Not to mention hydrogen embrittlement. Hydrogen is a "slippery" molecule and can even escape solid steel pipes. As the molecule passes through the pipe it creates a phenomenon called hydrogen embrittlement. Steel is eventually weakened to the point of failure. This is not only a safety issue, but a maintenance nightmare. Steel pipes need to be replaced a much faster rate when used with Hydrogen. I understand there are coating now to mitigate this problem, but they add cost and complexity.