1

May 2007

P. Sofronis, I. M. Robertson, D. D. Johnson

University of Illinois at Urbana-Champaign

2007 DOE Hydrogen Program ReviewMay 16, 2007

Hydrogen Embrittlement of Pipelines:Fundamentals, Experiments, Modeling

Project ID #PD13_sofronis

This presentation does not contain any proprietary or confidential information

2

May 2007

OverviewTimeline

Project start date:5/1/05Project end date: 30/4/09Percent complete: 15%

BudgetTotal project funding: 300k/yr

DOE share: 75%Contractor share: 25%

Funding received in FY2005$100 K

Funding received in FY2006$80 KDue to reduced funding Experiments and Ab-initio calculations were on hold

Funding for FY2007$80 K

BarriersHydrogen embrittlement of pipelines and remediation (mixing with water vapor?)Suitable steels, and/or coatings, or other materials to provide safe and reliable hydrogen transport and reduced capital costAssessment of hydrogen compatibility of the existing natural gas pipeline system for transporting hydrogen

PartnersIndustrial (SECAT)

DGS Metallurgical Solutions, Inc.Air LiquideAir ProductsSchott North America

National LaboratoriesOak Ridge National LaboratorySandia National Laboratories

Codes and StandardsASME

SCHOTTglass made of ideas

OAK RIDGE NATIONAL LABORATORYU.S. DEPARTMENT OF ENERGY

3

May 2007

ObjectivesTo come up with a mechanistic understanding of hydrogen embrittlement in pipeline steels in order to devise fracture criteria for safe and reliable pipeline operation under hydrogen pressures of at least 7MPa and loading conditions both static and cyclic (due to in-line compressors)

Existing natural gas network of pipeline steelsPropose new steel microstructures

It is emphasized that such fracture criteria are lacking and there are no codes and standards for reliable and safe operation in the presence of hydrogen

Hydrogen pipelines in service operate in the absolute absence of any design criteria against hydrogen-induced failureThere are no criteria (codes and standards) with predictive capabilitiesPipeline steels are extremely and dangerously susceptible to fatigue failure in the presence of hydrogen

Illinois mechanism-based approachDevelop design criteria to be used for codes and standards for safe and reliable operationAvoid unnecessary repairs and shut-downs by minimizing unnecessary levels of conservatism in the operation of pipelinesReduce capital cost by avoiding conservatism

4

May 2007

ApproachTension experiments to identify macroscopic plastic flow characteristics

Permeation experiments to identify diffusion characteristics

Experiments (subcritical crack growth) to determineThe hydrogen effect on crack initiation What constitutes “safe hydrogen concentrations” at Threshold Stress Intensities The stability of crack propagation to assess catastrophic failure scenarios

Identification of deformation mechanisms and potential fracture initiation sites under both static and cyclic loading conditions in the presence of hydrogen solutes

SEM studies of fracture surfaces in the presence of hydrogen and TEM analysis of the material microstructure Our contention, which needs to be verified through experiment, is that embrittlement is a result of the synergistic action between decohesion at an inclusion/matrix interface (void nucleation) accompanied by shear localization in the ligament between the opening void and the tip of the crack

Thermodynamics and first principles calculations for the determination of the cohesive properties of particle/matrix interfaces as affected by the presence of hydrogen solutes

Finite element simulations of the coupled problem of material elastoplasticity and hydrogen diffusion in the neighborhood of a crack tip accounting for stress-driven diffusion and trapping of hydrogen at microstructural defects.

Development of a mechanistic model that incorporates the fracture mechanisms to establish fracture criteria with predictive capabilities

5

May 2007

New Steel Microstructure-Oregon Steel Mills (OSM)

API Grade C Mn Si Cu Ni V Nb Cr Ti

X70/80 0.04 1.61 0.14 0.22 0.12 0.000 0.096 0.42 0.015

• High dislocation density in some regions

• Irregular grain boundaries and small grains, indicative of microstructure that has not been fully recrystallized and recovered.

Relatively low precipitate density (inside the matrix)

Defects in microstructure, particularly precipitates, act as trap sites for hydrogen

6

May 2007

Particle CompositionEnergy Dispersive Spectroscopy

a) EDS spectrum from particleb) Bright field TEM image of typical rectangular particlec) EDS spectrum from matrix

EDS analysis of fine precipitate inside ferrite grain suggests that precipitate is composed of Ti and Nb

(window detector: C, N, O not detected)

7

May 2007

Steel Microstructure-Air Liquide Pipeline

Large intergranular particles (cementite)

Small intragranular particles (carbides with Nb and Ti)

8

May 2007

0.00E+00

2.00E+14

4.00E+14

6.00E+14

8.00E+14

1.00E+15

1.20E+15

0 200 400 600 800 1000 1200

time (s)

flux

(ato

ms/

m^2

s)

0.00E+00

2.00E+14

4.00E+14

6.00E+14

8.00E+14

1.00E+15

1.20E+15

0 5 10 15 20 25 30 35 40

time (s)

flux

(ato

ms/

m^2

s)

0.0E+00

5.0E+17

1.0E+18

1.5E+18

2.0E+18

0 20 40 60 80 100 120 140

time (s)

Inte

gral

of f

lux

(ato

ms/

m^2

)

0.00E+00

5.00E+10

1.00E+11

1.50E+11

2.00E+11

2.50E+11

3.00E+11

3.50E+11

4.00E+11

4.50E+11

0 10 20 30 40 50 60 70

Sqrt Pressure Pa^1/2

Stea

dy S

tate

flux

* th

ickn

ess

(ato

ms/

m s

)

•Oregon Steel Mills sample: thickness •room temperature

Ultrahigh vacuum (10-9 torr)Hydrogen pressure (10 torr)

Hydrogen Permeation Measurements

2

6Teff

LtD

=6.8sTt =

Steady state:

12 H atoms6.26 10MPa.m.s

Φ = ×

4.7torr 627PaP = =

J

J L∞

120micronsL =

Jdt∫

Time lag

Permeabilityat room temperature

J∞

0.0E+00

5.0E+16

1.0E+17

1.5E+17

2.0E+17

2.5E+17

3.0E+17

0 5 10 15 20 25 30

time (s)

Inte

gral

of f

lux

(ato

ms/

m^2

)

9

May 2007

Hydrogen Transport Analysis Diffusing hydrogen resides at

Normal Interstitial Lattice Sites (NILS)Trapping Sites

Microstructural heterogeneities such as dislocations, grain boundaries, inclusions, voids, interfaces, impurity atom clusters

Hydrogen populations in NILS and trapping sites are assumed to be in equilibrium according to Oriani’s theory

Trap density may evolve dynamically with plastic straining

Hydrogen Transport Equation

Note the effect of stress and plastic strain

dislocationsinclusions

Grain boundaries

exp1 1

T L B

T L

WRT

θ θθ θ

⎛ ⎞= ⎜ ⎟− − ⎝ ⎠

Trap binding energyT=TemperatureR=gas constant

BW =

C NT T T= αθ3

NILS occcupancynumber of NILS per solvent atom.

=number of solvent atoms/m .

L

LN

θβ

==

C NL L L= βθ

, ,,3

pL H T

L ii L kk i T pieff

D dC DV N dDC CD dt RT dt

∂ εσ αθ∂ε

⎛ ⎞= − −⎜ ⎟⎝ ⎠

( )

( )

time differentiationHydrogen concentrationdiffusion coefficientEffective diffusion

= 1 accounting for trappinghydrostatic stress

plastic strainpartial molar volume of Htrap density

eff

T L

kkp

H

T

i

d dtCD

D

D C C

VN

,

σ

ε

====

+ ∂ ∂

=

===

( ) ix= ∂ ∂

3

trap occcupancynumber of sites per trap.

= number of traps/m .

T

TN

θα

==

10

May 2007

Material Data (OSM)

(2) Dislocation trapping modeling

0 . 0 0 . 2 0 . 4 0 . 6 0 . 8 1 . 0 1 . 2 1 . 4 1 . 6

2 0

2 1

2 2

2 3

2 4

E x p e r i m e n t a l r e s u l t s [ 8 1 ]

Lo

g(N T)

ε p

pε 0 0 .2 0 .4 0 .6 0 .8 1 .0 1 .2 1 .4 1 .6

24 23 22 21 20

( )TLog N 60.0 KJ/molBW =2

TNaρ

=

0 0.150 15

const. 0.15.

p p

p

γρ ε ερ

ε

⎧ + ≤⎪= ⎨⎪ >⎩

10 2 16 20 10 10,m mρ γ− −= =

20.2 KJ/molBW =

(1)Kumnick and Johnsontrapping model

Stress-strain

Plastic Strain

Stre

ss(M

Pa)

0 0.1 0.2 0.30

200

400

600

800

00

1np

Yεσ σε

⎛ ⎞= +⎜ ⎟

⎝ ⎠

0 595 MPaσ =

0.059n =

pε

, pσ ε

Experiment Model

8 21.271 10 m /sD −= ×Lattice diffusion coefficient

22 30 2.65932 10 H atom / mC = ×

183

H atoms6.54696 10m Pa

S = ×

21 30 2.084 10 H atom / mC = ×

15 MPa P =

1 atm P =

11

May 2007

Cracked Pipeline: Problem Statement

( ) 0LC t =

( )LC t S P= ×

0 100-200 200-100

( ) 0LC t =

( )LC t P∝

( ) 0J t =

( ) 0LC t =

( )LC t P∝

( ) 0J t =

Outer Radius: 8”Thickness: 0.375”

uncracked ligament: 0.3”initial crack opening: 1.5 μm

Hydrogen gas at pressure P

15 MPaHydrogen

gas

Hydrogen transport

15 MPa

time 1 min

1.5 hrs

P

t

dimensions are in mm

12

May 2007

Hydrostatic Stress at Pressure 15 MPa

-202 -200 -198 -196 -1940

2

4

6

8 2.32.22.121.91.81.71.61.51.41.31.21.110.90.80.70.60.50.40.30.20.10

-0.1-0.2

03kkσσ

195 200 2050

5

10

15

20

25

30

2.32.22.121.91.81.71.61.51.41.31.21.110.90.80.70.60.50.40.30.20.10

-0.1-0.2

03kkσσ

Geometric dimensions are in mm

Crack tip

13

May 2007

Plastic Strain at Pressure 15 MPa

-202 -200 -198 -196 -1940

2

4

6

8

10.950.90.850.80.750.70.650.60.550.50.450.40.350.30.250.20.150.10.050

pε

195 200 2050

5

10

15

20

25

30

0

pε

Geometric dimensions are in mm

14

May 2007

Lattice Hydrogen Concentration at Steady State

-202 -200 -198 -196 -1940

2

4

6

8

2.52.42.32.22.121.91.81.71.61.51.41.31.21.110.90.80.70.60.50.40.30.20.1

0

LCC

195 200 2050

5

10

15

20

25

30

10.90.80.70.60.50.40.30.20.1

0

LCC

Kumnick and Johnson trapping model

22 30 2.65932 10 H atom / mC = × 15 MPa P =

Time to steady-state: 1.5 hrs8 minsst =

15

May 2007

Transient to Steady State - Lattice Concentration

0/LC C

16

May 2007

Trapped Hydrogen Concentration at Steady State

-202 -200 -198 -196 -1940

2

4

6

8

6.56.2565.755.55.2554.754.54.2543.753.53.2532.752.52.2521.751.51.2510.750.50.25

0

TCC

195 200 2050

5

10

15

20

25

30

0.10.090.080.070.060.050.040.030.020.01

0

TCC

Kumnick and Johnson trapping model

22 30 2.65932 10 H atom / mC = × 15 MPa P =

17

May 2007

Total Hydrogen Concentration at Steady State

-202 -200 -198 -196 -1940

2

4

6

87.57.2576.756.56.2565.755.55.2554.754.54.2543.753.53.2532.752.52.2521.751.51.2510.750.50.25

0

L TC CC+

195 200 2050

5

10

15

20

25

30

10.90.80.70.60.50.40.30.20.1

0

L TC CC+

Kumnick and Johnsontrapping model

22 30 2.65932 10 H atom / mC = × 15 MPa P =

Time to steady-state is 1.5 hrs8 minsst =

18

May 2007

Total Hydrogen Concentration at Steady State

-202 -200 -198 -196 -1940

2

4

6

8

4.84.64.44.243.83.63.43.232.82.62.42.221.81.61.41.210.80.60.40.2

0

L TC CC+

195 200 2050

5

10

15

20

25

30

10.90.80.70.60.50.40.30.20.1

0

L TC CC+

Dislocation trapping model

22 30 2.65932 10 H atom / mC = × 15 MPa P =

19

May 2007

Fracture Mechanics Assessment

0 10 20 30 40 500.5

1

1.5

2

2.5

Full-field elastoplastic FEA on pipeline geometry

03kkσσ

(μm)R

Boundary layer formulation (SSY)

0 595 M Paσ =

0 10 20 30 40 501

1.5

2

2.5

Full-field elastoplastic FEA on pipeline geometry

0

LCC

(μm)R

Boundary layer formulation (SSY)

15MPaP =R

b

0

34.12 MPa m/ -0.316IK

T σ=

=

The deep-notch toughness data in the presence of hydrogen need not necessarily lead to a conservative fracture toughness assessment for shallow cracked geometries as is commonly assumed in the absence of hydrogen

•Constraint based fracture mechanics•J-T controlled fracture

0

Tσ

ICJ

safe

As crack gets longer-1 +1

unsafe

Operating conditions

20

May 2007

Accomplishments vs. Project Milestones and Objectives

Design of permeation measurement systemComplete. Measurements are underway

Microstructure characterization Ongoing for both new and existing pipeline steels

Macroscopic flow characteristics in uniaxial tension of new material microstructures (micro-alloyed steels)

Complete in the absence of hydrogen. Experiments in the presence of hydrogen are planned this summer (it depends on the funding situation)

Development of finite element code for transient stress-driven hydrogen transport analysis coupled with large-strain elastoplastic deformation

Complete. Code has been tested and validated against analytical solutions and code at Los Alamos National Laboratory

Simulation to the problem of hydrogen transport at a cracked pipelineOngoing

Collaboration with ASME on validating the proposed safety factors to be used for the design of pipeline steels under a range of hydrogen pressures

Done (Hayden Liu)

Validation of ab-initio calculations for decohesion energy calculationsComplete. Unrelaxed binding energies (eV) and their differences for H in Fe grain boundary (GB) and free surface (FS) calculated by VASP PAW-GGA and FLAPW (Zhong et al., 2000)Continuing research in this area depends on project funding

Cr23C6

H-interstitial

FePrecip.

Interface and unit cellunder shear

21

May 2007

Future WorkExperiment

Establish the diffusion characteristics of existing and new pipeline steel microstructures

Existing pipeline steel samples provided by Air Liquide and Air Products. Specimens are in our laboratoryNew micro-alloyed steels (new microstructures) provided by Oregon Steel Mills through DGS Metallurgical Solutions, Inc.

Collaboration with ORNL and Schott North America for coating of our samples

Determine uniaxial tension macroscopic flow characteristics in the presence of hydrogen

Carry out fracture testing: Collaboration with Sandia, Livermore

SEM and TEM studies on existing and new pipeline material microstructures

Fracture surfaces, particle, dislocation, and grain boundary characterization

API/C Mn Si Cu Ni V Nb Cr Ti

GradeA X70 0.08 1.53 0.28 0.01 0.00 0.050 0.061 0.01 0.014B X70/80 0.05 1.52 0.12 0.23 0.14 0.001 0.092 0.25 0.012C X70/80 0.04 1.61 0.14 0.22 0.12 0.000 0.096 0.42 0.015D X52/60 0.03 1.14 0.18 0.24 0.14 0.001 0.084 0.16 0.014

Typical natural gas pipeline steel

Ferrite/acicular ferriteFerrite/acicular ferrite

Ferrite/low level of pearlite

22

May 2007

Future WorkModeling and Simulation

Determine the time it takes for the hydrogen population profiles to reach steady state as a function of the crack depth.

Complete the stress analysis to establish the dependence of the stress profiles ahead of an axial crack tip in term of the Stress Intensity Factor and the T-stress

We expect strong dependence on hydrogen-induced material softeningSet hydrostatic constraint guidelines for testing standard fracture specimens in the presence of hydrogen

Simulate crack growth propagation in the presence of hydrogenRequires cohesive laws in the presence of hydrogenEstablish critical toughness for fracture initiationEstablish the tearing resistance of the material upon crack propagationExplore subcritical crack growth propagation in the presence of hydrogen

Ab-inito calculations of cohesive properties of Fe/MnS interfaceEstablish criteria for interfacial decohesion needed to assess void nucleation at Mns/Fe particlesExplore whether thermodynamic criteria (e.g. Hirth and Rice) are suitable to analyze hydrogen-induced decohesion at interfaces

23

May 2007

Long Term Objective: Multiscale Fracture Approach

3u

33Σ maxσ

Γ Dissipated energy

(c) Traction - separation law(b) Axisymmetricunit cell model(a) Crack tip

fracture process zone

TriaxialityHydrogen concentration

(e) Cohesive elements characterized bya traction-separation law based on the unit cell model

1 11,u Σ

3 33,u Σ

at time=0initialLc

(d) Cohesive element

Adjacent finite element

, LT c

Δa/D0

J/(σ

0D0)

0 2 4 6 8 100

2

4

6

8

10

12

With hydrogen softening in(1) cohesive zone and matrix(2) cohesive zone only

No hydrogen

24

May 2007

Future WorkOther Activities

Finite element analysis of residual stresses of a Schott Coating sitting on the substrate

Continue collaboration with ASME on establishing guidelines for codes and standards

Continue our ongoing collaboration with the Japan program for materials solutions for the Hydrogen Economy

Hydrogen National Institute for Use and Storage (Hydrogenius) Kyushu University (Prof. Y. Murakami)

Continue our ongoing collaboration with the NATURALHY Project sponsored by the European Union

Interaction of hydrogen in a pipeline with a corrosion induced-crack on the external wall

X1

X2

0 0.005 0.01 0.015 0.02 0.0250

0.005

0.01

0.015

0.02

0.20.150.10.050

-0.05-0.1-0.15-0.2

11

0

σσ

Average tensile stress in the coating is125 MPa

Note that substrate is under large compression (-100Mpa) at the edges (possible delamination cause)

11σ

11σ11σ

25

May 2007

SummaryRelevance

Identify the mechanisms of hydrogen embrittlement in pipeline steels and propose fracture criteria with predictive capabilities. There are no codes and standards for safe and reliable pipeline operation in the presence of hydrogen

ApproachMechanical property testing at the micro/macro scaleMicrostructural analysis and TEM and SEM observations at the nano/micro scaleAb-initio calculations of hydrogen effects on cohesion at the atomic scaleFinite element simulation at the micro/macro scale

Accomplishments and ProgressPermeation measurementsStudy of tensile properties of new micro-alloyed steels

Good in H2S sour natural gas serviceMicrostructural characterization of Air Liquide, Air Products, and OMS steelsFinite element analysis of hydrogen transportValidation of ab-initio calculations

CollaborationsActive partnership with SECAT, Oak Ridge National Laboratory, Sandia National Laboratories, ASME codes and Standards, JAPAN (Hydrgenius Institute)

Proposed future researchPermeation measurements for diffusion and solubility characteristicsFracture toughness testingCalculation of hydrogen effect on interfacial cohesion through first principles calculationsSimulation of hydrogen transport in conjunction with fracture-mechanism modelingUnderstanding R-curve response and threshold stress intensities in the presence of hydrogen