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2.5
Check the turbine alignment. The shaft runout and the perpendicularity
should meet normal pump standards. The concentricity may be much larger
than that typically seen in a pump. The flange for internally mounted seals
pilots on the turbine and requires a TIR < .020" for proper seal function.
Talk to the operations and maintenance personnel regarding the above
concerns. Find out if there are any other issues regarding turbine reliability and
performance.
3
Inspection of Steam Turbine Piping and Application
of Steam Traps
Water is a problem for turbines in general, but poses some unique challenges
for mechanical seals. Hot water under pressure at the OD of the seal faces will
flash to form steam as it crosses to the atmospheric pressure at the ID of the
faces. The expansion ratio when water is converted to steam is over 1600 to 1.
This generates a large force that causes the faces to separate, resulting in high
leakage. The GTS seal is robust and can recover from normal water slugs that
occur during start up. However, operation in water will result in high leakage that
is not generally acceptable for prolonged operation.
As a practical matter, altering the turbine piping to remove water and improve
performance of the turbine and mechanical seals is not an option for most
end users. However, inspecting the piping can yield useful information about
potential problems that may be reduced or eliminated through the application of
mechanical free float actuated steam traps.
Check your piping system for the following:
3.1
Piping should slope downward 10 cm per 10 m (4 inches per 30 ft) in the
direction of steam flow to aid condensate drainage.
3.2
Piping should be straight and free from sags where condensate could
collect and create a slug of water.
3.3
Eccentric reducers should be used instead of concentric reducers, to
prevent condensate from pooling upstream of the reducer and creating a
slug of water.
3.4
Equipment supply lines should be connected to the top of steam mains, not
the bottom, so that dirty condensate running along the bottom of the mains
does not flow into the equipment.
3.5
Steam traps should be installed at regular intervals (every 30 to 50 m or
100 to 150 ft) in the steam main with correctly sized condensate pockets.
3.6
Steam traps should be installed upstream of isolation valves that are
regularly closed.
3
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