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(#72) Bearing Failure Root Cause · Mechanical Engineering Made Simple

• 0:00
  Welcome back to mechanical engineering made simple.
• 0:02
  Today we are taking a a really critical look at the rolling
• 0:06
  bearing. I think it's fair to say it's
• 0:07
  the single most complex component in almost any machine.
• 0:11
  Absolutely. It operates at this this
• 0:14
  terrifying intersection of intense load speed, really
• 0:18
  complex lubrication needs, and of course, the constant threat
• 0:21
  of contamination. It really is the heart of the
• 0:23
  machine. And if you work in any industry
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  with rotating machinery, you know that unscheduled downtime,
• 0:29
  it's so often points directly back to a bearing failure.
• 0:33
  And I think the big mistake, the expensive mistake is assuming
• 0:37
  that failure is just because you exceeded the basic capacity that
• 0:40
  is. Almost never the full story.
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  So our deep dive today is focused on shifting your
• 0:44
  perspective from, you know, simple replacement to actual
• 0:47
  root cause identification. We're using the authoritative
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  structure of industry standards, specifically ISO 1524 three 2004
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  E to classify the damage. The mission is simple, If you
• 0:58
  can read the pattern of the damage, you can solve the
• 0:59
  problem permanently. I love that idea that the
• 1:03
  failure leaves a unique, like a path pattern or an imprint.
• 1:07
  Yeah, it turns every failed bearing into a forensic case
• 1:11
  study. That's precisely right.
• 1:14
  This damage imprint is physical evidence.
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  It tells the story of whether the failure started during
• 1:19
  installation or maybe during service.
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  And that's why you have to preserve it.
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  Exactly. Preserving that evidence through
• 1:26
  proper condition monitoring is the well It's a first step
• 1:30
  toward better reliability. So let's start framing that
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  story. What's the fundamental split?
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  How do you start classifying bearing damage?
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  We use two major families to classify almost all post
• 1:41
  manufacturing damage. You have the pre operational
• 1:43
  damage modes and the operational damage mode.
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  A faulty start versus a faulty run.
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  That's the perfect way to think about.
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  It so pre operational damage that means the bearing was
• 1:52
  basically doomed before anyone even pushed the start button.
• 1:55
  It was What are the key setup sins here?
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  These are all installation flaws.
• 2:01
  The big ones are incorrect shaft and housing fits.
• 2:04
  For example, if the interference fit is way too tight or if the
• 2:07
  housing seat itself is defective.
• 2:09
  What? Do you mean by defective?
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  Well, maybe it's concave or convex, or even slightly tapered
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  when it should be perfectly cylindrical.
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  The bearing ring gets physically deflected.
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  And once that ring is deflected, the internal geometry is ruined.
• 2:24
  Is. Correct.
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  The whole internal load distribution changes instantly.
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  So instead of the load being spread evenly, it concentrates
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  in these tiny little areas. And leads to spalling.
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  It leads rapidly to premature fatigue spalling, yes, which is
• 2:38
  generally classified under that ISO mode 2.2 fatigue spalling.
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  And beyond just the geometry, what if the actual, you know,
• 2:44
  the mounting technique itself? Oh, faulty mounting practices
• 2:48
  are catastrophic. This could be physical damage
• 2:50
  during transport or storage, or the classic mistake forcing a
• 2:54
  fit with the wrong tools. Old hammer trick.
• 2:56
  The old hammer trick exactly Hitting an outer ring when it's
• 2:59
  mounted in a housing, or vice versa.
• 3:02
  These actions can induce instantaneous internal cracks or
• 3:07
  massive false burnelling, causing immediate failure right
• 3:11
  on startup. OK.
• 3:12
  So that's the faulty start. But what if the bearing survives
• 3:16
  installation and then it fails six months, maybe a year later?
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  Then we're looking at operational damage, correct?
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  What categories are consistently responsible there during the
• 3:26
  service period? The top 2 culprits in operation
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  by a huge margin are ineffective lubrication and ineffective
• 3:33
  sealing. Which I guess leads directly to
• 3:35
  contamination. They're two sides of the same
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  coin. After that, we look at
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  operational misalignment, you know, which might develop as the
• 3:42
  machine settles. And then you get into things
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  like the passage of electric current and damage from static
• 3:46
  vibration. OK, let's dedicate some serious
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  time to lubrication because it feels like it's the biggest
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  single factor in bearing life. It is.
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  When we say lubrication failure, a lot of people just think, oh,
• 3:56
  I ran out of grease. But you mentioned that too much
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  lubrication is also a problem. It absolutely is.
• 4:01
  Lubrication failure is it's a complex topic.
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  It could be insufficient quantity, excessive quantity,
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  using the wrong type of lubricant, or you know, just
• 4:11
  having the incorrect viscosity for the temperature and speed.
• 4:14
  But hold on, why is excessive grease a failure mode?
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  Wouldn't more grease mean more protection?
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  It seems counterintuitive, I know, but no.
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  Excessive amounts of grease or over greasing it causes a rapid
• 4:27
  rise in operating temperature, especially at high speeds.
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  The bearing elements have to literally churn through this
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  dense block of lubricant and that generates immense heat.
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  We call it churning. And that heat just destroys the
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  lubricant. It degrades it chemically, which
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  reduces its effective viscosity, and that leads directly to
• 4:45
  premature failure. So quantity is one thing, but
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  you said is king. Why is that one property so
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  critical? Viscosity determines the film
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  thickness, and you have to think of that oil film not just as
• 4:57
  protection but as a critical nanometer thin layer of
• 5:00
  separation. Like a cushion.
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  A cushion exactly. If that film is too thin, the
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  asperities the microscopic high points on all the rolling
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  surfaces, they start to contact each other and that increases
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  friction, generates more heat and initiates wear and fatigue.
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  And if the machine's temperature fluctuates, say it runs hot and
• 5:19
  then cools down, that protective film is changing too.
• 5:22
  Exactly, and that's why we look at the viscosity index or 6
• 5:26
  Hyoscyc oils you want at least 95 ideally are recommended
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  because they maintain their stability.
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  They change less across white temperature ranges.
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  So your protection doesn't just finish because the ambient
• 5:36
  temperature went up. You got it.
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  OK. Moving to contamination, which
• 5:40
  you said is tied directly to lubrication and ceiling, what
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  are the two types we're worried about and how do they damage the
• 5:46
  bearing differently? Well, we mainly deal with solid
• 5:49
  particles and liquid contaminants.
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  Solid particles, dust, grit, little bits of wear, debris.
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  They cause indentations, a little dense.
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  Yeah. As a rolling element passes over
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  a particle, it creates these tiny craters in the Raceway.
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  Those craters become localized stress concentrators, which is
• 6:07
  the perfect starting point for surface fatigue spalling.
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  It's abrasive wear, pure and simple.
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  And what about liquid contaminants?
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  Liquids, water, acids, process fluids.
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  They're the chemical enemies. They attack the lubricant
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  itself, stripping its effectiveness and just tanking
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  its viscosity. If water gets in, it can cause
• 6:27
  corrosive etching. And that kind of damage often
• 6:29
  appears when the machine is idle, right?
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  Yes, the static etching phenomenon.
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  It's a great example of a failure that happens when the
• 6:35
  equipment is turned off. So how does that happen?
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  Well, corrosion often happens when the machine is idle because
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  it allows the contaminants to pool in one spot.
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  When you inspect the bearing later, you'll find these little
• 6:47
  damage spots, these etch Marks, and they're spaced at exact
• 6:50
  intervals. Corresponding to the rolling
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  elements. Exactly.
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  The spacing matches the rolling element spacing.
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  The simple fix for this is just to periodically rotate the shaft
• 7:00
  while it's idle, just to keep the surfaces wet and
• 7:03
  redistribute the load. Let's shift gears from
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  maintenance to the initial build.
• 7:10
  We said insulation is vital, but how do engineers get that hyper
• 7:13
  precision you need, especially with certain bearing types?
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  The installation window is incredibly narrow, especially
• 7:20
  for bearings with a tapered bore like carb toroidal bearings or
• 7:24
  spherical roller bearings mounted on adapter sleeves.
• 7:27
  These bearings are mounted by driving them up the taper, which
• 7:30
  intentionally reduces the internal radial clearance.
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  And if you drive them up too far?
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  If you have too much drive up on the taper, you completely
• 7:37
  eliminate that internal clearance.
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  You go from having necessary movement to having damaging
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  preload. And preload is the enemies.
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  Preload is the ultimate enemy. It dramatically increases
• 7:46
  friction, which causes the bearing to overheat, and it can
• 7:49
  reduce its fatigue life by a factor of 10 or even more.
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  So the challenge is getting that exact right amount of clearance
• 7:55
  reduction. For cylindrical bores it's a bit
• 7:58
  more straightforward, you use heating.
• 7:59
  Yeah, temperature or hot mounting is the preferred method
• 8:02
  for cylindrical bores. You use an induction heater or
• 8:05
  precision oven to heat the inner ring.
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  It expands and you can just slide the bearing onto the
• 8:09
  shaft, no force. So much safer and more accurate.
• 8:13
  Far safer and it's crucial to note that hot oil baths, they're
• 8:17
  just explicitly phased out of modern industrial practice.
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  Too many safety, environmental and contamination risks.
• 8:23
  OK, let's dive deep into the precision method for those
• 8:26
  tapered bores. The hydraulic drive up.
• 8:29
  This sounds like engineering is a closed loop measurement
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  system. It really is the gold standard
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  for high accuracy mounting. We use hydraulic nuts like the
• 8:37
  HMVE series, which are basically high precision hydraulic jacks,
• 8:42
  and these nuts are fitted with two critical instruments, a
• 8:45
  calibrated pressure gauge and a dial indicator.
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  And why do you need both? Why?
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  I just want. You need both to remove the
• 8:51
  guesswork of manual checks like using failure pages.
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  First you pressurize the nut until the bearing hits a
• 8:58
  specific calculated starting position.
• 9:00
  Pressure. OK, that pressure is determined
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  by the bearings geometry and it ensures the bearing is perfectly
• 9:06
  seated. That's your reference point.
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  That's a bait line. Exactly.
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  And from that baseline, you then measure a very specific axial
• 9:13
  drive up distance using the dial indicator.
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  Because the physics dictates exactly how much the clearance
• 9:19
  reduces for every nanometer of axial movement, measuring the
• 9:23
  distance guarantees you get the precise clearance reduction you
• 9:25
  need. Without inducing that
• 9:27
  destructive preload. Without any destructive preload,
• 9:29
  it converts a force problem into a highly accurate dimensional
• 9:33
  measurement. That level of rigor is really
• 9:35
  what separates basic maintenance from engineering reliability.
• 9:38
  So let's talk about monitoring. What signals warn us that
• 9:42
  something has gone wrong during operation?
• 9:44
  Noise and vibration. They are the Canary in the coal
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  mine. Analyzing the frequency and the
• 9:50
  pattern of the sound can tell you the root cause.
• 9:54
  For instance, A persistent low frequency rubbing noise that
• 9:58
  often means you've got misaligned housing seals.
• 10:01
  Or maybe a loose Loch nut tab hitting the cage exactly.
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  What about a high pitched sound? A scraping or a sliding sound?
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  That's often skidding. It happens when the rolling
• 10:09
  elements are sliding instead of rolling.
• 10:11
  Maybe the bearing doesn't have enough load on it, or the
• 10:14
  lubricant you picked is just too stiff for the operating
• 10:16
  temperature. And then there's a really modern
• 10:18
  failure mode. We see more and more electrical
• 10:21
  erosion or fluting. This is a massive issue,
• 10:24
  particularly in variable speed electric motors running on
• 10:27
  frequency converters. If the grounding is inadequate,
• 10:30
  the current finds the path of least resistance.
• 10:33
  Straight through the bearing. Straight through the bearing, as
• 10:35
  the current arcs through that thin lubricant film between the
• 10:39
  rolling element and the Raceway, it causes these micro craters.
• 10:43
  It's like thousands of tiny arc welds.
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  And over time, those micro craters create that distinct
• 10:49
  washboard look we call fluting. That's right, fluting is a
• 10:52
  visible pattern of axial grooves.
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  Looks just like a washboard on the Raceway.
• 10:57
  It quickly leads to heavy vibration and premature wear,
• 11:00
  and even using insulated bearings won't help if the rest
• 11:03
  of the system isn't properly grounded.
• 11:05
  Let's circle back to what I think is the core lesson here.
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  Sometimes the bearing is the victim, not the cause.
• 11:11
  Our sources had a couple of really high impact case studies
• 11:14
  about this. Yes, these are vital examples of
• 11:17
  system failure. Take the out of round housing.
• 11:20
  If the housing bore is Oval, even just slightly, it
• 11:24
  mechanically pinches the stationary outer ring.
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  So if the outer ring is stationary, it's getting
• 11:28
  squeezed in two spots 180° apart.
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  Correct, and that localized pinching is basically inducing a
• 11:34
  massive targeted preload. That preload creates high
• 11:38
  friction and high heat, but only in those two spots.
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  This leads to adhesive wear, rapid lubricant breakdown and
• 11:44
  premature failure. All because the housing, a non
• 11:47
  bearing component was made wrong or deformed over time.
• 11:50
  And the spacer mistake, the train derailment case study,
• 11:53
  that's even more dramatic. Yeah, it shows how one tiny
• 11:57
  error in an adjacent part can lead to total catastrophe.
• 12:01
  It's a chilling reminder. In that case, a critical spacer
• 12:04
  was installed that was just a little too short.
• 12:07
  And because it was too short, the bearing inner rings were
• 12:10
  never properly clamped stamped by the lock nut.
• 12:12
  So they can move around. It could shift and that induced
• 12:15
  heavy internal axial loads and excessive shaft bending.
• 12:19
  The resulting friction and internal stress LED directly to
• 12:22
  bearing seizure and catastrophic fracture.
• 12:24
  It's causing a derailment just from a small spacer.
• 12:27
  From a small spacer, it shows how precision in every single
• 12:30
  adjacent component is absolutely necessary for the bearing to
• 12:33
  survive. So whether it's thermal failure,
• 12:36
  electrical erosion or mechanical fracture, the message is the
• 12:39
  same. Vigilance and analysis are non
• 12:42
  negotiable. Condition monitoring devices,
• 12:44
  things like vibration analyzers, are essential to detect this
• 12:47
  damage early, but simple temperature checks are vital
• 12:50
  too. Anytime you see a temperature
• 12:52
  spike, especially a sudden rise right after startup or
• 12:55
  immediately after relubrication cycle, you have to investigate.
• 12:59
  It's often the simplest and earliest sign that something's
• 13:01
  wrong. This deep dive has really
• 13:03
  synthesized the critical layers of knowledge needed for rotating
• 13:07
  equipment. To maximize bearing life, it
• 13:11
  seems you have to master 3 areas, the precision of your
• 13:14
  installation, the correct volume and viscosity of your Lube, and
• 13:18
  just relentless contamination control.
• 13:20
  And I think the critical take away for you, the listener, is
• 13:23
  to always look upstream when you pull a bearing that shows
• 13:25
  fatigue spalling don't just automatically jump to capacity
• 13:28
  issues. Ask yourself, is the spalling
• 13:31
  the secondary damage? Is it the result of a much
• 13:34
  earlier primary failure? Maybe an unnoticed misalignment
• 13:38
  during installation that caused preload for years, or a bad seal
• 13:42
  that's been slowly letting in corrosive fluids.
• 13:45
  The spalling is the consequence, not the crime.
• 13:47
  Exactly. That's the mindset.
• 13:48
  That's it for today, Design junkies.
• 13:50
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