API 571 Damage Mechanisms
GENERAL MECHANICAL
AND METALLUGICAL
FAILURE MECHANISMS
Graphitization
Strain Aging
Brittle Fracture
A change in the
carbide phase of
C/S and 0.5 Mo
steels after long
term exposure to
800° F (427° C) to
1100°F (593° C)
temperatures
causing
decomposition
into graphite
nodules.
The deformation
and aging at an
intermediate
temperature of
older C/S and C-05 Mo low alloy
steels.
Rapid fracture
under stress with
little evidence of
plastic
deformation.
Short Term
Overheating
Localized
overheating
causing
deformation
and/or rupture at
low stress levels.
Thermal Shock
Occurs when high
and non-uniform
thermal stresses
develop over a
short period of
time. If restrained,
stresses above the
yield strength can
occur.
Softening
(Spheroidization)
A change in the
microstructure of
steels where the
carbide phase
change from
normal plate like
forms to
spheroidal in the
temperature range
of 850°F (454°C) to
1400°F (760°C)
885
Embrittlement
Creep/ Stress
Rupture
A loss of
toughness in alloys
containing a ferrite
phase (400 series
SS, duplex SS,
wrought and cast
SS, welds &
overlay) due to
exposure to
600°F(316°C) to
1000°F(538°C).
At high
temperatures
metals deform
under load below
the yield stress.
Steam Blanketing
A steam blanket
inside a tube
caused by a
"departure from
nucleate boiling"
that causes
localized
overheating and
deformation
and/or rupture.
Erosion/ Erosion
Corrosion
Temper
Embrittlement
Sigma Phase
Embrittlement
The accelerated
removal of
material from
impacts of solids,
liquids or vapors.
The erosion can be
increased when
corrosion removes
protective films or
scales.
A reduction in
toughness in low
alloy steel due to
long term
exposure to
650°F(343°C) to
1100°F(593°C).
Equipment may
fail during startup
or shutdown.
Brittle phase in SS
due to high temp
exposure of
1000°F (538°C)to
1750°F(954°C).
Increased
likelihood due to
higher ferrite,
chromium, and
molybdenum
content.
Thermal
Fatigue
Dissimilar
Metal Cracking
Cavitation
Thermal cycling
resulting in
cracking from
high stresses at
restrained areas
of equipment.
Cracking in the
ferritic side of a
weld between a
300 series SS
and a ferritic
material
operating at
high
temperature.
Localized
impact forces of
collapsing vapor
bubbles causing
erosion, usually
in pumps and
downstream of
orifices or
control valves.
Mechanical
Fatigue
Vibration-Induced
Fatigue
Refractory
Degradation
Cracking from
cyclical stresses
resulting from
mechanical
loading or thermal
cycling.
Mechanical fatigue
from dynamic
loading due to
vibration, water
hammer, or
unstable fluid flow
initiating at stress
risers or notches.
Mechanical
damage and
corrosion to
refractory due to
thermal shock,
expansion, and
oxidation,
sulfidation, and
high temperature
mechanisms.
Reheat Cracking
Cracking most often observed in
heavy wall sections due to stress
relaxation from PWHT and service
at elevated temperatures.
Gaseous Oxygen-Enhanced
Ignition and Combustion
Many metals are flammable in
oxygen and enriched air (>25%
oxygen) services even at low
pressures, whereas they are nonflammable in air. The spontaneous
ignition or combustion of metallic
and non-metallic components can
result in fires and explosions in
certain oxygen-enriched gaseous
environments if not properly
designed, operated and
maintained. Once ignited, metals
and non-metals burn more
vigorously with higher oxygen
purity, pressure and temperature.
API 571 Damage Mechanisms
UNIFORM OR
LOCALIZED LOSS OF
THICKNESS
Galvanic
Corrosion
Atmospheric
Corrosion
Corrosion Under
Insulation
Electrochemical
induced metal loss
of dissimilar
metals when
joined together in
a suitable
electrolyte such as
a moist or
aqueous
environment or
moist soil.
Corrosion from
moist atmospheric
conditions, more
severe in marine
and industrial
environments.
Corrosion from
water trapped
under insulation
or fireproofing.
Cooling Water
Corrosion
General or
localized corrosion
of C/S and other
metals caused by
dissolved salts,
gases, organic
compounds or
microbiological
activity.
Boiler Water
Condensate
Corrosion
General corrosion
and pitting in
boilers and
condensate return
piping from
dissolved oxygen
and CO2.
CO2 Corrosion
Carbonic acid from
CO2 in water
causing general or
pitting corrosion
of C/S.
Flue Gas DewPoint Corrosion
Microbiologically
Induced Corrosion
Sulfur and chlorine
species in fuel gas
with water vapor
condense and
form sulfurous
acid, sulfuric acid,
and hydrochloric
acid, leading to
corrosion.
Corrosion from
bacteria, algae, or
fungi in aqueous
environments
especially in
stagnant or low
flow conditions.
Soil Corrosion
The deterioration
of metals exposed
to soils related to
temperature,
moisture, and
oxygen availability
and other
variables.
Caustic
Corrosion
Corrosion either
local or general
caused by
caustic or
alkaline salts,
usually in high
heat transfer
conditions or
high solution
strengths.
Dealloying
Graphite
Corrosion
Preferential
attack on one
or more alloy
constituents
leaving a
dealloyed often
porous
structure.
Corrosion of the
cast iron matrix
of cast iron
leaving
corrosion
products and
porous
graphite.
HIGH TEMPERATURE
CORROSION 200°C (400°F)
Oxidation
Sulfidation
Carburization
Oxygen
combined with
C/S and other
alloys at high
temperature
creating oxide
scales.
Carbon
absorbed into a
material at
elevated
temperature
while in contact
with a
carbonaceous
material or
carburizing
environment.
Carbon
absorbed into a
material at
elevated
temperature
while in contact
with a
carbonaceous
material or
carburizing
environment.
Decarburization
Metal Dusting
The removal of
carbon from
mainly carbon
steel at high
temperatures
resulting in low
strength.
Carburization
resulting in
accelerated
localized pitting
occurring from
carburizing
gasses and
streams
containing
carbon and
hydrogen.
Corrosion
Fatigue
Fatigue cracking
from cyclic
loading and
corrosion
initiating from
stress risers.
Caustic Stress
Corrosion
(Caustic
Embrittlement)
Surface initiated
cracking of metal
surfaces exposed
to caustic
primarily adjacent
to non PWHT'ed
welds.
Fuel Ash
Corrosion
Nitriding
High temperature
wastage of metal
surfaces of fired
heaters, boilers,
and gas turbines
from fuel gas
contaminants like
sulfur, sodium,
potassium, and or
vanadium.
A hard brittle
surface layer on
C/S, low alloy, 300
& 400 series SS
from high levels of
N2 in ammonia
and cyanides
particularly under
reducing
conditions.
Chloride Stress
Corrosion
Cracking
Ethanol Stress
Corrosion
Cracking
Sulfate Stress
Corrosion
Cracking
Surface cracks of
300 SS and some
nickel alloys from
tensile stress,
temperature, and
an aqueous
chloride
environment.
Surface-initiated
cracks caused by
environmental
cracking of carbon
steel under the
combined action
of tensile stress
and a fuel grade
ethanol
Surface initiated
cracks caused by
environmental
cracking of copper
alloys in sulfate
solutions over
many years. Most
commonly found
in heat exchanger
tubes, primarily in
cooling water
services.
Ammonia Stress
Corrosion
Cracking
Aqueous ammonia
streams cause
cracking in some
copper alloys. C/S
cracks in
anhydrous
ammonia.
Liquid Metal
Embrittlement
Cracking when
certain liquid
metal contacts
specific alloys.
Hydrogen
Embrittlement
Hydrogen charging
of metals leading
to brittle cracking.
Charging can come
from
manufacturing,
welding, or service
environment.
REFINING INDUSTRY UNIFORM
OR LOCALIZED LOSS ON
THICKNESS PHENOMENA
Amine Corrosion
General or
localized corrosion
principally on C/S
in amine treating
processes.
Ammonium
Bisulfide Corr.
(Alkaline Sour
Water)
Alkaline sour
water corrosion in
hydro processing
reactor effluent
streams and in
alkaline sour water
streams.
Hydrofluoric Acid
Corrosion
HF acid causes
high rates of
general or
localized corrosion
with hydrogen
cracking,
blistering, and/or
HIC/SOHIC.
Naphthenic
Acid Corrosion
Ammonium
Chloride
Corrosion
High
temperature
corrosion from
naphthenic acid
content,
temperature,
sulfur content,
velocity and
alloy
composition.
General or
localized
corrosion
occurring under
ammonium
chloride or
amine salt
deposits, often
without free
water.
Hydrochloric
Acid (HCI)
Aqueous HCL
causing both
general and
localized
corrosion
aggressively
affects most
materials.
High Temp
H2/H2S Corrosion
Sulfuric Acid
Corrosion
Aqueous Organic
Acid Corrosion
Hydrogen in H2S
streams increases
high temperature
sulfide corrosion
above 500°F with
uniform loss in
thickness in hot
hydro processing
circuits
Sulfuric acid
corrodes CS both
generally and
locally in HAZ's
especially. Very
sensitive to flow
rates and water
concentration.
Organic
compounds
present in some
crude oils
decompose in the
crude furnace to
form low
molecular
weight organic
acids which
condense in
distillation tower
overhead systems
Phenol (Carbonic
Acid) Corrosion
Phosphoric Acid
Corrosion
Sour Water
Corrosion
Acid solvent
corrodes C/S in
phenol extraction
of aromatics in
lube oil feed
stocks.
Phosphoric acid
can cause pitting
and localized
corrosion of C/S
depending on acid
concentration,
temperature, and
contaminants (free
water content).
Corrosion of steel
due to acidic sour
water (H2S)
between 4.5 and
7.0 ph.
Environment-Assisted Cracking
Amine Stress
Corrosion
Cracking
Cracking most
often found at non
PWHT'ed carbon
steel weldments in
aqueous
alkanolamine
service.
Wet H2S Damage
(Blistering)
Hydrogen Stress
Cracking-HF
Hydrogen
blistering,
Hydrogen induced
cracking, Stress
oriented hydrogen
induced cracking,
and sulfide stress
corrosion cracking
from hydrogen
permeation of
steel and low alloy
steel.
Cracking of C/S
and low alloy
steels in weld
metal and HAZ's
from exposure to
aqueous HF acid
environments.
Carbonate Stress
Corrosion Cracking
Cracking adjacent
to C/S welds from
alkaline corrosion
and tensile stress.
Polythlonic Acid
Stress Corrosion
Cracking
Cracking due to
sulfide scale, air,
and moisture
acting on sensitized
austenitic SS.
Other Damage Mechanisms
High Temp Hydrogen
Attack (HTHA)
Hydrogen at high
temperatures reacts with
carbides to form methane
which cannot diffuse
through the steel and also
cause a loss of strength.
Titanium Hydriding
Hydrogen diffusing into
titanium creates a brittle
phase.
0
