Paints and coatings provide an essential barrier to protect industrial equipment from corrosive environments and extend their safe operating life. Yet, regardless of whether one is talking about storage tanks, offshore vessels or specialty tools and equipment, forming a robust and reliable barrier is about more than simply applying a coat of paint.
An important part of the process is to provide and maintain the right temperature to allow the paint to cure. In a field situation, low ambient temperatures complicate this process during refurbishment jobs in winter months. (In the northern United States, temperatures may stay well below freezing throughout the process.) In some regions, notably along the U.S. Gulf Coast, high humidity levels in the source air may necessitate the use of dehumidifiers to dry the air prior to heating it and introducing it to the vessel.
Industrial heating providers have responded to these challenges by developing a range of temporary heating systems that can meet the size and complexity of any curing application. Coupled with customizable temperature sensing and control systems, these heating solutions help ensure more uniform and efficient curing of coatings and paints in a range of ambient conditions — from cold to hot temperatures and from humid to dry climates.
Customizing Industrial Curing Systems Through Collaboration
Without a thorough understanding of the field conditions, the end use of the equipment and the owner’s expectations and requirements, the curing operation may not proceed as efficiently as possible. In a tank curing application, for example, if the heating solution raises the temperature in the vessel too quickly or above a desired range, the risk of non-uniform drying increases. The top surface of the paint layer may dry faster than the paint closer to the tank wall, resulting in the formation of a skin that slows the drying process. Conversely, too low a curing temperature raises the risk that the coating will cure too slowly, adding time and cost to the refurbishment process and extending the time to bring the vessel back into service.
Avoiding situations like these can only be accomplished through upfront communication and collaboration between the heating provider, the tank owner and, in many cases, the paint suppliers and contractors. Such collaboration will uncover important factors, including the size and thickness of the tanks, the presence or absence of insulation around the tanks, and the location and number of entry points and ventilation ports. If the tanks are located in high wind areas, it may be necessary to build some barrier around the tank to protect it from the wind.
The paint supplier must share the specifications and general composition of the coating to be applied, which will dictate the target temperature range for efficient curing. The type of heating is also a major consideration. In many cases, electric heat is preferred over propane-supplied heat because propane may introduce significant moisture that would hinder the curing process. Propane heat also introduces air quality concerns in enclosed areas where workers are present.
Deploying the Right Heating Solution for Curing Industrial Coatings
Once this background information has been collected and all parties are fully informed of the heating requirements for the application, the heating provider can deploy the most efficient solution. A rental heater with sufficient power can be deployed to the site and hooked to the tank via ductwork.
Temperature sensors are then affixed to various locations around the tank, with the number of sensors dictated by the size of the tank. During tank refurbishment operations when work crews are present (such as grinding out of old paint), the heating system pulls fresh air and heats it to a comfortable temperature range. The temperature sensors continuously monitor the interior temperature of the tank and relay this information to the thermostat on the heater. This allows the heater to regulate a safe and comfortable temperature for the work crews.
Once the new coating has been applied, the heater ramps up the temperature inside the tank to the desired range for the curing process. Once again, the temperature sensors relay real-time information back to the heater’s thermostat and control system. The control system then lowers or raises the output of the heater to keep the interior of the tank within the predetermined temperature window for optimal curing.
Case in Point: In-Field Curing for Wind Turbine Blades
The need for efficient in-field solutions is not limited to industrial tanks. For example, North American operators of large wind turbine farms also require a repair and coating solution that can be carried out efficiently in the field. After a decade in service, the turbine blades can exhibit coating failures and stress-related cracking. Due to the size of the blades — each one can be up to 150’ in length depending on the turbine — the operators can not transport the blades to an offsite repair facility without incurring significant transportation costs and risks of further damage to the blades during transport.
Further complicating the issue of in-field curing, many of these refurbishment operations are conducted in the northern United States, where ambient temperatures of -15 to -25°F (-26 to -31°C) are common during the winter months. An in-field, mobile heating solution that can be rigged up right next to a turbine and allow for safe and efficient refurbishment was developed.
The process was first carried out for a wind farm operator in Minnesota. Electric heating and power generation equipment was brought in on a trailer right next to the turbine. The blades were lowered to the ground. Heating ducts were introduced through the nose cone and split off into three sections, one for each blade.
Work crews then entered the three blades to grind off the old fiberglass coating and apply a new fiberglass treatment. During this time, the mobile generator supplied power to the heater (which maintained a comfortable temperature of approximately 77°F (25°C) for the work crews in each blade) and also powered the grinding equipment, lighting and other tools.
Once the new fiberglass had been applied and the workers exited, the blades were wrapped in cement blankets and the heater increased the internal temperature of the blades to approximately ins 190°F (88°C). This heating solution maintained the desired curing temperature for 8 to 12 hours, allowing each blade to be repaired in-field and bringing the turbines back online in a shorter period of time, with lower repair costs.
This mobile power generation and heating solution has since been conducted at other wind farms in Minnesota, Iowa, Oklahoma, Illinois, Texas and upstate New York, with similar results. Mobile power and heating was set up in tents, just outside a manufacturing facility, where workers would apply fiberglass coatings to both the inside and outside surfaces of each blade and cure them at a sustained 190°F temperature, using a steady supply of safe electric heat.
This mobile system was also deployed to repair blades entering the Port of Houston by ship. Racks containing up to 12 blades were treated with fiberglass and cured at the same time, using a combination of dehumidifiers to dry the ambient humid air and heaters to heat the air to the 190°F target temperature.
The applications described in this article are but a few examples of how mobile power and heating solutions help mitigate the operational hazards and costs associated with in-field equipment repair, painting and curing. The ultimate benefit of these turnkey systems can only be realized by partnering with a provider with the right technical, engineering and project management expertise to execute a customized solution.
Editor's Note: This article was published in the August 2015 issue of Process Heating with the headline, "Driving Curing Efficiency."