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In sour service, when there is H2S, hydrogen sulfide in the gas...

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    In sour service, when there is H2S, hydrogen sulfide in the gas the welds must be done to a higher standard then normal.DBNGL is welded to what is known as a sweet gas standard

    That is true, but I wouldn't consider it entirely relevant. Hydrogen gas is a completely different substance to Hydrogen Sulphide. One is odourless and non-toxic, the other will kill you with one breath.

    With sour gas (ie, gas containing hydrogen sulphide), the risk is that moisture in the pipe will absorb the H2S, creating sulphuric acid (H2SO4), which causes localised pitting corrosion. Not relevant here.

    With hydrogen (H2) service, it cannot dissolve to create sulphuric acid, as the molecules are covalently bonded. It is a noble (inert) gas. So, corrosion is not an issue. The issue is that hydrogen can dissolve into the metal (either into the pipe or the welds), which creates microbubbles of hydrogen in the steel, which can make the steel brittle, like a ceramic. This is bad because the steel pipe can crack and lead to a big release of gas, which might explode. The damage mechanism is called hydrogen embrittlement
    https://en.wikipedia.org/wiki/Hydrogen_embrittlement

    It is this damage mechanism which is probably going to limit the introduction of hydrogen into the DBNG pipeline to a small value, probably around 10% by volume (2.8% by energy content, not much), according to the figures put out by COAG Energy Council.
 
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