Corrosion Engineering - Online Tutorials - 24HourAnswers.com

Introduction to Degradation Mechanisms

There are few documents being prepared by industrial experts that address and provide guidelines regarding deterioration while in service and the associated breach of integrity.

Degradation mechanisms that are common to a variety of industries including refining and petrochemical, pulp and paper, and power generation may be divided into the following categories:

a) Mechanical and metallurgical Failure

b) Uniform or localized loss of thickness

c) High temperature corrosion [>400°F]

d) Environment assisted cracking

e) Other mechanisms

References –

https://www.asme.org/products/courses/api-5791asme-ffs1-fitness-service –06 July 2015

http://www.techstreet.com/products/1654247 –06 July 2015

 

Graphitization - Corrosion Engineering Topic #1 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is the formation of graphite nodules (free carbon) which occurs between 825°F to 1300°F range over a long period that has an embrittling effect on metal and may cause a loss in strength and ductility

b) Affected materials 

Certain carbon and low alloy steels

c) Critical parameters 

  • Chemistry, stress, temperature, and time. The rate of damage increases with increasing temperature
  • The rate of damage is usually described in a qualitative measure
  • Randomly distributed graphite nodules tend to cause only moderate reductions in strength
  • The effect is of most concern if the graphite nodules form in a continuous manner through a load-carrying member. The two forms of this type of damage occur at weld HAZ’s and along planes of localized yielding in steel

d) Affected units or equipment

  • Boiler tubes and related equipment
  • Buried cast iron pipe
  • Fluid catalytic cracking units and coker units

e) Appearance or morphology of damage 

  • Advanced stages of damage may include cracking

f) Prevention / mitigation 

  • Proper condition assessment techniques to identify and monitor through inspection.
  • Use chromium steels

g) Inspection and monitoring –

  • Damage due to graphitization can be observed using Remote Field Eddy current Testing, and Linear Polarisation Resistance (LPR) soil testing

h) Related mechanisms 

Spheroidization

References – Graphitization effects on high temperature ductwork

http://www.energy-tech.com/maintenance/article_f7211c68-904d-5881-97ac-733b7f4fb003.html - 30 June 2015

 

Spheroidization - Corrosion Engineering Topic #2 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Spheroidizing is a form of softening heat treatment. It is conducted at temperatures above 1025°F. Spheroidization may result in loss of mechanical and creep strength, but ductility is increased

b) Affected materials

Carbon steel and low alloy steels

c) Critical parameters 

  • Chemistry, stress level, initial microstructure, time, and temperature
  • Annealed and coarse-grained steels are more resistant to softening than normalized and fine-grained steels

d) Affected units or equipment

Furnace tubes, reactor/ regeneration equipment in fluid catalytic cracking units

e) Appearance or morphology of damage

  • The graphite content of steel assumes a spheroidal shape after spheroidizing, and after prolonged heating the pearlite layers are broken down and spherical lumps of cementite, or spheroidite, are formed. The graphite content of steel assumes a spheroidal shape after spheroidizing, and after prolonged heating the pearlite layers are broken down and spherical lumps of cementite, or spheroidite, are formed
  • Carbide phases become unstable and begin to agglomerate

f) Prevention / mitigation 

Exercising temperature control

g) Inspection and monitoring 

  • Spheroidization can only be detected by metallographic examination or performing field metallographic replication (FMR)

h) Related mechanisms 

Graphitization

 

Temper Embrittlement - Corrosion Engineering Topic #3 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Temper embrittlement refers to the decrease in notch toughness in some low alloy steels when heated in, or cooled slowly through, a temperature range of 650°F to 1070°F

b) Affected materials 

Plain carbon steels with greater than 0.5% Mn and additions of Ni and Cr will cause greater susceptibility to temper embrittlement

c) Critical parameters 

  • Alloy steel composition (chromium, nickel, manganese and silicon), heat treatment history, temperature and time
  • The main embrittling elements (in order of importance) are antimony, phosphorous, tin and arsenic

d) Affected units or equipment 

Hydroprocessing, catalytic reformer, coker and visbreaking units

e) Appearance or morphology of damage 

  • The irreversible mechanism causes intergranular cracking

f) Prevention / mitigation 

  • The best method of avoidance in existing materials is to reduce the embrittling impurities through control of raw materials and steel production
  • The embrittlement is reversible through short time heating at 1150°F followed by rapid cooling through the embrittling temperature range to room temperature resulting in the elimination of temper embrittlement

g) Inspection and monitoring –

  • Refer to API RP 571 2nd edition – section 4.2.3.7

h) Related mechanisms –

Brittle fracture

i) References – What is temper embrittlement, and how can it be controlled?

http://www.twi-global.com/technical-knowledge/faqs/material-faqs/faq-what-is-temper-embrittlement-and-how-can-it-be-controlled/ - 30 June 2015

 

 

Sigma Phase Embrittlement - Corrosion Engineering Topic #4 - Online Tutorials - 24HourAnswers.com

 

a) Description of damage 

Occurs when affected materials are heated above about 1000°F (540°C). Fracture toughness is reduced drastically

b) Affected materials 

High ferrite content materials

c) Critical parameters 

  • Alloy composition, exposure time, stress at start-up/shutdown and temperature

d) Affected units or equipment 

Stainless steel equipment

e) Appearance or morphology of damage 

  • Detection and verification through metallographic examination and impact testing on failed equipment
  • Damage appears in the form of brittle cracking.

f) Prevention / mitigation 

  • Temperature control or material selection/design (careful delta ferrite control) that have less susceptibility

g) Inspection and monitoring 

Impact testing

h) Related mechanisms 

Brittle fracture

 

Brittle Fracture - Corrosion Engineering Topic #5 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Brittle fracture occurs without warning, and quick fracture under stress (residual and/or applied) where the material exhibits loss of ductility or plastic degradation.

b) Affected materials 

Carbon and low alloy steels

c) Critical parameters 

  • Steel cleanliness, stress level, component thickness, grain size, presence of embrittling phases/critical sized flaw and ductile-to-brittle transition temperature (CVN) are the critical factors

d) Affected units or equipment 

  • Start-up and shutdown processes

e) Appearance or morphology of damage 

The surface will be composed of cracks

f) Prevention / mitigation –

  • API 579-1/ASME FFS-1 (Section 3), Fitness for Service and API 510 Code for Inspection of Pressure Vessels In-Service provides excellent guidance on how to prevent/mitigate the potential for brittle fracture of equipment

g) Inspection and monitoring 

Perform risk-based inspection of critical sized flaws

h) Related mechanisms 

Temper embrittlement, strain age embrittlement, 885oF (475oC) embrittlement, titanium hydriding, and sigma embrittlement

 

Creep and Stress Rupture - Corrosion Engineering Topic #6 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Materials/Components will, with the passage of time, deform under stress and higher/unusual temperatures by the mechanism known as creep. Unless stopped, creep terminates in rupture

b) Affected materials

All metals and alloys

c) Critical parameters

Stress, temperature and material composition

d) Affected equipment

  • Weld HAZ’s, high temperature equipment and welding dissimilar metal welds

e) Appearance or morphology of damage

First appear as voids/fissures and then cracks/bulges

f) Prevention / mitigation

  • Minimize hot spots/localized overheating, fouling deposits/scaling and stress concentrators

g) Inspection and monitoring

Volumetric non-destructive examination techniques

h) Related mechanisms

Short term overheating – stress rupture, reheat cracking

 

Thermal Fatigue - Corrosion Engineering Topic #7 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Thermal fatigue is a mechanism occurring from sudden and repeated swings in the temperature, exceeding 200°F (93°C), of processing equipment

b) Affected materials

All materials of construction

c) Critical factors

The degree of damage is affected by the magnitude and frequency of the temperature swings, startup and shutdown of equipment, notches and sharp corners

d) Affected equipment

Steam generating equipment, soot blowers, mixing points of hot/cold streams, coke drum shells, desuperheating equipment and reheaters

e) Appearance or morphology of damage

Cracks

f) Prevention / mitigation

  • Proper materials selection/design - reducing stress concentrators/thermal gradients, blend grinding weld profiles, and creating smooth transitions is also recommended. g) Inspection and Monitoring –
  • Magnetic particle testing and liquid penetrant testing are both effective inspection techniques. External surface wave ultrasonic testing (SWUT) can be used as well as a non-intrusive inspection tool

h) Related mechanisms

Corrosion fatigue and dissimilar metal weld cracking

References – Thermal Fatigue

https://inspectioneering.com/tag/thermalfatigue - 30 June 2015

 

Short Term Overheating – Stress Rupture - Corrosion Engineering Topic #8 - Online Tutorials - 24HourAnswers.com

a) Description of damage

A short-term overheating failure is one in which a single incident or a small number of incidents at high temperature yields, deforms and may eventually rupture equipment

b) Affected materials

All materials

c) Critical parameters

Temperature (Usually due to flame impingement or localized overheating), time and stress (reduction in wall thickness)

d) Affected equipment

Refractories, furnaces, boilers, hydro processing reactors and fire heater tubes

e) Appearance or morphology of damage

Such failures often are characterized as having a fish-mouth appearance - thin/sharp-edge fracture surfaces. Wall thinning and local bulging precede the actual fracture, because the strength of the material is reduced at high temperatures. Changes in tube diameters on the order of 3% to 10% are indicative of short-term overheating

f) Prevention / mitigation

Prevention/mitigation involves careful operation, instrumentation, and inspection and maintenance activities

g) Inspection and monitoring

These include infrared monitoring of susceptible equipment, heat sensitive paint on refractory lined equipment, furnace tube and vessel bed thermocouples and careful burner management of fired heaters

h) Related mechanisms

Creep/stress rupture

 

Steam Blanketing - Corrosion Engineering Topic #9 - Online Tutorials - 24HourAnswers.com

a) Description of damage

This mechanism occurs when the flow of heat energy is stratified to form a steam blanket which at high temperature yields, deforms and may eventually rupture equipment

b) Affected materials

Carbon and low alloy steels

c) Critical parameters

Heat energy and flow velocity are critical parameters

d) Affected equipment

All steam generating units

e) Appearance or morphology of damage

Similar to short-term, high-temperature failures with severe elongation of the grain structure

f) Prevention / mitigation

  • Proper boiler feed-water treatment
  • Installation of ferrules at the entrance to each tube in the area of high gas velocity

g) Inspection and monitoring

Proper maintenance management of burners and inspection of affected structures for bulging

h) Related mechanisms

Short-term overheating – stress rupture

References

BOILER PROBLEMS: - Banks Engineering Inc

http://www.banksengineering.com/boiler.htm - 06 July 2015

 

 

Dissimilar Metal Weld (DMW) Cracking - Corrosion Engineering Topic #10 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Cracking of dissimilar metal welds as a result of differences in thermal expansion

b) Affected materials

The most common are ferritic metals that are welded to the austenitic materials

c) Critical parameters

Weld parameters

d) Affected equipment

Equipment that has welds between ferritic materials and austenitic materials

e) Appearance or morphology of damage

Cracking at toe of the weld in the heat-affected zone

f) Prevention / mitigation

  • Use nickel base filler metals
  • The dissimilar metal weld should be located preferably out of the heat transfer zone
  1. g) Inspection and monitoring

Radiographic testing should be performed

h) Related mechanisms

Thermal and corrosion fatigue, creep and sulfide stress cracking

References:

Boiler Tubing Dissimilar Metal Welds (DMW's)

www.thielschfes.com/media/5746/dmw_s_tech.pdf - 06 July 2015

 

Thermal Shock - Corrosion Engineering Topic #11 - Online Tutorials - 24HourAnswers.com

a) Description of damage

A sudden form of thermal fatigue cracking which can occur when high and cyclical thermal stresses occurs due to differential expansion or contraction

b) Affected materials

All metals and alloys

c) Critical parameters

Temperature parameters

d) Affected equipment

High temperature/low ductility/cyclical temperature piping and equipment in any unit are susceptible

e) Appearance or morphology of damage

Surface cracks

f) Prevention / mitigation

Design to mitigate against flow disruptions, unnecessary restraint, cyclical temperatures and rain/fire water deluge situations

g) Inspection and monitoring

Non-destructive examination can be used to confirm cracking. Difficult to monitor and detect

h) Related mechanisms

Thermal fatigue

References

What is thermal shock? - Definition from Corrosionpedia

www.corrosionpedia.com/definition/1079/thermal-shock - 06 July 2015

 

Erosion – Corrosion - Corrosion Engineering Topic #12 - Online Tutorials - 24HourAnswers.com

a) Description of damage

  • Erosion occurs when surface material is removed as a result of external impact or movement between surfaces
  • Erosion-corrosion occurs when there is impingement corrosion as a result of liquid in the vapour stream/relative movement causing the corrosion rate to increase in the affected materials

b) Affected materials

All metals and alloys

c) Critical parameters

Corrosion rates depend on the qualities of the impacting media, the environment, and the impact itself

d) Affected equipment

Where there is moving fluids or catalyst

e) Appearance or morphology of damage

Erosion and erosion-corrosion are characterized by a localized loss in thickness over a short period

f) Prevention / mitigation

  • Improvements in design, process conditions and materials selection
  • Hardfacing surface treatments
  • Corrosion resistant alloys containing Molybdenum

g) Inspection and monitoring

  • Visual and Ultrasonic testing

h) Related mechanisms

Cavitation, liquid impingement erosion, fretting and other similar terms

References  

Erosion corrosion - Corrosion Doctors

corrosion-doctors.org/Forms-Erosion/erosion.htm – 06 July 2015

 

Cavitation Damage - Corrosion Engineering Topic #13 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is a form of erosion-corrosion which exerts high-pressure shockwaves in the stream and can thus lead to metal loss

b) Affected materials

Most common materials of construction

c) Critical parameters

Insufficient net positive suction head, high temperatures and the presence of abrasive media can result in cavitation

d) Affected equipment

Pump, pipeline and piping equipment

e) Appearance or morphology of damage

Pitting/gouging

f) Prevention / mitigation

Design/operational modifications

g) Inspection and monitoring

Visual examination and acoustic monitoring

h) Related mechanisms

Liquid impingement or erosion

References  

Cavitation corrosion - Corrosion Doctors

http://corrosion-doctors.org/Forms-cavitation/cavitation.htm – 06 July 2015

 

Mechanical Fatigue - Corrosion Engineering Topic #14 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Exposure to mechanical cyclical stresses

b) Affected materials

All engineering materials

c) Critical parameters

Stress

d) Affected equipment

Coke drums, boilers, water washing systems, pressure swing absorbers, rotating shafts, small diameter piping

e) Appearance or morphology of damage

 “Beach marks” that propagate

f) Prevention / mitigation

The best defense against fatigue cracking is improved design/operations that helps minimize cyclical loading of components that are in service

g) Inspection and monitoring

  • Non-destructive examination techniques can be used to detect cyclical movement and mechanical fatigue cracks at known areas of stress concentration
  • Vibration monitoring of rotating equipment to detect resonance and equipment out-of-balance is also common

h) Related mechanisms

Vibration-induced fatigue

References  

FAQ: What is fatigue failure and how can it be avoided? - TWI

www.twi-global.com/.../faq-what-is-fatigue-failure-and-how-can-it-be-av... – 06 July 2015

 

Vibration-Induced Fatigue - Corrosion Engineering Topic #15 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Exposure to vibratio- induced loading

b) Affected materials

All engineering materials/alloys

c) Critical parameters

The support characteristics, amplitude and frequency of vibration of the components

d) Affected equipment

  • Small bore piping/pipelines at or near rotating and reciprocating equipment
  • Safety relief/high pressure drop control valves
  • Heat exchanger tubes

e) Appearance or morphology of damage

Cracks

f) Prevention / mitigation

Proper design and the use of anchoring, gussets, flow stabilization and vibration dampening equipment

g) Inspection and monitoring

Check surface of insulation

h) Related mechanisms

Mechanical fatigue and refractory degradation

References  

EI | Guidelines for the avoidance of vibration induced fatigue

Guidelines for the avoidance of vibration induced fatigue – 06 July 2015

 

Refractory Degradation - Corrosion Engineering Topic #16 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Damage which occurs when refractories are susceptible to thermal stress

b) Affected materials

Refractory materials

c) Critical parameters

Refractory/anchor/filler material selection, design and application are critical to minimizing damage.

d) Affected equipment

  • Refractory equipment

e) Appearance or morphology of damage

Refractory may exhibit cracking, wall thinning, spalling or disbondment, softening or general degradation from exposure to moisture

f) Prevention / mitigation

Proper selection, design and application of refractory, anchors and fillers are critical to minimizing refractory damage

g) Inspection and monitoring

  • Conduct visual inspection and utilization of infrared monitor

h) Related mechanisms

Oxidation, sulfidation and dew point corrosion

References

Refractory Degradation Other temperature measurements

www.netl.doe.gov.../Crosscutting_20140520_1300A_UniversityUtah.p... – 06 July 2015

 

 

Stress Relief Cracking - Corrosion Engineering Topic #17 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Stress Relief Cracking may occur when the welded component is being subjected to post weld heat treatment( PWHT), or has been subjected to high temperature service (typically above 750°F (399°C)

b) Affected materials

High strength low alloy steels

c) Critical parameters

Material, grain size, residual stresses and stress from fabrication, section thickness, weld metal and base metal strength, welding and heat treating conditions

d) Affected equipment

Heavy wall sections of vessels and piping

e) Appearance or morphology of damage

Cracking is intergranular

f) Prevention / mitigation

The welding procedure can be used to minimize the risk of stress relief cracking by

  1. Limiting the degree of austenite grain growth – use low heat input, and
  2. Eliminating stress concentrations/notches - to grind the weld toes with the preheat maintained

 g) Inspection and monitoring

Embedded cracks can be detected by ultrasonics or time of flight diffraction technique

h) Related mechanisms

Stress relief cracking and stress relaxation cracking

 

Stress Relief Cracking - Corrosion Engineering Topic #17 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Stress Relief Cracking may occur when the welded component is being subjected to post weld heat treatment (PWHT), or has been subjected to high temperature service (typically above 750°F (399°C)

b) Affected materials

High strength low alloy steels

c) Critical parameters

Material, grain size, residual stresses and stress from fabrication, section thickness, weld metal and base metal strength, welding and heat treating conditions

d) Affected equipment

Heavy wall sections of vessels and piping

e) Appearance or morphology of damage

Cracking is intergranular

f) Prevention / mitigation

The welding procedure can be used to minimize the risk of stress relief cracking by

  1. Limiting the degree of austenite grain growth – use low heat input, and
  2. Eliminating stress concentrations/notches - to grind the weld toes with the preheat maintainence

 g) Inspection and monitoring

Embedded cracks can be detected by ultrasonics or time of flight diffraction technique

h) Related mechanisms

Stress relief cracking and stress relaxation cracking

 

Gaseous Oxygen-Enhanced Ignition and Combustion - Corrosion Engineering Topic #18 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Ignition and combustion of affected materials in oxygen-enhanced environments

b) Affected materials 

Carbon & low alloy steels, aluminum, plastic and titanium

c) Critical factors 

Pressure, oxygen content of the stream, line velocity/impingement areas, component thickness, design and piping configuration, presence of contaminants and temperature

d) Affected equipment 

Oxygen-enhanced combustion units and piping systems

e) Appearance or morphology of damage 

Oxygen fires can cause significant burning of metal components and extensive structural damage due to heat

f) Prevention / mitigation 

  • Keep systems clean and well-maintained
  • Precautions against pressure changes, high temperatures and velocities

g) Inspection and monitoring 

  • Check visually for external heat damage/abnormal equipment operation/equipment malfunction
  • UV Blacklights can be used to check for hydrocarbon contamination

h) Related mechanisms 

Not applicable

References 

Oxygen-enhanced combustion of alternative fuels - Global

www.cemfuels.com/.../320-oxygen-enhanced-combustion-of-alternative-... – 06 July 2015

 

Galvanic Corrosion - Corrosion Engineering Topic #19 - Online Tutorials - 24HourAnswers.com

a) Description of damage

When two dissimilar materials are coupled (joined electrically) in a corrosive electrolyte

b) Affected materials

All metals – very noble metals may be excluded

c) Critical parameters

Galvanic series position and anode to cathode area ratio

d) Affected equipment

Examples are ship hulls, buried pipelines, heat exchanges etc.

e) Appearance or morphology of damage

Damage (in the forms of pitting/crevices) occurs where two materials are joined at welded or bolted connections

f) Prevention / mitigation

By application of cathodic protection

g) Inspection and monitoring

Visual inspection and ultrasonic measurements are effective for monitoring galvanic corrosion

h) Related mechanisms

Soil corrosion

 

Atmospheric (External) Corrosion - Corrosion Engineering Topic #20 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is external degradation of a material due to electrochemical as well as the other reactions of its surface with the atmosphere

b) Affected materials

Carbon and low alloy steels and copper alloyed aluminum

c) Critical parameters

Critical parameters include the physical location, RH (trapped moisture), temperature up to about 250ºF, presence of salts, sulfur compounds Chlorides, fly ash and other pollutants

d) Affected equipment

Piping and equipment with poor coating, exposed to cyclical temperatures, moisture entrapment, abandoned/shutdown improperly

e) Appearance or morphology of damage

Localized loss of thickness may not be visually evident, although normally a distinctive iron oxide (red rust) scale forms

f) Prevention / mitigation

Proper coating application

g) Inspection and monitoring

Visual inspection and ultrasonic measurements are effective for monitoring external corrosion

h) Related mechanisms

N/A

 

Atmospheric (External) Corrosion - Corrosion Engineering Topic #20 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is external degradation of a material due to electrochemical as well as the other reactions of its surface with the atmosphere

b) Affected materials

Carbon and low alloy steels and copper alloyed aluminum

c) Critical parameters

Critical parameters include the physical location, RH (trapped moisture), temperature up to about 250ºF, presence of salts, sulfur compounds chlorides, fly ash and other pollutants

d) Affected equipment

Piping and equipment with poor coating, exposed to cyclical temperatures, moisture entrapment, abandoned/shutdown improperly

e) Appearance or morphology of damage

Localized loss of thickness may not be visually evident, although normally a distinctive iron oxide (red rust) scale forms

f) Prevention / mitigation

Proper coating application

g) Inspection and monitoring

Visual inspection and ultrasonic measurements are effective for monitoring external corrosion

h) Related mechanisms

N/A

 

Cooling Water (CW) Corrosion - Corrosion Engineering Topic #21 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Corrosion of cooling water caused by for example MIC

b) Affected materials

Carbon steel, all grades of stainless steel, copper, aluminum, titanium and nickel base alloys

c) Critical parameters

Process and CW temperatures, heat flux, water velocity, type and quality of water (salt, brackish, fresh) and type of cooling system

d) Affected equipment

Heat exchangers and cooling towers

e) Appearance or morphology of damage

CWC can manifest itself as general thinning, pitting, stress corrosion cracking and microbiologically induced corrosion (MIC)

f) Prevention / mitigation

Metallurgical upgrades

g) Inspection and monitoring

  • Cooling water should be monitored for critical parameters that affect corrosion and fouling
  • Heat exchanger fouling factors must be computed as well
  • Specialised flow meters can be used to check the velocity of water in the tubes
  • Tube sheets can be inspected via eddy current

h) Related mechanisms

Microbiologically induced corrosion, chloride stress corrosion cracking and galvanic corrosion

 

Boiler Feed water (BFW) Corrosion - Corrosion Engineering Topic #22 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Oxygen pitting corrosion and carbonic acid corrosion in the boiler system and condensate return piping

b) Affected materials

Primarily carbon steel and certain low alloy and 300 Series stainless steels and copper based alloys

c) Critical parameters

Dissolved oxygen, pH, temperature, quality of the feedwater, and the specific feedwater treatment system

d) Affected equipment

Corrosion can occur in boiler feed water and the condensate return system

e) Appearance or morphology of damage

It manifests itself as pitting type damage or smooth grooving

f) Prevention / mitigation

  • If the scale/deposit control/magnetite maintenance treatment scheme does not minimize carbon dioxide in the condensate return system, an amine inhibitor treatment might be required

g) Inspection and monitoring

  • Water analysis is the common monitoring tool used to assure that the various treatment systems are performing in a satisfactory manner
  • Deaerator cracking problems can be evaluated in accordance with NACE SP0590
  • There are no proactive inspection methods other than developing an appropriate remedial program when BFW corrosion-related issues arise

h) Related mechanisms

Carbon dioxide corrosion, corrosion fatigue, and erosion-corrosion

 

Carbon Dioxide Corrosion - Corrosion Engineering Topic #23 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Carbon dioxide gas dissolves in water and forms a “weak” carbonic acid that is more aggressive than hydrochloric acid at the same pH

b) Affected materials

Carbon and low alloy steels

c) Critical parameters

 (i) Concentration of CO2, (ii) chemistry

d) Affected equipment

Boiler feed water systems

e) Appearance or morphology of damage

Localized thinning and/or pitting corrosion of materials

f) Prevention / mitigation

  • Apply corrosion inhibitors
  • Upgrade to compatible stainless steel grade
  • Improve operability

g) Inspection and monitoring

  • Monitor water samples for further analysis

h) Related mechanisms

Boiler feed water corrosion and carbonate cracking

 

Dew-Point Corrosion - Corrosion Engineering Topic #24 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Flue gases produced by the combustion of fuels

b) Affected materials

Carbon and low alloy steels and 300 Series SS

c) Critical parameters

The concentration of contaminants in the fuel and the operating temperature of affected flue gas surfaces

d) Affected equipment

Flue-gas desulfurization (FGD) systems

e) Appearance or morphology of damage

It manifests itself as surface cracks and/or shallow pits

f) Prevention / mitigation

Maintain the surface metal temperatures of flue-gas desulfurization (FGD) systems above the DP or install a protective coating that is resistant to the acidic condensate and will withstand the temperatures to which it’s exposed

g) Inspection and monitoring

  • Use NDE methods to monitor/detect loss in wall thickness

h) Related mechanisms

Hydrochloric Acid corrosion and Chloride Stress Corrosion Cracking

 

Microbial Corrosion (MIC) - Corrosion Engineering Topic #25 - Online Tutorials - 24HourAnswers.com

a) Description of damage

MIC is caused by biological growth

b) Affected materials

Most common materials of construction and is most often a problem with carbon steel and 300 series SS

c) Critical parameters

The parameters in which MIC can occur are extremely varied and include multiple bacteria species

d) Affected equipment

Particular problem areas include cooling water systems, fire water equipment, heat exchangers

e) Appearance or morphology of damage

MIC manifests itself as cup-shaped pits, often under deposits, tubercles (blisters of corrosion product), or slime

f) Prevention / mitigation

  • Minimize low flow areas
  • Cleaning, Wrapping and Cathodic Protection application to underground structures have been effective in preventing MI
  • Maintain coatings and apply effective biocide treatment

g) Inspection and monitoring

  • Monitor effectiveness of biocide treatment and HEX fouling problems
  • Utilize ER probes to monitor and inspect for MIC damage

h) Related mechanisms

Cooling water corrosion 

Soil Corrosion (Oxidation) - Corrosion Engineering Topic #26 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Soil corrosion (underground corrosion) affects buried structures that are in direct contact with soil or bedrock

b) Affected Materials

Carbon steel, cast and ductile iron

c) Critical parameters

Temperature, moisture and oxygen availability, soil characteristics, cathodic protection, coating type, age, and condition

d) Affected equipment

Underground equipment

e) Appearance or morphology of damage

Soil corrosion appears as localized thinning and pitting

f) Prevention / mitigation

Cathodic protection in conjunction with effective barrier coating

g) Inspection and monitoring

Cathodic protection monitoring in accordance with NACE SP 0169 as well as MFL/internal inspection tools

h) Related mechanisms

Galvanic corrosio

 

Caustic Gouging - Corrosion Engineering Topic #27 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Concentration of caustic (NaOH or KOH) causing corrosion

b) Affected materials

Primarily carbon steel and 300 Series SS above about 150°F (66°C) and low alloy steels

c) Critical parameters

The presence of caustic (NaOH or KOH) and the mechanism of concentration i.e. departure from nucleate boiling, deposition (wicked boiling yielding under-deposit corrosion) and evaporation along a steam/water interface

d) Affected equipment

Boilers, steam generating equipment and heat exchangers

e) Appearance or morphology of damage

It manifests itself as as grooves in a boiler tube or locally thinned areas beneath heavy deposits

f) Prevention / mitigation

Reduce the amount of free and concentrated caustic, by ensuring adequate proper mixing and water flow, by ensuring proper burner management to minimize hot spots on heater tubes, and by minimizing the entry of alkaline producing salts into condensers

g) Inspection and monitoring

  • Ultrasonic thickness gauging and horoscope inspection is useful to detect and monitor general corrosion due to caustic

h) Related mechanisms

Departure from Nucleate Boiling (DNB)

 

Selective Leaching - Corrosion Engineering Topic #28 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Selective leaching refers to the selective removal of a constituent from an alloy by corrosion processes

b) Affected materials

Primarily copper alloys (brass, bronze, tin) as well as Alloy 400 and cast iron

c) Critical parameters

The composition of the alloy, exposure time, deposits, and soft waters (especially those containing CO2) and high-chloride waters

d) Affected equipment

Underground cast iron piping, heat exchanger tubing (brass, Al brass), BFW piping systems and after boiler components, bronze pumps, Monel strainers and brass pressure guage fittings

e) Appearance or morphology of damage

Colour change or a deep etched (corroded) appearance

f) Prevention / mitigation

  • Alter the exposure conditions or susceptible material with a resistant alloying element
  • Cathodic protection or protective coatings may also be effective

g) Inspection and monitoring

Metallographic examination/scale removal/hardness testing/acoustic testing may be required to confirm appearance or morphology of damage

h) Related mechanisms

Graphitic corrosion

References:

Dealloying, Selective Leaching and Graphitic Corrosion

http://www.corrosionclinic.com/types_of_corrosion/dealloying_selective_leaching_graphitic_corrosion.htm – 06 July 2015

 

 

Graphitic Corrosion - Corrosion Engineering Topic #29 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is a form of selective leaching in which the iron matrix is corroded, leaving corrosion products and porous graphitic shell

b) Affected materials

Ductile and gray cast iron

c) Critical parameters

  • Same as selective leaching – but worse in low flow areas and where concentration of sulfates are high

d) Affected equipment

Graphitic corrosion can occur in pump impellers

e) Appearance or morphology of damage

A deep etched (corroded) appearance

f) Prevention / mitigation

  • Coatings and/or cement linings and cathodic protection

g) Inspection and monitoring

Metallographic examination/scale removal/hardness testing/acoustic testing may be required to confirm appearance or morphology of damage

h) Related mechanisms

Selective leaching

References:

Dealloying, Selective Leaching and Graphitic Corrosion.

 

Ammonium Bisulfide Corrosion (Alkaline Sour Water) - Corrosion Engineering Topic #30 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Aggressive corrosion formed in units handling alkaline sour water

b) Affected materials

Carbon steel and admiralty brass tubes

c) Critical parameters

NH4HS concentration

d) Affected equipment

Hydropocessing reactor effluent streams, amine units, delayed coker units, fluid catalytic cracker units and sour water strippers (SWS)

e) Appearance or morphology of damage

Loss of wall thickness and under-deposit corrosion

f) Prevention / mitigation –

  • Carefully review service conditions
  • Use resistant materials of construction (e.g. Monel, Incoloy 800/ 825, duplex SS)
  • Properly design and maintain water wash injection systems

g) Inspection and monitoring

  • Determine NH4HS content through sampling and calculation
  • Regular ultrasonic and radiographic measurement of high and low velocity areas

h) Related mechanisms

Erosion corrosion

References:

Prediction and assessment of ammonium bisulfide corrosion

https://www.honeywellprocess.com/library/marketing/whitepapers/CorrosionNACE06_Paper_06576.pdf – 06 July 2015

 

Ammonium Chloride Corrosion - Corrosion Engineering Topic #31 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Corrosion occurring under ammonium chloride deposits

b) Affected materials 

All commonly used materials are susceptible

c) Critical parameters 

Concentration (NH3, HCl, H2O or amine salts

d) Affected equipment 

Crude tower and fractionator overheads, catalytic reforming and hydroprocessing units

e) Appearance or morphology of damage 

The salts lead to localized pitting

f) Prevention / mitigation 

  • Limit salts by limiting chlorides
  • Water washing
  • Filming amine inhibitors

g) Inspection and monitoring 

Radiography, corrosion probes or UT monitoring can be used to determine remaining wall thickness

  1. h) Related Mechanisms 

HCl corrosion, chloride SCC and organic acid corrosion of distillation tower overhead systems

 

Phenol (Carbolic Acid) Corrosion - Corrosion Engineering Topic #32 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Corrosion of spent phenol separated by vaporization

b) Affected materials 

In order of increasing resistance: carbon steel and 300 series SS

c) Critical parameters 

Temperature, water content, alloy chemistry and velocity are the critical parameters

d) Affected equipment 

Phenol extraction facilities in lubes plant

e) Appearance or morphology of damage 

Localized loss in thickness

f) Prevention / mitigation 

Corrosion is best prevented through proper materials selection and control of phenol solvent chemistry

g) Inspection and monitoring 

UT and radiographic testing as well as corrosion coupons are used to monitor for loss in thickness

h) Related mechanisms 

Not applicable

References 

What Is Carbolic Acid?

http://www.wisegeek.com/what-is-carbolic-acid.htm -06 July 2015

 

Phosphoric Acid Corrosion - Corrosion Engineering Topic #33 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Corrosion due to presence of phosphoric acid

b) Affected materials 

In order of increasing resistance: carbon steel and 300 Series SS

c) Critical parameters 

Acid concentration, temperature and contaminants

d) Affected equipment 

Polymerization units

e) Appearance or morphology of damage 

General or localised thinning

f) Prevention / mitigation 

Proper materials selection

g) Inspection and monitoring 

Ultrasonic and radiographic testing as well as corrosion coupons are used to monitor for loss in thickness

h) Related mechanisms 

Not applicable

 

Sour Water Corrosion (Acidic) - Corrosion Engineering Topic #34 - Online Tutorials - 24HourAnswers.com

a) Description of damage

This mechanism manifests itself when acidic sour water comprising H2S and CO2 at a pH between 4.5 and 7.0

b) Affected materials

Carbon steel

c) Critical parameters

H2S and CO2 content, pH, temperature, and velocity and oxygen concentration

d) Affected equipment

Overhead systems of fluid catalytic cracker

e) Appearance or morphology of damage

Localized under deposit attack

f) Prevention / mitigation

Use resistant materials – stainless steels, copper and nickel alloys

g) Inspection and monitoring

Evidence of corroded areas can be tested using process analysis

h) Related mechanisms

Carbonate SCC

References  

Sour Water Corrosion

https://quizlet.com/61296727/sour-water-corrosion-acidic-flash-cards/ - 06 July 2015

 

High-Temperature Oxidation - Corrosion Engineering Topic #35 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Oxygen reacts with affected materials at about 1000°F (538°C), converting the metal to oxide scale

b) Affected materials

All iron based materials

c) Critical parameters

Affected metal temperature and alloy composition

d) Affected equipment

Furnace equipment

e) Appearance or morphology of damage

Metal loss/thinning

f) Prevention / mitigation

Add chromium

g) Inspection and monitoring

Loss in thickness and high temperatures due to oxidation is usually monitored using UT, thermocouples or IR as well as process unit analysis

h) Related mechanisms

N/A

Sulfidic Corrosion - Corrosion Engineering Topic #36 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Corrosion of affected materials resulting from their reaction with sulfur compounds

b) Affected daterials

All iron based materials

c) Critical parameters

Alloy composition, temperature and concentration of corrosive sulfur compounds

d) Affected equipment

Sulfidic corrosion results in the thinning of the pressure containment envelope, affecting such components as piping and pipe fittings, heater tubes, and pressure vessels

e) Appearance or morphology of damage

Localised deposits/thinning

f) Prevention / mitigation

  • Add chromium.
  • Refer also to API 939-C for prevention/mitigation measures

g) Inspection and monitoring

Loss in thickness and high temperatures due to oxidation is usually monitored using UT, thermocouples or IR as well as process unit analysis

h) Related mechanisms

High temperature sulfidic corrosion in presence of hydrogen

References

Sulfidation Corrosion

https://inspectioneering.com/tag/sulfidation - 06 July 2015

 

Carburisation - Corrosion Engineering Topic #37 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Carbon is diffused into a material at high temperature (typically above 1100°F (593°C)) while in contact with a carbonaceous material or carburizing environment

b) Affected materials 

Carbon steel and low alloy steels

c) Critical parameters 

As mentioned above

d) Affected equipment 

Fired heater tubes and coking units

e) Appearance or morphology of damage 

Carburisation results in higher hardness levels, possible volume increase and change in magnetic properties

f) Prevention / mitigation 

Materials selection.

g) Inspection and monitoring 

Hardness testing and field metallography can be used. Non-destructive sampling and magnetic based techniques (Eddy Current) have also been used.

  1. h) Related mechanisms 

Metal dusting

References 

Carburisation

http://www.corrosionsource.com/(S(hqlagt2nieaigunvm1xmr355))/FreeContent/1/Carburisation - 06 July 2015

 

Decarburisation - Corrosion Engineering Topic #38 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

A high temperature. The weaker surface layer reduces wear resistance and facilitates fatigue failures

b) Affected materials 

Carbon and low alloy steels

c) Critical parameters 

Exposure time, temperature and carbon activity of the process stream are critical parameters

d) Affected equipment 

Decarburisation can occur in almost any equipment that is exposed to elevated temperatures, heat treated or exposed to a fire

e) Appearance or morphology of damage 

  • Damage can be verified by metallography
  • Damage occurs on the surface exposed to the gas environment but in extreme cases may be through wall
  1. f) Prevention / mitigation 
  • Refer to API RP 941
  • Alloy steels with chromium and molybdenum are more resistant to decarburisation

g) Inspection and monitoring 

Field replication (FMR) and hardness testing can confirm decarburisation

h) Related mechanisms 

High temperature hydrogen attack

References 

Decarburisation

http://www.corrosionpedia.com/definition/1253/decarburisation - 06 July 2015

 

Metal Dusting - Corrosion Engineering Topic #39 - Online Tutorials - 24HourAnswers.com

a) Description of damage

This mechanism is preceded by carburization occurring between temperature range of 900°F and 1500°F

b) Affected materials

Low alloy and heat resisting alloys

c) Critical parameters

Process stream composition, operating temperature and alloy composition

d) Affected equipment

Components operating in carburizing environments are affected

e) Appearance or morphology of damage

The wastage is a voluminous “carbon dust” containing metal particles and sometimes metal oxides and carbides

f) Prevention / mitigation

Add hydrogen sulfide to retard metal dusting

g) Inspection and monitoring

Field metallography, RT, compression wave UT are probably the most efficient methods of inspection

h) Related mechanisms

Catastrophic carburisation

References

Metal dusting

http://www.corrosionpedia.com/definition/769/metal-dusting - 06 July 2015

 

Fuel Ash Corrosion - Corrosion Engineering Topic #40 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Contaminants in the fuel ash deposits and form molten salts (slags) that dissolve the surface oxide and enhance the transport of oxygen to the surface to re-form the iron oxide at the expense of the tube wall or component

b) Affected materials 

All conventional alloys used for process heater and boiler construction are susceptible

c) Critical parameters 

The concentration of slag forming contaminants, metal temperature and alloy composition

d) Affected equipment 

Some components operating in carburizing environments are affected

e) Appearance or morphology of damage 

Glassy corrosion scale deposit and cracking/grooving

f) Prevention / mitigation 

  • Reduce contaminants and by operating equipment so that hot components are below the threshold temperature
  • Proper burner design and management utilization of additives, as well as low excess air firing can help to reduce flame impingement and localised hot spots
  • g) Inspection and Monitoring 

Visual and ultrasonic wall thickness testing is usually sufficient to detect hot ash corrosion

h) Related mechanisms 

Hot corrosion

References 

Fuel Ash Corrosion

http://www.corrosionpedia.com/definition/112/fuel-ash-corrosion - 06 July 2015

 

Nitriding - Corrosion Engineering Topic #41 - Online Tutorials - 24HourAnswers.com

a) Description of damage

It is the formation of a hard, brittle layer (above 600°F (316°C) ) in the presence of diassociated nitrogen compounds such ammonia or cyanides as a reduction reaction

b) Affected materials

  • Carbon, low alloy, 300 Series stainless and 400 Series stainless steels

c) Critical parameters

Temperature, time, partial pressure of nitrogen and metal composition

d) Affected equipment

Nitriding can occur at any location where circumstances are conducive

e) Appearance or morphology of degradation mechanism

Manifests itself on the surface with a dull, dark gray appearance with cracking and spalling

f) Prevention / mitigation

Changing to more resistant nickel alloys are usually required

g) Inspection and monitoring

  • Metallographic, magnetic and hardness testing is generally required to confirm nitriding
  • NDE techniques may also be used to inspect for nitriding

h) Related mechanisms

Carburisation and metal dusting

References

Nitriding

https://en.wikipedia.org/wiki/Nitriding - 06 July 2015

 

Chloride Stress Corrosion Cracking (Cl-SCC) - Corrosion Engineering Topic #42 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

It is a damage mechanism that results from exposure to an aqueous chloride environment

b) Affected materials 

All 300 Series SS and some nickel alloys

c) Critical parameters 

It is dependent on aqueous chloride and nickel composition

d) Affected equipment 

Insulated surfaces

e) Appearance or morphology of damage 

Branched trans granular surface cracks

f) Prevention / mitigation 

Use corrosion resistant materials or barrier coatings

g) Inspection and monitoring 

Inspection and monitoring via careful surface preparation and eddy current examination

h) Related mechanisms 

Caustic SCC and PTASCC

 

Corrosion Fatigue - Corrosion Engineering Topic #43 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Corrosion and cyclic loading combined effect

b) Affected materials 

All metals and alloys

c) Critical parameters 

It is dependent on the material, corrosive environment, stress level and area

d) Affected equipment 

Equipment prone to fatigue stresses in a corrosive environment

e) Appearance or morphology of damage 

Transgranular surface cracks with minimal branching

f) Prevention / mitigation 

Use corrosion resistant materials or barrier coatings

g) Inspection and monitoring 

Inspection and monitoring via ultrasonic examination

h) Related mechanisms 

Mechanical fatigue and vibration-induced fatigue

 

Caustic Stress Corrosion Cracking (Caustic Embrittlement) - Corrosion Engineering Topic #44 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Exposure to caustic, primarily adjacent to non-post weld heat treated welds

b) Affected materials

Carbon steels

c) Critical parameters

  • It is dependent on caustic strength, temperature and stress

d) Affected units or equipment

  • Piping and equipment that handles caustic

e) Appearance or morphology of damage 

  • It is a heat-affected zone (HAZ) and adjacent weld area phenomenon
  • Cracks are spider web oxide-filled cracks

f) Prevention / mitigation

  • Use nickel base alloys
  • Use post-weld heat treatment

g) Inspection and monitoring

Inspection and monitoring via alternating current flux specific instrument and wet fluorescent magnetic particle examination

h) Related mechanisms

Amine cracking and carbonate cracking

 

Ammonia Stress Corrosion Cracking - Corrosion Engineering Topic #45 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Moist process streams containing ammonia

b) Affected materials

Carbon steels and some copper alloys in a moist ammonia atmosphere

c) Critical parameters

It is dependent on stress level, pH, moisture content and level of contamination (oxygen)

d) Affected units or equipment 

Carbon steel and copper-zinc alloys which are used for ammonia equipment and heat exchangers

e) Appearance or morphology of damage 

Intergranular surface cracks

f) Prevention / mMitigation

  • Use 300 Series SS and nickel base alloys or lower zinc content (<15%)
  • Use post-weld heat treatment
  • Decrease oxygen levels, weld hardness should not be above 225BHN

g) Inspection and monitoring

Inspection and monitoring via eddy current or time of flight diffraction examination technque

h) Related mechanisms

Not applicable

References 

Ammonia Stress Corrosion Cracking

https://inspectioneering.com/tag/ammonia+stress+corrosion+cracking – 06 July 2015

 

Liquid Metal Embrittlement (LME) - Corrosion Engineering Topic #46 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Liquid metal cracking is the loss of ductility when stressed under contact with liquid metal

b) Affected materials 

Copper alloys

c) Critical parameters 

It is dependent on stress level and time of exposure to liquid metals

d) Affected units or equipment 

Liquid metal cracking can occur in any location where the galvanic couples are found

e) Appearance or morphology of damage 

Intergranular surface cracks

f) Prevention / mitigation

Prevent galvanic couple

g) Inspection and monitoring

Inspection and monitoring via metallographic and spectrographic examination and analysis

h) Related mechanisms

N/A

 

Hydrogen Embrittlement (HE) - Corrosion Engineering Topic #47 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Hydrogen Embrittlement (HE) is a damage mechanism (from ambient to 300ºF) that results from the infusion of atomic hydrogen

b) Affected materials 

Carbon steels

c) Critical factors 

It is dependent on the concentration of hydrogen, microstructure, heat treatment history and stress level

d) Affected units or equipment 

  • Carbon steel piping and vessels in wet hydrogen sulfide services and Bolts and springs made of high strength steel are susceptible to hydrogen embrittlement

e) Appearance or morphology of damage 

Intergranular surface cracks

f) Prevention / mitigation 

  • Use lower strength steels and apply post-weld heat treatment
  • Have regulated shutdown and start-up procedures
  • Apply protective coatings and stainless steel claddings
  • g) Inspection and monitoring 

Inspection and monitoring via radiographic, ultrasonic, hydrogen flux specific instrument and wet fluorescent magnetic particle examination

h) Related mechanisms

SSC and hydrogen stress corrosion cracking

 

Ethanol Stress Corrosion Cracking (SCC) - Corrosion Engineering Topic #48 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Damage mechanism in the presence of fuel grade ethanol

b) Affected materials 

Carbon steel (ferrite and pearlite) and alloys of copper

c) Critical parameters 

It is dependent on cyclic localised tensile stress and presence of dissolved oxygen/gas blend

d) Affected units or equipment 

Carbon steel storage tanks, pipelines and piping

e) Appearance or morphology of damage 

Intergranular and transgranular cracks that are parallel to the affected area

f) Prevention / mitigation 

API has a published Technical Report 939-D, Second Edition that explains guidelines for mitigation and prevention

g) Inspection and monitoring 

Inspection and monitoring via careful surface preparation and wet fluorescent magnetic particle examination

h) Related mechanisms

N/A.

 

 

Sulfate Stress Corrosion Cracking - Corrosion Engineering Topic #49 - Online Tutorials - 24HourAnswers.com

a) Description of damage 

Damage mechanism as a result of copper alloys, especially admiralty brass, in sulfate solutions

b) Affected materials 

Copper alloys

c) Critical parameters 

  • It is dependent on a combination of stress, time and presence of sulfates

d) Affected units or equipment 

Damage mechanism is most often associated with cooling water services

e) Appearance or morphology of degradation mechanism 

The cracks will have a highly branched and transgranular appearance

f) Prevention / mitigation 

Use non-copper based alloys and periodic cleaning of copper alloy equipment as well as addition of nickel

g) Inspection and monitoring 

  • Inspection and monitoring normally via eddy current or mechanical bend testing

h) Related mechanisms

Not applicable

 

Polythionic Acid Stress Corrosion Cracking (PTA SCC) - Corrosion Engineering Topic #50 - Online Tutorials - 24HourAnswers.com

a) Description of damage

PTA SCC occurs when exposed to polythionic acids under tensile stress

b) Affected materials

Austenitic stainless steels

c) Critical parameters

It is dependent on environmental conditions (for example pH, hydrogen sulfide content and temperature), material properties and stress level

d) Affected units or equipment

  • Usually adjacent to welds or high stress areas

e) Appearance or morphology of degradation mechanism

Intergranular cracks

f) Prevention / mitigation

NACE RP0170 provides guidelines on preventative or mitigation measures

 g) Inspection and monitoring

Inspection and monitoring via liquid penetrant non-destructive examination

h) Related mechanisms

Also known as intergranular corrosion (IGC) and intergranular attack (IGA)

 

 

Amine Stress Corrosion Cracking - Corrosion Engineering Topic #51 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Amine cracking occurs in lean amine services

b) Affected materials

Carbon and low alloy steels

c) Critical parameters

It is dependent on the combined level of tensile stress, amine concentration and temperature

d) Affected units or equipment

All non-post weld heat treated carbon steel piping and equipment in aqueous alkanolamine systems

e) Appearance or morphology of damage

  • Identification normally via advanced metallurgical techniques
  • Clearly identifiable surface breaking flaws

f) Prevention / mitigation

  • Post weld heat treatment as per API RP 45
  • See also NACE SP0472
  • Application of alloy cladding or CRA’s

 g) Inspection and monitoring

Inspection and monitoring via careful surface preparation, alternating current field measurement and wet fluorescent magnetic particle examination

h) Related mechanisms

Caustic stress corrosion cracking and carbonate stress corrosion cracking

 

Wet H2S Damage (Blistering/HIC/SOHIC/SSC) - Corrosion Engineering Topic #52 - Online Tutorials - 24HourAnswers.com

a) Description of damage

As per references below

b) Affected materials

Carbon and low alloy steels

c) Critical parameters

It is dependent on environmental conditions (for example pH, hydrogen sulfide content and temperature), material properties and stress level

d) Affected units or equipment

Refinery equipment with wet hydrogen sulfide damage

e) Appearance or morphology of damage

Described above in section a)

f) Prevention / mitigation

  • Application of effective protective coatings and alloy claddings
  • NACE Publication 8X194, NACE SP0296, NACE MR0103 and NACE RP0472 provide guidelines on preventative or mitigation measures
  • Susceptibility increases with increasing hardness, application of protective coatings, inhibitors and alloy claddings, effective post-weld heat treatment (good welding practices)

g) Inspection and monitoring

  • Inspection and monitoring via wet fluorescent magnetic particle examination, shear wave ultrasonics and process engineering as well as compliance with above-mentioned NACE documentation

h) Related mechanisms

  • Blistering and sulfide stress cracking (SSC) are forms of hydrogen stress cracking (hydrogen embrittlement)

References –

Wet H2S Cracking

https://inspectioneering.com/tag/wet+h2s+cracking – 06 July 2015

8X194, Materials and Fabrication Practices for New Pressure Vessels Used in Wet H2S Refinery Service (2006 Edition)

https://www.nace.org/cstm/Store/Product.aspx?id=f7c02f56-4a6d-4e1d-8840-58374a3a3548 – 06 July 2015

NACE SP0472, "Methods and Controls to Prevent In-Service Environmental Cracking of Carbon Steel Weldments in Corrosive Petroleum Refining Environments"

http://www.nace.org/cstm/Store/Product.aspx?id=b90f79d8-4ed7-4bb8-a968-4ea275fec3f9 – 06 July 2015

SP0296-2010 (formerly RP0296), Detection, Repair, and Mitigation of Cracking in Refinery Equipment in Wet H2S Environments

http://www.nace.org/cstm/Store/Product.aspx?id=7cb52542-154b-448f-ace6-41dd77f1b126 – 06 July 2015

NACE MR0103-2012, Materials Resistant to Sulfide Stress Cracking in Corrosive Petroleum Refining Environments

http://www.nace.org/cstm/Store/Product.aspx?id=6e58e286-6132-4753-82d3-632d5e178892 – 23 August 2015.

 

Carbonate Cracking (CC) - Corrosion Engineering Topic #54 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Carbonate cracking is stress corrosion cracking mechanism in the presence of carbonate and some amount of hydrogen sulfide

b) Affected materials

Carbon and low alloy steels

c) Critical parameters

It is dependent on the stress level and water chemistry

d) Affected units or equipment

Refinery catalytic cracking units

e) Appearance or morphology of degradation mechanism

  • It is a heat-affected zone (HAZ) and adjacent weld area phenomenon
  • CC cracks are spider web oxide-filled cracks

f) Prevention / mitigation

  • Application of a stress-relieving heat treatment as per WRC 452
  • Proper dosing and oxidation of a metavanadate inhibitor must be maintained

g) Inspection and monitoring

  • Inspection and monitoring via pH and wet fluorescent magnetic particle examination

h) Related mechanisms

N/A

References

Carbonate Cracking

https://inspectioneering.com/tag/carbonate+cracking – 06 July 2015

WRC 452

https://forengineers.org/bulletin/wrc-452 – 06 July 2015

 

 

High Temperature Hydrogen Attack (HTHA) - Corrosion Engineering Topic #55 - Online Tutorials - 24HourAnswers.com

a) Description of damage

  • HTHA results from exposure to hydrogen at high temperatures and pressures above 13.79 bar. This causes carbide content to drop and causes an overall loss in load carrying ability
  • Increase in methane content may cause cracks if under stress

b) Affected materials

Carbon and low-alloy steels

c) Critical parameters

  • Additional information on HTHA can be found in API RP 941

d) Affected units or equipment

  • Hydrogen manufacturing/cleaning equipment/refinery units

e) Appearance or morphology of damage

  • Identification normally via advanced metallurgical techniques or mechanical testing

f) Prevention / mitigation

  • Use alloy steels with tungsten, vanadium, chromium and molybdenum to increase carbide stability which reduces methane content
  • Normal design practice is as per the API RP 941 curves

g) Inspection and monitoring

  • Inspection and monitoring via advanced ultrasonic backscattering techniques (AUBT) and time of flight diffraction (TOFD)
  1. h) Related Mechanisms

N/A

 

Titanium Hydriding - Corrosion Engineering Topic #56 - Online Tutorials - 24HourAnswers.com

a) Description of damage

Titanium hydriding is a mechanism in which hydrogen migrates into the titanium, solubility of hydrogen is above tolerable limit, which results in an embrittlement effect with a complete loss of ductility

b) Affected materials

Titanium alloys and where corrosion of iron occurs

c) Critical parameters

  • It is dependent on metal temperature, solution chemistry and alloy composition
  • Temperatures range above 165oF (74oC)

d) Affected units or equipment

  • Where level of cathodic protection (CP) potentials

e) Appearance or morphology of damage

  • Identification normally via metallurgical techniques or mechanical testing
  • Cracking of embrittled component

f) Prevention / mitigation

  • Titanium should not be used in known affected units

g) Inspection and monitoring

  • Inspection and monitoring normally via eddy current techniques

h) Related mechanisms

N/A

References

Hydride Embrittlement

http://www.corrosionclinic.com/types_of_corrosion/hydride_embrittlement.htm -   06 July 2015.

 

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