Page 390 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

Steam ltrrbines and Turboexpanders 369

personnel should thoroughly understand, and at all times observe, all
safety precautions related to turbine maintenance. It is of primary impor-
tance to ensure the turbine is isolated from all utilities to prevent the pos-
sibility of applying power or steam to the turbine when performing inter-
nal maintenance. Therefore, it is absolutely necessary to close, lock and
tag all isolating valves and open all drains to depressurize the turbine
casing and steam chest before performing any internal turbine mainte-
nance. Also, take necessary precautions to prevent possible turbine rota-
tion due to reverse flow through the driven machinery.
Nondestructive type testing is recommended for determining opera-
tional reliability of parts during turbine inspections. If major parts re-
placement (such as turbine shaft, disks, blading ek.) becomes necessary,
it is advisable that the repair work be supervised by a vendor’s represen-
tative or be done in a qualified repair shop.

Scheduled Maintenance
Scheduled maintenance inspections are necessary for safe and efficient
turbine operation. Actual intervals between inspections cannot be speci-
fied rigorously because maintenance scheduling is dependent on factors
best known by those directly involved with the turbine and its particular
application. Table 8-6 serves as a general guideline for establishing a sched-
uled preventative maintenance program.
The actual frequency of required maintenance inspections can only be
determined after carefully considering turbine performance records,
maintenance history, corrosioderosion rates, tests, observations and an-
ticipated service demands. The established inspection schedule will usu-
ally be consistent with the availability of the turbine, necessary man-
power and an adequate supply of repair parts. At the same time,
scheduled inspections must be frequent enough to avoid unsafe operating
conditions.
It is also necessary to test and adjust all safety devices on a definite
schedule to ensure their operational reliability. These devices are de-
signed to prevent injury to personnel and/or major equipment damage. If
these devices are not operated at frequent intervals, they may not work
when needed.

Turbine Casing and Miscellaneous Joints

The turbine steam joints are carefully made up and factory tested under
pressure, to ensure steam tightness. Two types of sealing compounds are
used on general purpose and moderate pressure (not to exceed 600 psig)
turbines. For sealing of special purpose turbines, refer to Volume 3,
Chapter 10 of this series. Of the sealing compounds used for general pur-