Lubrication Fundamentals Series — Week 3
Last week we established that 65% of equipment failures are caused by surface wear — and that the vast majority of those failures are preventable. This week we go one level deeper: not all wear is the same, and your equipment is telling you exactly which type is happening if you know how to read the signs.
There are four distinct wear modes. Each has a different cause, a different appearance, and a different corrective action. Treating them the same is one of the most common and costly mistakes in maintenance practice.
The Framework: How Equipment Actually Fails
Before we examine each mode, it helps to see how they fit into the larger picture.
Of all equipment failures, 80% are caused by surface degradation — wear and corrosion working against your assets continuously. Within that 80%, wear accounts for 65% of total failures, broken down as follows:
- Adhesive Wear — 30%
- Abrasive Wear — 25%
- Fatigue Wear — 8%
- Corrosive Wear — 2%
These are not random numbers. They represent decades of failure analysis across industrial equipment worldwide. And they tell you something important: the two most preventable wear modes — adhesive and abrasive — together account for 55% of all equipment failures. Both are directly controlled by your lubrication program.
Wear Mode 1: Adhesive Wear — 30% of All Failures
What it is: Adhesive wear occurs when the lubricant film is too thin to prevent direct contact between surface asperities. When those microscopic peaks touch under load and relative motion, they weld together momentarily — and then tear apart. The result is material transfer from one surface to the other, heat generation, and the production of wear particles that immediately begin driving the next failure mode.
You know this is happening when you see: scoring, galling, seizing, smearing, or scuffing. These are not four different problems — they are the same problem at different stages of severity, from early surface distress all the way to catastrophic seizure.
What it is telling you: Your lubricant film is inadequate for the load and speed conditions your equipment is experiencing. Either the viscosity is too low to maintain a separating film, the additive package is insufficient to protect surfaces when the film thins, or both.
The corrective priority:
- First — correct lubricant viscosity
- Second — additive chemistry
Viscosity gets you the film. Additives protect the surfaces when the film is challenged. You need both, in that order.
Wear Mode 2: Abrasive Wear — 25% of All Failures
What it is: Abrasive wear occurs when hard particles — either generated internally or introduced from outside — become trapped in the lubricant film and act as a grinding compound between moving surfaces. The failures present as polishing, scouring, scratching, grinding, gouging, or erosion.
There are two distinct mechanisms at work here:
Two-body abrasion happens when wear particles generated by adhesive wear become the abrasive — the machine is essentially grinding itself with its own debris. This is why adhesive wear and abrasive wear are so often found together and why the damage can accelerate so rapidly once it starts.
Three-body abrasion happens when external contaminants — dirt, dust, process particles — enter the lubrication system and become trapped between surfaces.
What it is telling you: Your contamination control has broken down. Hard particles are in your lubricant that should not be there — either from inadequate filtration, improper handling, or a failure that has already generated debris.
The corrective priority:
- First — filtration and contamination control
This is not primarily a lubricant selection problem. You can have the best lubricant in the world and still destroy your equipment if hard particles are circulating through it. Contamination control is a system discipline, not a product choice.
Wear Mode 3: Fatigue Wear — 8% of All Failures
What it is: Fatigue wear is different in character from the first two modes. Rather than being driven primarily by lubrication film failure, it results from the cumulative effect of cyclic stress on metal surfaces under load. Every time a rolling element bearing passes over its race, every time a gear tooth engages under load, the metal at the contact zone flexes. Do that millions of times, and microscopic cracks form — first below the surface, then propagating upward until a piece of the surface fractures away.
This is called Hertzian cyclic fatigue, and the failures present as pitting, spalling, or delamination — the characteristic flaking of bearing races and gear tooth surfaces that signals a component nearing the end of its useful life.
Under electron microscopy, the progression is visible in cross-section. A bearing race running at 1,500 rpm shows measurable metallurgical changes in as little as four days. By two months, the subsurface deformation is substantial. By one year, the material has lost its original hardness and fatigue life is exhausted.
What it is telling you: Your equipment may be operating beyond its designed load or speed parameters, or the lubricant is not forming an adequate elastohydrodynamic film to distribute contact stress across a sufficient surface area.
The corrective priority:
- First — load management
- Second — speed management
Lubrication still matters here — the right viscosity is essential to forming the elastohydrodynamic film that spreads load and extends fatigue life. But if the equipment is fundamentally overloaded, no lubricant will fully compensate.
Wear Mode 4: Corrosive Wear — 2% of All Failures
What it is: Corrosive wear is chemical rather than mechanical in nature. When the lubricant film becomes acidic — through oxidation over time, through additive breakdown, or through water and chemical contamination — it attacks the metal surfaces directly. The result is rust, pitting, and surface corrosion that degrades the precision geometry your equipment depends on.
At 2% of failures, this mode gets less attention than the others. That is a mistake. Corrosive wear rarely announces itself dramatically. It progresses quietly, degrading surface quality and accelerating the other three wear modes by roughening surfaces that were once smooth.
What it is telling you: Your lubricant is contaminated with water, has oxidized beyond its useful service life, or is reacting adversely with process chemicals entering the system.
The corrective priority:
- First — water contamination control
- Second — lubricant oxidation management
Water is the primary driver. Even small amounts — invisible to the naked eye — can dramatically accelerate corrosive wear in bearings, gears, and hydraulic systems. Proper breathers, seals, and storage practices are the first line of defense. Lubricant service intervals and oxidation monitoring are the second.
Reading the Four Modes Together
Here is the practical takeaway: these four wear modes rarely operate in isolation.
Adhesive wear generates the debris that drives abrasive wear. Abrasive wear roughens surfaces that then accelerate fatigue wear. Water contamination promotes corrosive wear while simultaneously attacking the additive package that protects against adhesive wear. A failure analysis that identifies only one mode and stops there is probably incomplete.
The four modes are a diagnostic framework. When you see a failed bearing or gear, the wear pattern tells you what happened — if you know what you are looking at. A galled surface points to viscosity failure. A polished-out race points to contamination. Spalling points to overload or inadequate EHD film. Pitting with rust points to water ingress.
Your equipment is communicating. The four wear modes are the language.
Next week: Why We Lubricate — The Science and the Business Case. We will look at what lubrication is actually accomplishing inside your equipment, and why the investment in a proper program returns multiples of its cost.
Danny Stephens is a Certified Lubrication Specialist, recognized by the Society of Tribologists and Lubrication Engineers (STLE), and a National Account Manager with Hydrotex, specializing in reliability-led lubrication programs across multi-site manufacturing operations.
The views expressed in this article are my own and do not represent those of my employer or any affiliated organization.
