Field life extension through controlling the combined material degradation of fatigue and hydrogen (HyF-Lex)

The project duration will be from January 2015 to December of 2018. Four closely interlinked scientific work packages (WPs) form the building blocks of the project, supported by two administrative WPs as illustrated in Figure 3. The project management team (PM + WP-leaders) consists of a well-balanced group of ambitious and experienced scientists which collectively have a long record of research within the different fields that are brought together in the HyF-Lex project. The project team has a wide network both nationally and internationally and is acknowledged for its competence within the international community of H and materials interaction. The three international partners further strengthen the project, contributing with their state-of-the-art instrumentation and competence. They will host and co-supervise PhDs for a period of 2-3 months. An advisory group with members from industry is set up to ensure close communication with users.

WP01: Project coordination
(A. Barnoush, NTNU)

This WP will coordinate the project and report the progress and facilitate the WP-leaders in their decision process. The project leader will be the intermediary between the partners and the research council (NRC) and will perform all tasks assigned in the Consortium Agreement.

WP02: Dissemination and communication of the results
(V. Olden, SINTEF)

This WP will be responsible for the dissemination and communication of the results. Scientific papers in peer-reviewed journals and conferences proceedings are the primary way of disseminating scientific and technical results. Social media will also play an important role in the dissemination of the results to the general public.

WP1: Fatigue testing and verification
(A. Alvaro, SINTEF)

The aim of this WP is dual: to identify the testing parameters and give the samples which will be used for testing and characterization in WP2 and to provide the final verification for of the model framework which will be developed in WP4. Information of hydrogen charging conditions is given by WP2.

1.1 Fatigue crack growth test: Includes standard fatigue crack growth experiments with and without in situ H-charging. Screening of the main testing parameters, i.e. frequency, stress ratio, stress intensity range and load cycle shape, will be performed in this task. Fractography of selected fracture surfaces through optical microscope and SEM will also be carried out.

1.2 Preparation of pre-cracked samples: Pre-cracked specimens with fatigue cracks of appropriate length for advanced characterization and testing in WP3 will be prepared.

1.3 Verification of the model framework: Final verification of the model will be performed by running fatigue testing of fracture mechanics specimens made of pipeline steel in air and H charging conditions.

WP2: H uptake in CP and H₂S conditions
(R. Johnsen, NTNU)

WP2 is linked to all the other WPs. It will provide information of charging conditions to WP1 and WP3 and H related properties and boundary conditions to the model framework in WP4. One PhD candidate will be allocated to this WP. PoliMi and LaSIE will co-supervise the PhD.

2.1 Hydrogen uptake and diffusion: H uptake and diffusion measurements will be performed in an advanced Devanathan diffusion cell (ISO 17081:2014).

2.2 Quantification of hydrogen content: The H content of samples charged under different charging conditions (CP and H₂S) and environmental parameters will be quantified with a melt extraction technique and in-situ electrochemical quartz crystal microbalance (EQCM). The connection between environmental parameters and the bulk H content will be established.

WP3: In situ crack growth and advanced characterization
(A. Barnoush, NTNU)

Samples with fatigue cracks from WP1 and appropriate H-charging parameters from WP2 will be delivered to WP3. Outcomes of WP3 will be delivered to WP4. One PhD candidate will be allocated to this WP. LaSIE and UdS will co supervise the PhD.

3.1 Advanced characterization: Plastic zone of the cracks will be characterized using advanced techniques including EBSD, ECCI and TEM. ToF-SIMS will be used in combination with cooling stage to measure the H content in the plastic zone. FIB will be used to cut nano- and micron-sized samples out of the plastic zone for further mechanical testing with and without in situ H-charging. The possibilities of performing similar tests inside an environmental SEM for charging the sample within an H₂ gaseous atmosphere will be explored.

3.2 In situ crack growth test : Crack propagation in pre-cracked samples inside SEM or under AFM with a miniaturised loading stage will be observed with nanoscale resolution. Electrochemical H charging and charging from gas phase will be done in the case of the AFM and SEM respectively.

WP4: Multiscale modelling of H and materials interaction
(V. Olden, SINTEF)

Quantifiable information from WPs 1-3 will be given as information to this WP. One PhD candidate will be allocated to this WP. UdS and PoliMi will co supervise the PhD.

4.1 MD and NEB: This task will provide activation energies for dislocation cross-slip, pair interactions and kink-pair nucleation in presence of H for the DDD simulations.

4.2 DDD: Mesoscopic rules for the evolution of dislocation densities and interaction coefficients between slip systems in the presence of H will be provided. These rules will be used to parameterize the crystal plasticity model.

4.3 CPFEM: The H information from the meso-scale is provided to the micro-scale. The resulting behaviour of dislocations densities in fatigue influenced by H in a microstructure informed model will be then obtained.

4.4 CZM: Transgranular fatigue cracking will be represented by H influenced cohesive elements informed from the previous tasks. Finally, the models will be validated against carefully chosen experimental tests with and without the presence of H.