SUPPLY CHAIN | SOURCING STAINLESS STEEL
Stainless supply chain challenges
Stainless steel’s corrosion resistance and durability enables
long-lasting process equipment, pipework, tanks and structural elements in the nuclear industry. However, fabricators may find themselves facing a procurement challenge due to special requirements
By Andy Backhouse, Lead Technical Manager, Outokumpu
THE MAJORITY OF STAINLESS STEELS used in the nuclear industry are based on well-established commercial grades that are widely available. However, it’s not always simple to secure material when ordering stainless steel for components in critical nuclear applications, for example where there is contact with the primary coolant. Austenitic stainless steels are typically used in these
applications. These steels contain 8 to 10% nickel to give the steel the correct microstructure and mechanical properties. However, the drawback is that nickel ores often contain trace quantities of cobalt that cannot be easily separated, so commercial stainless steels containing nickel normally also contain a trace quantity of cobalt. When exposed to radiation, this cobalt transmutes into a radioactive isotope that accumulates over time, steadily raising the health and safety risk. To avoid this the industry uses stainless steel produced to exacting standards with tight control over even minor trace elements such as cobalt. This requires the use of nickel ores obtained
from mines with naturally low levels of cobalt. In addition, individual nuclear projects may have specifications covering other trace elements such as boron, tantalum and phosphorus.
Special production run Although producing low-cobalt stainless steel for the nuclear industry is technically viable, it is more costly as it disrupts a mill’s normal production. Modern mills in Europe and the USA produce stainless steel by remelting scrap in an electric arc furnace, for example Outokumpu uses around 94% scrap. This aligns with society’s drive towards the circular economy and away from use of virgin raw materials. It also cuts the carbon footprint as remelting scrap requires less energy than processing ore. However, trace elements in scrap make it unsuitable for nuclear projects. Therefore, a steel mill must incur additional costs by switching temporarily to ore-based production and purchasing specialist low-cobalt nickel ore.
Above: The nuclear industry uses stainless steel with tight control over minor trace elements, such as cobalt 32 | September 2023 |
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