Kelly Anderson from Strasburg wrote the following:
When steam locomotives were in widespread production, they had their own ASME boiler code. When they stopped being built, the locomotive code was dropped and ASME Section I for power boilers became the single rule for all new boilers. Over the course of time ASME Section I has evolved with new technology to the point that it is a poor fit for someone trying to design a locomotive boiler.
For example, dome throttles, which most steam locomotives use, are not allowed. ASME Section I allows higher staybolt stresses and a lower factor of safety than the FRA requires, meaning that a new ASME locomotive boiler can be designed and built which the FRA will not allow to operate at its designed pressure. I’m sure other issues are in the current code, and it will make life easier for steam railroaders if they are corrected.
The "National Board Inspection Code Committee (NBIC), Subgroup on Locomotive Boilers" is the "Engineering Standards Committee" of Part 230 fame, a.k.a The Gods of Steam. As I understand it, in their usual semi annual meetings they will start building the new locomotive boiler code using the parts of old and current codes that work with the needs of locomotive boilers, the FRA requirements, and today’s technology, and weeding out the parts of the current ASME Section I that are counterproductive with regard to locomotive boilers. That is where they need input from others with experience dealing with the ASME Code to be sure they cover all of the bases, and don’t miss anything.