Page 357 - Practical Machinery Management for Process Plants Major Process Equipment Maintenance and Repair

336 Major Process Eauipment Mixintencame and Repair

Special Purpose Tbrbine Inspection and Repair

Inspection and overhaul have been traditional activities around special
purpose steam turbines. These activities have gained importance as the
possibilities of nondestructive testing and the complexity of large steam
turbine installations have increased. Attempts to lengthen intervals be-
tween inspections and overhauls have been instigated by a number of iso-
lated reports of steam turbines being operated without overhauls. May,
periods between major overhauls range from two to five years depending
on the degree of technological advancement of a particular installation.
In the case of new large turbines with many prototype components, indi-
vidual casings have been opened up every one or two years. Thus far, no
disadvantageous accumulations of failure incidents have been encoun-
tered after pum’uZ overhuuls, where the inspection of individual turbine
components during the available shutdown time has been practiced.*
However, it is obvious that the suitability for complete and independent
inspection and overhaul of individual components differs widely among
the various types of steam turbines. Investigating this “suitability” or
maintainability at the very beginning of a planned large steam turbine
acquisition is therefore of the utmost importance.
Internal inspections must be scheduled to suit plant load demand.
However, it is obvious for economic reasons that to reduce forced outage
for corrective maintenance, general knowledge of the internal condition
of the turbine at all times is desirable. A systematic check during opera-
tion to detect significant change in this condition is a valuable guide. In-
spections may then be regarded as preventive rather than necessarily cor-
rective.
A complete and detailed “case history” starting at the time of installa-
tion should be compiled for each turbine. This should include a descrip-
tion and analysis of any unusual circumstance during its operation as well
as any noteworthy condition found during inspection: also a statement of
the corrective measures taken or planned. The first complete inspection
of a new turbine forms the most valuable datum point in its history and
we recornmend that a very thorough inspection be made at or near the
end of the first year of operation.
Before taking the turbine out of service for inspection a number of pa-
rameters should be checked and the past “case history” reviewed to de-
termine items requiring special attention and investigation. Here is a
comprehensive listing :