Chapter 5 Environmental Conditions Flashcards
- High humidity in the air during coating application can cause which of the following:
A. Solvent entrapment
B. Rapid solvent evaporation
C. Solvent combustion
D. Shorter induction times
The correct answer is:
A. Solvent entrapment
High humidity can cause moisture to condense on the substrate or mix with the coating, leading to improper curing and solvent entrapment. This can result in defects such as blistering, poor adhesion, and reduced coating performance.
- Which of the following conditions are not suitable for coating application?
A. Surface Temperature of 16°C (60°F) and a Dew Point of 11°C (52°F)
B. Surface Temperature of 18°C (64°F) and a Dew Point of 16°C (60°F)
C. Surface Temperature of 16°C (60°F) and a Dew Point of 9°C (48°F)
D. Surface Temperature of 20°C (68°F) and a Dew Point of 16°C (60°F)
B. Surface Temperature of 18°C (64°F) and a Dew Point of 16°C (60°F)
Coating applications require the surface temperature to be at least 3°C (5°F) above the dew point to prevent condensation and ensure proper adhesion. In this case, the difference between the surface temperature and the dew point is only 2°C or 4 Degrees Farenheit
(64°F - 60°F), which is insufficient and can result in moisture on the surface, leading to coating defects.
In general, the Relative Humidity should be below what level for coating operations to
continue?
A. 75%
B. 85%
C. 95%
D. 100%
The correct answer is:
B. 85%
In general, coating operations should not proceed when relative humidity exceeds 85%. High humidity increases the risk of moisture condensation on the substrate, leading to poor adhesion, improper curing, and potential defects like blistering or delamination. Always follow manufacturer specifications, but 85% is a common industry limit.
Where should environmental conditions be measured?
A. Every four meters
B. At the highest point on the structure
C. Only in the coolest areas on the structure
D. Where the work will be performed
The correct answer is:
D. Where the work will be performed
Environmental conditions, including temperature, humidity, dew point, and surface temperature, should be measured at the actual location where the coating application is taking place. This ensures that the conditions are suitable for proper adhesion and curing of the coating. Conditions can vary across different parts of a structure, so multiple measurements may be necessary.
- You are an inspector on a jobsite. The air temperature is 28ºC (84ºF), your relative humidity is
below 85% and your steel temperature is 26ºC (79ºF). Which of the following is the highest
acceptable dew point for coating work to continue?
A. 29ºC (85ºF)
B. 28ºC (84ºF)
C. 26ºC (79ºF)
D. 23ºC (74ºF)
The correct answer is:
D. 23ºC (74ºF)
For coating work to continue, the steel temperature must be at least 3°C (5°F) above the dew point to prevent condensation and ensure proper adhesion.
Given that the steel temperature is 26°C (79°F), the highest acceptable dew point would be:
26°C - 3°C = 23°C (79°F - 5°F = 74°F)
Any dew point higher than 23°C (74°F) would risk condensation forming on the surface, which could lead to coating failure.
Identify some of the defects that can be caused by incorrect application temperatures.
Incorrect application temperatures can lead to several coating defects, including:
Solvent Entrapment – If the temperature is too low, solvents may not evaporate properly, leading to bubbles, blisters, or pinholes in the coating.
Poor Adhesion – If the substrate is too cold, condensation can form, preventing proper bonding of the coating to the surface.
Cracking – Applying coatings at high temperatures may cause rapid drying, leading to stress in the coating and cracking.
Orange Peel Texture – Uneven drying due to improper temperature control can result in a rough, textured finish.
Sagging and Runs – High temperatures can lower the coating’s viscosity, causing it to become too fluid and creating drips or runs.
Chalking – Excessively high temperatures during curing can accelerate oxidation, leading to a powdery surface over time.
Brittleness – If the coating cures too quickly due to high temperatures, it can become brittle and more prone to mechanical damage.
Extended Drying or Curing Times – Low temperatures can slow the curing process, leading to extended downtime and potential contamination before full cure.
Describe relative humidity.
Relative Humidity (RH) is the amount of water vapor in the air compared to the maximum amount the air can hold at a given temperature, expressed as a percentage.
Key Points:
Higher temperatures allow the air to hold more moisture, while lower temperatures reduce its capacity.
When RH reaches 100%, the air is fully saturated, leading to dew formation and condensation on surfaces.
In coating applications, high RH (above 85%) increases the risk of condensation, leading to poor adhesion, blistering, and improper curing.
Low RH can cause coatings to dry too quickly, resulting in defects like cracking or improper film formation.
What is the dew point temperature?
The dew point temperature is the temperature at which air becomes fully saturated with moisture (100% relative humidity) and condensation begins to form on surfaces.
Key Points:
When air cools to its dew point, it can no longer hold all its moisture, causing water droplets (condensation) to appear.
The closer the air temperature is to the dew point, the higher the risk of condensation forming on surfaces.
In coating applications, the steel temperature must be at least 3°C (5°F) above the dew point to prevent moisture from affecting adhesion and curing.
Dew point is influenced by air temperature and relative humidity—higher humidity increases the dew point.
Proper dew point monitoring is crucial to prevent coating failures like blistering, poor adhesion, and solvent entrapment
Like any process on a coating project, the required ambient conditions will be specified
within the guidance documents.
Review the specification excerpt and then answer the questions.
Specification - Ambient Conditions
The pipe surface temperature, at every point where coating will be applied, shall be greater than
10°C (50°F) and a minimum of 3°C or 5°F above the dew point temperature. Relative humidity
shall be less than 85%. The maximum steel surface temperature shall be 40°C (104°F).
The relative humidity, the steel surface temperature, curing temperature shall be within the
limits recommended by the coating manufacturer. This process shall be monitored, and the
values recorded at least once every three hours.
A. Identify the required:
i. Surface Temperature
ii. Dew Point
iii. Relative Humidity
B. How often do the conditions need to be monitored and documented?
C. Does the specification contain all the information the inspector needs to monitor the
ambient conditions?
A. Required Ambient Conditions
i. Surface Temperature:
Must be greater than 10°C (50°F)
Must be at least 3°C (5°F) above the dew point
Cannot exceed 40°C (104°F)
ii. Dew Point:
The dew point must be measured, and the steel temperature must be at least 3°C (5°F) higher than the dew point.
iii. Relative Humidity:
Must be less than 85%
B. Frequency of Monitoring and Documentation
Ambient conditions must be monitored and recorded at least once every three hours.
C. Does the Specification Contain All the Information the Inspector Needs?
Partially. The specification outlines basic environmental requirements, but the inspector may need additional information from:
The coating manufacturer’s product data sheet, which specifies ideal temperature, humidity, and curing conditions.
Job-specific guidelines that may require more frequent monitoring or additional parameters.
Project scope documents for any additional quality control requirements.
Thus, while the specification provides essential limits, the inspector should also refer to manufacturer recommendations and project-specific guidelines for complete inspection criteria.
Name some of the effects wind may have on a coatings project.
Wind can have several effects on a coatings project, including:
Overspray and Contamination – Wind can carry paint particles away from the intended surface, causing overspray and affecting nearby equipment, workers, or the environment.
Uneven Application – High wind speeds can cause uneven coating distribution, leading to thin spots or dry spray, which reduces the coating’s effectiveness and durability.
Premature Drying – Wind accelerates solvent evaporation, which can cause poor film formation, adhesion issues, and defects like orange peel or dry spray.
Dust and Debris Contamination – Wind can blow dust, dirt, and debris onto wet coatings, leading to surface contamination and poor finish quality.
Difficult Environmental Control – Maintaining humidity, temperature, and dew point conditions becomes harder in windy conditions, potentially causing moisture-related coating failures.
Worker Safety Hazards – Strong winds can pose safety risks for applicators working on scaffolding or lifts, increasing the risk of falls, spray drift, or loss of control over application equipment.
Mitigation Strategies:
Use wind barriers or enclosures around the work area.
Monitor wind speed and direction, stopping work if conditions exceed safe limits.
Adjust spray techniques or switch to brush/roller application if needed.
Schedule coating application for periods of lower wind activity.
Based on the given air and surface temperature and relative humidity, what is the lowest
acceptable dew point for abrasive blasting to commence?
Ambient Temp is 84F
Relative Humidity is 84%
Surface Temperature is 79F
To determine the lowest acceptable dew point for abrasive blasting to commence, we need to follow the 3°F (5°C) rule, which states that the surface temperature must be at least 3°F (5°C) above the dew point to prevent condensation.
Step 1: Find the Dew Point Using a Dew Point Chart or Formula
Using standard dew point calculations, with:
Ambient Temperature = 84°F
Relative Humidity = 84%
The estimated dew point temperature is 79°F.
Step 2: Apply the 3°F Rule
Since the surface temperature is also 79°F, it is equal to the dew point, meaning condensation can occur, and abrasive blasting should not commence under these conditions.
Step 3: Determine the Lowest Acceptable Dew Point
For abrasive blasting to begin, the dew point must be at least 3°F lower than the surface temperature:
Surface Temperature = 79°F
Required Dew Point = 79°F - 3°F
Lowest Acceptable Dew Point = 76°F
Final Answer:
The lowest acceptable dew point for abrasive blasting to commence is 76°F. If the dew point is higher than 76°F, the risk of condensation increases, and blasting should not proceed.
