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

Sling Psychrometer

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•Dehumidification•Humidification

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

Monitoring Environmental Conditions for Cleaning & Painting

Operations

THE ENDTHE END