4. Forms of Corrosion; Corrosion-Fatigue; Erosion-corrosion

NTT Consultancy

Corrosion-fatigue

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Corrosion fatigue crack in carbon steel St. 33

150 m

NTT Consultancy

SEM fracture surface (with striations) of fatigue crack in copper

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SEM fracture surface of fatigue crack in AISI 310 labyrint of gas turbine

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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

NTT Consultancy

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

NTT Consultancy

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

NTT Consultancy

Paris’ law

da/dN = C.Kn

A CB

Kth

KIC

log K

logda/dN

NTT Consultancy

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

NTT Consultancy

Compact Tension (CT) test piece

K=f(a,W,B,P)

KIC PC

a

P

P

V

W

B

NTT Consultancy

Signalamplifier

Servo controller

Signalamplifier

BFS

F

Process computer

Background terminal

Schematic lay-out of corrosion fatigue test arrangementPower cell

Cylinder

crack

NTT Consultancy

• 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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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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Changing corrosivity:

•by means of inhibitors.

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Corrosion fatigue in traverse beam of vibration dryer

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Ammonium sulfate vibration dryer

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Fatigue fracture surface of shaft of extruder

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Corrosion fatigue in AISI 316L heat exchanger tube material

200 m

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Erosion - Corrosion

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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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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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

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Liquid erosion in (small diameter) carbon steel sulphuric acid line

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Liquid erosion in (small diameter) carbon steel sulphuric acid line

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Liquid erosion in outer bend of carbon steel line in sulphuric acid service

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Liquid erosion in 304L sulphuric acid line

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Liquid erosion in sulphuric acid line

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Liquid erosion in carbon steel pipeline

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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



Two-faceErosion-corrosion(bilateral)

without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

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Schematic representation of steps in cavitation (R.W. Henke)

1 2 3

4 5 6

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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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Cavitation in cast iron pump impeller

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Cavitation in plug and valve seat of DN50 Stainless steel (Globe) control valve

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Cavitation in 316L control valve

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Cavitation in 316L control valve

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Cavitation in 316L urea grade valve

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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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


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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Impingement attack in copper heat exchanger tube

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Impingement attack in (finned) copper heat exchanger tube

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Impingement attack in carbon steel body of water ring compressor

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Impingement attack in carbon steel body of water ring compressor

NTT Consultancy

• 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

NTT Consultancy



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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

NTT Consultancy

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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Liquid abrasion of a 304 cast impeller of pump in fertilizer plant

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Liquid abrasion in C30E wear partition wall of pump

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Liquid abrasion in 316L pipeline in urea slurry

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Liquid abrasion in outlet gutter of (NH4)2SO4 (Krauss-Maffei) centrifuge

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Liquid abrasion at carbon steel stirrer blade

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Liquid abrasion at Guronit V35 (GX250Cr25) wear tips of granulating screw

NTT Consultancy

Granulating screw with wear tips

NTT Consultancy

Granulating screw with wear tips

NTT Consultancy

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.

NTT Consultancy

Morphology of marl; CaCO3

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Morphology of dolomite, CaMg(CO3)2

NTT Consultancy



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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

NTT Consultancy

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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Dip-leg of cyclone in ACN reactor

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Gas abrasion in carbon steel dipleg of catalyst cyclone

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Repair of dip-leg of cyclone by means of metal spraying

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Cyclone in reactor melamine plant

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Gas abrasion in cyclone of reactor melamine plant

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Gas abrasion in cyclone of reactor melamine plant

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Melamine Reactor R-2101 MELAF 2

A1

A4

A3

A5

A2

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Morphology of spent catalyst, round shape

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Morphology of new catalyst, rocky shape

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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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

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Drop erosion in carbon steel (saturated LP steam) line

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Drop erosion in carbon steel U-bend of steam line

NTT Consultancy



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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

NTT Consultancy

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

NTT Consultancy

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.

NTT Consultancy

Erosion in dolomite transport line

NTT Consultancy

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

NTT Consultancy

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

NTT Consultancy

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.

NTT Consultancy

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.

NTT Consultancy


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.

NTT Consultancy


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.

NTT Consultancy


Electroplating

Hard chromium plating. Application: Tuflin valves.

Diffusion layers:

Cr-diffusion. Application: control valves,

dust extraction system

Nitriding. Application: axles, stirrers, agitators.

NTT Consultancy


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



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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

NTT Consultancy

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.

NTT Consultancy

Example of typical location of fretting corrosion (press-fitted ball-bearing race on a shaft)

Fretting at tight fits subject tovibration

NTT Consultancy

Coldweld

Before After

Contactpoint

Schematic illustration of the wear-oxidation theory of fretting corrosion

Oxidizedparticles

NTT Consultancy

Oxidelayers

Before After

Exposedmetal

Schematic illustration of the oxidation- wear theory of fretting corrosion

Oxideparticles

NTT Consultancy

• 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

Shaft of syngas compressor

NTT Consultancy

Fretting corrosion in axle of compressor

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

Rotor of syngas compressor with hydrolic-fit of axial thrust disc

Hydrolic fit

NTT Consultancy



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




without solids

with solidssolid

liquid

liquid and/or gas

vacuum

arc


Single-face erosion

mediumsolids

erosion (wear)

NTT Consultancy

Baffle hammering in heat exchanger tube

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

4. Forms of Corrosion; Corrosion-Fatigue; Erosion-corrosion

Documents

carbon steel

sem fracture

reactor melamine

water ring

316l control

corrosion

liquid abrasiongas

reduce corrosion