May I ask how to prevent corrosion of bolts used in the steel structures of offshore platforms?

What I need for now is that the bolts themselves can resist corrosion in a marine climate

Spraying Teflon material can be used for corrosion protection; after spraying, a salt spray test is conducted. Our company handles bolt spraying services for many enterprises.

Reply to 4# wu*changye: Coating for corrosion protection was used, which makes disassembly rather troublesome. This method is simple, but the consequences can be severe

Actually, Dacromet is the best coating for bolts – it offers excellent corrosion resistance. Moreover, the coating thickness is less than 10 microns, so it does not affect installation or use, nor does it impact the tightening force. Dacromet is essentially a zinc coating.

Material alone cannot solve the fundamental problem; no matter how good the material is, gaps will still remain, and corrosion occurs quite rapidly. It’s better to use materials with better corrosion resistance, along with coatings.

Reply to 7# lymeiyue: Could you briefly explain the specific steps? Information on what kind of bolts and coatings to use, etc. Thank you

Monel alloy is a suitable choice, such as MONEL400 and MONEL K500

Monel400 (UNS N04400/W.Nr.2.4360) in the form of sheets, pipes, forgings, and round bars. Chemical composition of Monel 400: Alloy % Nickel Copper Iron Carbon Manganese Silicon Sulfur; Minimum values for Monel400: 63, 28; Maximum values: 34, 2.5, 0.3, 2, 0.5, 0.024. Physical properties of Monel 400: Density – 8.83 g/cm3; Melting point – 1300–1390 °C. Minimum mechanical properties of this alloy at room temperature: Alloy and condition, Tensile strength Rm in N/mm2, Yield strength RP0.2 in N/mm2, Elongation A5 in %. For Monel400, these values are 480, 170, 35 respectively. This alloy possesses the following characteristics: Monel400 is a corrosion-resistant alloy that is used the most frequently, has the widest range of applications, and exhibits excellent overall performance. This alloy exhibits excellent corrosion resistance in hydrofluoric acid and fluorine gas environments, as well as good resistance to hot concentrated alkaline solutions. It is also resistant to corrosion by neutral solutions, water, seawater, the atmosphere, organic compounds, and more. An important feature of this alloy is that it generally does not develop stress corrosion cracks, and it has good machinability. Microstructural structure of Monel 400: The structure of the Monel 400 alloy is a high-strength single-phase solid solution. Corrosion resistance of Monel 400: The Monel 400 alloy exhibits excellent corrosion resistance in fluorine gas, hydrochloric acid, sulfuric acid, hydrofluoric acid, and their derivatives. It also exhibits greater corrosion resistance in seawater than copper-based alloys. Acidic medium: Monel400 is corrosion-resistant in sulfuric acid with concentrations below 85%. Monel400 is one of the very few important materials that can resist hydrofluoric acid. Water corrosion: In most cases of water corrosion, the Monel400 alloy exhibits excellent corrosion resistance; pitting and stress corrosion are also rarely observed, with a corrosion rate of less than 0.025 mm/a. High-temperature corrosion: The maximum temperature at which Monel400 can operate continuously in air is generally around 600°C; in high-temperature steam, the corrosion rate is less than 0.026 mm/year. Ammonia: Due to its high nickel content, the Monel400 alloy can resist corrosion in anhydrous ammonia and under ammoniation conditions at temperatures below 585°C. Applications of Monel 400: Monel 400 alloy is a versatile material that can be used in many industrial fields: 1. Seamless water pipes and steam pipes in power plants; 2. Sea water exchangers and evaporators; 3. Environments involving sulfuric acid and hydrochloric acid; 4. Crude oil distillation; 5. Pump shafts and propellers in equipment that operates in sea water; 6. In the nuclear industry, for manufacturing equipment used in uranium processing and isotope separation; 7. Pumps and valves used in equipment for producing hydrochloric acid

Anti-corrosion can be achieved by spraying Teflon; a salt spray test is conducted after spraying

Use Dacromet; it will not affect the tightening force of the bolts at all. Applying Teflon not only results in extremely high costs but also reduces the tightening strength, so it is not recommended. PS: Teflon is not a panacea.