ASME B31.1 Power Piping governs piping in steam power generating stations, utility boilers, combined cycle plants, cogeneration — Boiler External Piping (BEP per Section I I-stamp), main steam + hot reheat + cold reheat + feedwater + balance-of-plant. Material SA-106 Gr B carbon to SA-335 P11/P22/P91 Cr-Mo supercritical 565-625°C. 5 welding requirements (WPS Section IX / mandatory PWHT Cr-Mo / Charpy / 100% RT BEP+main steam / 1.5× hydrotest). 5 project scenarios + B31.1 vs B31.3 comparison.