Rolling induction preheating for roll-welded pipe
Preheating pipe before welding can be a cumbersome, tedious task. A new technology, rolling induction heating, addresses some of the concerns associated with other heating methods.
It’s well-documented that preheating pipe before welding can save time and money by reducing the potential for a failed weld. Preheating is standard for meeting code and quality requirements when the pipe is chrome alloy, more than 1 in. thick, or stored in environments colder than 50 degrees F.
It also is common in fabrication shops to rotate the pipe while welding, a practice that eliminates out-of-position welding, reduces welding operator fatigue, and improves productivity via high wire feed speeds and increased deposition rates.
The various preheating methods all have benefits and drawbacks. However, rolling pipe while welding limits the options that can be used to successfully preheat, maintain preheat temperatures, and adhere to interpass temperatures.
A new technology — rolling induction heating —builds on the advantages of rolled pipe welding while also addressing some of the concerns associated with other popular heating methods, such as open flame and resistance heating.
What Is Induction Heating?
Induction heating has been around for decades, but in the past, it wasn’t easily applied to roll-welded applications because of heating cables that had to be wrapped around the pipe. Rolling induction heating technology features an inductor that sits on the pipe and does not interfere with the rotation of the pipe. The inductor operates on a standard pipe stand and connects to a specified power source.
As with standard induction heating, this new technology uses a noncontact method of quickly heating conductive metals by inducing current into the part.
Induction does not rely on a heating element or flame to transfer heat. Instead, an alternating current passes through the device, creating a magnetic field around it. As the magnetic field passes through the conductive workpiece, it creates eddy currents within the part. The resistance of the metal fights against the flow of the eddy currents, generating heat in the part. The part becomes its own heating element, heating from within, which makes induction very efficient because little heat is lost in the process.
Productivity and Ease of Use
The rolling induction technology is designed for quick setup. It’s easy to move or reposition the inductor.
The hinged arm and rolling inductor mount on a standard pipe stand, which allows the welder to align the induction head on the pipe. The power source recognizes the attachment, so only the maximum output and time parameters need to be set.
Induction heating brings the part to temperature quickly and holds the machine at a steady output, making it an efficient option for getting consistent temperature levels.
Workplace safety and workers’ compensation costs are major concerns for employers, with burn injuries and fatalities among the most common safety issues in the workplace. Fires and explosions were the sixth most common cause of death on the job in 2012, causing 116 workplace fatalities that year, according to preliminary data from the Bureau of Labor Statistics.
Because no open flame is involved, induction heating is a safe method that can reduce the potential for burns. The heat generates within the part, which eliminates heat transfer and helps create a safer environment for the welding operator. Also, since there is no need to use and store explosive gases with induction heating, it eliminates potential explosion hazards.
Worker fatigue and comfort also are considerations. The efficiency of induction heating — less heat is lost into the air in the surrounding area — means it often results in a more comfortable environment that can help reduce operator fatigue.
Induction heating generates little fume, smoke, and noise, which also contributes to a comfortable environment and can promote safety for the welding operator and others working in the area.
Maintaining consistent temperatures is critical, particularly when welding today’s high-strength steels. It’s important to have a heating method that maintains a consistent temperature in the part and allows welding operators to check and adjust the temperature easily.
Rolling induction technology provides steady output as the pipe rolls and ensures consistent heating throughout the part, reducing hot and cold spots. It provides a maximum preheat temperature of 600 degrees F in rolled applications, and it can preheat pipe 8 in. and greater in diameter. Multiple systems can be used to heat larger diameters.
While the initial investment in rolling induction heating is higher than the cost of other heating methods, it’s important to consider the return on the investment over the life of the equipment. It’s an efficient technology and, therefore, often is less expensive to operate on a per-hour basis. Productivity gains and safety benefits also are important cost considerations.
Induction heating requires electricity, which is an ongoing cost for using the process. It does, however, eliminate the need to purchase consumables, such as gas.
While rolling induction is exclusive to the preheating process, the power source it connects to is compatible with other accessories and tools. Welders can use the equipment for other functions, such as hydrogen bake-out, shrink-fit, and postweld heat treatment, thereby increasing versatility and the value of the investment.
It’s important to consider the safety, quality, and environmental issues associated with the various preheating methods. As an increasing number of jobs require electric preheat, the ability to use induction heating while welding rolled pipe can provide a viable alternative for fabrication shops.