The Effects of Purity and Pressure on

Hydrogen Embrittlement of Metallic

Materials (ID 149)

3rd INTERNATIONAL CONFERENCE3rd INTERNATIONAL CONFERENCE

ON HYDROGEN SAFETYON HYDROGEN SAFETY

AJACCIOAJACCIO –– SEPTEMBER 16SEPTEMBER 16--18th, 200918th, 2009

Hervé Barthélémy

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Overview

Introduction to Hydrogen Embrittlement(HE)

Causes and Mechanisms

Scope of Research

Results and Data

Test Methods

Effects of Pressure

Effects of H2 gas purity

Issues to Address

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Loss of ductility and deformationcapacity in the presence of hydrogen

Strongly affects high-strength steels

Maximum embrittlement at roomtemperature (~20°C)

Causes hydrogen transport bydislocations

Hydrogen Embrittlement in Steels

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Factors affecting HE

Environment

Material properties and surface condition

Possible Mechanisms of HE

Stress-induced hydride formation

Hydrogen-enhanced localized plasticity(HELP)

Hydrogen-induced decohesion

Hydrogen Embrittlement in Steels

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Gas purity

Pressure

Temperature

Exposure time (affects diffusion ininternal HE)

Stress and strain rates

Environment

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Chemical composition of metal

Heat treatment, welding

Microstructure

Cracks, corrosion pits, and other surfacedefects

Material Properties related to HE

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Metals

Carbon, Low alloy, and Stainless Steels

Aluminum and Copper

Focusing on three aspects of HE for steels

Effective testing methods for HE

Effects of H2 gas pressure (700-1000 bar)

Effects of H2 gas purity

Scope of Research

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Austenitic alloys suffer lessembrittlement than ferritic alloys

Martensitic specimens are very sensitiveto HE

Steels often become less ductile, butstrength is not significantly reduced byHE

Aluminum and copper alloys have shownhigh resistance to HE in tensile testing

Hydrogen Embrittlement

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TESTING METHODS

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Need to simulate in-service stresses ofpressure vessels -external HE effects

High sensitivity

Capable of being reproduced

Small cells for lower cost and easycleaning

Testing for HE

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Compare behavior under pressurizedhydrogen vs. inert gas

Provide data for changes in ductility-elongation and %RA

Tensile stresses are uniaxial

%100% xA

AARA

i

fi

Tensile Tests

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Wedge Opening Load (WOL)

Test of threshold stress intensity factor, KTH

Crack growth

Compact Tension (CT)

Fatigue crack growth rate, da/dN

KTH

Plane-strain fracture toughness, KIC

Fracture Mechanics

Acceptable criteria: KTH>(60/950) x Rm

(MPa-m0.5), where Rm is UTS of metal [1]

Maximum acceptable crackgrowth: 0.25mm [1]

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Disk rupture

Provides strength comparison in H2

and He environments

Creates triaxial stress state

Delayed rupture

Disk fatigue test

Good for simulating life of a pressurevessel

Disk Tests

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EFFECTS OF HYDROGEN GAS

PRESSURE

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HE generally increases with partialhydrogen pressure

Some tests showed maximum HE at acertain pressure level

~100 bar for carbon and low alloyswhere UTS<1000 MPa

~25 bar for AISI 321 stainless steel [2]

Pressure Effects

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Large ductility loss with increase of hydrogenpressure for carbon steel [3]

HE Test Results

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Hydrogen pressure

HE Test Results – Disk test

Influence of H2S partial pressurefor AISI 321 steel

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Successful performance of 316 steel intensile tests with high pressure hydrogen [4]

316 Stainless Steel

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Cracking threshold significantly decreases ashydrogen pressure increases for low alloy steel [4]

Pressure Test Results

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HE effects on type 4147 appear to level off atpressures higher than 60 MPa [4]

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HY-100 showed significantly increased crackgrowth rate in 52 MPa hydrogen [4]

Effects of 52 MPa hydrogen on fatiguecrack growth for HY-100 Steel

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In tests performedat 103.4 MPa on SA-105 steel, fatiguecrack growth wasslower at higherfrequencies [5]

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Losses in ductility increase with pressure,although several steels reached maximumembrittlement at a threshold pressure

Fracture toughness and resistance to crackpropagation decrease

Strength of the material is usually notsignificantly affected

Results of High Pressure Tests

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Fatigue resistance decreases at higherpressures

A286 and 316 stainless steels have shownthe most resistance to HE

Aluminum and copper alloys appear to beresistant to HE

More fatigue testing at high pressure needsto be performed on these materials

Effects of High Pressure Hydrogen

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EFFECTS OF HYDROGEN GAS

PURITY

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Impurities Affecting HE

HE Inhibitor No EffectEmbrittling

Effect

O2

SO2 N2 CO2

CH4 H2S

H2O has demonstrated both embrittling andinhibiting effects

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Oxygen has shown inhibiting effects indelayed disk rupture

Varying results for impurities such as CH4

and CO2

H2S has consistently accelerated HE

Impurity Effects

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Effects of gas impurity on HE for carbonsteels [4]

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Impurity effects on fatiguecrack growth

Comparison between pure gas andH2 with additives [4]

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Inhibiting effects of SO2

Sulfur dioxide exhibited inhibitory effectsas a pretreatment for steel sheet [6]

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Inhibiting effects of oxygen on crack

growth in H-11 steel

[7]

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O2 consistently acts as an inhibitor

H2S has consistently accelerated HE

Pretreating with SO2 had inhibiting effectsduring pretreatments

More data and information is neededregarding purity at higher pressures

Results from Impurity Tests

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More information needed about thresholdpressures at which maximum embrittlementoccurs

Fatigue data for metals demonstrating goodHE resistance (A286, 316, Al and Cu alloys)

More information needed about effects ofinhibitors

Resolve conflicting claims

Specific concentrations for mixtures

Inhibiting at higher pressures

Areas for Further Research

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1. ISO 11114-4: Transportable gas cylinders, compatibility of cylinder and valvematerials with gas contents, 2006.

2. Barthelemy, H. Compatibility of Metallic Materials with Hydrogen. Air Liquide.

3. Gutierrez-Solana, F. and M. Elices. High Pressure Hydrogen Behavior of aPipeline Steel, ed. by C. G. Interrante and G. M. Pressouyre. Proceedings of theFirst International Conference on Current Solutions to Hydrogen Problems inSteels, November 1 (1982), pp. 181-185.

4. San Marchi, C., and B. Somerday Technical Reference on HydrogenCompatibility of Materials. Sandia National Laboratories, March 2008.

5. Lam, P S., R. L. Sindelar, and T. M. Adams. Literature Survey of GaseousHydrogen Effects on the Mechanical Properties of Carbon and Low AlloySteels. Savannah River National Laboratory, ASME Pressure Vessels andPiping Division Conference, 22 July 2007.

6. Srikrishnan, V. and P. J. Ficalora. The Role of Gaseous Impurities in HydrogenEmbrittlement of Steel. September 7, 1976.

7. Balch, D., San Marchi, C., and B. Somerday. Hydrogen-Assisted Fracture:Materials Testing and Variables Governing Fracture. Sandia NationalLaboratories. Hydrogen Pipeline Working Group Workshop, August 30-31,2005.

References