High Pressure and Low pressure steam turbine 00923006902338

1. Submitted by
Salman jailani
Steam leakage
High Pressure and Low pressure
steam turbine

2. High pressure and High temperature steam
leakage form HP to IP due to seals
damaged or weakened by misalignment,
poor start-ups, or multiple temperature
excursions will cause leakage

4.  Increases in calculated heat rate.
 Increases in calculated IP efficiency.
 Decreases in calculated LP efficiency.
 Decreases the mass flow rate through
the HP turbine down stream.

5.  LOSING LOAD-
1) A turbine’s output and reliability can be affect by
high internal leakage. An enlarging internal leak
will initially increases the unit’s capacity in a
manner similar to reheat spray. The cycle flow
restriction in the first few stages of the HP turbine
will be by passed. Eventually, the effects of
reduced boiler re-heater flow will cause
overheating of the re-heater tubes and more tube
leaks. Load may have to be curtailed to avoid
overheating the re-heater.

6. 2) Nut and bolt aside, the thrust balance can also
be affected by a change in internal flow
distribution . It may not be possible to achieve
full load following such a change if it triggers a
thrust bearing alarm.
3) Trouble controlling reheat temperature- this
situation could involve in to one where the flow
capacity of reheat spray is “topped out”. At this
point, the only alternatives for control would be
reduce load or to lower superheat temperature.

7. 4) TURBINE PRESSURE CHANGES AT VALVE
WIDE OPENING- The main steam flow
calculated from the first stage curve will
decreases, whereas the main steam flow
determined by the feed water flow (plus superheat
spray flow, if applicable) will increases.
5) TURBINE SHELL TEMPERATURE
DIFFERENCE- Verified difference of over 100
degrees F between the upper and lower shell
metal and steam temperature could be a sign that
an internal leak is coming an upper or lower
section

8.  Seal damage or weakened by
misalignment.
 Poor start-ups.
 A water induction incident will causes
seal rubs and HP inner shell distortion.

9.  Upper and lower main steam inlet snout rings clearance
increases.
 The N2 packing head’s horizontal joint and how to fits in
to inner shell.
 The HP inner shell horizontal joint (if the shell distorts or
the joint develops a loose bolt).
 The turbine blow down pipe’s snout/piston rings.
 The first stage pressure flanged probe and how to fits in
the lower inner cylinder.

10.  Replace N2 packing seals if they have
excessive clearance or broken teeth.



Proper alignment and a controlled start-up
after the turbine outage are critical to
maintaining the clearance.
Replacing snout rings (For main steam and
the N2 packing blow down pipe) that have
excessive clearance, taper, or erosion.
The snout pipe themselves may be eroded
enough to require refurbishment

11.  Weld build up and machining the HP inner
shell horizontal joint surface, including an
evaluation of its studs and shell threads,
leakage can actually flow up through shell
holes, eroding the studs.


The stud nuts should be “sounded” with a
hammer to determine if any loose prior to
dismantling the unit.
It is very important to know the both stud
material and the nut tightening spacs.

12. TWO METHODS ARE THERE
1) Temperature Variance Method
2) Blow down method

13. The temperature variance method uses the
difference between the enthalpy at the first
stage of the HP turbine and the enthalpy at the
IP turbine, upstream of the intercept valve, to
estimate N2 leakage.
Because of lower enthalpy of the N2 leakage
form first stage, there is cooling effect on the
steam at the IP turbine inlet, which carries on
the down cross over .
This effect is maximized by decreasing
throttle temperature, and minimized by
decreasing hot reheat temperature

14. To run the temperature variance test
1) The hot reheat and super heat temperature are
set to a temperature differential of
approximately 75 degree F for example, set hot
reheat to 1000 degree F and superheat
925 degree F. test data is collected and IP
efficiency is calculated using assumed value of
N2 leakage from 0 to 10 percent of first stage
flow and result of this calculations plotted as an
IP efficiency Vs leakage flow trend
HRH- 1000 degree F MS – 925 degree F

15. 2) Next the unit is set up with reheat and super heat
temperature are set to a temperature differential of
approximately 75 degree F for example, set hot reheat to
925 degree F and superheat 1000 degree
F. Another set of test data is collected and IP
efficiency is calculated using the same assumed
value of N2 leakage and result of this calculations
plotted on the same graph.
HRH- 925 degree F MS – 1000 degree F
3) Calculate IP efficiency at same temperature and plot
on the same graph.
The intersection of these trends indicates the true HP
to IP leakage and the true IP efficiency and

16. The blow down method uses the
emergency blow down valve to divert the
N2 leakage from IP turbine inlet to the
condenser.
The emergency blow down valve Is safety
mechanism design to prevent turbine over
speed by removing HP turbine leakage
steam and passing it directly to the
condenser, bypassing the entire IP and LP
turbine section.

17. According to GE,
The blow down test should be run below 50 percent load, with the
blow down valve open for no longer than 30 minutes and .
This allows approximately 15 minutes for the unit to stabilize
and 15 minutes to data collect
1) Bring unit load to 50 percent load.
2) Allow unit to stabilize at design throttle and hot reheat
condition.
3) Begin data acquisition and collect 30 to 60 minutes of
performance test data.
4) After checking unit stability, begin data acquisition for blow
down test.
5) Open blow down valve.
6) After data is collected for 30 minutes, close blow down
valve.

18. 1) Advantage of the blow down test is that a true
IP turbine efficiency is calculated at the tested
load, allowing N2 leakage to be calculated
directly.
2) In addition , only 60 minutes of test data is
required at one load.
How ever , these are only
advantages if the blow down system is
capable of passing the entire N2 flow before
attempting to run a blow down test, the flow
passing capability of the blow down valve
should be calculated

19. References.
Downloads/unit-9-leakges -
steam-power plant.
Thank You.