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The three models of loading
III III
MODE IOpening MODE
MODE IISliding MODE
MODE IIITearing MODE
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Approaches of (corrosion-) fatigue
- Classical approach:Woehler / Smith curves
- Fracture mechanics approach:Paris’ law: da/dN = C.Kn
C and n are constants for a given material and stress ratios
The stress intensity factor K is determined by: K = f. . .a N/mm3/2
f = geometry factor = nominal stressa = crack length
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S-N curves of X6CrNiMoTi17-12-2 in air and acetic acid
(Woehler / Smith curves)C
yclic
str
ess
rang
e S
(±
c
kg/m
m2)
105 106 107 108
Frequency N
Environment:
air 25°C
acetic acid12%
smooth testspecimen
notched testspecimen
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SN–curve; area of low cycle fatigue (LCF) and high cycle fatigue (HCF)
10 3 104 104 106 107 108
Nf
LCF HCF
yield strength
determined
by determined
by
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Corrosion fatigue crack propagation rate as a function of the cycle crack tip stress intensity factor
Region I Region II Region III
Slow crackgrowth
Power law behaviour
da /dN = C.(K) n
Fractureinstability
Aggressive environment Perturbations due toSCC, hydrogen embrittlement etc.
Inertenvironment
Log
(da
/dN
)
Log (K)
KICKISCC
KthKICFC
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Signalamplifier
Servo controller
Signalamplifier
BFS
F
Process computer
Background terminal
Schematic lay-out of corrosion fatigue test arrangementPower cell
Cylinder
crack
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• Surface conditions
• surface roughness
• properties of surface metal like hardness and
strength
• residual stress condition of surface
• Stress/load/cycle frequency parameters
• stress intensity range
• load frequency
• stress ratio
Parameters influencing corrosion fatigue
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Parameters influencing corrosion fatigue (continued)
• Environmental aspects• composition of aggressive environment (pH,
temperature)• electrode potential
• Alloy properties• chemical composition• microstructure• yield strength
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Wood’s model for initation of a micro crack in sliding zone
free surface
fresh surface
1e cycle 2e cycle
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cyclic sliding
initiation ofmicro crack
propagation ofmicro crack
propagation ofmacro crack
finalfracture
initiation period (stage I)
propagation period (stage II)
initial fracture
(stage III)
Different stages of fatigue process
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Model of wood for initiation of a microcrack in
sliding zone
cyclic sliding
initiationof crack
propagation ofmicro crack
propagation ofmacro crack
finalfracture
initation period propagation period
initial fracture
Different stadia of fatigue process
free surface
fresh surface
1e cycle 2e cycle
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Stage I and stage II of fatigue crack propagation
load direction
free surface
Stage I Stage II
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Improvement of design:
• reduce the stress and number of stress cycles;
• avoid abrupt changes in diameter and sharp angles;
• use (full penetration) butt welds instead of fillet welds;
• avoid internal stresses;
• enlarge the dimensions, mass or strength of critical
components;
• ensure a sufficiently flexible construction in order to
absorb excessive stresses due to thermal expansion,
vibrations, shocks, and load and pressure variations.
Preventive measures to eliminate or reduce corrosion fatigue
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Preventive measures to eliminate or reduce corrosion fatigue (continued 1)
Using more resistant materials:
• with improved corrosion resistance;• with improved ductility and impact strength.
Duplex stainless steel are generally speaking morecorrosion fatigue resistant then austenitic stainlesssteels. Copper and copper alloys are better than carbonsteel and aluminium.
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Preventive measures to eliminate or reduce corrosion fatigue (continued 2)
Improvement of surface condition:
• by removing tensile stresses and/or creating compressive stresses by stress relief annealing or shot peening, hammering, rolling;
• by decrease in surface roughness: as forged – hot rolled – machined – ground;• by autofrettage (e.g. high pressure piping in HDPE
plants)• by nitriding or carburizing;• by application of coating and/or cathodic protection;
(be careful with (cracked) chrome plating).
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Stress distribution in a shot-peened item
A. Distribution of residual stress in a shot peened beam having no external load
0TensionPeened surface
compression
compressiontension
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Preventive measures to eliminate or reduce corrosion fatigue (continued 3)
Changing corrosivity:
•by means of inhibitors.
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceErosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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• A cavitation bubble forms on the protective film
• The bubble collapses and destroys the film
• The newly exposed metal surface corrodes and the
film is reformed
• A new cavitation bubble forms at the same spot
• The bubble collapses and destroys the film
• The exposed area corrodes and the film reforms
Mechanism of cavitation
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Impingement attack of tube wall
Corrosion film
Impingementcorrosion pits
Original metalsurface
Metal tube wall
Water flow
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• Avoid bubbles of gas and solids
• Use more impingements resistant materials like f.i.
cupro-nickel alloys
• Install impingement plates
• Install inserts at entrance side of heat exchangers
Preventive measures to minimize or avoid impingement attack
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Parameters influencing liquid abrasion
Process side:• form and magnitude of particles• velocity of particles• hardness of particles• corrosivity of liquid (or particles)
Material of construction:• hardness• alloy composition• microstructure• corrosion resistance
Interaction between environment and material of construction:• angle of incidence
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Locations with erosion-corrosion in fertilizer plant
VULMERGEL50m3
STOFBUNKER
Peil
1
2
3
4
Dak
Vulmergel van NF2
Plaatsen met erosie
Filters Droogstraat 1Verlaad +
corr.stof
Luchtverhitter
Stofdoseerschroef
Mengschroef
Doseer inrichting
Buiten
Straat 2
Droogtrommel 1 Kooi
Recycle band
Geluidsdemper
W.R.
Emmerladder
goed stofgrof
goedstof
grof
Straat 2
Trilgoot 1B Trilgoot 1A
Zeef 1B Zeef 1A
Grofbreker 1B
Trilgoot
A.N.v. NF2
condens
Granuleerschroef
W.R.
Lucht ± 100°C 5000 m3/h
• •
•
Product koeler
stoom
Band B2108 Band B2114
Via band B2108 en/of B2114 naar Corr. Zeven en Coating NF2
Stofafzuiging filter
Fijn-breker
Grofbreker 1A
Zeef-brekerprod.
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Area with serious gas abrasion
Ø 168
ø
-xøDipleg
Ø 657
Gas outlet
ø
Gas inlet
Gas abrasion in cyclone of acrylonitrile reactor
Top view
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Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
NTT Consultancy
Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Parameters influencing erosion
Process side:• form and magnitude of particles• velocity of particles• hardness of particles
Material of construction:• hardness• alloy composition• microstructure
Interaction between environment and material of construction:• angle of incidence
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Angle of incidence of erosive particle on material
small angle of incidence
α v cos α
v sin α
v cos αα
v sin αlarge angle of incidence
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Survey of angles of incidence applicable for erosion resistant materials
glassbas
alt
90°
30°
45°
60°
75°
0°
15°
C-ste
el
X22CrN
i17-
2
Verbund s
tahl
Casto
lin 6
710
RCH 100
0
polyure
than
e
Skega
rubber
epoxy
san
d
Al 2O 3
tile
s
linatex
Angle of incidence
applicable
doubtful applicability
not applicable
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Applicabilty of several materials of construction
Ang
le o
f in
cide
nce
90º
80
60
70
50
40
20
30
10
0
Erosion resistant
C-s
tee
l
X2
2C
rNi1
7-2
X2C
rNiM
oN
22-5
-3
Ver
bun
d st
ahl
Cas
tolin
67
10
Met
colo
y 2
RC
H 1
000
Epo
xy s
and
Rhi
no H
yde
poly
ure
tha
ne
Ske
ga r
ubbe
r
Lina
tex
Bas
alt
Alu
m o
xide
Arm
ed g
lass
Pol
ypro
p.
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Survey of design solutions to minimize erosion(-corrosion)
1. Pipe with dead end instead of elbow
erosioncorrosion
Old situation
filled withproduct
New situation Old situation New situation
2. Use of U-beams under pipes
U-beamfilled withcement mortar
erosioncorrosion atthe bottom
Old situation New situation
erosion-corrosion
3. Welding of ribs in bunkers and funnels
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Design solutions to minimize erosion (-corrosion) in product pipelines
O 200 pipelineerosion-corrosionat bottom side
Old situation New situation
O 200 pipeline
Gutter at bottomand side walls (partially)coated with Al2O3 tiles
O 200 pipeline
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Survey of application of erosion-corrosion resistant materials
Cast alloys:
Ni-hard: C: 2.9; Si: 0.3 – 0.8; Cr: 1.5 – 2.5;
Ni: 4.15 – 4.75; Mn: 0.4 – 0.6.
Application: fine crushers.
GX260CrMoNi20-2-1.
Application: fine crushers.
Guronit V35; GX250Cr25.
Application: tips of granulation screws.
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Survey of application of erosion-corrosion resistant materials (continued 1)
Hardening steels
Verbundstahl SPM 2304, a hardening steel (composition
C: 0.9; Cr: 1.9; Mn: 0.4; Mo: 0.35) cladded on a non
hardening steel e.g. steel St. 33. Hv after hardening about
800.
Application: spin buckets, funnels, hoppers, distribution
plates.
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Survey of application of erosion-corrosion resistant materials (continued 2)
Overlay welds:
Covered electrodes:
Castolin 6710: C: 5.5; Cr: 43.
Abrassadur 43: C: 6.5; Cr: 24; Nb: 7.
Application: overlay welding of granulation screws and
cage mills.
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Survey of application of erosion-corrosion resistant materials (continued 3)
Metallic, ceramic spray layers (wire, powder or
plasma spray:
Metcoloy 2: Co: 3; Cr: 13; balans: Fe.
Application: troughs, granulation screws (applied with
wire gun).
Al2O3, Cr2O3, SiO2 ceramic spray layers.
Application: valve seats and plugs.
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Survey of application of erosion-corrosion resistant materials (continued 4)
Electroplating
Hard chromium plating. Application: Tuflin valves.
Diffusion layers:
Cr-diffusion. Application: control valves,
dust extraction system
Nitriding. Application: axles, stirrers, agitators.
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Survey of application of erosion-corrosion resistant materials (continued 5)
Ceramic materials:
Aluminium oxide. Application: tiles in gutters, funnels.Sillicon carbide. Application: wear rings in pumps. Silicon nitride. Application: spray nozzles.
Cementation (trowel and spray layers):
Epoxy-sand. Application: gutters.Cement mortar. Application: filler material for U-profiles at bottom side of lines.
Plastic types:
RCH 1000; Polyurethane; Linatex; Skegarubber.Application: as a liner in hoppers, funnels, gutters.
NTT Consultancy
Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
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Fretting corrosion
Basic requirements for the occurrence of fretting
corrosion are:
• The interface must be under load.• Vibration or repeated relative motion between the two
surfaces must occur.• The load and the relative motion of the interface must
be sufficient to produce slip or deformation of the surfaces.
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Example of typical location of fretting corrosion (press-fitted ball-bearing race on a shaft)
Fretting at tight fits subject tovibration
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Coldweld
Before After
Contactpoint
Schematic illustration of the wear-oxidation theory of fretting corrosion
Oxidizedparticles
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Oxidelayers
Before After
Exposedmetal
Schematic illustration of the oxidation- wear theory of fretting corrosion
Oxideparticles
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• Lubrication with oil or grease; preferably in conjunction with phosphate coatings (Parkerizing). Molybdenum sulfide is effective as a solid lubricant.
• Combination of a soft metal with a hard metal.
• Increasing the surface hardness by shot peening or cold working.
• Use elastomer gaskets to absorb vibration.
• Decreasing the load or on the other hand increasing the load to avoid slip completely (by hydrolic fit).
Preventive measures to minimize or avoid fretting corrosion
NTT Consultancy
Key-fit
fretting
Coupling at the part of MP casing edge
Coupling at the part of steam edge
Shaft of syngasscompressorAFA 2/3
Rotor of syngas compressor with key-fit of axial thrust disc
NTT Consultancy
Forms of erosion-corrosion
Single-faceerosion-corrosion(unilateral)
mediumliquid
mediumgas
mediumelectrons
without solids
with solids
turbulence
vapor
gas
Failure mode
liquid erosion
cavitation erosion
Impingement attack
liquid abrasion
gas erosion
gas abrasion
drop erosion
spark erosion
electron beamerosion
fretting corrosionbaffle hammering
Two-faceerosion-corrosion(bilateral)
without solids
with solidssolid
liquid
liquid and/or gas
vacuum
arc
irradiation withelectron beams
Single-face erosion
mediumsolids
erosion (wear)
NTT Consultancy
General measures to combat erosion - corrosion
Aspect Specific for 1 aspect Valid for both aspects
(electro-)
chemical
decrease of temperature
inhibitor dosing
cathodic protection
material of construction
surface protection
- organic layers
- inorganic layers
- metallic layers
mechanical
deaeration
filtration
decrease of velocity
- Tees
- 90° elbows
avoid - elbows with
small radius
design
- impingement
use plates
- replaceable
wear plates