Transcript Leak Detection with Thermography and Ultrasonic Acoustics

Leak Detection with
Thermography
&
Ultrasonic Acoustics
Presented by:
Matthew Crockett, Engineer
Plant Engineering Programs
APP Site Visit
October 30 – November 4, 2006
Background
Detecting leaking fluids, whether it be steam,
water or different types of gases, is of major
concern at AEP power plants. These leaking
fluids can affect safety, operation, maintenance,
heat rate, and work performance. Detecting leaks
can be difficult in a power plant environment.
AEP has discovered that the combined application
of Infrared Thermography and Ultrasonic
Acoustics as part of a plant Predictive
Maintenance Program can efficiently identify
leaks in many areas.
Infrared Thermography
Infrared Thermography (IR) can be used to detect
leaks on the following equipment/systems :
1.
2.
3.
4.
5.
6.
Leaking Process Valves
Steam Traps
Condensers
Heaters
Safety Valves
Boiler Casing
Valve leakage
396.0°F
A R 01: >364.3° F
This leaking valve is
over 177oC (350oF).
Most leaking valves
are less evident.
66.5°F
• Identifying leaking valves is probably the most effective
use of thermography to reduce heat rate losses and
operational problems.
• Temperature is key to identifying leaking valves. A small
temperature rise can indicate a leak through.
• Piping to a valve should be cool when it has a water leg.
If the line is hot the valve probably is leaking.
Valve leakage
• Valves and lines going to the condenser,
boiler blowdown, miscellaneous drain tank,
reclaim tank, drip receiver, and priming for
pumps under vacuum should be checked.
• All boiler, turbine, stop valve, valve chest,
etc., drain lines need to be checked for leak
through.
• DO NOT over tighten valves!
Valve leakage
488.6°F
400
300
200
S P 01: 393.3° F
100
93.7°F
Leaking drain
A R 01: * 598.0° F
667.2°F
600
500
S P 01: 533.9° F
400
300
• All boiler, turbine, stop
valve, valve chest, etc.,
drain lines need to be
checked for leak
through.
• Make sure a valve is
totally closed before
inspecting.
200
176.6°F
Turbine reheat steam line drain
valve leaking through.
Steam Traps
361.0°F
• IR can identify leaking
bypass lines and
improper operation (must
monitor).
Steam trap stuck open.
• One must know the trap
cycle of operation.
• Comparison between like
equipment that is
Steam trap working normally.
operating the same often
confirms problems.
• Use Ultrasonic Acoustics
to confirm problems
350
300
S P 01
250
200
150
118.6°F
103.2°F
100
95
S P 01
90
85
80.2°F
Steam trap by-pass leaking.
Condenser Air In-leakage
• Condenser air in-leakage can be identified with IR by
changes in temperature before and after flanges, valves
(packing), welds, safeties, etc. Detection can be
difficult and surface conditions always need to be
compensated for.
• Expansion joints are often difficult to see but should be
scanned.
• Checking a condenser tube sheet for leaks while the
unit is on can pinpoint the tube to plug. Remember to
confirm the leak with another method such as
Ultrasonic Acoustics or plastic. Water vapor can make
this difficult but once mastered it is very effective. A
large temperature difference between the air and tubes
help in identifying the leak.
Condenser Air In-leakage
116.1°F
115
A R 01: 100.8° F
110
A R 02: 103.1° F
105
100.9°F
• Check all bolts,
diaphragms and access
doors on the condenser
and turbine shell.
Leaking condenser access cover.
Leaking condenser
expansion joint.
• Condenser expansion
joints can be large source
of leakage but are often
difficult to view.
Ultrasonic Acoustics is a
good alternative method.
Condenser Air In-leakage
144.3°F
140
120
100
85.5°F
Notice the temperature
difference at flange.
196.2°F
180
160
S P 01: 153.4° F
140
120
S P 02: 173.9° F
100
67oC
79oC
80
75.8°F
• Visually these heater
vents look alike,
thermally there is a
difference. Cool air inleakage can cause this.
• There is approximately a
12oC (20oF) difference
across the flange.
Condenser Air In-leakage
• Using IR for air in-leakage requires a small
temperature span since the leakage cools the
downstream piping only by a few degrees.
• Changes in surface conditions (paint, rust,
etc.) must be accounted for or false
positives can result.
• Using ultrasonics or other methods to
confirm any leak is highly recommended.
Heaters
• Heaters can also be checked with IR to
identify heat rate loss items.
• Shell safety valves, vents, drains, and
pumps are items to check during a survey.
• Both high pressure and low pressure heaters
should be scanned.
• Vacuum pumps, LP drain pumps, and other
types should be checked.
Heaters
186.4°F
180
160
S P 01: * 156.6° F
140
120
• Vacuum pumps, LP drain
pumps, and other types
should be checked.
100
93.1°F
Shell vent has a vacuum leak
at the first union on the line
after the shell.
• Shell safety valves are a
common leak found. Once
they begin to leak they
normally do not re-seat
themselves.
Safety Valves
• All safety valves should be scanned.
Especially those that do not vent to
atmosphere. Those that vent to reclaim or
miscellaneous drain tanks are often
overlooked. High energy piping safeties are
usually reset during outages and vent to
atmosphere.
Boiler
• Infrared is very effective when used to identify
boiler and ductwork casing leaks.
• Boiler casing leaks increase auxiliary power
use by increasing load on fans and pulverizers.
• Reducing casing leaks improves combustion
and reduces excess air.
• Total air flow is often reduced (especially on
balance draft units) which decreases emissions
since precipitators, SCRs and FGDs treat less
exit gas.
Boiler
S P 01
• Casing leaks such as this one can be easily
identified with infrared.
Ultrasonic Acoustics
Ultrasonic Acoustics (UA) can be used to detect
leaks on the following equipment/systems :
Leaking Process Valves Steam Traps
Condensers
Safety Valves
How Ultrasonic Acoustic Leak Detection Works
During a leak, a fluid (liquid or gas) moves from a high
pressure to a low pressure. As it passes through the leak
site, a turbulent flow is generated. This turbulence has
strong ultrasonic components which can be heard with
specialized detection equipment.
Ultrasonic Acoustics
• Ultrasonic Acoustics requires skilled personnel with
the proper training.
• When used to detect piping leaks it can be effective to
pin point small sources.
• Large leaks and background noise can ‘overwhelm’
many detectors and require continual adjustments to
find the source. Ultrasonic Acoustic requires turbulent
flow between low and high pressure sources.
• Vacuum leaks sound different than pressure leaks and
an experienced user can differentiate between the two.
• Shielding of the detector is a useful tool to eliminate
background noise.
Ultrasonic Acoustics
•
•
Inspection methods vary depending on the type of valve or steam
trap. Therefore the primary rule is to know the way a specific trap or
valve may work under specific conditions.
To determine trap/valve conditions such as leakage or blockage:
1. Touch upstream of the valve or trap with a contact waveguide
probe and reduce the sensitivity of the instrument until the
meter/display panel reads about 50% of scale. If the instrument
has frequency tuning, you may also use this feature to hear the
trap or valve sound quality more clearly. Tune the frequency
until the sound you would expect to hear becomes clear.
2. Next, touch downstream of the valve or trap and compare
intensity levels. If the sound is louder down stream, the fluid is
passing through. If the sound level is low, the valve or trap is
closed.
3. When recording decibel levels and trending make all settings on
the ultrasonic instrument repeatable.
Ultrasonic Acoustics
Example of a
Good Valve
•
•
•
•
Test Point A = 50 db
Test Point B = 40 db
Test Point C = 17 db
Test Point D = 8 db
Ultrasonic Acoustics
•
•
•
Ultrasonic valve and steam trap inspection is considered
a "positive" test in that an operator can instantly identify
sound quality and intensity differentials and thereby
determine operating condition accurately. A steam trap
troubleshooting guide is usually available from the
factory upon request.
Ultrasonic Acoustic is best when used with Infrared
Thermography to find leakage.
Newer equipment can record Ultrasonic Acoustic wave
patterns and sound levels.
Air leak
Steam leak
Steam Trap
Performing A Survey
• To perform an accurate and effective Infrared
Thermography or Ultrasonic Acoustic survey takes
training on the equipment, planning of what is to be
surveyed, a method of progression, and a knowledge of
the systems involved.
• If not trained in the use of this equipment then seek
assistance.
Performing A Survey
Questions prior to a survey
1.
2.
3.
4.
5.
6.
7.
8.
Scope of survey?
Do you have safe access to perform the inspection and what
Personal Protection Equipment is needed?
Does the equipment/systems need to be placed in service? What
other conditions need to be met?
Is the equipment operating such to give meaningful results?
Will it be cost effective to perform the inspection?
Will you be needing additional resources to perform the
inspection?
Can you take advantages of other technologies or procedures to
supplement the findings of the inspection?
When are the results needed/expected?
Analysis
• Analysis should be done in a systematic
repeatable format.
• Determine the baseline or other industry
accepted standards.
• Document source of acceptance criteria.
• Problems or anomalies should be reviewed
for determination as to what corrective
actions, if any is required.
• Problems should be itemized and prioritized
according to severity, cost, location or other
process specific criteria.
Reporting
Accurate reporting should include the following:
1. Cover Letter/Executive Summary
2. Spread sheet of events sorted according to severity
3. Time/Date/Unit Conditions
4. Equipment identification
5. Location/Diagram
6. Specific problem details with priority
7. Corrective action recommended (if any)
8. Problem action criteria (Severity)
9. Visible Photograph/IR Image/Ultrasound Plot
10. Inspectors Name
Training/Experience
• The quality of a Thermography or Ultrasonic Acoustic survey
depends upon training and experience.
• Only trained individuals should perform these surveys.
• Training can be “In-house” or vendor supplied.
• Apprenticeship type training is highly recommended and
provides the best experience development.
• Experience allows for more accurate assigning of severity based
upon component history, or system conditions that differ from
the guidelines provided.
• Experience should be communicated through proper reporting.
• Experience allows one to improve on techniques.
• Trade information and Users Groups are a good source of
experience.
Summary
Infrared Thermography and Ultrasonic Acoustics
both provide accurate detection of fluid leaks
that commonly occur at a power plant.
When combined, the effectiveness of these leak
detection methods increases dramatically.
Confirming a suspected leak detected with one
technology by repeating the detection with a
separate technology is always a best practice.
Proper reporting of findings is key to the
successful application of these technologies.
Questions?