The technology of removing coatings by heat induction was developed by Tom Arne Baann and Bjorn Erik Alveberg of Norway in 1996.1 A ship owner had challenged them to remove bacteria from the steel surfaces of a ballast tank. The bacteria were causing serious corrosion problems on the ship.
Their idea was to kill the bacteria by heat. The intention was to kill the bacteria using heat induction without affecting the coating. The heat killed the bacteria, but the coating disbonded and came off in sheets. And so, coating removal by heat induction was born.
This is the story of RPR Technologies AS of Norway that now holds several patents in the field. From that moment, the two inventors started the journey of developing, testing, and battling the obstacles up to where the company finds itself today.
This novel technology is gaining its place and acceptance in the surface treatment industry as a valid and safe technique and an exciting complement to conventional abrasive and hydro-jetting methods. Facility owners and coating contractors are looking for options where the old coating can be removed and disposed of without disturbing ongoing processes and work.
As regulations are getting stricter and disposal costs are going up, it is critical to reduce the disposal volume. As there is no grit or water involved in coating removal by heat induction, only the hazardous material itself needs to be disposed of. Heat induction is sometimes chosen as a method because it is silent. Noise level is often a key factor when working near living quarters on ships and offshore installations.
How Heat Induction Works
An electromagnetic field is created by sending an alternating current through a hand-held induction coil. This electromagnetic field sets up eddy currents in the steel surface, which creates heat. As the steel surface underneath the coating is rapidly heated, the chemical bond between the coating and steel is broken.
Heat induction is a clean, fast, safe, cost-effective, silent, and environmentally friendly way to remove coatings from ferrous substrates. Heat induction can easily remove coatings up to a thickness of 25 mm (1 in). This makes heat induction highly competitive for removing thick coatings and coatings that are hard to remove by other methods. It is common to see production rates three times higher than traditional methods. It is also advantageous in environments sensitive to water and dust.
Heat induction is environmentally friendly, as the coating comes off in easy-to-dispose-of sheets, and no contaminants are being spread. Other work can be conducted as usual while coatings are removed by heat induction. Heat induction does not wear, reduce the thickness of, or otherwise weaken the treated material. Contaminants, such as chlorides, are removed together with the coating.
Coating removal by heat induction is beneficial for projects such as pipeline refurbishment, removal of pipeline coating before pipes are scrapped, storage tank refurbishment, refurbishment of steel bridges, and elevated storage tanks. The method is approved for asbestos removal. Heat induction provides a convenient way of removing rubber linings, fire protective coatings, insulation, as well as thick coatings from a steel surface.
A technology institute conducted a study on the induction disbonder and concluded that the technique saves 75% on the electricity/fuel bill compared to conventional methods.2 When adding the savings in grit and water and the time spent in cleaning up, one is starting to envisage that coating removal through heat induction is very cost-effective. The thicker and harder to remove the coating, the greater the advantage over abrasive blasting and hydro-jetting.
Although the surface profile from the previous paint application is generally preserved, sometimes the surface needs further preparation to achieve the surface profile and cleanliness required by the paint manufacturer. A quick grit sweep typically accomplishes this. Even when such additional tasks are necessary, the heat induction process saves the project time and money.
Hazardous Coating Abatement
Heat induction is useful in removing hazardous materials such as lead paint, polychlorinated biphenyls (PCBs), and asbestos from steel surfaces. The dangerous material is not mixed with grit or water, keeping the volume of hazardous waste down. This makes for significant savings in the cost of collection, transportation, and disposal.
Pipeline Work
Pipelines are an area of application suitable for heat induction for several reasons. The coating is typically very thick and hard to remove by traditional methods such as grit blasting. Pipelines are often located in areas where pollution from the blasting media and the coating being removed is unacceptable. Transportation of blasting media to and from remote work sites is troublesome. Collection, transport, and disposal cost of the grit and coating debris are difficult and expensive.
Conversely, heat induction work is performed from a self-contained truck towing a diesel-powered generator. As the coating comes off in sheets, it is easy to collect and dispose of. The volume of the material for disposal is only a tiny fraction of what is experienced with grit blasting.
Working on a Live Pipeline in Thailand
A buried live gas pipeline of 116 km length in Thailand belonging to the Petroleum Authority of Thailand was refurbished by heat induction (Figure 1). The pipe diameter varied between 610 mm (24 in) and 711 mm (28 in). Trenches of 28- to 30-m (90- to 100-ft) lengths were dug out. In all, ~4,000 trenches were made.
The pipeline had 8- to 12-mm (315- to 470-mils) thick coal tar enamel with asbestos mesh. The coating was removed using ten RPR 1650† heat induction machines. The machines were operated in auto mode, meaning that the power is automatically controlled to avoid overheating the live pipeline. Coating removal by heat induction also ensured that workers and the environment were not exposed to asbestos. Workers were wearing masks to further protect them from asbestos.
The pipeline job started in June 2015, and it took three years to complete. Work was performed 10 months a year, 10 hours per day, six days a week. That is a total of 864 days, 134 m per day. That’s pretty impressive when considering challenges such as reduced excavation pace in areas with dense population, road crossings, and wetlands. Work was also slowed by torrential rain in the monsoon season and sliding trench walls in wetlands.
After removing the coating by heat induction, the pipe was sweep blasted to SSPC-SP 103 and coated with a 2K liquid epoxy.
Project Achievements
- The average coating removal rate was five to six m an hour on the 711-mm pipeline throughout the project.
- No accidents or incidents were reported for the entire project.
- Under normal conditions, it took four days from the start of excavating a trench until it was filled back in.
- The heat induction equipment had minimum wear and tear and required no major repairs during the project.
- The project carried a low cost for disposal, as the material was easily collected, transported, and disposed of.
Disposal of Pipelines
Before one can melt and recycle old pipelines, the protective coating needs to be removed. The coating is easy to remove after the pipeline has been dismantled into easy-to-handle lengths. Pipes can be placed on a roller bed. The coating can then be removed by rotating the pipe while moving the heat induction head along the pipe (Figure 2).
Storage Tanks
Heat induction is most competitive for removing the coating from the bottom of storage tanks (Figure 3). These coatings are usually fiber-reinforced plastic (FRP), which are very tough to remove using conventional methods.
As with most thick coatings, these coatings disbond easily from the steel substrate using heat induction. The method is useful when the entire floor of the tank is being refurbished or when smaller FRP patches need to be removed in the way of steelwork or inspections. The normally handheld transformer/induction head assembly can be fitted to a pushcart for easy operation. Motorized crawlers are also available.
Steel Structures
Steel structures such as bridges and towers in environmentally sensitive spaces are areas where heat induction is a superior method of removing old coatings (Figure 4). Heat induction is useful for structures such as wind turbine towers, both on and offshore.
Heat induction goes well with rope access operations as no forces are pushing the climber away from the work area.
The Kanmon Bridge, Japan
The Kanmon bridge, which connects with Honshu-island and Kyushu-island in Japan, was refurbished using heat induction (Figure 5). The use of grit or water was not allowed due to the risk of contaminating air and water. Heat induction was preferred as the existing coating contained PCBs and lead.
A total area of 20,000 m2 was refurbished. During the entire project, which took less than four months, there was no interruption to the traffic on the bridge.
Before recoating, the surface was blasted with sodium bicarbonate (NaHCO3) to obtain the required cleanliness standard. This is an example of how heat induction works well in combination with other environmentally friendly options such as wet blasting, waterjetting, dry-ice blasting, laser, and NaHCO3 blasting.
These methods are inefficient in removing thick and hard-to-remove coatings by themselves. The bulk of the coating can easily be removed by heat induction while preserving the previous application’s surface profile. The other methods mentioned can be useful in obtaining the surface cleanliness required.
The Eiffel Tower
A demonstration was conducted on the Eiffel Tower in Paris. As can be seen in Figure 6, the coating comes off in large pieces, even in the way of rivets. As heat induction is silent and does not make a mess of any kind, work was performed without affecting visitors to the Eiffel Tower.
Wind Turbine Towers
Wind turbine towers are another example of structures situated in environmentally sensitive areas and lend themselves to heat induction for paint refurbishment. Access to the tall columns, both internally and externally, can be achieved by traditional scaffolding or rope access. Several companies in the wind turbine industry are now utilizing this technology.
Marine
Dry Dockings
During a dry-docking, when hundreds of people are doing several tasks simultaneously, it is essential to use a surface preparation method that does not stop all other work in the area. The grit and dust from grit blasting get into bolts, nuts, ventilation systems, and engines, causing damage to machinery and workers’ health.
Some shipyards are in populated areas. The dust from grit blasting can travel a long distance and affect the environment and health of the population. Heat induction solves these problems.
Voyage Repair
Coating refurbishment can also be performed during a voyage with heat induction, either by the ship’s crew or a riding squad. Note that coating removal by heat induction will, in most cases, be considered hot-work, and the safety of the crew and ship must be considered accordingly.
Offshore
Typical areas of applications on offshore oil rigs include the following:
- Accommodation areas where noise is not permitted
- Anti-skid surfaces on helicopter deck and escape routes
- Fire protective coatings
- Tank linings
The cost of disposal is high as the debris is transported by supply ships. It is therefore essential to minimize the volume of disposal.
Conclusion
Coating removal by heat induction is superior to traditional methods when removing thick or tough coatings. It is exceptional when removing coatings in areas where dust and water are not accepted, in environmentally sensitive areas, and when noise is a concern. Heat induction is also a preferred method of removing hazardous materials such as paints containing PCBs, asbestos, and lead from steel surfaces.
Heat induction is faster, safer, and more energy-efficient than traditional methods. In some cases, final surface preparation is required before applying the new coating.
† Trade name.
References
- T.A. Baann, B.E. Alverberg, private communication, verbal, G. Solhaug (1996).
- I. Lien, M. Berntsen, “Disbond,” Task 4.2, National Institute of Technology Department Environment and Safety, C3STCT-2001-50159, March 2004.
- SSPC-SP 10, “Near White Metal Blast Cleaning” (Pittsburgh, PA: SSPC).