Preparing a Coating Inspection Plan
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Transcript Preparing a Coating Inspection Plan
Monitoring Environmental
Conditions for Cleaning &
Painting Operations
William D. Corbett
KTA-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 monitored
during surface preparation and coating work
Describe the instrumentation that is commonly used to
measure environmental conditions
Document environmental conditions
Compare on-site conditions to specification requirements
Describe the frequency and location of measurements
Describe methods for altering the environment to attain
conforming 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 Temperature
Too cold or too hot can affect coating application &
curing
• Relative Humidity
Too damp or too dry can affect coating application
& curing
• Surface Temperature
Too 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 Speed
Too 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 Instruments
Sling Psychrometers*
Battery-powered
Psychrometers*
Electronic
Psychrometers
Analog, Thermocoupletype & 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°F
Depression wet bulb thermometer: 5°F
Dew Point temperature: 51°F
Determining Relative
Humidity
Example:
Air temperature: 60°F
Depression wet bulb thermometer: 5°F
Relative Humidity: 73%
Relative Humidity and Dew
Point Calculators
1.
2.
3.
4.
5.
Convert oF to oC using right
“window”
Align dry bulb & wet bulb
temperatures (top of
calculator)
Read Dew Point from upper
“window”
Align dry bulb & dew point
temperature (bottom of
calculator)
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 Thermometer
Position & stabilize for
minimum of 2 minutes
• Thermocouple-Type
Thermometers
Stabilize quickly
• Infrared (non-contact)
thermometers
Watch distance
Assessing Wind Speed
• Analog wind meters
• Digital wind meters
• Rotating Vane
Anemometers
Air flow inside
containment
Wind speed
Documenting Ambient Conditions
and Surface Temperature
Condition
Data
Date
2/23/11
Time
1300 hours
Dry Bulb Temperature (DB)
16oC (60oF)
Wet Bulb Temperature (WB)
13oC (55oF)
Depression (DB-WB)
Relative Humidity
3oC (5oF)
73%
Dew Point Temperature
11oC (51oF)
Surface Temperature
15oC (59oF)
Wind Speed
Measurement Location
11 km/Hr (7 mph)
West side of tank, ground level
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: 50-110oF
Relative humidity: < 85%
Surface temperature: 50120oF 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: 35-110oF
Relative humidity: < 95%
Surface temperature: 35120oF 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
• Frequency
Prior to final surface
preparation
Prior to mixing of
coatings
Four-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.
• Refrigeration
Air cooled over
refrigeration coils
Condensation
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 refrigerationtype 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 END