Hydrogen Embrittlement of Pipelines: Fundamentals ......Fundamentals, Experiments, Modeling Project...
Transcript of Hydrogen Embrittlement of Pipelines: Fundamentals ......Fundamentals, Experiments, Modeling Project...
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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
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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
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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
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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
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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
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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)
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May 2007
Steel Microstructure-Air Liquide Pipeline
Large intergranular particles (cementite)
Small intragranular particles (carbides with Nb and Ti)
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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
)
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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
==
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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 =
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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
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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
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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
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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 =
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Transient to Steady State - Lattice Concentration
0/LC C
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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 =
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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 =
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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 =
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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
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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
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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
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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
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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
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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
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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