The NEC does not address separation between electrical wiring methods and other piping systems. 110.26(F)(1)(b) does require that foreign systems not be located above the dedicated space required by this section.
Well yes its not in the NEC but its a practice done meaning space between areas of high temp like a boiler vessel tubes and piping as already posted good point made there PTRIP .
When you do a power plant the Engineer will route all your conduits for you no electrical will ever cross or be in conflict with other piping the contract drawns will reflect this and you run your conduit per that route .
But in commercial electrical its up to the electrician to layout his or her work per what is needed to go from point A to point B and its kinda our job to look at the mechcanical drawns to avoid these conflicts .
But in my opinion this should be in the NEC but how can they determine how far or what distance it would be as most electricians never even think about this ambient temp is never used in the real world of electrical work ?
There's an article in there about maintaining conduit spacing when conduits are buried. Our inspector likes to make his own interpretation on how much spacing there should be...