5.ambient conditions
DESCRIPTION
paintTRANSCRIPT
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
AMBIENTCONDITIONS
HumidityAir Temperature
Substrate Temperature
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Parameters influencing the corrosion speed.Atmospheric corrosion
Humidity Temperature Concentration of salts Amount of air pollution,
including acid rain, soot and dust particles
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Atmospheric corrosion rate depends onhumidity
Relative Humidity, %
Corrosion rate
0 20 40 60 80 100
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Surface temperature of the
structure must be minimum
3 C above the dew point
of the surrounding atmosphere
Atmospheric conditions.Atmospheric conditions.Requirement during blasting and paintingRequirement during blasting and painting
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
B-24/2-4
4847-693
ISO 8502 - 4Estimating probability of condensation
Cold liquid inside hull and warm air outside causescondensation
See how frames inside keeps the cold longer
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Why Temperature & Humidity areimportant
Frozen overnightcondensation, followsthe frames of the ship
Condensation follows the contoursof the double-bottom tank
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Temperature of substrate shouldbe at a temperature of
min. 3oC
above dew point of the air in thevicinity
Main rule for pre-treatmentand paint application:
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Measuring ambient conditions
Electronic multi-function gauge
Electronic humidity gauge
Sling Psychrometer (SlingHygrometer, Dry and Wet bulb)
(Hair hygrometer, not suitable!)
Dew point calculator
Steel thermometer
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Needs frequentcalibration.
Dependent onbatteries
Multi-functionmodels will measureair temperature,surface temperature,relative humidity,and calculate dewpoint and T (*)
(*) difference between dew point andsurface temperature)
Electronic humidity gauge
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
A dry and a wet thermometer put together inone unit.
The difference in the measured temperaturesindicate the amount of humidity:
Large difference = low RH%
Small or none = high RH%
Sling Psycrometer
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
ISO 8502-4Measuring the relative humidity
Photo: SlingPsychrometer formeasuring:
- Dry temperature- Wet temperature
Measure thetemperature in thevicinity.
Calculate the relativehumidity
Use together with dewpoint calculator
Cd-4932-88
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
ISO 8502-4Dew point calculator
For calculation of dewpoint
To be used together withsurface temperaturethermometer and slingpsychrometer.
Use this frequently duringpre-treatment, applicationand drying of the paint.
Recommendation: Every 6hours and when weatherconditions are changing
Cd-4932-89
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
1. Air temperature2. % Relative humidity3. Steel temperature4. Dew point
ISO 8502ISO 8502 -- 44HumidityHumidity
Guidance on the estimation of the probabilityof condensation prior to paint application
Steel temperature min. 3 oC above the dew point
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Contact thermometer
Electronic instrument for measuring the steeltemperature
Other types of thermometers are also available. E.g.magnetic thermometers
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Ambient conditions, general
Painting should not be started when:
The relative humidity exceeds 85% (unlessthe paint manufacturer consider it safe)
The substrate temperature is less than 3oC above the dew point
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Ways to control the climatic conditions
Dehumidifier, reduces the actual humidityin the surroundings
Heather, heat the objects (surfaces) priorto application in order to reduce thedanger for condensation.
Forced ventilation is a must in order tosecure a proper evaporation of thesolvents from the paint film.
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Ambienttemperature willinfluence: shelf life (storage) potlife (two-pack
paints: time betweenmixing and no longeruseable)
induction time (pre-reaction beforeapplication)
viscosity/sprayability
Steel Temperature
Ambient Temperature and Steel Temperature
Is the temperature important ? YES !
Steel temperaturewill affect: probability for
condensation solvent evaporation speed of cure (drying
time) degree of cure recoating interval service life of the
coating
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Ventilation. Good practice
Solvent vapoursare heavier
than air
Suction fromlowest points
in enclosed areas
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Ventilation. Bad practice
Solvent vapour Solvent vapour
Using an inlet fan Using an exhaust fan
Air flow Air flow
Air out
Solventvapours Air i
n
Inlet fan, air through pipe
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Control of relative humidityand temperature
Check the atmosphericconditions before thework starts
If required: Installproper ventilation
Check the atmosphericconditions while thework is ongoing andduring drying / curing
Paint technology: Humidity_control1
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Temperature and humidityof air used for drying.
Supply of heated air immediately after applicationmay lead to skin drying and entrapped solvents
Cold air will keep the film open longer and ensureproper evaporation
Avoid high air temperature (especially epoxy) High humidity will slow down the drying time Exhaust from heating equipment using propane or
paraffin oil contain water and Carbon dioxide andmay create Amine sweating
-
Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007
Blisters inside a tank due to poor ventilation.Entrapped solvents
Blisters sometimecontain water
Rust will not be formedinside intact blisters, dueto the high pH
As soon as the blistersbreak corrosion will start
Use cathodic protectionto back up the paintsystem.
Cd-4934-68