Con-Ed Manhattan Steam Distribution
Submitted by Michael Mark, WEI Mechanical Engineer
Due to the difficulties associated with snaking nearly 3,000 feet of 30 diameter steam main plus conduit and concrete encasement through the web of utilities located beneath the streets of Manhattan, Con Edison elected to install a significant portion of the new ERRP steam main in microtunnel construction. Waldron Engineering Inc. worked directly for Con Edison to engineer the new four hundred psi steam main as well as the pipe supports, concrete encasement and concrete reaction blocks required to support the microtunnel construction.
A key component in the design was a ninety degree change in direction required beneath the streets, just south of the recently re-powered East River Generating Station. The intended use of slip-type expansion joints in the system, in combination with the limited access to the piping that is the nature of microtunnel construction, created a situation in which the large thrust loads from either side of the change-in-direction in the piping system converged at the same location. WEI designed a custom elbow, integral support structure and concrete reaction block to accommodate this combined loading which was in excess of 450,000 lbs of force. The entire design had to fit within the confines of a single shaft and maintain the integrity of the conduit piping system which encases and protects the steam main.
In order to develop and validate the design, Waldron Engineering Inc. relied on finite element analysis techniques to accurately model and refine the support and piping system at this location. The use of this analysis method allowed WEI engineers to ensure that stresses within the piping system and support attachments were within the limits of the ASME B31.1 Power Piping Code for all conceivable load conditions. The final design consisted of a custom fabricated long-radius elbow with a large trunnion attachment that was designed to transmit the developed forces directly into a reinforced concrete structure at the base of the shaft.