FMW VP – Engineering Wolf Fengler, MSME, has been responsible for undertaking Form 4 calculations of some of the largest steam locomotives operating in the preservation era. He was approached by the Pennsylvania Railroad T1 Steam Locomotive Trust in 2016 with the opportunity to be the lead designer of the engineering team associated with building the new boiler for the 4-4-4-4 Duplex locomotive, which is the largest new-build locomotive boiler project undertaken since the end of the steam era.
Fengler began work by re-engineering the boiler barrel for fabrication using modern welding techniques (the original design was of riveted steel construction). This included parallel iterative efforts studying original blueprints, creating 3D CAD models of boiler components in SolidWorks, and calculating stresses per ASME and FRA requirements. Once the design of components were satisfactory, he produced construction drawings from which a selected boiler contractor could begin work.
Of particular importance as it pertains to PRR boilers is the design and fabrication of the Belpaire firebox, including the inner and outer knuckles and the thickness of the sheets themselves. The “Form 4” calculation, as it is referred, requires that the boiler be designed with at least a safety factor of four. Original PRR designs did provide for such a factor of safety, but often it was with a very small margin for corrosion. The design work undertaken for the PRR T1 Trust included verification and modification to the original design to improve the factor of safety and, thus, longevity of the boiler. Staged fabrication work on the cylindrical barrel courses commenced in early 2018.