Chemical Engineering October 2020 - 38

Temperature
transmitter
Temperature
transmitter
Heat exchanger
T1
T2
T3
214°F
299°F
FIGURE 6. There is a high temperature differential
across the steam trap shown here
to determine the inlet steam pressure
to the steam trap station and the
condensate line backpressure.
To achieve a representative temperature,
scan the exposed metal
surfaces of the upstream and
downstream piping/tubing around
the steam trap station. Some installations
may have several inches exposed,
while other installations may
only have pipeline components,
such as unions, valves or fittings,
exposed. The steam-trap station
examiner must consider what is
available for temperature scanning
when incorporating the temperature
reading in evaluating the steam
trap station operation. The following
are suggested:
* Measure the inlet temperature of
steam/condensate line to the inlet
of the steam trap. A significantly
lower temperature than the saturation
temperature of the steam line
pressure can indicate that there are
issues with the steam trap, that flow
is reduced due to plugged fittings
or strainer screens, or even that the
steam trap has been valved off
* Measure the temperature to the
inlet of the steam consumer (equipment)
and compare it to the inlet
of the steam trap. Generally, these
temperatures should be close in
measurement (±20°F/±11°C)

Record the reading
T3
280°F
FIGURE 7. This example shows a low temperature
differential across the steam trap
* Measure the outlet temperature in
the condensate line downstream
of the steam trap

Heat exchanger
T1
T2
284°F
299°F
T3
212°F
FIGURE 8. There is a low temperature differential
across this steam trap station at low pressure
There should be some decrease
in the outlet temperature
versus the inlet temperature

This
measurement can also
be used to determine the
backpressure present in the
condensate line
 Record the reading
In concluding this section, we can
say that temperature measurement
is an important part of steam-trap
station evaluation, but it is only one
of the methods. Others are important,
too.
ULTRASOUND
When using high-frequency ultrasound,
the main question is where
the sensitivity should be set to conduct
the test. If the testing instrument
is set with a sensitivity that is
too high, all of the steam traps will
test as failed; using too low a sensitivity
will indicate that all steam traps
are operating properly.
The solution is using a field-proven
comparison method, which will provide
an accurate test on each steam
trap. The comparison method uses
three or more test points on the
steam trap station. Two of the test
points are the sensitivity baseline
settings on the ultrasound unit, and
the third is for testing the steam trap.
The comparison method allows the
steam-trap station assessor to establish
a base reading to filter out any
competing ultrasounds that can be
generated upstream or downstream
of the steam trap. Without using the
comparison method of testing, it is
very difficult to assess the steam
trap's performance because the assessor
will not know the correct sensitivity
setting. Each steam trap will
be in slightly different installations
and situations in the steam system,
so the comparison method is the
most accurate method for setting
the ultrasound sensitivity.
Sensitivity settings
Most digital ultrasound
devices
have a stethoscope module. With
the stethoscope module, contact
each point on the steam trap station,
as shown in Figure 10. The
steam and condensate line should
have baseline test points that are
between 6 and 10 in. upstream or
downstream of the steam trap that
is being tested. More test points
can be taken to establish a baseline,
but at least two need to be done for
each steam trap location (these estimated
values will vary depending
on the piping).
A
B
Temperature
transmitter
Heat exchanger
T1
T2
212°F
220°F
Test point no. 3
at the discharge side
of the steam trap
Test point no. 1
before steam trap
Test point no. 2
after the steam trap
FIGURE 9. A temperature measurement is being
performed in this picture
38
FIGURE 10. The three test points shown here are
used to establish a baseline for ultrasound testing
FIGURE 11. Shown here is a dial reading of a typical
ultrasound unit
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