Page 374 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Steam Turbines and Turboexpanders 353

water injection rate is again increased. The wash is considered completed
when the inlet steam is saturated and the exhaust conductivity is down to
200 micromhos.
After the wash is completed, the inlet temperature is raised to normal
at a maximum rate of change of 180°F per hour.
Initiation of the normal steam flow path, bypassing the desuperheater,
is the last hazard. We have found that water builds up in the line upstream
of the valve, even when the bypass is left open. We now always leave the
main valve cracked open to prevent the water buildup.
Over the past 13 years, we have successfully completed about 30 tur-
bine washings. These involved six different machines, located in four
plants. Based on this, we conclude that on-load washing is safe provided
reasonable care is exercised. We have, however, observed that deposit
solubilities vary considerably between subsequent washes on the same
machine. This same variability has been observed on two machines sup-
plied by steam from the same source for the same time period. Some ma-
chines can be successfully cleaned without making the inlet saturated but
most have required a wet inlet.
During our earliest washes, we believed that condensate was essential
as the desuperheating medium. We reasoned that any other water would
leave salts behind during the temperature-increasing phase. Five of the
machines have now been washed using boiler feedwater, without any ob-
servable problems or deterioration of the cleaning.
Also during our earliest washes we noted an apparent accelerated foul-
ing rate during the first few days after a wash. We have no reasonable
explanation of this phenomenon. It levels out quickly and does not appear
to affect either the maximum mass flow or the efficiency. Currently, we
merely warn the operators to disregard it if it is observed.*
Another form of steam turbine cleaning is by the use of chemical foam.
Reference 7 describes this method.

General Purpose
Steam Turbine Malntenance and Repair

Although steam turbine operation is not generally considered within
the scope of this text, an overview is deemed appropriate here,
Turbine applications differ widely, therefore, operating and mainte-
nance procedures must be tailored to each particular installation. The in-
structions here provide a recommended procedure for the initial startup

* Adapted from “On-Stream Cleaning of Turbomachinery,” by B. kner. Proceedings of
Second Turbomachinery Symposium, Gas ”hrbine Laboratories Texas A&M Univer-
sity. October 1973. By permission.