Page 55 - ECLECTIC MARCH-2022 INSIDE PAGES_p2.indd
P. 55
ers and thus it is difficult to do a break-even analysis b) Issues with the bypass line of the valve: Motorized
for maintenance people regarding renewal of valves. valves of turbine drains are generally configured with
a bypass line with steam traps. Any internal leakage
Without any proper mode for detection the probable through the bypass line or poor performance of
solution could be steam trap can also aid to the high temperature of the
valve bonnet.
1. Continue the generation with all losses and then
during annual overhauling renew all the valves c) Valve bonnet seal / gland leakage: A proper visual
showing a high bonnet temperature. inspection is needed to confirm if there is a gland or
bonnet leakages from the valve. Sometimes these
2. To take intermittent unit outages and inspect the leakages may not be even visible to the naked eye
valve internals and renew accordingly. and the conclusion could be an internally passing
valve. But the 5 point measurement described in the
But these are not at all feasible as it will incur a huge later part of the paper will provide us the required
maintenance cost and a longer duration of plant outage. affirmation.
The former will result in budget constraints for other
equipment maintenance and the later will be responsible d) Leakage from upstream pipeline adjacent to the
for a low plant load factor. valve: Check for any leakage in the adjacent upstream
pipe line which may cause a flow of steam in the drain
PROPOSED METHOD header thus increasing valve bonnet temperature.
Factors to be considered while e) Valve located close to a live steam header (<1m):
Considering Suitable detection and Conductive heat from any live steam header will
quantification method result in high temperature of valve installed near to
the header.
To choose a suitable technique to detect and quantify
internal leakages one needs to consider the following These 5 points needs to be verified before proceeding
factors: further to 5 point measurement section. Presence of any
one or more of these 5 points will eliminate the chances
1. The proposed technique needs to be quick and of passing of a valve internally. Thus the cost and time for
easy to enable any responsible person to identify renewing the valve can be saved.
problematic valves swiftly.
If all the five points turn out to be negative, then the valve
2. It needs to be an in-situ inspection method without can be considered as an internally passing valve. Then
sacrificing generation/ load. there remains the question of quantification of the loss.
3. All piping should be properly insulated as any Mathematical Model
bare portion or damaged insulation can cause in a
temperature rise of the surrounding region. Basic Principle
Prior to concluding that a certain HED valve is passing, The underlying principle in fluid leak detection is that
there should be a few preliminary actions/ checks as the hot fluid that is leaking internally through the valve
follows: will increase the temperature of the downstream piping
network. As the fluid flows through the downstream
a) Partially shut valves or improper limit setting: If the pipework, heat energy contained in the fluid will be
bonnet temperature is high, a HED valve needs to be transferred from the high temperature fluid through the
further tightened by hand to eliminate any possibility pipe walls to the pipe surroundings. This will result in an
of improper closure of the valve. Temperature of the increase in the outer surface temperature of the pipe.
bonnet needs to be checked after 24 hours after this The thermal radiation from the pipe surface can then
operation.
55
for maintenance people regarding renewal of valves. valves of turbine drains are generally configured with
a bypass line with steam traps. Any internal leakage
Without any proper mode for detection the probable through the bypass line or poor performance of
solution could be steam trap can also aid to the high temperature of the
valve bonnet.
1. Continue the generation with all losses and then
during annual overhauling renew all the valves c) Valve bonnet seal / gland leakage: A proper visual
showing a high bonnet temperature. inspection is needed to confirm if there is a gland or
bonnet leakages from the valve. Sometimes these
2. To take intermittent unit outages and inspect the leakages may not be even visible to the naked eye
valve internals and renew accordingly. and the conclusion could be an internally passing
valve. But the 5 point measurement described in the
But these are not at all feasible as it will incur a huge later part of the paper will provide us the required
maintenance cost and a longer duration of plant outage. affirmation.
The former will result in budget constraints for other
equipment maintenance and the later will be responsible d) Leakage from upstream pipeline adjacent to the
for a low plant load factor. valve: Check for any leakage in the adjacent upstream
pipe line which may cause a flow of steam in the drain
PROPOSED METHOD header thus increasing valve bonnet temperature.
Factors to be considered while e) Valve located close to a live steam header (<1m):
Considering Suitable detection and Conductive heat from any live steam header will
quantification method result in high temperature of valve installed near to
the header.
To choose a suitable technique to detect and quantify
internal leakages one needs to consider the following These 5 points needs to be verified before proceeding
factors: further to 5 point measurement section. Presence of any
one or more of these 5 points will eliminate the chances
1. The proposed technique needs to be quick and of passing of a valve internally. Thus the cost and time for
easy to enable any responsible person to identify renewing the valve can be saved.
problematic valves swiftly.
If all the five points turn out to be negative, then the valve
2. It needs to be an in-situ inspection method without can be considered as an internally passing valve. Then
sacrificing generation/ load. there remains the question of quantification of the loss.
3. All piping should be properly insulated as any Mathematical Model
bare portion or damaged insulation can cause in a
temperature rise of the surrounding region. Basic Principle
Prior to concluding that a certain HED valve is passing, The underlying principle in fluid leak detection is that
there should be a few preliminary actions/ checks as the hot fluid that is leaking internally through the valve
follows: will increase the temperature of the downstream piping
network. As the fluid flows through the downstream
a) Partially shut valves or improper limit setting: If the pipework, heat energy contained in the fluid will be
bonnet temperature is high, a HED valve needs to be transferred from the high temperature fluid through the
further tightened by hand to eliminate any possibility pipe walls to the pipe surroundings. This will result in an
of improper closure of the valve. Temperature of the increase in the outer surface temperature of the pipe.
bonnet needs to be checked after 24 hours after this The thermal radiation from the pipe surface can then
operation.
55
