Before we start, we need to know more about normalization. Put simply, it’s the air-cooling of metal to reestablish a homogenous and finegrained microstructure in the HAZ. There are two requirements when normalizing. You have to limit the temperature of the pipe’s external surface closest to the coil to avoid grain re-growth. And you have to reach a high enough austenitisation temperature in a sufficiently wide zone at the inner surface. EFD Induction has designed three systems that satisfy those requirements. We call the designs Seam Annealing with Horizontal Tracking, Seam Annealing with Orbital Tracking and a Travelling Seam Annealer. Each deserves a closer look.
Seam Annealing with Horizontal Tracking can be supplied with either fully automated or manual tracking. Here, induction coils are adjusted according to the weld seam in a horizontal plane. Seam Annealing with Orbital Tracking can also be supplied with either fully automated or manual tracking. The coil follows a twist in the seam here, keeping a constant distance between the coil and the weld seam. This design is most common for pipes with large outer dimensions (OD). Finally, a Travelling Seam Annealer, part of the normal annealing system, reduces scrap in shut down situations. Because the last section of the seam annealer is movable, the unit can still seam anneal pipes not properly annealed when the line has stopped.
One of several processes
Besides Normalization, we supply seam annealing equipment for the Normalization, Quenching and Tempering process (NQT) and the Normalizing, Quenching and Normalization process (NQN). For example, our Baoshan Steel installation in Shanghai, China, designed for pipes with a maximum OD of 24” and wall thickness of 19.6 mm, uses the NQN process. Seam annealing, in all its variations, is one more area where we apply induction heating.