> (1)Pipes change size with heat. Getting the external empty pipe to reliably keep position over the smaller pipe would be tricky. It's not like this space has

> (1)Pipes change size with heat. Getting the external empty pipe to reliably keep position over the smaller pipe would be tricky. It's not like this space has to be particularly small. Double walled pipes are relatively common in many forms. Long-distance heating uses double walled stainless steel piping with insulation between the walls. HV systems sometimes use double walled conduits to have a second layer for the insulating gas (e.g. SF6) in case the inner layer leaks. Double walled pipes are used for lines containing especially hazardous materials. The inter-wall space is often monitored for ingress of "stuff", triggering a controlled shutdown if it is flooded. > In burried sections this may be a non-issue but wrapping all the valves and above-ground facilities in layers would make inspection problematic. This is about risk mitigation, so total mitigation is not required. Protecting, say, 80-90 % of a pipeline would reduce spill risk a lot. Also, the facilities you mention may be suitable to other forms of mitigation (e.g. walls, flood basins). > That would be very hard to engineer. I don't think engineering is the real problem here. Cost and incentives are.