1. Hydrogen will not embrittle existing natural gas pipelines. The stories one hears about hydrogen embttlement are caused by monoatomic hydrogen getting into steel from external corrosion or cathodic protection.Hydrogen at pressure does not cause these problems. .
 
2. The diffusion of hydrogen out of polyethylene distribution pipes will not be a problem. The R&D on the Hythane programme has looked into this, and from the published data it can be shown that hydrogen leakage from a hydrogen only system is not a significant issue.
 
3. Although hydrogen has a much lower calorific value than natural gas, because of its low density  it does not require much energy to push it through the high pressure transmission system. The two factors are almost in balance, but in practice there is a 12 % increase in the pressure drop to get the same energy flow.This is insignifcant.
 
4. The biggest problem with transmission is that the compressor station will have to be placed at shorter intervals than at present. This is because of the low density of hydrogen.However, the total amount of power required by the compressor station will be only about 12% higher than at present.Again this is negligible.
 
5. The local distribtion system  will not be so effective at storing energy as it is at present becuase of the low CV problem. That is building up the pressure at night will not be so effective…If hydrogen was used for transport the distribution grid would need massive re-building.
 
Best regards
 
Fred S (Claverton Group)