Eliminating Steam Blow Piping Overcleaning During Power Plant Startup

Abstract

This paper investigates and justifies the use of a minimum necessary cleaning force ratio or cleaning factor for steam blows. Steam line blowing is an operational cleaning method used to clean steam piping and reheaters prior to turbine powering for steam power plants. The steam blows remove weld bead deposits, slag, debris, surface scale, and other foreign materials which could be carried into the steam turbines and damage the turbine blades during normal plant operation. Piping is blown, bypassing the turbine, with sufficient boiler pressure to ensure the dynamic pressure throughout the piping is greater than would be experienced during all plant operating conditions. By providing flow rates corresponding to the maximum service condition for any given section of piping, there will be sufficient kinetic energy to ensure complete removal of any impurities from the pipe. Historically, the required steam blow pressures are calculated to achieve a cleaning force ratio of 1.2. Cleaning Force Ratio (CFR) or Cleaning Factor (CF) is an industry-accepted factor that quantifies the ratio of required dynamic pressure for cleaning to maximum dynamic pressure experienced during system operation. For CFRs, the turbine vendors tend to have guidelines or ranges rather than definitive acceptance criteria. It is usually left up to the commissioning engineer, the Project Startup Manager and Owner to determine what is necessary for final acceptance. It is desirable to reduce the required minimum blowout pressure and flow rate to facilitate plant startup. By reducing the required minimum blowout pressure and flow rate, permanent plant equipment and temporary steam blow piping wear can be reduced and over cleaning avoided. Further, time between steam blows can be reduced. This paper examines the CFR guidelines for various turbine vendors and justifies reducing the CFR from 1.2 to 1.0. Advantages of the use of a minimum necessary CFR include reduced required steam blow pressures which result in safer steam blows, and less expensive temporary steam blow piping. Use of a minimum necessary CFR will still maintain the effectiveness of the steam blow.