By: Frank Caprio | On: February 20, 2019
Today, most steel is produced using either an Electric Arc Furnace (EAF), or a Basic Oxygen Furnace (BOF). The EAF employs huge electrodes which supply an electrical current, melting the charged material (usually steel scrap) into molten steel. The BOF uses (mostly) molten iron, which is then converted into steel by blowing huge volumes of oxygen at high velocity down through the slag layer and into the molten metal, driving various reactions that refine and convert the iron into steel. It should be noted, however, that oxygen is used for many applications in both BOF and EAF steelmaking, so let’s take a look at some common applications, and why hoses must be specially cleaned when used for oxygen transfer service.
Oxygen is available in different grades: medical, aviation (breathable), welding, and research. Most oxygen is produced by chilling air until it liquefies, then slowly increasing the temperature. The oxygen, nitrogen, and argon all boil at different (sub-zero) temperatures, allowing them to be separated, collected, and stored. This produces very high-purity oxygen, but subsequent storage and transfer differ depending on the intended use. Regardless of how the oxygen will be used, it must be kept free of any hydrocarbons (oil, etc.) or particulate matter, both of which can spontaneously combust in the presence of pure oxygen. Any lubricants, thread sealants, etc. must also be specially formulated for oxygen service.
One interesting fact about pure oxygen is that, by itself, it is not flammable. However, it reacts readily with other materials which then may spontaneously combust in an oxygen-enriched environment. While normal atmosphere contains between 20.8 and 21 percent oxygen, OSHA defines an oxygen enriched atmosphere as containing more than 22 percent oxygen, which presents a significant fire and explosion risk. This is why hoses and expansion joints intended for the transfer of oxygen must undergo special cleaning processes, which can vary depending on the intended use. Certain high-purity applications (such as medical or aviation use) use specially cleaned non-metal hoses, which are economical and sanitary, but most industrial applications prefer metal hose for its fire safety, resistance to permeation, and rugged reliability even at extreme temperatures. This includes cryogenic liquids, where metal hoses can resist the frost build-up that may occur on the hose exterior during transfer operations.
For most standard industrial oxygen transfer applications, the hose must be cleaned and degreased, dried, and capped to prevent the ingress of any contaminants. Hose Master employs various cleaning methods conforming to the requirements of the Compressed Gas Association (CGA) standard G-4.1: Cleaning Equipment for Oxygen Service. Some industrial gas producers have their own unique cleaning requirements, so check with your customer to verify which specification meets their needs. Hose Master has also achieved certification by several of the industrial gas producers so we may already be approved to clean to their more stringent specifications.
In the steel industry, oxygen is a necessary ingredient in steelmaking, casting, and finishing operations. Obviously, oxygen is required for a BOF to convert iron into steel; the oxygen is injected into the iron bath at supersonic speeds through a water-cooled lance, which in turn is supplied with oxygen and cooling water through flexible lance hoses. But EAFs may also benefit from oxygen injection, which is why many EAFs incorporate an oxygen lance, although usually a smaller diameter than a BOF lance. EAF lances can be either a water-cooled design, or a design where the lance pipe is gradually consumed during lancing.
Other oxygen applications include hand-held oxygen lances used to cut large scrap items into manageable pieces (watch this very cool youtube video – you can see how the lance pipe is consumed during the cutting process). This same process is used to remove hardened steel or slag from ladles and tundishes. Also, oxyfuel burners are used in the EAF to preheat or help to melt the scrap, and Oxy-fuel torches are used to cut steel slabs or billets after casting. Air-fuel or oxy-fuel burners are used to preheat the ladles and the tundish to prevent damage to the refractory layer when the molten steel flows into the ladle, tundish, and mold during casting. After casting, oxygen scarfing hoses are used on equipment that removes surface imperfections from steel slabs through high-temperature oxidation.
In summary, remember that any hose transferring oxygen must be cleaned and degreased for that service, and high-velocity media usually requires an internal liner to protect the corrugations in metal hoses from impact by high-velocity media. In oxygen lancing operations, the liner serves the additional purpose of preventing flow-restricting currents from building up inside the hose, thus increasing oxygen flow and decreasing tap-to-tap times. Hose Master has decades of experience in providing solutions to the steelmaking industry, and many more oxygen applications outside of steelmaking. Contact us if we can help you determine which products, accessories, or fabrication options will provide the safest, longest lasting oxygen transfer assemblies you can buy!