"An effective repair program can minimize the adverse problems associated
with cavitation pitting. The main objectives of such a program are:
with cavitation pitting. The main objectives of such a program are:
· Restoration of runner and other components within the turbine water
passages to "as new" condition;
passages to "as new" condition;
· Correction of any profile errors or irregularities which are responsible
for the pitting; and
for the pitting; and
· Avoidance of blade shape distortion and its affect (sic) on further
damage.
damage.
"As with any equipment, excessive repairs to a turbine can lead to reduction in
its performance and useful operating life. Extensive weld repairs can result in
runner Blade distortion, acceleration of further cavitation damage, and possible
reduction of turbine efficiency. Also, extensive repair can cause residual
stressing in the runner resulting in structural cracking at areas of high stress.
its performance and useful operating life. Extensive weld repairs can result in
runner Blade distortion, acceleration of further cavitation damage, and possible
reduction of turbine efficiency. Also, extensive repair can cause residual
stressing in the runner resulting in structural cracking at areas of high stress.
"To maximize equipment life and to maintain high availability and good operating
efficiency, cavitation pitting repairs should be done in a logical and methodical
manner. The basic steps of such a repair program are as follows:
efficiency, cavitation pitting repairs should be done in a logical and methodical
manner. The basic steps of such a repair program are as follows:
·
Inspection
·
Identify cause of pitting
·
Plan best approach to repairs
·
Perform repairs
"Thorough periodic inspection of equipment within a preventive maintenance
program is a prerequisite to long-term reliability, and routine inspection for
cavitation damage is no exception to this concept. Additionally, clear and
concise inspection records assist in reporting the causes of cavitation pitting and
monitoring the effectiveness of repair programs.
program is a prerequisite to long-term reliability, and routine inspection for
cavitation damage is no exception to this concept. Additionally, clear and
concise inspection records assist in reporting the causes of cavitation pitting and
monitoring the effectiveness of repair programs.
"Identifying the cause of cavitation pitting on turbine equipment is often a
significant step toward mitigating the problem. In many cases, identification will
be difficult and may not be conclusive; nevertheless, some attempt at
ascertaining the cause of the damage is warranted and should not be
overlooked.
significant step toward mitigating the problem. In many cases, identification will
be difficult and may not be conclusive; nevertheless, some attempt at
ascertaining the cause of the damage is warranted and should not be
overlooked.
"Prior to making repairs, consideration should be given to the options
available for doing the work. There are two general approaches:
available for doing the work. There are two general approaches:
"One is to restore the runner to original profiles; and the other is to
perform runner modifications to eliminate or reduce the cause(s) of the
perform runner modifications to eliminate or reduce the cause(s) of the
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