Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Ambient Conditions For Surface Preparation

Last updated: January 11, 2019

What Does Ambient Conditions For Surface Preparation Mean?

Ambient conditions for surface preparation refer to the prevailing air and surface temperature, relative humidity, and the dew point of the environment in which the preparation process is taking place. An optimal surface preparation depends on the ambient conditions and is essential for a long-lasting and durable coating that offers maximum corrosion protection performance.

It is therefore important to determine the conditions before the preparation and monitor them throughout the preparation and coating process to ensure strong adherence between the surface and coating.


Corrosionpedia Explains Ambient Conditions For Surface Preparation

The surface preparation and the coating process should be carried out within the range of ambient conditions recommended by the manufacturer. The conditions that can affect and impair the coating or painting process include extremely high or low temperatures, dust, strong winds, rain, leakage of water or steam, and air pollution.

Determining the ambient conditions is important, particularly when the weather keeps on changing as the work progresses. The five main ambient conditions that should be determined include:

  • Surface temperature – must be at least 5°F (3°C) above the dew point temperature of the surrounding air.
  • Air temperature – should be within the manufacturer's recommendation and not below 40°F (4.5°C) degrees
  • Relative humidity (RH) recommended at 85%.
  • Dew point temperature – this is the temperature at which moisture will start condensing on the surface and is a function of the relative humidity and air temperature.
  • Difference between the dew point and surface temperatures – moisture is likely to form if they are too close or equal; the recommended value is at least 5°F (3°C).

There are both electrical and mechanical measuring devices that are used to measure these conditions. Air temperature is determined using either a mercury thermometer or the electronics digital thermometers, while the relative humidity is determined using the psychrometer. The digital instruments are simple and provide faster and more accurate measurements compared to the mechanical methods. In addition, these can be available in all-in-one instruments, and capabilities include alarms that alert when the surface and dew point temperatures are too close.

Most coatings will not cure properly at a high RH, low temperature, or in dusty or rainy environments. The surface moisture affects the life and performance of the coatings and may arise due to the extreme environmental conditions. If the preparation or coating is done outside the recommended limits, the quality of the coating will reduce and affect the long-term performance.


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