Hydrogen Induced Corrosion

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Hydrogen Induced Corrosion
March 22nd, 2001 Matthew Avery Benjamin Chui Y.
Gordon Kariya Kenneth Larson
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Outline

• Mechanisms
• Hydrogen Embrittlement
• Hydrogen Induced Blistering
• Precipitation of Internal Hydrogen
• Hydrogen Attack
• Cracking from Hydride Formation
• Prevention
• Case Studies
• Questions

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Hydrogen Embrittlement

• Hydrogen in steel reduces the tensile ductility
  causes premature failure under static loads.
• Only a few parts per million of hydrogen is
  necessary to embrittle steel.
• Three primary theories
• Decohesion Theory
• Reduced Surface Theory
• Planar Pressure Theory

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Hydrogen Embrittlement

• Basic Mechanism

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Crack Tip
H2(gas)
s
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Hydrogen Embrittlement

• Basic Mechanism

s
H2(gas)
Dissociative Chemical Adsorption
Physical Adsorption
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Hydrogen Embrittlement

• Basic Mechanism

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H2(gas)
Hydrogen Diffusion
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Hydrogen Embrittlement

• Decohesion Theory

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s
smax
H2(gas)
x
s
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Hydrogen Embrittlement

• Reduced Surface Theory
• The absorption of hydrogen decreases the surface
  free energy of the metal
• Propagation of the crack tip is enhanced
• Explains crack propagation of high-strength
  steels in low-pressure hydrogen environments

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Hydrogen Embrittlement

• Planar Pressure Theory
• Occurs when metals are charged with hydrogen
  during solidification
• High-pressure hydrogen can form in microvoids
• Same mechanism as hydrogen blistering

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Hydrogen Embrittlement

• Crack Direction

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Hydrogen Embrittlement

• General Trends
• Tendency to embrittle increases with decreased
  strain rate
• Embrittlement is more prevalent at room
  temperature
• Tendency to embrittle decreases with increasing
  temperature

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Hydrogen Embrittlement

• Prevention in Design
• High-strength metals and alloys are more
  susceptible to embrittlement
• Common mistake is to overcompensate on strength
  requirements for service
• At ambient conditions
• Minimize strength of material!

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Hydrogen Embrittlement

• Prevention in Processing
• Embrittlement can originate from poor production
  techniques
• Problems arise when hydrogen is allowed into
  production environment
• Remedies
• Maintain low hydrogen atmosphere
• Heat treatment

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Hydrogen Embrittlement

• Prevention in Welding
• Embrittlement can be localized around a weld
• Welding rods containing hydrogen are the source
• Remedies
• Low hydrogen welding rods stored in a dry place
• Local heat treatment before after welding

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Hydrogen Embrittlement

• Prevention
• Design Minimize strength of material
• Production Minimize hydrogen sources in
  production area Heat treatment
• Welding Welding rod storage Heat treatment
• Reversal Baking 100-650C under vacuum
  conditions can rid a metals of hydrogen
  inclusions

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Hydrogen Embrittlement

• Case Study
• Unalloyed steel
• High pressure boiler
• Evaporator tube
• Time to failure over 10 years
• Environment flue gas deposits with sulphuric
  acid compounds
• Remedy Use low-alloyed (hydrogen-resistant) steel

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Hydrogen Embrittlement

• Case Study
• Steel Fastener
• Multiple fracture origins
• Subsurface cracking at inclusions

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Hydrogen Induced Blistering

• Hydrogen is absorbed into metal, diffuses inward,
  and precipitates as molecular hydrogen
• Precipitates as laminations, inclusions, matrix
  interfaces
• When cracks are just below surface, the exterior
  layer of metal will bulge
• Enough pressure builds to produce internal cracks

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Hydrogen Induced Blistering

• Basic Mechanism

Physical Adsorption
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Hydrogen Induced Blistering

• Basic Mechanism

H2(gas)
Dissociative Chemical Adsorption
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Hydrogen Induced Blistering

• Basic Mechanism

H2(gas)
Hydrogen Diffusion
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Hydrogen Induced Blistering

• Basic Mechanism

H2(gas)
Blister Formation
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Hydrogen Induced Blistering

• General Notes
• Hydrogen induced blistering can be seen as a
  special case of hydrogen embrittlement
• Blistering most prevalent in low-strength alloys
  or metals that have been exposed to
  hydrogen-charging conditions

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Hydrogen Induced Blistering

• Prevention
• Surface phenomenon
• Source Hydrogen absorbed from the environment
• Minimized hydrogen at surface
• Corrosion inhibitors
• Avoid cathodic protection and galvanic couples

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Hydrogen Induced Blistering

• Case Study
• Unalloyed steel wall
• Carbon dioxide scrubbing tower
• Time to failure many years
• Environment water and CO2
• Use a non-corrosive scrubbing liquid,
• Accept corrosion monitor its progress

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Precipitation of Internal Hydrogen

• Processing
• Introduces 5-8 ppm
• RT equilibrium at 0.1 ppm
• Diatomic precipitation
• Occurs at existing inclusions
• Pressure causes enlargement of cracks
• Cracks Embrittlement

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Precipitation of Internal Hydrogen

• Transgranular Cleavage

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Precipitation of Internal Hydrogen

• How hydrogen gets there
• Atmospheric moisture
• Impurities
• Welding
• Atmosphere
• Surface contaminants
• Welding rod

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Precipitation of Internal Hydrogen

• Fracture
• Reduced ductility
• Fracture initiation
• inclusions
• pores
• Fracture surface
• Fisheyes
• Flakes
• Typical of heavy steel forgings
• Caused by internal residual hydrogen
• Hairline cracks in center of part
• Below 200 degrees C

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Precipitation of Internal Hydrogen

• Prevention
• Internal phenomenon
• Source Hydrogen absorbed during processing
• Improved processing techniques with added heat
  treatment under vacuum

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Precipitation of Internal Hydrogen

• Prevention in Processing
• Hydrogen solubility in iron
• Low in ?-iron (low T)
• High in ?-iron (high T)
• Diffusivity increases with temperature
• Result Quenching metals aids hydrogen corrosion
• Low diffusivity traps hydrogen in metal
• Hydrogen precipitates internally

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Precipitation of Internal Hydrogen

• Hot metal during processing

• Hydrogen diffuses in at high temperatures

• Cool the metal ..

Hydrogen is trapped!
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Precipitation of Internal Hydrogen

• Hot metal during processing

• Longer annealing time under vacuum conditions

• Hydrogen is able to diffuse out as the
  solubility decreases

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Precipitation of Internal Hydrogen

• Case study
• Viton B (rubber)
• Environment oil well workover fluids
• Time to failure months
• Failure due to pressure buildup at voids in the
  material
• The interiors of the blisters are similar to that
  of hydrogen flakes in steel

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Hydrogen Attack

• Mechanism
• Environment
• High P, high T hydrogen environment
• Petrochemical plants
• Hydrocarbon processing at 21 MPa, 540C
• Stress level, exposure time, steel composition
• Mechanism
• Hydrogen reacts with carbides to form methane
• Methane bubbles form at grain boundaries
• Bubbles merge to create fissures

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Hydrogen Attack
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Hydrogen Attack
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Hydrogen Attack
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Hydrogen Attack
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Hydrogen Attack

• Characteristics
• Symptoms
• Unexpected failure
• Microstructure
• Decarburization along grain boundaries
• Fissuring along grain boundaries
• Embedded methane bubbles

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Hydrogen Attack

• Rapid cooling can cause
• Hydrogen embrittlement
• Blistering

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Hydrogen Attack

• Prevention
• High temperature phenomenon
• Petroleum processing reaches up to 540 C
• Reaction with carbon
• Methane and decarburized structures formed
• Minimize carbon content for high temperature
  operation!

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Hydrogen Attack

• Case Study
• Hydrogen attack at the ID weld in a high pressure
  carbon steel boiler tube

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Hydrogen Attack

• Case Study
• Cracking due to hydrogen attack at the ID weld in
  a high pressure carbon steel boiler tube

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Hydrogen Attack

• Case Study
• Carbon steel cooler pipe from heat exchanger
• Time to Failure Several years.
• Environment high internal pressure, gas mixture
  of hydrogen, nitrogen and ammonia at approx.
  240C.
• Remedy Use 0.5 Mo steel or one of the Cr Mo
  steels

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Hydride Formation Cracking

• Affects Ti, Ta, Zr, U, Th
• Hydrogen picked up during processing
• Melting
• Welding
• Hydride formation upon cooling

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Hydride Formation Cracking

• Characteristics
• Lower density than metal matrix
• Increases strength
• Decreases ductility, toughness
• Platelets
• Preferred orientation in lattice
• Applied stress can cause hydride alignment

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Hydride Formation Cracking

• Hydrides in Titanium
• Passivating at 100 C
• Slow diffusion
• 0.4 mm layer of TiH2
• Spalling
• Rapid formation above 250 C
• Low hydrogen solubility
• No spalling
• Formation of hydride particles throughout
• High susceptibility to failure
• Typically occurs upon cooling from higher T

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Hydride Formation Cracking

• Passivation

Ti
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Hydride Formation Cracking

• Passivation

Ti
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Hydride Formation Cracking

• Passivation

Ti
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Hydride Formation Cracking

• Passivation

Ti
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Hydride Formation Cracking

• Prevention
• Internal phenomenon
• Results from high-temperature reactions between
  hydrogen and the metal
• Remedies
• Minimize operating temperatures
• Heat treatment

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Prevention Review

• Design Specifications
• Minimize material strength
• Minimize carbon content for high-temperature
  operation
• Avoid titanium for high-temperature operation
• Minimize Hydrogen Content
• Heat treatment (processing welding)
• Use corrosion inhibitors
• Maintain dry environment (storage)

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Hydride Formation Cracking

• Case Study
• Titanium pipe
• Used in Ammonium carbonate condenser.
• Time to failure 5 years
• Temp. 130C
• Remedies reduce operating temperature, use
  stainless steel

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Questions?!
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Have a Great SPRING BREAK!!!!!!
Have a Great SPRING BREAK!!!!!!
Have a Great SPRING BREAK!!!!!!
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