[Steven Smith]

I'm not sure if I follow the logic that because other components would fail first, the ruling does not relate to safety.

Regardless of whether the tubing or the tanks would fail first, the sole purpose of including a safety relief valve is to ensure that the entire system stays below the rated working pressure of the components. Connecting the safety relief to the system with flexible tubing that could potentially be kinked by a robot mechanism or any other number of things would render the safety relief worthless, therefore the rule is that it must be connected with rigid fittings.

Seems pretty cut and dry to me?