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