Large Steam Turbine Crossovers

The pipe that carries steam from the high pressure turbine to the intermediate pressure turbine on a base load power plant is generally called a crossover pipe. The crossover pipe is really a pressure balanced expansion joint assembly that accepts axial and lateral movements without imposing pressure thrust on the turbine nozzles. The movements are caused by differential growth between the crossover pipe and turbine casing as the system heats up to an operating temperature of 700 to 800 degrees F. The steam in the crossover pipe is typically at a pressure of 100 to 200 psig.

With these operating conditions, the structural components on the crossover are required to be very heavy. The assembly in the photo is a GE style crossover weighing over 35,000 pounds.

The real difficulty in building a crossover is the control of the tolerances during fabrication. The turbine nozzles are machined to precise tolerances that must be matched by the crossover pipe connections. Control of welding heat and fabrication sequence is critical so that these tolerances can be held throughout fabrication.

To find out more about Pathway’s crossover experience, contact Senior Flexonics Pathway.