Pitfalls
• Correlations
– Nickel on its own suggests bearing overlay wear
– Nickel and chromium together, without significant iron, suggest coating wear
– Nickel, chromium and iron increasing proportionally suggest alloy part wear
Chromium – Common Cause
• Wear metal
– Chromium is commonly used in plating or coating of steel parts (valves, rods, rings and bearings)
• Proportional increase of chromium and iron often indicate alloy steel wear
• Disproportional increase of chromium (and possibly nickel or silicon) and iron may indicate coated steel parts
Chromium – Exceptions
• Piping wear– Stainless steel, used in piping and coolers, can be subjected to corrosion and/or erosion• Proportional increase of chromium and iron (1:10 to 1:4 ratio) in conjunction with either an elevated AN (corrosion) or particle count (erosion)
Chromium – Pitfalls
• Correlations
– Chromium and nickel together, without significant iron, suggest coating wear
– Chromium, nickel and iron increasing proportionally suggest alloy part wear
– Chromium and iron increasing proportionally suggest stainless steel part wear
Titanium – Common Cause
• Wear metal
– Titanium may be alloyed with iron (ferrotitanium) for use in shafts
• Proportional increase of titanium and iron
– Titanium parts (e.g. connecting rods) are alloyed with aluminum and vanadium
• Proportional increase in titanium, aluminum and vanadium
Titanium – Exceptions
• Paints– Machinist’s layout fluid contains titanium
– Bright and/or reflective paints contain titanium, so overspray and aerosol may enter the system
Titanium – Pitfalls
• Oil‐wetted?– Not all titanium parts are oil‐wetted and wearing (e.g. turbo manifolds, turbine blades), so they cannot be sources of titanium
Vanadium – Common Cause
• Wear metal
– Vanadium is a common alloy for hard steel
• Proportional increase of iron and vanadium
– Vanadium is used in some coatings
• Disproportional increase of vanadium with iron, possible increase in chromium
Vanadium – Exceptions
• Unburnt fuel
– Bunker C fuel contains leftover vanadium from crude oil (typically from Caribbean area or Mexico)
• Reasonably stable vanadium values, may correlate with nickel, iron, potassium, sodium, aluminum, copper and/or silicon
Silver – Common Cause
• Wear metal– Silver may be used as on overlay in bearings (e.g. wrist pin bearings in EMD locomotive engines, some gas turbines and most aviation engines)• Disproportional increase in silver with iron
Silver – Exceptions
• Solder– Some solders contain silver• Increase in both silver and tin, often with an increase in Acid Number
• Wrong oil– Zinc additized oils react strongly with silver• Increase is silver in conjunction with presence of zinc
• Tricresyl Phosphate (TCP) is an acceptable alternative AW additive
