III.10 Hydrogen Embrittlement of Pipeline Steels: Fundamentals, Experiments, Modeling Technical Targets P. Sofronis (Primary Contact), I.M. Robertson, This project is conducting fundamental studies D.D. Johnson of hydrogen embrittlement of materials using both University of Illinois at Urbana-Champaign numerical simulations and experimental observations 1304 West Green Street Urbana, IL 61801 of the degradation mechanisms. Based on the Phone: (217) 333-2636 understanding of the degradation mechanisms the E-mail: [email protected] project’s goal is to assess the reliability of the existing natural gas pipeline infrastructure when used for DOE Technology Development Manager: hydrogen transport, suggest possible new hydrogen- Monterey Gardiner compatible material microstructures for hydrogen Phone: (202) 586-1758 delivery, and propose technologies (e.g. regenerative E-mail: [email protected] coatings) to remediate hydrogen-induced degradation. DOE Project Officer: Paul Bakke These studies meet the following DOE technical targets for Hydrogen Delivery as mentioned in Table 3.2.2 of the Phone: (303) 275-4916 E-mail: [email protected] FCT Multi-Year RD&D Plan: • Pipelines: Transmission—Total capital investment Contract Number: GO15045 will be optimized through pipeline engineering Start Date: May 1, 2005 design that avoids conservatism. This requires Projected End Date: December 31, 2011 the development of failure criteria to address the hydrogen effect on material degradation (2012 target). • Pipelines: Distribution—Same cost optimization as Objectives above (2012 target). • Pipelines: Transmission and Distribution—Reliability • Mechanistic understanding of hydrogen relative to H2 embrittlement concerns and integrity, embrittlement in pipeline steels in order to devise third party damage, or other issues causing cracks fracture criteria for safe and reliable pipeline or failures. The project’s goal is to develop operation under hydrogen pressures of at least 15 fracture criteria with predictive capabilities against MPa and loading conditions both static and cyclic. hydrogen-induced degradation (2017 target). It is • Explore methods of mitigation of hydrogen-induced emphasized that hydrogen pipelines currently in failures through inhibiting species (e.g., water vapor) service operate in the absence of design criteria or regenerative coatings (e.g., surface oxidation). against hydrogen-induced failure. • Explore suitable steel microstructures to provide • Off-Board Gaseous Hydrogen Storage Tanks safe and reliable hydrogen transport at reduced (Tank cost and volumetric capacity)—Same cost capital cost. optimization as in Pipelines: Transmission above. • Assess hydrogen compatibility of the existing natural Current pressure vessel design criteria are overly gas pipeline system for transporting hydrogen. conservative by applying conservative safety factors on the applied stress to address subcritical cracking. Design criteria addressing the hydrogen effect on Technical Barriers material safety and reliability will allow for higher storage pressures to be considered (2015 target). This project addresses the following technical barriers from the Delivery section (3.2.4) of the DOE Fuel Cell Technologies Program Multi-Year Research, Accomplishments Development and Demonstration Plan (FCT Multi-Year RD&D Plan): • Discovered the nature and characteristics of the hydrogen degradation mechanisms of two promising (D) High Capital Cost and Hydrogen Embrittlement of microalloyed, low-carbon steel microstructures Pipelines (G) Storage Tank Materials and Costs (K) Safety, Codes and Standards, Permitting DOE Hydrogen Program 296 FY 2010 Annual Progress Report Sofronis – University of Illinois at Urbana-Champaign III. Hydrogen Delivery designated as B1 and D2 hereafter. The samples pipeline distribution system for hydrogen transport and were provided by the DGS Metallurgical Solutions, of the susceptibility of new alloys tailored for use in Inc. The mechanisms of fracture were identified hydrogen related applications. by using focused ion beam (FIB) machining to Last year we focused our attention on identifying lift-out sections from fracture surfaces along with and characterizing the mechanisms by which hydrogen transmission electron microscopy (TEM) analysis of induces fracture in microalloy steels B and D. We the extracted thin foils. used FIB machining to lift out sections underneath • Characterized the microstructure of pipelines the fracture surfaces in order to examine whether steels through optical analysis, scanning electron hydrogen-induced fracture follows a crystallographic microscopy (SEM), and TEM, and identified particle cleavage plane or a slip plane. We carried out finite composition through energy dispersive spectroscopy element calculations of transient hydrogen transport for: a) laboratory specimens from Air Liquide, Air simulating hydrogen uptake and transport through an Products, and Kinder-Morgan industrial pipelines; axial crack on the inner diameter surface of a pipeline, b) new microalloyed, low-carbon steels from and determined through constraint fracture mechanics Oregon Steel Mills provided by DGS Metallurgical that the SENT specimen is the appropriate laboratory Solutions, Inc. specimen for the study of the fracture resistance of a • Developed a thermodynamic theory of hydrogen- pipeline. induced decohesion that was used to model and simulate hydrogen-induced subcritical cracking in high strength steels. Approach • Augmented our modeling and simulation Our approach integrates mechanical property testing capabilities of transient hydrogen transport to at the microscale, microstructural analyses and TEM account for the mechanical deformation and observations of the deformation processes of materials hydrogen-induced grain boundary decohesion in at the micro- and nano-scale, first principle calculations high strength steels. Predictions have been made of interfacial cohesion at the atomic scale, and finite of threshold stress intensities associated with element modeling and simulation at the micro- and subcritical crack growth. macro-level. • Demonstrated environmental similitude between To understand the hydrogen-induced fracture the single edge notch specimen (SENT) and a processes, we use high resolution SEM with three- pipeline with an axial crack on the inner diameter dimensional (3-D) visualization and TEM studies of surface. Hence, the SENT specimen can be used samples taken from just below the fracture surface by the as a laboratory specimen to reliably estimate the lift-out technique using FIB machining. In order to come fracture resistance of a pipeline steel in the presence up with fracture criteria for safe pipeline operation under of hydrogen. hydrogen pressures of at least 15.0 MPa, we investigate the interaction of hydrogen transient transport kinetics G G G G G with material elastoplastic deformation ahead of an axial crack either on the inside diameter or the outer diameter surface of a pipeline. Using finite element simulations Introduction of the hydrogen transport in the neighborhood of the Hydrogen is a ubiquitous element that enters crack tip, we explore the transient and steady-state materials from many different sources. It almost always hydrogen population profiles and how their development has a deleterious effect on material properties. The influences the fracture processes/events. goal of the project is to develop and verify a lifetime To quantitatively describe the hydrogen effect on prediction methodology for failure of materials used in internal material cohesion as a function of the hydrogen pipeline systems and welds exposed to high-pressure concentration under transient hydrogen conditions, gaseous environments. Development and validation we devised a thermodynamic theory of decohesion at of such predictive capability and strategies to avoid internal material interfaces such as grain boundaries, material degradation is of paramount importance to the precipitate/matrix, and second-phase/matrix interfaces. rapid assessment of the suitability of using the current We used first-principles calculations of the hydrogen effect on these interfaces, which constitute potential 1 Steel B is a typical low carbon (0.05% by wt) Mn-Si-single fracture initiation sites, to calibrate the parameters of the microalloy API/Grade X70/X80 capable of producing a ferrite/ acicular microstructure. The alloy was found to perform well in thermodynamic theory such as the ratio of the reversible sour natural gas service. work of separation in the presence of hydrogen to 2 Steel D is a typical low carbon (0.03% by wt) Mn-Si- that in the absence of hydrogen. The information single microalloy API/Grade X60, a predominantly ferrite for the fracture mechanisms from the experiments microstructure with some pearlite. The alloy was found to and the hydrogen concentration profiles from the perform very well in sour natural gas service. FY 2010 Annual Progress Report 297 DOE Hydrogen Program III. Hydrogen Delivery Sofronis – University of Illinois at Urbana-Champaign simulations help to establish the regime of critical technique can identify microstructural features such as hydrogen concentrations and critical elapsed time for grain boundaries and secondary phases such as carbides a crack to remain stable under high hydrogen pressure. immediately below the fracture surface. Quantitatively this is assessed through the development Examination of the fracture surfaces reveals several of engineering fracture criteria