d) The unit is flushed with clean water as a final rinse to remove any
remaining loose deposits.
The two generally accepted methods in chemical cleaning are continuous
circulation and soaking.
e) Continuous Circulation. In the circulation method, after filling the
unit, the hot solvent is recirculated until cleaning is completed. Samples of the
return solvent are tested periodically during the cleaning. Cleaning is considered
complete when the acid strength and the iron content of the returned solvent reach
equilibrium indicating that no further reaction with the deposits is taking place. The
circulation method is particularly suitable for cleaning once-through boilers,
superheaters, and economizers with positive liquid flow paths to assure circulation of
the solvent through all parts of the unit.
f) Soaking. In cleaning by the soaking method after filling with the hot
solvent, the unit is allowed to soak for a period of four to eight hours, depending on
deposit conditions. To assure complete removal of deposits, the acid strength of the
solvent must be somewhat greater than that required by the actual conditions, since,
unlike the circulation method, control testing during the course of the cleaning is not
conclusive, because samples of solvent drawn from convenient locations may not truly
represent conditions in all parts of the unit. The soaking method is preferable for
cleaning units where definite liquid distribution to all circuits by the circulation
method is not possible without the use of many chemical inlet connections or where
circulation through all circuits at an appreciable rate cannot be assured, except by
188.8.131.52 Main Steam Blowout. The main steam lines, reheat steam lines, auxiliary steam
lines from cold reheat and auxiliary boiler, and all main turbine seal steam lines shall
be blown with steam after erection and chemical cleaning until all visible signs of mill
scale, sand, rust, and other foreign substances are blown free. Cover plates and
internals for the main steam stop valves, reheat stop, and intercept valves, shall be
removed. Blanking fixtures, temporary cover plates, temporary vent and drain piping,
and temporary hangers and braces to make the systems safe during the blowing operation
shall be installed.
After blowing, all temporary blanking fixtures, cover plates, vent and drain
piping, valves, hangers, and braces shall be removed. The strainers, valve internals,
and cover plates shall be reinstalled. The piping systems, strainers, and valves shall
be restored to a state of readiness for plant operation.
a) Temporary Piping. Temporary piping shall be in stalled at the inlet to
the main turbine and the boiler feed pump turbine to facilitate