Leak Detection with Thermography & Ultrasonic AcousticsPresented by: APP Site VisitMatthew Crockett, Engineer October 30 – November 4, 2006Plant Engineering Programs
BackgroundDetecting leaking fluids, whether it besteam, water or different types of gases, is ofmajor concern at power plants. These leakingfluids can affectsafety, operation, maintenance, heat rate, andwork performance. Detecting leaks can bedifficult in a power plant environment. AEP hasdiscovered that the combined application ofInfrared Thermography and Ultrasonic Acousticsas part of a plant Predictive MaintenanceProgram can efficiently identify leaks in manyareas.
Infrared ThermographyInfrared Thermography (IR) can be used to detectleaks on the following equipment/systems :1. Leaking Process Valves2. Steam Traps3. Condensers4. Heaters5. Safety Valves6. Boiler Casing
Valve leakage 396.0°F This leaking valve is over 177oC (350oF). AR01: >364.3°F 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 • All boiler, turbine, stop 488.6°F valve, valve 400 300 200 chest, etc., drain lines SP01: 393.3°F 100 need to be checked for leak through. 93.7°FLeaking drain AR01: *598.0°F 667.2°F 600 • Make sure a valve is SP01: 533.9°F 500 400 totally closed before 300 inspecting. 200 176.6°FTurbine reheat steam line drainvalve leaking through.
Steam Traps 361.0°F • IR can identify leaking 350 300 SP01 bypass lines and 250 200 improper operation 150 (must monitor). 118.6°F Steam trap stuck open. • One must know the trap 103.2°F 100 SP01 95 90 cycle of operation. • Comparison between like 85 80.2°FSteam trap working normally. equipment that is operating the same often confirms problems. • Use Ultrasonic Acoustics to confirm problemsSteam 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 • Check all 116.1°F 115 AR01: 100.8°F bolts, diaphragms and 110 AR02: 103.1°F access doors on the 105 condenser and turbine 100.9°FLeaking condenser access cover.shell. • Condenser expansion joints can be large source of leakage but are often difficult to view. Ultrasonic Acoustics is aLeaking condenser good alternative method.expansion joint.
Condenser Air In-leakage • Visually these heater 144.3°F 140 120 vents look alike, thermally 100 there is a difference. Cool 85.5°F air in-leakage can causeNotice the temperature this.difference at flange. 196.2°F • There is approximately a 180 160 12oC (20oF) difference SP01: 153.4°F 140 across the flange. 120 SP02: 173.9°F 10067oC 79oC 80 75.8°F
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 • Vacuum pumps, LP drain 186.4°F 180 pumps, and other types 160 SP01: *156.6°F 140 120 should be checked. 100 93.1°FShell vent has a vacuum leakat the first union on the lineafter 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 SP01• Casing leaks such as this one can be easily identified with infrared.
Ultrasonic Acoustics Ultrasonic Acoustics (UA) can be used to detect leakson the following equipment/systems :Leaking Process Valves Steam TrapsCondensers Safety ValvesHow Ultrasonic Acoustic Leak Detection WorksDuring a leak, a fluid (liquid or gas) moves from a highpressure to a low pressure. As it passes through the leaksite, a turbulent flow is generated. This turbulence hasstrong ultrasonic components which can be heard withspecialized 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 AcousticsExample of aGood 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 survey1. Scope of survey?2. Do you have safe access to perform the inspection and what Personal Protection Equipment is needed?3. Does the equipment/systems need to be placed in service? What other conditions need to be met?4. Is the equipment operating such to give meaningful results?5. Will it be cost effective to perform the inspection?6. Will you be needing additional resources to perform the inspection?7. Can you take advantages of other technologies or procedures to supplement the findings of the inspection?8. 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.
ReportingAccurate reporting should include the following:1. Cover Letter/Executive Summary2. Spread sheet of events sorted according to severity3. Time/Date/Unit Conditions4. Equipment identification5. Location/Diagram6. Specific problem details with priority7. Corrective action recommended (if any)8. Problem action criteria (Severity)9. Visible Photograph/IR Image/Ultrasound Plot10. 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.
SummaryInfrared 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.