Learnings

Outcomes

Data generated during the project suggest that oxygen reduced the effects of hydrogen on fracture and fatigue resistance. During fracture toughness tests conducted on X60 specimens, hydrogen resulted in a reduction of JQ from 87 kJ/m2 in air to 31 kJ/m2 in pure hydrogen. Oxygen additions resulted in an increase of the average JQ, which at 250 ppm O2 was 74 kJ/m2, 87% of the in-air value. Furthermore, the additions of oxygen also resulted in a reduction of the standard deviation of JQ. This recovery in fracture resistance was consistent with fractographic observations that show a progressive transition from quasi-cleavage fracture in pure hydrogen to dimpled collapse in 250 ppm O2 and above, resembling the in-air behaviour. These observations suggest that the addition of oxygen results in a change of failure mode. It was not possible to generate quantitative fracture toughness data for X52 and X80 specimens due to material related challenges. However, the examined fracture surfaces were consistent with those seen in X60 specimens, and suggested that the addition of oxygen promotes ductile failure.

The effects of oxygen were also visible on fatigue. Frequency scans on X60 specimens showed that exposure to pure hydrogen resulted in crack growth rates up to two orders of magnitude above the BS7910 in-air mean curve, depending on the test conditions. There was a significant effect of the frequency on the resulting crack growth rates, which continued to increase to 1 mm/cycle as the frequency was reduced to 1E-4 Hz. The dependence of the crack growth rate with the frequency was reduced by the introduction of 250 ppm O2. In Paris curve type fatigue tests, crack growth rates in pure hydrogen were high, over an order of magnitude above the BS7910 in-air mean, and were generally consistent with Paris laws available in the literature e.g. ASME B31.12 and Sandia National Laboratory master curves. With oxygen additions of 50 ppm, crack growth rates approached those of the in-air curve. Further increase of the oxygen concentration slightly reduced the crack growth rates, especially for high ∆K and high Kmax. The recovery of the fatigue performance was consistent with the fractography observations of increased plastic strain in presence of oxygen. The fracture surface of specimens tested with oxygen additions had a more ‘fibrous’ aspect with readily visible striations than those tested in pure hydrogen which had a quasi-cleavage surface.

Based on the data generated in this work, 250 ppm are considered the minimum oxygen concentration to achieve inhibition of hydrogen effects. This concentration provided a recovery over 85% of the in-air fracture resistance and crack growth rates close to in-air levels. Fracture surfaces of specimens tested under this concertation generally showed ductile features indicative of high toughness failure mechanisms.

The project value tracking is listed below: 

·       Maturity 

o   TRL 4-5.  Project was at a proof-of-concept phase and generated data that would be used to assess effectiveness of technology.

·       Opportunity 

o   100% & multiple asset classes. In theory technology could help reduce/prevent embrittlement of all gas-facing metallic components.

·       Deployment Costs  

o   TBD. Cost of deployment very uncertain at this stage. Project was proof of concept and did not address potential deployment costs.

·       Innovation Cost 

o   £ 664,871. Cost of Innovation project (including internal costs).

·       Financial Saving 

o   TBD. Technology could enable operation of hydrogen or hydrogen-natural gas blend network at, or near to, existing operational parameters. This would optimise the costs of 100% hydrogen networks and could enable a blended network without additional pipeline build to accommodate expected required pressure reductions.

·       Safety 

o   0% improvement. No direct safety benefits expected. 

·       Environment 

o   0 tonnes CO2e savings. No direct environmental benefits expected. Although if technology is successful it could reduce the extent of new build pipeline, with associated avoidance of environmental impact.

·       Compliance 

o   No change. No direct compliance benefits identified. 

·       Skills & Competencies 

o   Individuals. Work will augment knowledge of individuals involved in project. 

·       Future Proof 

o   Supports business strategy. Results will support operation of future 100% hydrogen and hydrogen-natural gas blends national transmission system. 

Lessons Learnt

The project proposal and delivery plan were designed with a degree of flexibility to accommodate changes to the scope of testing based on early test data – this was realised following delivery of K1H testing which was later removed from the scope and the associated budget re-allocated to more appropriate test methods. 

The primary issue relating to project delivery was the result of underestimated timescales and complexity of developing and commissioning the test equipment. The significant contributing factor was the challenging global procurement conditions evident at the end of 2022 which resulted in delays to the test rig manufacturing and were out with the control of the project team. Upon test rig delivery, significant effort was required to commission the machine and develop the associated internal operating procedures and processes which proved difficult within the allocated project timescales and considering the complexity of the task and novel nature of the test methods. When it became clear that completion of the project within the allocated schedule was under threat, ROSEN pro-actively sought support through a third party to deliver part of the remaining programme. Future work scopes which involve procurement and development activities should be realistically estimated and changes to the project schedule should continue to be communicated clearly to the project lead.

Once commissioned, ROSEN’s fracture toughness test rig was not able to apply the required loads to X52 materials within the required specification tolerances due to the reduced size of specimen and accuracy of load application at the lower load range. Although the test machine was designed to accommodate the wide range of potential sample geometries and material properties, it was not possible with the information known at the time to validate these conditions with respect to specific samples. Future work scopes may benefit from closer liaison with test equipment suppliers to validate design details on receipt of sample material, however early identification of sample materials would also be beneficial to support the initial design process.

Common to all testing conducted within this scope was the extended test durations when compared with more common laboratory material testing methodologies. Fatigue crack growth rate (FCGR) testing at low load rates was demonstrated to take up to 8 weeks to complete a full dataset which compromised the volume of testing able to be complete within the project timescales. At the time of developing the test programme, the test methodologies were novel and there was little industry experience in completing such scopes. Future work scopes, should consider the findings of this project in terms of test timescales to define accurate project durations.

Reaction to the above issues and resultant effects on the project delivery were communicated in a clear and transparent way through the adoption of regular bi-weekly meetings between the project lead and supplier. The project also benefited from regular engagement with the project lead to support technical discussion and decision making.