The document discusses various types of machine deterioration and failure. It describes common types of ferrous and non-ferrous metals used in machines, such as steel, cast iron, stainless steel, copper, bronze, and aluminum alloys. It then explains common forms of deterioration for these metals, including rusting, corrosion, and pitting. The document also discusses several common causes of machinery failure, such as misalignment, unbalance, resonance, bearing issues, looseness, and flow-related problems. Prevention methods are provided for metal deterioration, including plating and surface treatments.

1. Chapter 2
Machine Deterioration and
Failure

2. Deterioration
 The act or process of becoming worse or lower in quality, value
or character.
Breakdown
Adjustments
Down Time
Increment
Defects
Reworks
Effect of
Deterioration

3. Ferrous Metal
 Wrought Iron - An iron alloy with very low carbon content containing fibrous
inclusions caused by the integration of slag during the manufacturing
process. Historically, it was known as "commercially pure iron", however it
no longer qualifies because current standards for commercially pure iron
require a carbon content of less than 0.008% by weight.

4. Continue Ferrous Metal
 Steel - Alloy of iron and carbon, whereby between 0.07- 2.1 % carbon, by
weight, is dissolved in the iron. Varying the amount of alloying elements and
form of their presence in the steel (solute elements, precipitated phase)
controls qualities such as the hardness, ductility, and tensile strength of the
resulting steel.

5. Ferrous Metal
 Cast iron – Ferrous metal containing between 2.1 – 4% carbon
and often contains between 1-3% silicon. The melting point of
cast iron is about 300oC lower than pure iron. Cast iron tends to
be more resistant to corrosion than wrought iron or steel.

6. Continue Ferrous Metal
 Stainless steel - A steel alloy with a minimum chromium content of 10.5% by
weight. The chromium forms a passive surface layer of chromium oxides on
the surface, which prevents corrosion. Depending on its designed use,
stainless steels can also contain nickel, manganese, molybdenum, sulphur,
phosphor, lead, aluminium, titanium, silicon, nitrogen and copper, plus
others.

7. Ferrous Metal Deterioration
 The main deterioration problem with ferrous metals is rust. Rust is caused
by the oxidation of iron in the presence of moisture.
 Red/orange rust is chemically unstable, and porous, which allows moisture,
oxygen, chlorides, sulphides and sulphates to rear bare metal, so a
protective layer is not formed. Dark brown/black rust (typically magnetite) is
usually chemically stable.
 When rust forms, it can also cause mechanical damage, because as it forms
it occupies a larger volume than the metal, so in some situations it will
cause parts to bend or even break.
 Illustration of Rust = https://www.youtube.com/watch?v=EXaa5Ex5y1g

8. Prevention of Ferrous Metal Deterioration
 Ferrous metals are often plated to provide corrosion protection.
 Typical plating are :
1. zinc (galvanizing)
2. tin (tinplate)
3. lead (ternplate)
4. chrome
5. nickel.
Illustration on Prevention of corrosion =
https://www.youtube.com/watch?v=jQoE_9x37mQ

9. Cuprous Metals
 Cuprous metals include copper, bronze (copper/tin alloys) and brass (copper zinc
alloys).
 These alloys are fairly corrosion resistant. A protective layer of oxide is usually
formed, giving them a dull, dark appearance. If exposed to organic acids, or
moisture and carbon dioxide, pale green and/or blue copper carbonates may be
formed. These are generally stable and are not an ongoing corrosion concern,
although they may appear unsightly.
 Sulphides cause tarnish, which on copper and its’ alloys is typically a thin
rainbow coloured patina. Copper sulphides are generally chemically stable.
 Brass and bronze in conditions where they are subjected to mildly acid flowing
water, are liable to de-alloying. This is known as “dezincification” and
“destannification” respectively. The zinc and tin are gradually leached out of the
alloys, leaving a porous, physically weak copper matrix.

10. Cuprous Metals
 Surface Treatment - Soaking in sodium carbonate—which does not form a
complex ion with copper and is unlikely to affect the patina but is slower
than the sesquicarbonate—or benzotriazole aqueous solutions may also be
used. The carbonate is similar in effect to the sesquicarbonate. The
benzotriazole does not remove the chlorides or neutralise the acid present
but acts as a physical barrier to water, oxygen, and chlorides and so can be
used as a final step in all cases but as a first or only step in only minor cases.
 Internal Treatment - Then soaking in a benzotriazole (BTA)– ethanol solution
to chelate the copper and make it unreactive. Pits and holes may be filled
with zinc powder which is then painted over with shellac coloured to look
like the specimen.

11. Copper Alloys
 Copper alloys - vulnerable to active corrosion by chlorides. In the right
conditions chlorides will result in pitting, and it is often referred to as “Bronze
Disease” since it is possible for the corrosion to “infect” other nearby parts.
 Chloride corrosion of copper and its alloys is a cyclic process. The chlorides react
with copper to form cupric chloride, which then in turn reacts with moisture to
form hydrochloric acid, which then attacks un-corroded copper
 Surface treatment - In practise this first involves physical cleaning (with a
wooden or even metal pick) to remove the bulk of the chlorides and then
chemical treatment. One chemical treatment is soaking the object in a 5%
sodium sesquicarbonate solution. This serves to neutralise the acid that attacks
the metal as well as converting the reactive cuprous chloride to largely inert
cuprous oxide. The oxide may coat the artefact with unsightly but harmless
black spots or generally darken the metal.

12. Aluminium alloys
 Alluminium alloys - include copper, magnesium, zinc, silicone.
 Aluminium alloys have very good corrosion resistance, because of a thin
layer of aluminium oxide that forms rapidly on the surface. Chlorides and
sulphates are the most common causes of corrosion encountered. If the
protective oxide layer is interrupted in the presence of chlorides, pitting
usually results. Chloride pitting of aluminium is similar to bronze disease, in
that it becomes a self-propagating cycle.

13. Machine Failure
 Faulty design
 Material defects
 Process and manufacturing deficiencies
 Assembly of installation defects
 Off-design or unintended service conditions
 Improper operation
 Maintenance deficiencies

14. Machinery Failure
Many causes of failure in machinery exist and their predominance will vary to
some degree from industry to industry. However, the most common causes, in
order, are:
 Misalignment
 Unbalance
 Resonance
 Bearings
 Looseness
 Flow-related problems
 Electrical

15. Misalignment
 Misalignment exists when the center lines of two adjacent machines
deviate from each other.
 Misalignment is universally recognized as the leading contributor to
machinery failure. For the same level of vibration it is much more serious
than unbalance for its effect in reducing bearing life, largely because of the
parasitic axial thrust.

16. Principal Causes of Misalignment
 Lack of appropriate Standards and Specifications
 Poor Tolerances and Poor Methods
 Good Methods, but bad practices
 Lack of understanding of precision process
 Dynamic movement (thermal growth, pipe strain etc.)
 Misdiagnosis with Unbalance or Looseness

17. Unbalance
 Unbalance exists when the mass center line of a rotor is not coincident with
the geometric center line. The resultant orbital motion has a severe impact
on the life of bearings and on seals.

18. Principal Causes of Unbalance
 Accumulation of assembly tolerances
 Poor attention to assembly
 Inappropriate use of standards
 Non-homogeneous materials (casting blow holes)
 Operational – uneven build up of product
 Erosion of rotor material

19. Resonance
 Resonance is a condition which occurs when a machine forcing frequency
(related to rotational speed) becomes coincident with, or close to, the
natural frequency of a machine component or appendage.
 The condition is like that of a mechanical amplifier and can result in a very
severe vibration at that frequency when the forcing vibration is already too
high.
 Tacoma bridge collapses due to resonance

20. Bearing Failure
 The most common cause of bearing failure is loss or contamination of the
lubricant. Mechanical defects such as misalignment and unbalance have a
severe impact upon bearing life.
 There is a cubic relationship between fatigue (vibration velocity) and
bearing life; thus a halving of vibration velocity can theoretically give 8X the
bearing life.

21. Bearing Failure Categories

22. Looseness
 Looseness may be considered as being where parts are not fitted tightly
together. Typically this fits into three categories;
 Structural looseness/weakness of machine feet, baseplate or foundation.
Also by deteriorated grouting, loose hold-down bolts at the base and
distortion of the frame or base. This may be seen as Soft Foot.
 Loose Plummer block bolts, cracks in frame structure or bearing pedestal.
 Improper fit between component parts, e.g. excessive clearance in a sleeve
or rolling element bearing, impeller loose on its shaft.

23. Flow Related Problems
 Flow related problems such as cavitation and recirculation are caused by pumps
operating outside of their design parameters.
 When a centrifugal pump is operated below its design capacity, or with extreme
suction conditions, it is likely to experience cavitation. Cavitation occurs when
vapour bubbles are formed in the pump low pressure regions and then collapse
in a higher pressure region; the collapse leads to erosion of the impeller, and
sometimes the casing.
 Another common problem with centrifugal pumps is recirculation. Liquid returns
from the impeller discharge either externally to the impeller suction through
worn wear rings, or may return internally, and impacts on the impeller vanes.
The problem is worse when the discharge is throttled or when the impeller is
axially displaced so that it does not align with the pump discharge. The result is
increased vibration at vane passing frequency and there may be a significant
temperature increase. The reverse flow in the pump and mixing of the liquid
results in a random vibration not unlike cavitation and can lead to erosion of the
impeller.