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mismatch between the required and under stress, it concentrates arounds
available knowledge. cracks. This causes loss of ductility in the
DNV GL
A common classification is to divide metal, called hydrogen embrittlement.
uncertainty into objective and subjective Experiments have shown that the
uncertainties¹. The latter include the detrimental effect of hydrogen is highly
inability to apply appropriate moral dependent on the hydrogen pressure and
rules or where moral rules do not exist. the steel grade (strength). It is shown that
Subjective uncertainties are recognised the loss of material ductility increases
by the fact they cannot be objectively with hydrogen pressure and, at pressures
defined, but are based on internalised above 50bar, the effects are significant for
experiences and moral values. Subjective the high strength steels used in offshore
uncertainties are highly relevant for natural gas transmission.
policy decisions, however, the main Because of hydrogen embrittlement,
focus in this setting is on the objective offshore transmission pipelines must
uncertainties. Objective uncertainties are be operated at much lower pressures
subdivided into two categories, which (potentially <50%⁵) when transporting
also guide how we must treat them²: pure hydrogen compared to natural gas.
Epistemological uncertainty is related With only a third of the volumetric energy
H2 DEFLAGRATION AT SPADEADAM TESTING AND RESEARCH to (lack of) knowledge, and only density of hydrogen versus natural gas
describes our state of knowledge of (under the same conditions), it becomes
we need to understand the technical the world – it does not change the very important to optimise the hydrogen
aspects of transporting and distributing outcome of future decisions. flow with respect to the pipeline capacity
100 per cent hydrogen. Ontological uncertainty is related to for it to be a viable option, compared to
For large scale transportation, variability inherent to the nature, or the transmission of natural gas.
pipelines are currently the most viable existence, of the problem. It cannot
option. The question is: what effect will be reduced except through physical Effective reduction of
pure hydrogen have on the existing changes of the system under study. quantifiable uncertainties
transmission pipeline networks? To reduce uncertainty in technical It is important to understand the
Our challenge is thus to assess and systems, we need to understand when onset of hydrogen embrittlement of
address the technical uncertainties it is related to a lack of knowledge and natural gas transmission pipelines, and
we can quantify through experiments when it is related to variability, so that how this affects the service life of the
and simulations in an effective way, we can make a rational decision on pipelines. Currently there are significant
together with economic and market whether to increase our knowledge uncertainties related to the deterioration
uncertainties, and to combine this with or change the system to achieve a of ductile capacity of natural gas pipelines
the more qualitative uncertainties of sufficiently low uncertainty with respect when transporting pure hydrogen at high
3,4
policy choices and social acceptance. to our objectives (see Figure 1) . pressures. This is further complicated
by the fact that the deterioration is also
Understanding uncertainties Technical uncertainty of hydrogen transport dependent on the actual load conditions
To enable effective and rational Hydrogen has a detrimental effect on the pipeline experiences.
decision-making it is important high strength steels. Due to its small To reduce our epistemological
to understand the different types molecular size, hydrogen can be uncertainty, we need to conduct
of uncertainty and the particular absorbed into the metal lattice, and, experiments and physics-based

FIGURE 1 REDUCING UNCERTAINTY

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