Annealing is a steel heat treatment process in which the steel is heated rapidly to a specific temperature for sufficient time and then cooled at an appropriate rate (usually slow, sometimes controlled cooling). Annealing of steel pipe is commonly used to remove internal stress, restores ductility, soften a metal for cold working, enhance electrical conductivity,which can improve machinability and property.
During the annealing process, heating the pipe to austenitic temperature region which is approximately above 750°C. Then allow heat to be uniformly distributed in the pipe, lasting time may vary depending on the pipe size and then switch off the heating source and cool it inside the furnace.During cold working, the metal can become hardened to the extent that any more work will result in cracking. By annealing the metal beforehand, cold working can take place without any risk of cracking, as annealing releases mechanical stresses produced during machining or grinding. Do you know how to identify if steel pipe is annealed?
1. By the echo. Tap a tube and listen to the echo at the end. If the echo is loud and sharp, it can be judged that it has been annealed. Because annealing can make the metal tissue more uniform and dense, which produce higher tone echo. By contrast, unannealed steel pipes absorb some of the acoustic energy, so their echoes sound dull. Sonar can be used if the condition permits.
2. By digital multimeter. The resistance of each steel tube can be measured with a high-precision digital multimeter. The resistance value of steel tube after annealing is less than that without annealing. Make sure the tubing surfaces are clean and without liquid before testing.
3. By hardness. As we cool steel pipe to room temperature when annealed, it goes through different structures. Annealing is slow cooling, giving time to cool after nucleation which means grain growth is more. If this transformed rapidly, the carbon atoms are allowed to diffuse out and iron atoms are able to move more freely, making the material weaker and more prone to deformation.
There are many types of annealing such as full annealing, spheroidizing annealing, diffusion annealing and so on for steel pipe, which making them usable in further processes like forming, bending, machining, sheet metal forming etc. More details about pipe processing, contact us now.
