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Somerday, Brian P.

Publications and source records attributed to Somerday, Brian P..

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Hydrogen-assisted fracture resistance of pipeline welds in gaseous hydrogen

Fracture resistance of pipeline welds from a range of strength grades and welding techniques was measured in air and 21 MPa hydrogen gas, including electric resistance weld of X52, friction stir weld of X100 and gas metal arc welds (GMAW) of X52, X65 and X100. Welds exhibited a decrease in fracture resistance in hydrogen compared to complementary tests in air. A general trend was observed that fracture resistance in 21 MPa hydrogen gas decreased with increasing yield strength. To accommodate material constraints, two different fracture coupon geometries were used in this study, which were shown to yield similar fracture resistance values in air and 21 MPa hydrogen gas; values using different coupons resulted in less than 15% difference. In addition, fracture coupons were removed from controlled locations in select welds to examine the potential influence of orientation and residual stress. The two orientations examined in the X100 GMAW exhibited negligible differences in fracture resistance in air and, similarly, negligible differences in hydrogen. Residual stress exhibited a modest influence on fracture resistance; however, a consistent trend was not observed between tests in air and hydrogen, suggesting further studies are necessary to better understand the influence of residual stress. A comparison of welds and base metals tested in hydrogen gas showed similar susceptibility to hydrogen-assisted fracture. The overall dominant factor in determining the susceptibility to fracture resistance in hydrogen is the yield strength.

08 HYDROGEN↗
DOE OSTI2020

On the fatigue crack growth behavior of Ti–10V–2Fe–3Al in gaseous hydrogen

Here, the fatigue crack growth behavior of Ti–10V–2Fe–3Al in gaseous hydrogen (H 2 ) was assessed through comparative experiments conducted in laboratory air and 8.3 MPa H 2 . The measured fatigue crack growth rate (da/dN) versus applied stress intensity factor range (ΔK) relationships and observed fracture morphologies for laboratory air and H 2 were comparable up to ΔK ≈ 6.9 MPa√m, when tested at a load ratio of 0.1 and frequency of 10 Hz. At higher ΔK values, significant crack deflection and subsequent catastrophic failure occurred in the specimen tested in H 2 . This degradation was not observed in a specimen pre-exposed to 8.3 MPa H 2 for 96 h and then immediately tested in laboratory air. X-ray diffraction of the failed H 2 -tested specimen revealed that the material remnants were predominantly composed of TiH 2 , suggesting that hydride formation was the catalyst for catastrophic failure in H 2 . The mechanistic implications of these results and their impact on current material compatibility assessments for Ti alloys in hydrogen service are then discussed.

08 HYDROGEN↗
DOE OSTI2020

Stacking Fault Energy Based Alloy Screening for Hydrogen Compatibility

The selection of austenitic stainless steels for hydrogen service is challenging since there are few intrinsic metrics that relate alloy composition to hydrogen degradation. One such metric, explored here, is intrinsic stacking fault energy. Stacking fault energy has an influence on the character and structure of dislocations and on the formation of secondary crystalline phases created during mechanical deformation in austenitic alloys. In this work, a data-driven model for the intrinsic stacking fault energy of common austenitic stainless steel alloys is applied to compare the relative degradation of tensile performance in the presence of hydrogen. A transition in the tensile reduction of area of both 300-series and manganese stabilized stainless steels is observed at a calculated stacking fault energy of approximately 43 mJ m -2 , below which pronounced hydrogen degradation on tensile ductility is observed. The model is also applied to suggest alloying strategies for low nickel austenitic stainless steels for hydrogen service. Lastly, through this investigation, we find that calculated intrinsic stacking fault energy is a high-throughput screening metric that enables the ranking of the performance of a diverse range of austenitic stainless steel compositions, as well as the identification of new alloys, with regard to hydrogen compatibility.

08 HYDROGEN↗
DOE OSTI2019

Hydrogen-Assisted Fracture of Stainless Steel

Symmetric four-point bending (S4PB) and anti-symmetric four-point bending (AS4PB) were applied to assess the effect of hydrogen on crack initiation and propagation in a stable, nitrogen-strengthened austenitic stainless steel (21Cr-6Ni-9Mn). Specimens of a high strength aluminum alloy (AA2219-T851), which has also been identified as hydrogen-compatible, were used for test method development prior to completing the stainless steel test matrix. Single edge notched bend (SEN(B)) specimens were extracted from forged 21Cr-6Ni-9Mn bar and AA2219 plate. The 21Cr-6Ni-9Mn specimens were then hydrogen charged with ~200 wt. ppm hydrogen; AA2219 specimens were not charged. Aluminum specimens were tested in S4PB to induced mode I (pure bending), and AS4PB to attain varying levels of mode I/II mixity and mode II (pure shear), where the ratio of mode I to mode II varies with the position of the crack plane relative to the load line. After test method troubleshooting and validation, hydrogen charged stainless steel specimens were then subjected to mode I and two ratios of mixed mode I/II. Mode II loading was not achieved due to high load limitations. Analyses of fracture profiles for both materials reveal a marked effect of loading mode mixity on initial crack propagation orientation, however a specific contribution of hydrogen was not readily identifiable. Fracture initiation toughness in the presence of hydrogen, J IH , was calculated following the J-integral approach; the mode I J IH calculated for stainless steel samples fractured in S4PB were consistent with published values determined from compact tension specimens. The peak loads required to initiate fracture during AS4PB far exceeded those required during S4PB. This is attributed to the increasing shear force applied to the specimens as the degree of mode mixity increases. Ultimately, understanding the fracture response of hydrogen exposed stainless steels subjected to mixed mode I/II loading is critical for designing hydrogen containment vessels or gas transfer systems (GTS).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Elucidating the contribution of mobile hydrogen-deformation interactions to hydrogen-induced intergranular cracking in polycrystalline nickel

Uniaxial mechanical testing conducted at room temperature (RT) and 77 K on hydrogen (H)-exposed nickel was coupled with targeted microscopy to evaluate the influence of deformation temperature, and therefore mobile H-deformation interactions, on intergranular cracking in nickel. Results from interrupted tensile tests conducted at cryogenic temperatures (77 K), where mobile H-deformation interactions are effectively precluded, and RT, where mobile H-deformation interactions are active, indicate that mobile H-deformation interactions are not an intrinsic requirement for H-induced intergranular fracture. Moreover, an evaluation of the true strain for intergranular microcrack initiation for testing conducted at RT and 77 K suggests that H which is segregated to grain boundaries prior to the onset of straining dominates the H-induced fracture process for the prescribed H concentration of 4000 appm. Lastly, recent experiments suggesting that H-induced fracture is predominately driven by mobile H-deformation interactions, as well as the increased susceptibility of coherent twin boundaries to H-induced crack initiation, are re-examined in light of these new results.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Probing the Effect of Hydrogen on Elastic Properties and Plastic Deformation in Nickel Using Nanoindentation and Ultrasonic Methods

Hydrogen effects on small-volume plasticity and elastic stiffness constants are investigated with nanoindentation of Ni-201 and sonic velocity measurements of bulk Ni single crystals. Elastic modulus of Ni-201, calculated from indentation data, decreases ~22% after hydrogen charging. This substantial decrease is independently confirmed by sonic velocity measurements of Ni single crystals; c 44 decreases ~20% after hydrogen exposure. Furthermore, clear hydrogen-deformation interactions are observed. The maximum shear stress required to nucleate dislocations in hydrogen-charged Ni-201 is markedly lower than in as-annealed material, driven by hydrogen-reduced shear modulus. Additionally, a larger number of depth excursions are detected prior to general yielding in hydrogen-charged material, suggesting cross-slip restriction. Together, these data reveal direct correlation between hydrogen-affected elastic properties and plastic deformation in Ni alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Assessing Gaseous Hydrogen Assisted Fatigue Crack Growth Susceptibility of Pipeline Steel Weld Fusion Zones and Heat Affected Zones

The objective of this work was twofold: (1) measure reliable fatigue crack growth relationships for X65 steel and its girth weld in high-pressure hydrogen gas to enable structural integrity assessments of hydrogen pipelines, and (2) evaluate the hydrogen accelerated fatigue crack growth susceptibility of the weld fusion zone and heat-affected zone relative to the base metal. Fatigue crack growth relationships (da/dN versus ΔK) were measured for girth welded X65 pipeline steel in high pressure hydrogen gas (21 MPa) and in air. Hydrogen assisted fatigue crack growth was observed for the base metal (BM), fusion zone (FZ), and heat-affected zone (HAZ), and was manifested through crack growth rates reaching nearly an order of magnitude acceleration over rates in air. Addditionally, at higher ΔK values, crack growth rates of BM, FZ, and HAZ were coincident; however, at lower ΔK, the fatigue crack growth relationships exhibited some divergence with the fusion zone having the highest crack growth rates. These relative fatigue crack growth rates in the BM, FZ, and HAZ were provisional, however, since both crack closure and residual stress contributed to the crack-tip driving force in specimens extracted from the HAZ. Despite the relatively high applied R-ratio (R = 0.5), crack closure was detected in the heat affected zone tests, in contrast to the absence of crack closure in the base metal tests. Crack closure corrections were performed using the adjusted compliance ratio method and the effect of residual stress on K max was determined by the crack-compliance method. Crack-tip driving forces that account for closure and residual stress effects were quantified as a weighted function of ΔK and K max (i.e., K norm ), and the resulting da/dN versus K norm relationships showed that the HAZ exhibited higher hydrogen accelerated fatigue crack growth rates than the BM at lower K norm values.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hydrogen accelerated fatigue crack growth of friction stir welded X52 steel pipe

Friction stir welded steel pipelines were tested in high pressure hydrogen gas to examine the effects of hydrogen accelerated fatigue crack growth. Fatigue crack growth rate (da/dN) vs. stress-intensity factor range (ΔK) relationships were measured for an X52 friction stir welded pipe tested in 21 MPa hydrogen gas at a frequency of 1 Hz and R = 0.5. Tests were performed on three regions: base metal (BM), center of friction stir weld (FSW), and 15 mm off-center of the weld. For all three material regions, tests in hydrogen exhibited accelerated fatigue crack growth rates that exceeded an order of magnitude compared to companion tests in air. Among tests in hydrogen, fatigue crack growth rates were modestly higher in the FSW than the BM and 15 mm off-center tests. Select regions of the fracture surfaces associated with specified ΔK levels were examined which revealed intergranular fracture in the BM and 15 mm off-center specimens but an absence of intergranular features in the FSW specimens. In conclusion, the X52 friction stir weld and base metal tested in hydrogen exhibited fatigue crack growth rate relationships that are comparable to those for conventional arc welded steel pipeline of similar strength found in the literature.

08 HYDROGEN↗
DOE OSTI2016

Hydrogen Assisted Fracture of Stainless Steels

The Enhanced Surveillance Sub-program has an annual NNSA requirement to submit a comprehensive report on all our fiscal year activities right after the start of the next calendar year. As most of you know, we collate all of our PI task submissions into a single volume that we send to NNSA, our customers, and use for other programmatic purposes. The functional objective of this report is to formally document the purpose, status, and accomplishments and impacts of all our work. For your specific submission, please follow the instructions described below and use the template provided. These are essentially the same as was used last year. We recognize this report may also include information on specific age-related findings that you will provide again in a few months as input to the Stockpile Annual Assessment process (e.g., in the submittal of your Component Assessment Report). However, the related content of your ES AR input should provide an excellent foundation that can simply be updated as needed for your Annual Assessment input.

36 MATERIALS SCIENCE↗