The Design, Fabrication, and Installation of the Inconel 740H Piping System for a 10 MW sCO2 Pilot Plant

The STEP (Supercritical Transformational Electric Power) 10 MWe sCO2 (supercritical CO2) pilot plant operates on a recompression cycle (RCBC) up to 715 °C and 255 bar at the turbine inlet. Initial testing phases for this facility will operate a simple-recuperated cycle with turbine inlet temperatures up to 500 °C as a stepwise risk mitigation. While the uncooled turbine design includes novel thermal management, the surrounding piping must also withstand these conditions. This paper summarizes the design, fabrication, and installation of the high temperature piping throughout the system. These piping sections include pipe materials of the high-nickel alloy, Inconel 740H. Through this experience, supply chain, weld procedures, general handling, and inspection were among key challenges. To support this project the supply chain needed to produce extruded pipe, pipe fittings including elbow and tees along with flanges and flange clamps. The high temperature pipe sections that used the Inconel 704H material utilized Grayloc flanges (clamp type flanges) to connect the piping to the equipment. This project involved pipe sizes and schedules that have not been previously produced with Inconel 740H. Inconel 740H requires careful attention when performing welds to ensure that the weld is not contaminated and that the correct temperatures are used with the proper shielding and purge gas mixture. With the proper weld procedure and attention to detail consistent quality welds can be produced. The paper will detail these challenges and the lessons learned that came from them resulting in a successful installation.