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Mining and extraction of minerals and metals are two activities conducted in extremely trying and difficult conditions. A lot of different materials are used to manufacture the equipment required for these challenging activities. Every part of the machines need to withstand some of the most difficult conditions such as soaring temperatures and rocky earth surface. Materials used in mines predominantly degrade because of wear, corrosion, and fatigue. Alloys with a high measure of corrosion resistance find profitable applications in the mining industry.
Steel is an alloy that has numerous applications in the mining industry. It is strong, lightweight, corrosion-resistant, durable, sustainable, and, most importantly, inexpensive. Steel can withstand harsh and abrasive mine environments and is used to manufacture tools, drill rigs, demolition equipment, grinding media, pumps, heat exchangers, cathode plates etc.
It is also used to manufacture heavy mining machinery such as mass excavators and bulldozers. It must be mentioned here that structural steel without expensive protective coatings is susceptible to corrosion. Stainless steel is a composite of austenitic and ferritic steels, and typically contains 25% chromium and 5% nickel with molybdenum and nitrogen. Molybdenum is the element that imparts the required corrosion resistance to stainless steel.
In the United Kingdom, INCONEL and INCOLOY alloys are widely used in the mining industry. These alloys possess a combination of corrosion resistance and the ability to withstand high temperatures. They are often used for ancillary applications (pumps, piping and separation machinery), as well as drilling equipment and the construction of downhole shafts. The components used in such heavy-duty applications are subject to both extreme pressure and heat and, therefore, need to be strong while also providing excellent resistance to abrasion, oxidation, and corrosion.
Some of the commercially used mining alloys that are used regularly within the mining industry are discussed below:
INCONEL alloy 600
This alloy is used as a standard engineering material because of its high strength, good workability, and ability to resist the effects of corrosive media and heat. Alloy 600 has a high nickel content that allows it to resist corrosion by many organic and inorganic compounds. It also contains chromium which imparts resistance to sulfur compounds, enhancing its durability substantially.
INCONEL alloy 617
Much like alloy 600, alloy 617 is the go-to alloy when exceptionally high strength is required. This nickel-chromium blend also includes molybdenum, which is the key element that imparts strength to alloys. The carefully balanced composition has good metallurgical stability and oxidation resistance even at elevated temperatures.
INCONEL alloy 690 and INCONEL alloy 693
These alloys contain a substantial amount of chromium and nickel. As discussed previously, this combination results in great strength, stability and easy fabricability. Both alloy 690 and 693 provide good high-temperature resistance.
INCONEL alloy 693 in particular has a high chromium content which, in turn, provides excellent resistance to oxidation and sulfidation, as well as high-temperature corrosion.
INCOLOY alloy 825
This alloy is a superalloy used in screening wires that are required to size mineral particles. Alloy 825 offers excellent resistance to reducing and oxidizing acids, stress-corrosion cracking, and pitting and crevice corrosion. One of the salient features of this alloy is its resistance to sulphuric and phosphoric acids, which makes it an ideal candidate for use in oil and gas well piping.
This alloy is composed of 12% chromium stainless steel. It can be heat treated to achieve varying degrees of strength and ductility. Alloy 410 is used where moderate corrosion resistance is required. It can withstand the corrosive properties of atmospheric conditions, water, and certain chemicals. Its strength makes it a suitable material for ore processing and manufacturing mining equipment that is subject to high mechanical demands and repeat abrasion and wear.