571 Damage Mechanisms

7/27/2019 571 Damage Mechanisms

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API 571 Damage Mechanisms

GENERAL MECHANICALAND METALLUGICAL

FAILURE MECHANISMS


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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 to 1100F

temperatures causing decomposition

into graphite nodules.

The deformation and aging at an

intermediate temperature of older

C/S and C-0-5 Mo low alloy steels.

Rapid fracture under stress with little

evidence of plastic deformation.


3/29

Short Term

OverheatingThermal Shock

Softening

(Spheroidization)

Localized

overheating

causingdeformation

and/or rupture at

low stress levels.

Occurs when high

and non-uniform

thermal stressesdevelop over a

short period of

time. If restrained,

stresses above the

yield strength canoccur.

A change in the

microstructure of

steels where thecarbide phase

change from

normal plate like

forms to

spheroidal in thetemperature range

of 850F to 1400F


4/29

885

Embrittlement

Creep/ Stress

RuptureSteam Blanketing

A loss of

toughness in alloys

containing a ferritephase (400 series

SS, duplex SS,

wrought and cast

SS, welds &

overlay) due toexposure to 600F

to 1000F.

At high

temperatures

metals deformunder load below

the yield stress.

A steam blanket

inside a tube

caused by a"departure from

nucleate boiling"

that causes

localized

overheating anddeformation

and/or rupture.


5/29

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 removesprotective films or

scales.

A reduction in

toughness in low

alloy steel due to

long termexposure to 650F

to 1100F.

Equipment may

fail during startupor shutdown.

Brittle phase in SS

due to high temp

exposure of

1000F to 1750F.Increased

likelihood due to

higher ferrite,

chromium, andmolybdenum

content.


6/29

Thermal

Fatigue

Dissimilar

Metal CrackingCavitation

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 athigh

temperature.

Localized

impact forces of

collapsing vapor

bubbles causing

erosion, usually

in pumps and

downstream oforifices or

control valves.


7/29

Mechanical

Fatigue

Vibration-Induced

Fatigue

Refractory

Degradation

Cracking from

cyclical stresses

resulting from

mechanicalloading or thermal

cycling.

Mechanical fatigue

from dynamic

loading due to

vibration, waterhammer, or

unstable fluid flow

initiating at stress

risers or notches.

Mechanical

damage and

corrosion to

refractory due tothermal shock,

expansion, and

oxidation,

sulfidation, andhigh temperature

mechanisms.


8/29

Reheat CrackingGaseous Oxygen-Enhanced

Ignition and Combustion

Cracking most often observed inheavy wall sections due to stress

relaxation from PWHT and service

at elevated temperatures.

Many metals are flammable inoxygen and enriched air (>25%

oxygen) services even at low

pressures, whereas they are non-

flammable in air. The spontaneous

ignition or combustion of metallicand non-metallic components can

result in fires and explosions in

certain oxygen-enriched gaseous

environments if not properly

designed, operated andmaintained. Once ignited, metals

and non-metals burn more

vigorously with higher oxygen

purity, pressure and temperature.


9/29

API 571 Damage Mechanisms

UNIFORM OR

LOCALIZED LOSS OFTHICKNESS


10/29

Galvanic

Corrosion

Atmospheric

Corrosion

Corrosion Under

Insulation

Electrochemicalinduced metal loss

of dissimilar

metals when

oined together ina suitable

electrolyte such as

a moist or

aqueous

environment or

moist soil.

Corrosion frommoist atmospheric

conditions, more

severe in marine

and industrialenvironments.

Corrosion fromwater trapped

under insulation

or fireproofing.


11/29

Cooling Water

Corrosion

Boiler Water

Condensate

Corrosion

CO2 Corrosion

General or

localized corrosion

of C/S and other

metals caused bydissolved salts,

gases, organic

compounds or

microbiological

activity.

General corrosion

and pitting in

boilers and

condensate returnpiping from

dissolved oxygen

and CO2.

Carbonic acid from

CO2 in water

causing general or

pitting corrosionof C/S.


12/29

Flue Gas Dew-

Point Corrosion

Microbiologically

Induced CorrosionSoil Corrosion

Sulfur and chlorinespecies in fuel gas

with water vapor

condense and

form sulfurousacid, sulfuric acid,

and hydrochloric

acid, leading to

corrosion.

Corrosion frombacteria, algae, or

fungi in aqueous

environments

especially instagnant or low

flow conditions.

The deteriorationof metals exposed

to soils related to

temperature,

moisture, andoxygen availability

and other

variables.


13/29

Caustic

CorrosionDealloying

Graphite

Corrosion

Corrosion either

local or general

caused by

caustic or

alkaline salts,

usually in high

heat transfer

conditions or

high solution

strengths.

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.


14/29

HIGH TEMPERATURECORROSION (400F)


15/29

Oxidation Sulfidation Carburization

Oxygen

combined with

C/S and other

alloys at hightemperature

creating oxide

scales.

Carbon

absorbed into a

material at

elevatedtemperature

while in contact

with a

carbonaceousmaterial or

carburizing

environment.

Carbon

absorbed into a

material at

elevatedtemperature

while in contact

with a

carbonaceousmaterial or

carburizing

environment.


16/29

Decarburization Metal DustingCorrosion

Fatigue

The removal of

carbon from

mainly carbon

steel at hightemperatures

resulting in low

strength.

Carburization

resulting in

accelerated

localized pittingoccurring from

carburizing

gasses and

streams

containing

carbon and

hydrogen.

Fatigue cracking

from cyclic

loading and

corrosioninitiating from

stress risers.


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18/29

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 gradeethanol

Surface initiated

cracks caused by

environmental

cracking of copper

alloys in sulfate

solutions over

many years. Most

commonly foundin heat exchanger

tubes, primarily in

cooling water

services.


19/29

Ammonia Stress

Corrosion

Cracking

Liquid Metal

Embrittlement

Hydrogen

Embrittlement

Aqueous ammonia

streams cause

cracking in some

copper alloys. C/Scracks in

anhydrous

ammonia.

Cracking when

certain liquid

metal contacts

specific alloys.

Hydrogen charging

of metals leading

to brittle cracking.

Charging can comefrom

manufacturing,

welding, or service

environment.


20/29

REFINING INDUSTRY UNIFORM

OR LOCALIZED LOSS ON

THICKNESS PHENOMENA


21/29

Amine Corrosion

Ammonium

Bisulfide Corr.

(Alkaline Sour

Water)

Hydrofluoric Acid

Corrosion

General or

localized corrosion

principally on C/Sin amine treating

processes.

Alkaline sour

water corrosion in

hydro processingreactor effluent

streams and in

alkaline sour water

streams.

HF acid causes

high rates of

general orlocalized corrosion

with hydrogen

cracking,

blistering, and/orHIC/SOHIC.


22/29

Naphthenic

Acid Corrosion

Ammonium

Chloride

Corrosion

Hydrochloric

Acid (HCI)

High

temperature

corrosion fromnaphthenic acid

content,

temperature,

sulfur content,velocity and

alloy

composition.

General or

localized

corrosionoccurring under

ammonium

chloride or

amine saltdeposits, often

without free

water.

Aqueous HCL

causing both

general andlocalized

corrosion

aggressively

affects mostmaterials.


23/29

High Temp

H2/H2S Corrosion

Sulfuric Acid

Corrosion

Aqueous Organic

Acid Corrosion

Hydrogen in H2Sstreams increases

high temperature

sulfide corrosion

above 500F withuniform loss in

thickness in hot

hydro processing

circuits

Sulfuric acidcorrodes CS both

generally and

locally in HAZ's

especially. Verysensitive to flow

rates and water

concentration.

Organiccompounds

present in some

crude oils

decompose in thecrude furnace to

form low

molecular

weight organic

acids which

condense in

distillation tower

overhead systems


24/29

Phenol (Carbonic

Acid) Corrosion

Phosphoric Acid

Corrosion

Sour Water

Corrosion

Acid solventcorrodes C/S in

phenol extraction

of aromatics in

lube oil feed

stocks.

Phosphoric acidcan cause pitting

and localized

corrosion of C/S

depending on acid

concentration,

temperature, and

contaminants (free

water content).

Corrosion of steeldue to acidic sour

water (H2S)

between 4.5 and

7.0 ph.


25/29

Environment-Assisted Cracking


26/29

Amine Stress

Corrosion

Cracking

Wet H2S Damage

(Blistering)

Hydrogen Stress

Cracking-HF

Cracking most

often found at non

PWHT'ed carbon

steel weldments inaqueous

alkanolamine

service.

Hydrogen

blistering,

Hydrogen induced

cracking, Stressoriented 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'sfrom exposure to

aqueous HF acid

environments.


27/29

Carbonate StressCorrosion Cracking

Polythlonic Acid

Stress Corrosion

Cracking

Cracking adjacent

to C/S welds from

alkaline corrosion

and tensile stress.

Cracking due to

sulfide scale, air,

and moisture

acting on sensitized

austenitic SS.


28/29

Other Damage Mechanisms


29/29

High Temp Hydrogen

Attack (HTHA)Titanium Hydriding

Hydrogen at high

temperatures reacts with

carbides to form methane

which cannot diffusethrough the steel and also

cause a loss of strength.

Hydrogen diffusing into

titanium creates a brittle

phase.

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571 Damage Mechanisms

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