Drgdarf - Correct. High concentrations of Hydrogen will damage and embrittle the existing natural gas pipelines. This is why the natural gas pipelines who are testing hydrogen are diluting the hydrogen by 80 to 90 % with natural gas (as a buffer).
A separate stream (100% hydrogen, would certainly damage a natural gas grid).
So when you blend hydrogen with natural gas you end up with contaminated hydrogen and expensive natural gas.
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