Projects : Low Pressure Turbine, Guide Blade Drain Design

DPT conducted a comprehensive design and confirmatory analysis for Siemens-Westinghouse Power Corporation (SWPC) for the addition of new steam drain lines routed from the Low Pressure (LP) turbine cylinder and out through the condenser wall to an existing extraction line at Detroit Edison’s Monroe Unit 3. The LP turbines were being retrofitted and therefore required a means for protecting the last row of blades from erosion due to water droplets in the wet steam. This was to be accomplished by routing superheated extraction steam through the inside of the hollow last-row stationary blades. The resulting temperature difference between the hotter inside and colder outside of the hollow blades evaporates and prevents the formation of water droplets on the outside surfaces. Because some of the steam inside the blades will condense in the process, new drain lines were required.

DPT worked with SWPC engineering to optimize the requirements for the system, including details of a loop seal and check valve. During the course of the design, various pipe routings were investigated and analyzed, in accordance with ASME B 31.1 requirements, to minimize material and field fabrication costs. The final arrangement is unique and cost effective because no pipe supports were required inside the condenser. In addition, a single expansion joint at the condenser wall was used in lieu of what would normally be specified as one bellows at each of the two LP cylinder nozzles. The flexibility analysis, illustrated by the stress plot above, considered deadweight, thermal effects (including LP cylinder movements), pressure and the effects of steam flow on the outside of piping contained within the condenser.