1st step: forging
After a preliminary “series preparation” phase where requirements, deadlines, and the delivery schedule are validated by engineers and technicians, production begins with hot forging of the tubes using the patented Premium Forged Pipes® process. In this process, steel billets are heated to 1,200°C in a furnace with a rotating floor. They are pierced by a punch, using a process known as the “Mannesmann process” and then forged, meaning hammered, coming out hollow and elongated.
The seamless tubes have then been manufactured, but they are still in an unfinished state. The Aulnoye-Aymeries forge is world-renowned for its ability to adapt and its responsiveness to even the most stringent customer requirements for tolerance, shape, dimensions, and related services.
2nd step: finishing
To get the required mechanical properties for this type of application, the tubes then go through a heat treatment step where they are “quenched and tempered”.
“Quenched” because the tubes, after being heated to 950°C in a furnace, are then immersed in a room-temperature water “bath”, rapidly cooling them. This process hardens the steel.
The tubes are then “tempered” by being reheated to a cooler temperature than during the quenching process, which reduces the weaknesses caused by quenching and develops the required mechanical properties.
3rd step: inspection
After air cooling, the tubes then go through a crucial non-destructive inspection step. They undergo a magnetic particle inspection. Iron powder is used to identify any cracks in the pre-magnetized tubes, which can then be repaired.
4th step: polishing
When tubes are to be visible in a structure, and to help with their bending (a delicate process for curving the tube), as is the case with the Orly walkway, the exterior walls of the tubes are polished, a process known as “grinding”. Grinding down the tubes by just a few tenths of a millimeter gives them a more aesthetically-pleasing appearance.