5.ambient conditions

Nguyen Cong Thuan/JPS DNV Vinashin Training/ 2007

AMBIENTCONDITIONS

HumidityAir Temperature

Substrate Temperature


Parameters influencing the corrosion speed.Atmospheric corrosion

Humidity Temperature Concentration of salts Amount of air pollution,

including acid rain, soot and dust particles


Atmospheric corrosion rate depends onhumidity

Relative Humidity, %

Corrosion rate

0 20 40 60 80 100


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


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


Why Temperature & Humidity areimportant

Frozen overnightcondensation, followsthe frames of the ship

Condensation follows the contoursof the double-bottom tank


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:


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


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


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


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


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


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


Contact thermometer

Electronic instrument for measuring the steeltemperature

Other types of thermometers are also available. E.g.magnetic thermometers


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


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.


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


Ventilation. Good practice

Solvent vapoursare heavier

than air

Suction fromlowest points

in enclosed areas


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


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


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


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

5.ambient conditions

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