hydrogen damage

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HYDROGEN DAMAGE OF HYDROGEN DAMAGE OF METALLIC MATERIALS METALLIC MATERIALS T.K. G. NAMBOODHIRI T.K. G. NAMBOODHIRI PROFESSOR OF METALLURGICAL ENGINEERING PROFESSOR OF METALLURGICAL ENGINEERING (Retired) (Retired) BANARAS HINDU UNIVERSITY BANARAS HINDU UNIVERSITY VARANASI VARANASI

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Hydrogen, in small quantities, damages metallic materials and reduces their serviceability. Several phenomena associated with hydrogen are shown here.

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Page 1: Hydrogen Damage

HYDROGEN DAMAGE OF HYDROGEN DAMAGE OF METALLIC MATERIALSMETALLIC MATERIALS

T.K. G. NAMBOODHIRIT.K. G. NAMBOODHIRIPROFESSOR OF METALLURGICAL ENGINEERING PROFESSOR OF METALLURGICAL ENGINEERING

(Retired)(Retired)BANARAS HINDU UNIVERSITYBANARAS HINDU UNIVERSITY

VARANASIVARANASI

Page 2: Hydrogen Damage

IntroductionIntroduction

• Hydrogen-most ubiquitous elementHydrogen-most ubiquitous element

• Minute amounts can damage metalsMinute amounts can damage metals

• Can be easily picked up by metals Can be easily picked up by metals during melting, casting, working, during melting, casting, working, fabrication and usefabrication and use

• Many forms of hydrogen damageMany forms of hydrogen damage

Page 3: Hydrogen Damage

Classification of hydrogen Classification of hydrogen damagedamage

HYDROGENENVIRONMENTEMBRITTLEMENT CRACKING

DEGRADATION OFOTHER MECHANICAL

PROPERTIES

LOSS IN TENSILE

DUCTILITY

SLOW STRAIN RATEEMBRITTLEMENT

HYDROGENEMBRITTLEMENT

HYDRIDE

EMBRITTLEMENTHYDROGEN

DAMAGESOLID SOLUTION

HARDENING

HIGH STRAIN RATE

EMBRITTLEMENT

CREATION OFINTERNAL DEFECTS

POROSITYSHATTER CRACKS,

FLAKES, FISH EYESBLISTERING

HYDROGENATTACK

HYDROGEN STRESS

Page 4: Hydrogen Damage

Solid solution Solid solution hardening.hardening.

• Hydrogen hardens metals like Hydrogen hardens metals like Nb,Ta and Ti at concentrations Nb,Ta and Ti at concentrations within solid solubility limits. These within solid solubility limits. These metals may be Embrittled at high metals may be Embrittled at high strain rates.strain rates.

Page 5: Hydrogen Damage

HYDROGEN HYDROGEN EMBRITTLEMENTEMBRITTLEMENT

HYDROGEN EMBRITTLEMENT

HYDROGEN ENVIRONMENT EMBRITTLEMENT

HYDROGEN STRESS CRACKING

LOSS IN TENSILE DUCTILITY & OTHER MECHANICAL PROPERTIES

Page 6: Hydrogen Damage

Hydride embrittlementHydride embrittlement

• Seen in hydride forming metals like Ti, V, ZrSeen in hydride forming metals like Ti, V, Zr

• Low strain rate embrittlementLow strain rate embrittlement: At low H : At low H concentrations. Similar to H.E.. Caused by concentrations. Similar to H.E.. Caused by stress-nucleated hydridesstress-nucleated hydrides

• High strain rate embrittlementHigh strain rate embrittlement: At high : At high H concentrations. Due to hydride H concentrations. Due to hydride precipitates. Enhanced by high strain rates.precipitates. Enhanced by high strain rates.

Page 7: Hydrogen Damage

Creation of internal Creation of internal defectsdefects

• BlisteringBlistering: : Formation and collection of Formation and collection of molecular hydrogen at internal defects like grain molecular hydrogen at internal defects like grain boundaries, inclusions and laminations, build-up of boundaries, inclusions and laminations, build-up of high pressures leading to formation and growth of high pressures leading to formation and growth of blistersblisters

• Shatter cracks and flakesShatter cracks and flakes: Internal : Internal fissures seen in large forgings due to segregated Hfissures seen in large forgings due to segregated H

• Fish-eyesFish-eyes: bright patches of embrittled regions : bright patches of embrittled regions visible on fracture surfaces of weldments.visible on fracture surfaces of weldments.

Page 8: Hydrogen Damage

Creation of internal Creation of internal defectsdefects• Micro-perforations: Micro-perforations: Exposure to high hydrogen Exposure to high hydrogen

pressures at R.T. may develop small fissures or pressures at R.T. may develop small fissures or micro-perforationsmicro-perforations

• Porosity: Porosity: Liquid metals containing large amounts Liquid metals containing large amounts of H liberate it during solidification causing porosity of H liberate it during solidification causing porosity in Fe, Al and Mg. H content, cooling rate, external in Fe, Al and Mg. H content, cooling rate, external pressure and H partial pressure control porositypressure and H partial pressure control porosity

• Hydrogen attackHydrogen attack: Exposure of steels to high : Exposure of steels to high pressure H at high temperatures causes H to react pressure H at high temperatures causes H to react with carbon of steel to produce methane. Leads to with carbon of steel to produce methane. Leads to decarburization, dissolution of carbides and decarburization, dissolution of carbides and weakening of the steel. weakening of the steel.

Page 9: Hydrogen Damage

CHARACTERISTICS OF CHARACTERISTICS OF IMPORTANT H. D. IMPORTANT H. D. PROCESSESPROCESSES

• HYDROGEN EMBRITTLEMENTHYDROGEN EMBRITTLEMENT

• HYDROGEN INDUCED BLISTER HYDROGEN INDUCED BLISTER CRACKINGCRACKING

• HYDROGEN ATTACKHYDROGEN ATTACK

Page 10: Hydrogen Damage

Characteristics of Hydrogen Characteristics of Hydrogen EmbrittlementEmbrittlement

•Strain rate and temperature Strain rate and temperature sensitivitysensitivity

•Delayed failureDelayed failure

•Sub critical cracking and threshold Sub critical cracking and threshold stress intensitystress intensity

•Effects on tensile propertiesEffects on tensile properties

•Fracture mechanismsFracture mechanisms

Page 11: Hydrogen Damage

Strain rate and temperature Strain rate and temperature sensitivity of H.E.sensitivity of H.E.• Most pronounced at Most pronounced at

slow strain rates and slow strain rates and ambient ambient temperaturestemperatures

• Decreases Decreases monotonically with monotonically with increasing strain increasing strain raterate

• Minimum at around Minimum at around room temperatureroom temperature

Page 12: Hydrogen Damage

Delayed failure in H.E.Delayed failure in H.E.

• Incubation period Incubation period independent of stressindependent of stress

• Time to failure Time to failure increases with increases with decreasing stressdecreasing stress

• Discontinuous crack Discontinuous crack propagationpropagation

• Lower critical stress Lower critical stress below which no failurebelow which no failure

• H causes delayed H causes delayed failure in many failure in many materialsmaterials

• Parameters strongly Parameters strongly dependent on H contentdependent on H content

Page 13: Hydrogen Damage

Effects of H on tensile Effects of H on tensile propertiesproperties

• Increased/decreased/unaffected Y.S.Increased/decreased/unaffected Y.S.

• Strain localization/Luders Strain localization/Luders band/serrated yieldingband/serrated yielding

• Increased/decreased flow stress and Increased/decreased flow stress and work hardening ratework hardening rate

• Increased screw dislocation velocity Increased screw dislocation velocity and dislocation multiplicationand dislocation multiplication

• Loss in tensile ductilityLoss in tensile ductility

Page 14: Hydrogen Damage

Fracture mechanisms in Fracture mechanisms in H.E.H.E.

• H promotes all fracture mechanismsH promotes all fracture mechanisms

• MVC in low strength steelsMVC in low strength steels

• Ductile, quasi-cleavage or I.G. fractures Ductile, quasi-cleavage or I.G. fractures in high strength steelsin high strength steels

• I.G.failure in NiI.G.failure in Ni

• I.G. or Transgranular cleavage(fluted I.G. or Transgranular cleavage(fluted morphology) in Ti alloys.morphology) in Ti alloys.

• I.G., cleavage or M.V.C. in Al alloys.I.G., cleavage or M.V.C. in Al alloys.

Page 15: Hydrogen Damage

H induced fracture H induced fracture morphologymorphology

Page 16: Hydrogen Damage

Hydrogen Induced Blister Hydrogen Induced Blister Cracking (HIBC)Cracking (HIBC)

• Metallurgical parameters: Non-metallic Metallurgical parameters: Non-metallic inclusions, Sulfur content, alloy inclusions, Sulfur content, alloy segregation and microstructure. Very low segregation and microstructure. Very low S levels and inclusion shape control to S levels and inclusion shape control to eliminate HIBC nucleation. Reduction in eliminate HIBC nucleation. Reduction in hardness of segregated zones to prevent hardness of segregated zones to prevent HIBC propagation.HIBC propagation.

• Environmental parameters: Hydrogen Environmental parameters: Hydrogen fugacity. A threshold fugacity below fugacity. A threshold fugacity below which HIBC does not occur.which HIBC does not occur.

Page 17: Hydrogen Damage

HYDROGEN INDUCED HYDROGEN INDUCED BLISTERSBLISTERS• Top picture shows Top picture shows

hydrogen induced hydrogen induced blisters in a pipe blisters in a pipe line carrying line carrying hydrogen sulfide hydrogen sulfide containing fluidscontaining fluids

• Bottom picture Bottom picture shows the cross shows the cross section of a blistersection of a blister

Page 18: Hydrogen Damage

Hydrogen Induced Blister Hydrogen Induced Blister Cracking (HIBC)Cracking (HIBC)

• Hydrogen blisters Hydrogen blisters nucleate on nucleate on inclusion stringers inclusion stringers and cause cracking and cause cracking when their internal when their internal gas pressure gas pressure exceeds the exceeds the fracture stress- fracture stress- HSLA/Line pipe HSLA/Line pipe steels. Straight or steels. Straight or step-wise crackingstep-wise cracking

Page 19: Hydrogen Damage

HYDROGEN ATTACKHYDROGEN ATTACK

• Equipment in contact with hydrogen at Equipment in contact with hydrogen at temperatures above 260 C and hydrogen temperatures above 260 C and hydrogen partial pressures above 690 KPa may suffer partial pressures above 690 KPa may suffer from high temperature hydrogen attack. from high temperature hydrogen attack.

• Atomic hydrogen diffuses readily in steels Atomic hydrogen diffuses readily in steels and reacts with carbon present to form and reacts with carbon present to form methane which collects at grain boundaries methane which collects at grain boundaries and in minute voids. and in minute voids.

• Methane pressure build-up leads to crackingMethane pressure build-up leads to cracking

Page 20: Hydrogen Damage

Hydrogen attack : Nelson Hydrogen attack : Nelson curves for steelscurves for steels

• Nelson curves Nelson curves show safe show safe operating limits of operating limits of temperature and temperature and hydrogen partial hydrogen partial pressure for pressure for steels. Empirical steels. Empirical curves drawn from curves drawn from actual experienceactual experience

Page 21: Hydrogen Damage

Prevention of Hydrogen Prevention of Hydrogen damagedamage

• Metallurgical control: Metallurgical control: Alloy Alloy chemistry, crystal structure, chemistry, crystal structure, microstructure and substructure.microstructure and substructure.

• Environmental control: Environmental control: Inhibition Inhibition by organic compounds like nitriles, by organic compounds like nitriles, sulfoxides, azoles and amines.sulfoxides, azoles and amines.

Page 22: Hydrogen Damage

CONCLUSIONSCONCLUSIONS

• SMALL QUANTITIES OF HYDROGEN CAN SMALL QUANTITIES OF HYDROGEN CAN SERIOUSLY AFFECT THE PROPERTIES OF SERIOUSLY AFFECT THE PROPERTIES OF MANY STRUCTURAL MATERIALSMANY STRUCTURAL MATERIALS

• HYDROGEN DAMAGE HAS MANY FORMSHYDROGEN DAMAGE HAS MANY FORMS

• CAREFUL SELECTION OF MATERIALS, CAREFUL SELECTION OF MATERIALS, PROCESSING STEPS AND ENVIRONMENTS PROCESSING STEPS AND ENVIRONMENTS CAN PREVENT HYDROGEN DAMAGECAN PREVENT HYDROGEN DAMAGE