Inspection of Lining Application in Steel and Concrete Equipment – NACE SP0288
Inspection Equipment – Section 3
Inspection equipment commonly used by the inspector for inspecting lining application includes the following:
Psychrometer (sling or automatic fan type)
National Weather Service relative humidity-psychrometric tables
Surface thermometer
Inspection Requirements – Section 4
Application of Lining Material
The substrate, ambient, and lining material temperatures shall be verified to be within the range agreed to at the pre-job conference or as specified by the lining material manufacturer. The humidity shall be measured, and the dew point determined.
Standard Guide for Painting Inspectors (Metal Substrates) – ASTM D3276
Weather Considerations – Section 7
Drying—Temperature and relative humidity limitations presented in the specification or manufacturer’s product data sheet are mandatory. Environmental conditions such as temperature and relative humidity can affect the cure of most
coatings.
Low Temperature—Many specifications indicate temperature limits between which painting may be undertaken.
High Temperature—The maximum reasonable surface temperature for application is 50°C (125°F) unless clearly specified otherwise.
Moisture—Painting should not be performed in rain, snow, fog, or mist, or when the temperature of the surface is less than 3°C (5°F) above the dew point.
Wind—The wind direction and velocity should be considered when applying coatings in areas where airborne overspray could damage automobiles, boats, and structures nearby.
Inspection Equipment – Section 10
Thermometers—The paint inspector may need several types of thermometers and should have at least an accurate pocket thermometer with a range from about −18 to 65°C (0 to 150°F) for measuring the air temperature. Flat surface temperature thermometers are also available for measuring the substrate temperature, as in an infrared gun.
Relative Humidity and Dew Point—A psychrometer containing a wet and dry-bulb thermometer for determining relative humidity and a dew point chart is a useful inspection tool. Hand-held sling or electrical types are available as well as a direct-reading digital type. Atmospheric conditions, including air temperature, relative humidity, dew point, and surface temperature should be measured and recorded at the location where work is being performed.
Dehumidification and Temperature Control During Surface Preparation, Application, and Curing for Coatings/Linings of Steel Tanks, Vessels, and Other Enclosed Spaces – SSPC-TR 3/NACE 6A192
Refrigeration
The cooling of air to below its dew point is an economical method of dehumidification. This method is commonly used at ambient temperatures of approximately 85°F (29°C) and high humidity. Ambient air is circulated over a system of refrigeration coils. The surface temperature of the coils is set at temperatures considerably lower than the temperature of the incoming ambient air. As the air cools, it reaches saturation, and condensation forms. This condensation is collected and removed from the system. The air exits the cooling-coil section of the dehumidifier at a reduced temperature, dew point, and absolute humidity. This refrigeration-based dehumidification system is illustrated in Figure 1. The cooler air, which has a lower dew point, can then be reheated to lower the relative humidity.
Refrigeration is often used to pre-cool and dehumidify inbound air before it reaches a desiccant system in order to obtain lower dew points after desiccation. The air can be re-cooled, if necessary, by refrigeration.
Desiccant
Solid-sorption dehumidification systems utilize either granular beds or fixed desiccant structures. These structures are contained within machines through which an air stream is passed. The desiccant used is in an active, dehydrated state and has a vapor pressure below that of the air to be dehumidified. The most commonly used desiccants are silica gel and lithium chloride. Air is passed through beds or layers of the desiccant, which absorb moisture from the air stream, producing a hydrated salt. Regeneration of the hydrated salt is accomplished with heated air, which drives off the water of hydration, returning the sorbent to its dehydrated state. The previously sorbed moisture is diverted to a separate air stream.
The exothermic hydration reaction typically raises the temperature of the exiting air stream by 10 to 15°F (6 to 8°C). Therefore, in hot climates, refrigeration-type dehumidifiers are frequently used in combination with desiccant equipment to cool the air entering the space. A typical desiccant dehumidification system is illustrated in Figure 2. Because this type of system absorbs moisture as vapor, it is commonly used at all temperatures and levels of humidity.
NACE SP0288-2011 (formerly RP0288) Inspection of Lining Application in Steel and Concrete Equipment
ASTM D3276-15e1, Standard Guide for Painting Inspectors (Metal Substrates), ASTM International, West Conshohocken, PA, 2015, www.astm.org
SSPC-TR 3/NACE 6A192 (2000), Dehumidification and Temperature Control During Surface Preparation, Application, and Curing for Coatings/Linings of Steel Tanks, Vessels, and Other Enclosed Spaces
SSPC-Guide 6 (2015) Guide for Containing Surface Preparation Debris Generated During Paint Removal Operations, SSPC: The Society for Protective Coatings, Pittsburgh, PA, 2015, www.sspc.org
SSPC-Guide 12 (2016) Guide to Illumination of Industrial Coating Projects, SSPC: The Society for Protective Coatings, Pittsburgh, PA, 2016, www.sspc.org