Special conditions of chemical industry
China's economy has been developing rapidly, with the scale of the chemical industry growing rapidly. In the chemical production process, a large number of chemical equipment is used, which generally withstands high or low temperatures, high pressure, and strongly corrosive media. The connecting fasteners in chemical equipment face a harsh service environment and may experience fatigue fracture or corrosion cracking during long-term use, which affects the normal use of the equipment. For example, petroleum exploration is an important field in the chemical industry. With the development of ultra-deep, ultra-inclined oil and gas wells, as well as oil and gas fields with H₂S, CO₂, Cl⁻, etc., and the continuous improvement of technical levels, drilling speed is accelerating, and drilling depth is increasing (the deepest well reaches about 7300 meters), the demand for fastener products with anti-corrosion performance is increasing day by day.
Austenitic stainless steel is widely used in the chemical industry.
In the chemical industry, austenitic stainless steel fasteners are extensively utilized due to their superior properties. The series of austenitic stainless steel fasteners, such as 304, 316, and 321, are known for their non-magnetic or weakly magnetic characteristics, along with high toughness and ductility. They possess excellent cold working properties, and their strength grades meet the requirements of everyday use. Moreover, they exhibit resistance to corrosion from oxidizing acid media. Fasteners made from 316 material stainless steel contain elements like Mo and Cu, which provide additional resistance to corrosion from sulfuric acid, phosphoric acid, as well as from formic acid, acetic acid, and urea, among others. Additionally, by controlling the carbon content in these austenitic stainless steels to below 0.03% or by adding elements like Ti or Ni, the resistance to intergranular corrosion of the stainless steel fasteners can be significantly improved. Products such as hexagonal head bolts, flange bolts, stud bolts, socket screws, double-ended bolts, and stud bolts, as well as handwheel nuts made from 304, 316, and 321 stainless steels, are extensively used in the chemical industry.
solution treatment
Austenitic stainless steel fasteners, such as the series 304, 316, and 321, are extensively used in the chemical industry. These austenitic stainless steel fasteners typically exhibit non-magnetic or weakly magnetic properties, along with high toughness and ductility, and possess good cold working performance. Their strength grades meet the requirements of everyday use, and they also have the ability to resist corrosion from oxidizing acid media. Fasteners made of 316 material stainless steel contain elements like Mo and Cu, which can also withstand corrosion from sulfuric acid, phosphoric acid, as well as formic acid, acetic acid, and urea. At the same time, controlling the carbon content in such austenitic stainless steels, with a carbon content of less than 0.03% or containing elements like Ti, Ni, etc., can significantly improve their resistance to intergranular corrosion. Products such as hexagonal head bolts made of 304, 316, and 321 stainless steels, stainless steel flange bolts, stainless steel stud bolts, stainless steel socket screws, stainless steel double-ended bolts, stainless steel stud bolts, and handwheel nuts are widely used in the chemical industry. When austenitic stainless steel fasteners are used in chemical scenarios, the American Standard ASTM requires solution treatment. After solution treatment of stainless austenitic fasteners, carbide phases are completely or essentially dissolved, carbon is dissolved in the austenite, reducing the formation of chromium carbide, significantly enhancing the corrosion resistance of austenitic stainless steel, and strengthening the ductility of austenitic fasteners. These types of fasteners are primarily products that meet the ASTM A193 or ASTM A320 standards, such as B8, B8C, B8M, B8P, B8F, B8T, B8LN, B8MLN, etc.
Carbon steel/alloy steel fasteners
Carbon steel/alloy steel fasteners are also widely used in the chemical industry. Commonly used grades include 4.8, 5.6, 5.8, 8.8, 10.9, and 12.9, as well as ASTM A193 B7, B7M, B16, ASTM A320 L7, L7M, A325, A325M TYPE 1, 30CrMo/35CrMo, ASTM A194 2H, 2HM, 4, 7, 7M, and chemical industry standards such as HG20613, HG20634 heavy hex nuts, cone anchor bolts, chemical anchors, hot-dip galvanized fasteners, and so on.
Duplex Stainless Steel
To enhance the strength and corrosion resistance of fasteners, dual-phase stainless steel fasteners can also be chosen.
Compared to austenitic stainless steel fasteners, dual-phase stainless steel has higher strength and better resistance to intergranular corrosion, chloride stress corrosion, pitting corrosion, crevice corrosion, and hole corrosion. It is recommended to select materials such as standard duplex stainless steel (type 2205) or super duplex stainless steel (type 2507). Duplex stainless steel combines the characteristics of ferrite and austenite. The presence of austenite improves the steel's corrosion resistance, complementing the toughness and weldability of ferritic steel. The presence of ferrite enhances the strength of austenitic steel and improves its resistance to stress corrosion cracking and reduces the tendency for hot cracking during welding. To enhance the strength and corrosion resistance of fasteners, dual-phase stainless steel fasteners can also be selected.
Nickel-based alloy fasteners
In chemical environments with high temperatures, it is recommended to choose fasteners made of high-temperature alloy materials.
For example, nickel-based materials are completely stable in all alkaline solutions, whether they are hot or molten. In the chemical industry, in equipment such as ethylene cracking furnace tubes, heat exchangers, hydrocracking, and hydrodesulfurization, it is recommended to choose Incoloy 800 series, Incoloy 800 or Incoloy 825 nickel-based alloy fasteners, which have excellent resistance to oxidation and sulfidation. On oil drilling platforms, it is recommended to use Monel alloy series fasteners, which are more corrosion-resistant than nickel in reductive media and more resistant to corrosion than copper in oxidative media. Monel alloys are also more resistant to corrosion than nickel and copper in phosphoric acid, sulfuric acid, hydrochloric acid, salt solutions, and organic acids.
Surface treated fastener
In the process of preventing corrosion of fasteners, surface corrosion protection treatments can be added to separate the fasteners from corrosive media, reducing contact with air and other media, and forming an effective protective layer.
In the chemical industry, it is recommended to use hot-dip galvanizing,Dacromet coating, Xylan coating, hot-dip galvanizing, Teflon coating, etc., which can form an effective protective layer on the surfaces of bolts, nuts, and washers without affecting the actual installation of the fasteners. Teflon coatings have the advantages of non-stick, wear resistance, anti-static, self-lubrication, high-temperature resistance, and corrosion resistance. They also come in a variety of colors. There are blue PTFE Teflon bolts, blue PTFE Teflon nuts, gray PTFE Teflon bolts, orange PTFE Teflon bolts, gray PTFE Teflon nuts, and so on.
Hot-dip galvanized plated fasteners
