monitoring environmental conditions for cleaning & painting operations william d. corbett...
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Monitoring Environmental Conditions for Cleaning & Painting Operations
William D. CorbettKTA-Tator, Inc.
Introduction• Webinar Content:
Overview of Commonly Monitored Conditions during Surface Preparation
Overview of Commonly Monitored Conditions during Coating Work
Instrumentation for Measuring Environmental Conditions
Documentation of Conditions Determining Conformance to Project Specifications
and/or Manufacturer’s PDS Location and Frequency of Data Acquisition Altering the Environment to Achieve Conformance
Learning Objectives/Outcomes
• Completion of this webinar will enable the participant to:
Describe the environmental conditions commonly Describe the environmental conditions commonly monitored during surface preparation and coating workmonitored during surface preparation and coating work
Describe the instrumentation that is commonly used to Describe the instrumentation that is commonly used to measure environmental conditionsmeasure environmental conditions
Document environmental conditionsDocument environmental conditions Compare on-site conditions to specification requirementsCompare on-site conditions to specification requirements Describe the frequency and location of measurementsDescribe the frequency and location of measurements Describe methods for altering the environment to attain Describe methods for altering the environment to attain
conforming conditionsconforming conditions
Definitions
• Air Temperature (Ta)
• Wet Bulb Temperature (Tw)
• Depression of Wet Bulb Temperature from Dry Bulb Temperature (Ta-Tw)
• Relative Humidity (RH)
• Dew Point Temperature (Td)
• Surface Temperature (Ts)
Definitions
• Air Temperature (Ta): Temperature of the surrounding air
• Wet Bulb Temperature (Tw): A measurement of the latent heat loss caused by water evaporation from a wetted sock on the end of a bulb thermometer in a psychrometer
• Depression of Wet Bulb Temperature from Dry Bulb Temperature (Ta-Tw): The calculated difference between the air temperature and the wet bulb temperature
Definitions
• Relative Humidity (RH): The percentage of moisture or water vapor in the air, relative to the maximum attainable at the same temperature
• Dew Point Temperature (Td): The temperature at which condensation of water vapor occurs on a surface
• Surface Temperature (Ts): The temperature of the surface to be prepared and coated
Converting Temperature
Temperature expressed in Celsius or Fahrenheit
Celsius– Freezing is 0; boiling is
100
Fahrenheit– Freezing is 32; boiling is
212
Converting Temperature
Converting Fahrenheit to Celsius oC = (oF-32oF) ÷ 1.8
Example: (83oF-32oF) ÷ 1.8 = 28.3oC
Converting Celsius to Fahrenheit oF = (1.8 x oC) + 32oF
Example: (1.8 x 5oC) + 32oF = 41oF
Environmental Conditions for Surface Preparation “Rough” surface
preparation work can occur when conditions are less than desirable (unless prohibited by contract)
“Final” surface preparation work should occur when conditions preclude moisture formation on prepared surfaces
Measuring Ambient Conditions Prior to Final Surface Preparation• If air temperature and relative humidity
are such that moisture from the air condenses on the surface, the surface may rust bloom, or rust back prior to coating
• Recommend verifying that the temperature of the surface is at least 5°F (3°C) higher than the dew point temperature to preclude condensation (requirement may be invoked by specification)
Significance of 5°F (3°C)
• Theoretically, a small (<1°F) increase (surface temperature over dew point) will preclude moisture formation
• Minimum increase of 5°F (3°C) compensates for: Instrument tolerances Varying conditions Changing conditions
Environmental Conditions for Coating Application• Air Temperature
(min. & max.)• Relative Humidity
(min. or max)• Dew Point
Temperature• Surface Temperature
[min. 5 °F (3°C)] above Dew Point Temperature
• Wind Speed (max.)
Significance of Conditions
• Air TemperatureToo cold or too hot can affect coating application
& curing
• Relative HumidityToo damp or too dry can affect coating application
& curing
• Surface TemperatureToo cold or too hot can affect application & curing
• Surface temperature at or below dew point temperature will result in condensation
Significance of Conditions, con’t.
• Wind SpeedToo windy can affect application (dry spray)
and cause overspray damage
• Mixing/application of coatings under adverse weather conditions can void the manufacturer’s warranty and is considered a specification non-conformance
History of Environmental Condition Measurement• Whirling apparatus
containing wet & dry bulb thermometers developed in the 1600’s
We’ve Come A Long Way Baby!
• Use of Sling psychrometers to obtain dry bulb/wet bulb measurements is still mainstream
• Electronic measurement is possible
• Some electronic psychrometers adversely affected by “outdoor” conditions
Ambient Conditions & Surface Temperature• Measuring
InstrumentsSling Psychrometers*Battery-powered
Psychrometers*Electronic
PsychrometersAnalog,
Thermocouple-type & Non-contact Surface Thermometers* Used in conjunction with
psychrometric charts or calculators
Using Sling Psychrometers
• ASTM E337• Verify wick cleanliness• Saturate wick and/or fill
reservoir with DI water• Whirl 20-30 second
intervals until wet bulb stabilizes (2 readings within 0.5o)
• Record wet & dry bulb temperatures
Using Battery-Powered Psychrometers
• ASTM E337• Verify wick cleanliness• Saturate wick• Operate until wet bulb
stabilizes (2 readings within 0.5o; typically 2 minutes)
• Record wet & dry bulb temperatures
Using Psychrometric Charts
• Locate Chart (relative humidity or dew point)
• Verify Barometric Pressure (e.g., 30.0 in.)
• Intersect air temperature with wet bulb depression (Ta-Tw)
Determining Dew Point Temperature
Example: Air temperature: 60°FDepression wet bulb thermometer: 5°FDew Point temperature: 51°F
Determining Relative Humidity
Example: Air temperature: 60°FDepression wet bulb thermometer: 5°FRelative Humidity: 73%
Relative Humidity and Dew Point Calculators1. Convert oF to oC using
right “window”2. Align dry bulb & wet
bulb temperatures (top of calculator)
3. Read Dew Point from upper “window”
4. Align dry bulb & dew point temperature (bottom of calculator)
5. Read %RH from lower “window”
2, 3
1
4, 5
Using the Psychrometer Slide Scale• Intersect air
temperature and wet bulb temperature
• Base of “Y” points to relative humidity
• Cannot determine dew point temperature
• White ink fades over time/usage (left image)
Electronic Psychrometers
• Measure/Record: Air Temperature Surface Temperature (ST) Relative Humidity Dew Point Temperature (DP) Spread between
DP and ST
• Features Auto-logging allows for
automatic data collection Magnetic surface probe Data graphing and uploading
using software Audio/visual alarm
Electronic Psychrometers
• Measure/Record: Air Temperature Surface Temperature (ST) Relative Humidity Dew Point Temperature (DP) Spread between DP and ST
• Features Auto-logging Integral magnets Data uploading using software Audio/visual alarm BlueTooth® Data Output Another model (right) offers infrared
surface temperature
Measuring Surface Temperature• Dial-Type
ThermometerPosition & stabilize for
minimum of 2 minutes
• Thermocouple-Type ThermometersStabilize quickly
• Infrared (non-contact) thermometersWatch distance
Assessing Wind Speed
• Analog wind meters
• Digital wind meters
• Rotating Vane AnemometersAir flow inside
containmentWind speed
Documenting Ambient Conditions and Surface Temperature
ConditionCondition DataDataDateDate 2/23/112/23/11
TimeTime 1300 hours1300 hours
Dry Bulb Temperature (DB)Dry Bulb Temperature (DB) 1616ooC (60C (60ooF)F)
Wet Bulb Temperature Wet Bulb Temperature (WB)(WB)
1313ooC (55C (55ooF)F)
Depression (DB-WB)Depression (DB-WB) 33ooC (5C (5ooF)F)
Relative HumidityRelative Humidity 73%73%
Dew Point TemperatureDew Point Temperature 1111ooC (51C (51ooF)F)
Surface TemperatureSurface Temperature 1515ooC (59C (59ooF)F)
Wind SpeedWind Speed 11 km/Hr (7 mph)11 km/Hr (7 mph)
Measurement LocationMeasurement Location West side of tank, ground West side of tank, ground levellevel
Verification of Accuracy - Thermometers• ASTM E 337• Remove wick from
thermometer• Compare dry & wet bulb
temperatures quarterly• Compare thermometers
to a traceable thermometer in controlled environment at minimum of 4 temperatures annually
Calibration of Electronic Psychrometers• Some manufacturers
provide “Calibration Kits”Used to verify
accuracy only
• Annual calibration by the manufacturer or approved laboratory recommended
Verification of Accuracy – Surface Thermometers• No “Standard” method• Equipment manufacturers
provide instruction• Surface probes integral to
electronic psychrometers are calibrated by the manufacturer
• Compare thermometers to “Traceable” thermometer in controlled environment
Determining Conformance to Project Specifications
• Compare actual conditions to project specification requirements
• Example:Air temperature: 50-110oFRelative humidity: < 85%Surface temperature: 50-
120oF and a minimum of 5oF higher than dew point temperature
Wind speed: < 15 mph
Determining Conformance to Product Data Sheets
• Compare actual conditions to manufacturer’s recommendations
• Example:Air temperature: 35-110oFRelative humidity: < 95%Surface temperature: 35-
120oF and a minimum of 5oF higher than dew point temperature
Wind speed: Typically not addressed
Location and Frequency of Data Acquisition• Location
Dictated by where the work is being performed (e.g., inside vs. outside of a containment; balcony of elevated storage tank vs. ground level)
If interior, with ventilation in operation
Shops: Blast or Paint bay area
• FrequencyPrior to final surface
preparationPrior to mixing of
coatingsFour-hour data
collection intervals is common
More frequent measurement if conditions are changing
Achieving Conditions by Changing the Environment• Heat
Achieve & maintain temperature during application & cure
Indirect fired propane AC powered equipment
with thermostatic controls
Ventilation to exhaust solvent vapors is critical
Dehumidification
• Dehumidification (DH) equipment removes air moisture, reducing opportunity for condensation
• Conditions monitored using computer software (component to DH equipment) or by manual measurements
• SSPC/NACE Joint Technical Report– SSPC-TR3/NACE 6A192, “Dehumidification and
Temperature Control During Surface Preparation, Application and Curing for Coatings/Linings of Steel Tanks, Vessels and other Enclosed Spaces”
Dehumidification, con’t.
• DH accomplished by: Compression Refrigeration Desiccation (liquid or solid sorption) Combination of methods listed Refrigeration and desiccation (solid
sorption) most common for field work
Dehumidification, con’t.
• RefrigerationAir cooled over
refrigeration coilsCondensation
occurs on coils and is collected
Dry air exits the DH system (at reduced temperature, humidity and dew point)
Source: SSPC-TR3/NACE 6A192
Dehumidification, con’t.• Desiccant
Air passed over/through granular beds or fixed desiccant structures
Desiccant (silica gel or lithium chloride) is active and dehydrated (low vapor pressure)
Desiccant absorbs moisture from air. Hydration reaction causes exothermic reaction (heated air), so may be used with refrigeration-type DH
Source: SSPC-TR3/NACE 6A192
Achieving Conditions by Changing the Environment• Humidification
May be required for moisture cure coatings
Moisture generated by wetting down floors or dampening the applied coating after initial drying
Summary
• During this webinar, we have: Reviewed commonly monitored conditions during
surface preparation and coating work Described the instrumentation used to measure
environmental conditions, including methods of calibration and accuracy verification
Illustrated documentation procedures Described the importance of determining conformance
to project specifications and/or manufacturer’s PDS Described the location and frequency of data
acquisition Described three methods to altering the environment,
in order to achieve conformance
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