This article originally appeared in Connector Magazine, Fall 2020 Edition
Erectors can save cost and time by taking this welding technique in-house
Large steel erection projects commonly require heat treatment for welding because of the thick materials used in structural steel construction. Proper implementation is critical; so often this work is outsourced. The perceived level of expertise to perform this work can make the prospect of using in-house personnel daunting. However, most welding contractors are actually fully capable of performing on-site heat treatment operations.
The two primary methods for heat treating metal are preheating and post-weld heat treatment (PWHT). Preheating is the process of heating the base metal to a specific temperature prior to welding to minimize the temperature difference between the welding arc and the base metal. This process helps to reduce internal stresses that occur as substantial temperature differences between the weld and the base metal normalize, which can cause cracking and distortion. Slowing the cooling rate also allows hydrogen to escape from the weld, which minimizes the potential for cracking.
One of our customers was trying to heat 42” diameter pipe using pear burners so that welders could weld out the joints. Our team saw an opportunity to create a solution that would help our customer get the job done much more quickly. To make this in-the-field heating job go faster, we put together a package including a Miller ProHeat 35 induction heating system, a 60kVA generator and a DP25 power distribution panel.
With this setup we were able to get the pipe up to 250 degrees in about 5 minutes. Our customer was able to beat the competition’s target time by over 19 hours and has been asked to quote on other pipeline work for their client. Needless to say they were pleased with the solution and the opportunity for extra work it created.
This portable induction turnkey package is a great way to heat pipes in remote locations. There is less risk to the welders from the hot pipe and the process is much, much faster.
Custom turnkey packages like the one described here are Red-D-Arc’s specialty. Our team of experts has created turnkey solutions to solve challenges in diverse industries including, mining, oilfield, offshore, nuclear and manufacturing. We enjoy helping our clients find new ways to grow their businesses, by combining the latest technology, depth of experience and flexible leasing options that fit their needs.
Remote worksites pose no obstacle. We’ll bring portable generators with enough power for your portable welders, induction heaters, lighting and anything else that needs power.
Pre-weld and post-weld heat treating is critical for many welding operations. Without proper thermal manipulation, welds and heat affected zones can have mechanical properties that are undesirable. Worse yet, inadequate heat treatment can result in cracks and devastating weld failures. While temperature and time are the primary concerns when heat treating a weld, the heating method should also be considered diligently when selecting a process. Induction heating is one of the most popular types of heat treating methods, and rightfully so. The benefits of induction heating are many, and Red-D-Arc has the equipment you need to successfully implement an induction heat treating operation for your projects.
What is Induction Heating?
Induction heating is a heat treating process that, when used properly, can alter the mechanical properties of a weld and its adjacent base metal in a way that meets the demands of the application in which the weld is being used. Induction heating relies on the science of electromagnetism to heat the part. Induction coils are placed around the material being heat treated, and alternating current is fed through them. This alternating current going through the induction coils creates a rapidly alternating magnetic field.
The eddy currents that occur as a result of this heat the material surrounded by the coils. Magnetic materials are even more easily heated by the alternating magnetic fields.
Induction Heating Equipment
Setups for weld induction heat treating can vary somewhat from application to application, but Red-D-Arc has the equipment needed for most common scenarios. Every induction heating system requires a power source. The power source converts electricity from a power grid into an electrical current that can be used to energize another critical piece of equipment in an induction heating setup: the induction coils. Induction coils are typically made out of copper and are not required to be in contact the workpiece. The power source and the induction coils are the two main components of an induction system, although other pieces of equipment such as blankets can be used to shield the induction coils and aid the heating process.
Why Use Induction Heating Over Other Heating Processes?
Induction heating has many benefits over other processes. Torch heating operations do not have the accuracy of induction heating methods. The flame heats the workpiece in an extremely varied way. Also, a torch heating operation must start with its heating on the outside and let the temperature “soak” its way into the part. Induction heating can use a variety of electrical frequencies to adjust the initial heating position within the depth of the material to some extent. Additionally, the width and length of the heated material can be adjusted precisely with induction heating, unlike torch heating.
Torch heating requires the use of combustible gases, which can be dangerous. Volatile gases can explode and cause injury to workers and destruction of property. These combustible gases also release hazardous fumes that may require respiration or fume removal, especially in confined spaces. On the other hand, induction heating, when used properly, releases no harmful fumes. Since combustible gases are not used during induction heating, there is no risk of explosion.
Another common heat treating process is furnace heating using electrical resistors as heating coils. This process can take a very long time for thick parts, and, similar to torch heat treating, works by heating the exterior surfaces of a base material first and allowing the temperature to soak into the core. Conversely, induction heat treating can be performed rapidly, potentially shaving many minutes off of a resistance furnace operation. The core can be heated much quicker as well with induction heating. Induction coils used with a piece of equipment such as the Miller ProHeat 35 are much more portable than furnace operations as well, allowing for far more practical use in the field.
While there are many advantages to induction heating and induction heat treating, there are some disadvantages. One disadvantage is part geometry. Unless an induction furnace is being used, parts will simpler geometries such as pipe or plate are more readily induction heat treated than ones with more complex geometries simply because the induction coils must be placed around the part.
Another disadvantage is that the initial cost of an induction heating system is typically more expensive than a torch heating system. However, this is where Red-D-Arc has you covered. With our induction heat equipment rentals, you can see firsthand the benefits of induction heating without large capital investment so you can keep on welding!
Importance of Preheating in Welding – Equipment Options
Preheating reduces the risk of cracking in weld metal and heat-affected zone (HAZ) by:
- Lowering the cooling rate of the weld – prevents formation of brittle weld metal/HAZ, allows more time for hydrogen to escape the molten weld.
- Removing moisture (hydrogen source) from the part.
- Reducing shrinkage by lowering the temperature differential.
Preheat or not?
The requirement and level of preheating for steel is determined by the relevant welding code and is dependent on the weld heat input, chemical composition of steel (carbon equivalent), thicknesses, diffusible hydrogen etc. Non-ferrous materials generally require preheat because of their high thermal conductivity.