Seawater-resistant stainless steel coating anti-corrosion method for spray splashing area for ocean engineering facility

Abstract

The invention belongs to the field of marine corrosion and protection, and particularly relates to a seawater-resistant stainless steel coating corrosion prevention method for a spray splashing area for marine engineering facilities. The seawater-resistant stainless steel cover plate is adopted to wrap the steel structure in a welding mode, inert gas is filled between the seawater-resistant stainless steel cover plate and the steel structure, and then corrosion prevention is achieved. According to the method, the stainless steel cover plate resistant to seawater corrosion and fouling is adopted to wrap the steel structure, then the steel structure is separated from the corrosion environment by welding the cover plate, inert gas (nitrogen or argon) is arranged in the middle space for protection, the ordinary steel structure is separated from the marine environment, and the method has the advantages of corrosion resistance, impact resistance, abrasion resistance and the like; according to salt spray test data, it is deduced that the single-time anti-corrosion service life is longer than 100 years, the frequency of anti-corrosion construction is greatly reduced, and waste of manpower and material resources caused by multiple times of construction and the influence on facility safety are avoided.

Description

Technical Field

[0001] The present invention belongs to the field of marine corrosion and protection, and in particular relates to a method for coating and anti-corrosion of seawater-resistant stainless steel in a wave splash zone for marine engineering facilities. Background Art

[0002] Steel pile construction at port terminals spans multiple marine corrosion zones. The splash zone, in particular, is subject to periodic wetting by seawater, resulting in long-term alternating dry-wet conditions. This area also experiences abundant oxygen, combined with the combined effects of sunlight and wind, often leading to the most severe corrosion. Currently, the cheapest corrosion protection technology for steel structures in this zone is anti-corrosion coatings. However, these coatings have significant drawbacks, including a short lifespan, poor water curing, and a single corrosion protection lifespan of typically only 3-5 years. Furthermore, repairing existing structures is extremely difficult. Currently, the longest-lasting corrosion protection technology for steel structures in this zone is multi-layer petrolatum coating. This technology consists of four closely connected protective layers: petrolatum anti-corrosion paste, petrolatum anti-corrosion tape, a sealing buffer layer, and an anti-corrosion shield. This single-layer protection can provide up to 30 years of protection for steel structures in this zone. However, this 30-year corrosion protection lifespan is significantly out of line with the 100-year design service life of major offshore structures. Repeated corrosion protection work on offshore structures throughout their lifecycle not only wastes manpower and resources but also significantly reduces their safety.

[0003] Therefore, there is an urgent need to develop a method with long anti-corrosion life and good anti-corrosion effect. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems of short service life and complex construction of existing anti-corrosion technology in the splash zone of marine engineering facilities, and to propose a new anti-corrosion method for seawater-resistant stainless steel coating in the splash zone of marine engineering facilities.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] The steel structure is covered with seawater-resistant stainless steel cover plates by welding, and inert gas is filled between the seawater-resistant stainless steel cover plates and the steel structure to achieve corrosion protection.

[0007] The seawater-resistant stainless steel cover plate is made of austenitic stainless steel containing rare earth element scandium (Sc). The thickness of the cover plate is 2-3 mm, and the austenitic stainless steel is UNS S32053-Sc, UNS S31254-Sc, or UNS N04400-Sc alloy.

[0008] The composition of UNS S31254-Sc by mass is C ≤ 0.03%, Si ≤ 0.40%, Mn ≤ 0.50%, Cr: 19.00% to 21.00%, Ni: 17.00% to 19.00%, Mo: 5.50% to 7.50%, Cu: 0.50% to 1.00%, Scandium (Sc) 0.3% to 0.5%, and the remainder is Iron (Fe) and unavoidable impurities. The preparation method of UNS S31254-Sc is as follows: First, the raw materials are charged into an electric furnace for smelting according to the proportions, and the tapping temperature is controlled above 1600°C. At this point, the composition of the molten steel is approximately C ≤ 2.00%, Si ≤ 0.40%, P ≤ 0.025%, Cr: 19.00% to 21.00%, Ni: 17.00% to 19.00%, and the balance is Fe. The molten steel is then refined and decarburized by blowing oxygen until the carbon content in the molten steel is ≤0.010%. A deoxidizer is then added for deoxidation treatment, and alloying elements are added to adjust the various components to the target values. The molten steel is then transferred to a ladle for refining in a ladle refining furnace (LF). Boron ore is added for further refining, and rare earth elements wrapped in aluminum foil are added to refine the grains and remove inclusions. Next, mold casting is carried out, argon is introduced and protective slag is added for casting. After casting, the mold is cooled to obtain a steel ingot. Finally, the steel ingot is finished and subjected to high-temperature homogenization treatment at 1160℃~1200℃ to eliminate component segregation. It is then rolled into a coil at a temperature ≥1050℃.

[0009] The composition of UNS S32053-Sc is as follows by mass: C ≤ 0.03%, Si ≤ 1.00%, Mn: 4.00% to 6.00%, Cr: 22.00% to 24.00%, Ni: 24.00% to 26.00%, Mo: 5.00% to 6.00%, N: 0.17% to 0.22%, scandium (Sc) 0.3% to 0.5%, and the rest is iron (Fe) and unavoidable impurities. The rest of the preparation process is the same as that of UNS S31254-Sc alloy.

[0010] The composition of UNS N04400-Sc by mass is: C ≤ 0.30%, Si ≤ 0.50%, Mn ≤ 2.00%, Cu: 28.00% to 34.00%, Scandium (Sc) 0.3% to 0.5%, and the remainder is nickel (Ni) and unavoidable impurities. The UNS N04400-Sc production method involves vacuum induction melting, where the raw materials are fed into the melting furnace according to the proper proportions, and the tapping temperature is controlled above 1600°C. The molten steel is then refined and decarburized by oxygen blowing until the carbon content is ≤ 0.010%. A deoxidizer is then added for deoxidation, and alloying elements are added to adjust the composition to the target values. The molten steel is then transferred to an electroslag remelting furnace for remelting, yielding a pure steel ingot. Next, mold casting is performed, using argon gas and mold slag. After casting, the mold is cooled to yield the steel ingot. Finally, the steel ingot is finished and subjected to high-temperature homogenization treatment at 1100℃~1200℃ to eliminate component segregation, and then rolled into coils at a temperature ≥900℃.

[0011] Furthermore, the seawater-resistant stainless steel cover plate is welded to both ends of the steel structure in the longitudinal direction to form a seawater-resistant stainless steel cover plate covering the steel structure. The welding current is 110-130A, the welding voltage is 20-25V, the welding speed is 5-10cm / min, the welding material is Hastelloy system, the shielding gas is 99.99% argon, and the shielding gas flow rate is 8-15L / min.

[0012] Furthermore, the seawater-resistant stainless steel cover plate is welded to both ends of the steel structure, with 2-3mm reserved in the middle. Before welding and sealing, inert gas is filled into the gap between the seawater-resistant stainless steel cover plate and the steel structure to exclude oxygen, and finally the hole is sealed to ensure that the welding area is dense and leak-proof.

[0013] After welding, the welding area is ground and polished to remove surface debris such as welding spatter, and passivation treatment is performed. The passivation treatment is to use 10% to 20% nitric acid solution to apply to the weld, and act at room temperature for 10 to 30 minutes. After rinsing with clean water, it is neutralized with 1% to 3% sodium carbonate solution, and finally rinsed with pure water to form a passivation film.

[0014] The seawater-resistant stainless steel cover sheet should cover an area extending from 1 meter below the maximum low tide line to 2 meters above the maximum high tide line, with a single section covering no less than five times the diameter of the steel pile. Preferably, the cover should cover the splash zone. After welding is complete, pile driving can proceed, ensuring that the weld area is leak-proof during the re-driving process.

[0015] The inert gas is nitrogen or argon.

[0016] Compared with the prior art, the present invention has significant advantages:

[0017] The method of the present invention uses a stainless steel cover plate that is resistant to seawater corrosion and fouling to cover the steel structure, and then isolates the steel structure from the corrosive environment by welding the cover plate. Inert gas (nitrogen or argon) is used in the middle hollow space for protection to isolate the ordinary steel structure from the marine environment. The method has the advantages of corrosion resistance, impact resistance, and wear resistance. According to salt spray test data, the single anti-corrosion life is inferred to be greater than 100 years, which greatly reduces the frequency of anti-corrosion construction and avoids the waste of manpower and material resources caused by multiple constructions and the impact on facility safety.

[0018] Compared with the existing steel structure coating anti-corrosion technology, the method of the present invention is simpler in construction convenience, easy to operate and implement, and can be well adapted and applied to both newly built and in-service marine engineering facilities. At the same time, the anti-corrosion effect and anti-corrosion time are longer, which is of great significance to the safe operation of in-service and newly built marine engineering facilities and major equipment. In terms of economy, the present invention uses stainless steel materials, but due to its excellent corrosion resistance and ultra-long service life, in the long run, it greatly reduces the overall maintenance cost and replacement cost, and has good economic benefits. In terms of safety, the present invention avoids stress concentration and other structures that are not conducive to corrosion resistance through reasonable welding technology and structural design, ensures the density and reliability of the welding area, and thus ensures the safe operation of the entire marine engineering facility. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the anti-corrosion method of seawater-resistant stainless steel coating in the splash zone, where 1-ordinary carbon steel pile, 2-annular welding area, 3-seawater-resistant stainless steel cover plate, 4-filled inert gas, and 5-seawater immersion area.

[0020] Figure 2 This is the surface appearance of the stainless steel cover plate and steel structure after the salt spray test in Example 1 of the present invention.

[0021] Figure 3 This is the surface appearance of the stainless steel cover plate after the salt spray test in Example 2 of the present invention.

[0022] Figure 4 This is the surface appearance of the stainless steel cover plate after the salt spray test in Example 3 of the present invention.

[0023] Figure 5 This is the surface appearance of the stainless steel cover plate after the salt spray test of Comparative Example 1 of the present invention.

[0024] Figure 6 This is the surface appearance of the stainless steel cover plate after the salt spray test of Comparative Example 2 of the present invention.

[0025] Figure 7 This is the surface appearance of the stainless steel cover plate after the salt spray test of Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0026] The embodiment of the present invention adopts the stainless steel cover plate resistant to seawater corrosion, and the cover plate is tightly connected to the steel structure by a welding process so that the steel structure is completely covered to form a closed protection system, and an inert gas (nitrogen or argon) is filled between the seawater-resistant stainless steel cover plate and the steel structure for protection, oxygen is excluded, and the contact between the steel structure and the marine environment is completely isolated. Finally, the sealing ensures that the welding area is dense and leak-proof, thereby significantly improving the anti-corrosion effect. After welding, the welding area is polished and polished to remove surface debris such as welding spatter, and passivation treatment is performed. 10% to 20% nitric acid solution is used to apply the weld seam, which acts at room temperature for 10 to 30 minutes. After rinsing with clean water, it is neutralized with 1% to 3% sodium carbonate solution, and finally rinsed with pure water to form a passivation film. The advantages of the present invention are not only reflected in the selection of materials, but also in the systematic and synergistic nature of the overall technical solution. Through the careful design and optimization of each link, a qualitative leap in anti-corrosion performance is achieved.

[0027] Example 1

[0028] The original size of the carbon steel piles used in the experiment is φ50mm×500mm, of which the size of the covered section is 300mm, and 100mm exposed sections are reserved in each section for comparison.

[0029] A UNS S31254-0.35Sc austenitic stainless steel cover plate with a thickness of 2.5mm was selected. The actual composition of the UNS S31254-Sc molten alloy is as follows: C: 0.01%, Si: 0.20%, Mn: 0.40%, Cr: 20.15%, Ni: 18.32%, Mo: 6.80%, Cu: 0.78%, Scandium (Sc) 0.35%, and the remainder is Iron (Fe) and unavoidable impurities. The preparation process begins with electric furnace smelting, where the raw materials are charged according to the proportions and the tapping temperature is controlled above 1600°C. The molten steel is then transferred to an argon oxygen degassing (AOD) furnace for refining. Aluminum is then added for deoxidation, and alloying elements are added to adjust the composition to the target values. The molten steel is then transferred to a ladle for refining in a ladle refining furnace, where boron ore is added. Aluminum-coated rare earth elements are then added for grain refinement and inclusion removal. Argon gas is introduced and mold slag is added for casting. After casting, the mold is cooled to obtain a steel ingot. The steel ingot is finished and subjected to high-temperature homogenization treatment at 1200℃. It is then rolled into a 2.5mm coil at a temperature ≥1050℃.

[0030] Welding process: Welding material: Hastelloy C-276 welding wire (PRE value ≥ 40). Welding current: 120A, voltage: 22V, welding speed: 8cm / min, interlayer temperature: ≤100℃. Cover the carbon steel piles with the stainless steel cover plate in sections (each section should be no less than 5 times the diameter of the protected steel piles), and weld them longitudinally. A 2.5mm gap is reserved between the cover plate and the steel piles. Before welding and sealing, fill the gap with nitrogen (purity ≥ 99.99%), and the oxygen content is tested to be <0.1%. Finally, seal the hole to ensure that the welding area is dense and leak-proof. After sealing, use a mass spectrometer to detect the leakage rate, and the leakage rate is <1×10 -6 Pa·m 3 / s. The welding area is polished to remove surface debris such as welding spatter, and passivation treatment is performed. The weld is coated with 12% nitric acid solution and allowed to react at room temperature for 20 minutes. After rinsing with clean water, it is neutralized with 3% sodium carbonate solution and finally rinsed with pure water to form a passivation film. The surface roughness Ra is ≤ 0.8 μm. Figure 1 .

[0031] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the surface of the stainless steel cover plate has no pitting, cracks or discoloration, and the surface of the internal protected carbon steel pile has no corrosion, see Figure 2 .

[0032] The neutral salt spray test (ASTM B117) is an accelerated corrosion test that simulates a harsh corrosive environment through a high-concentration salt spray (5% NaCl, 35°C). The accelerated corrosion factor allows for an approximate estimate of a material's corrosion life in a seawater environment. A 24-hour spray test is generally considered equivalent to one year's worth of corrosion in a seawater environment. Based on this, it is estimated that a 100-year service life requires approximately 2,400 hours of salt spray testing. This conversion requires the material to exhibit primarily uniform corrosion and that the seawater environment meets typical conditions. It also incorporates material properties and environmental classification to compensate for limitations of the salt spray test, such as its inability to replicate dry-wet cycles and biological attachment. Therefore, a 3,000-hour salt spray test can be used to estimate a 100-year corrosion life.

[0033] Example 2

[0034] The original size of the carbon steel piles used in the experiment is φ50mm×500mm, of which the size of the covered section is 300mm, and 100mm exposed sections are reserved in each section for comparison.

[0035] UNS S32053-0.42Sc duplex stainless steel cover plates with a thickness of 3.0mm were selected. The actual composition of the UNS S32053-Sc alloy is as follows: C: 0.02%, Si: 0.60%, Mn: 5.20%, Cr: 23.25%, Ni: 25.86%, Mo: 5.80%, N: 0.19%, Scandium (Sc) 0.42%, and the remainder is iron (Fe) and unavoidable impurities. The preparation process is similar to that of UNS S31254-Sc alloy. The preparation process begins with electric furnace smelting. The raw materials are charged into the furnace according to the proportions, and the tapping temperature is controlled above 1600°C. The molten steel is then transferred to an argon oxygen degassing furnace (AOD) for refining. Aluminum is then added for deoxidation, and alloying elements are added to adjust the composition to the target values. The molten steel is then transferred to a ladle for refining in a ladle refining furnace, where it is refined with boron ore. Rare earth elements coated with aluminum foil are then added to refine the grains and remove inclusions. Argon gas is introduced and mold slag is added for casting. After casting, the ingot is mold-cooled to produce a steel ingot. The ingot is then finished and homogenized at 1200°C before being rolled into 3.0mm coils at temperatures ≥1050°C.

[0036] Welding process: Welding material: Inconel 625 welding wire (PRE value ≥ 35); welding current: 110A, voltage: 20V, welding speed: 10cm / min, interpass temperature: ≤80°C. Before welding and sealing, argon gas (purity ≥99.99%) was filled into the gap, and the oxygen content was tested to be <0.1%. Finally, the hole was sealed to ensure that the weld area was dense and leak-proof. After sealing, a mass spectrometer leak detector was used to test, and the leakage rate was <1×10 -6 Pa·m 3 / s. The weld area was ground and polished to remove surface debris such as weld spatter, and the weld was coated with 12% nitric acid solution for 30 minutes at room temperature. After rinsing with clean water, it was neutralized with 3% sodium carbonate solution and finally rinsed with pure water to form a passivation film with a surface roughness of Ra ≤ 0.8μm.

[0037] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the surface of the stainless steel cover plate has no pitting, cracks or discoloration, and the surface of the internal protected carbon steel pile has no corrosion, see Figure 3 .

[0038] The neutral salt spray test (ASTM B117) is an accelerated corrosion test that simulates a harsh corrosive environment through a high-concentration salt spray (5% NaCl, 35°C). The accelerated corrosion factor allows for an approximate estimate of a material's corrosion life in a seawater environment. A 24-hour spray test is generally considered equivalent to one year's worth of corrosion in a seawater environment. Based on this, it is estimated that a 100-year service life requires approximately 2,400 hours of salt spray testing. This conversion requires the material to exhibit primarily uniform corrosion and that the seawater environment meets typical conditions. It also incorporates material properties and environmental classification to compensate for limitations of the salt spray test, such as its inability to replicate dry-wet cycles and biological attachment. Therefore, a 3,000-hour salt spray test can be used to estimate a 100-year corrosion life.

[0039] Example 3

[0040] The original size of the carbon steel piles used in the experiment is φ50mm×500mm, of which the size of the covered section is 300mm, and 100mm exposed sections are reserved in each section for comparison.

[0041] A 2.8mm thick UNS N04400-0.48Sc nickel-based alloy cover plate is used. The actual composition of the UNS N04400-Sc alloy is as follows: C: 0.10%, Si: 0.30%, Mn: 1.20%, Cu: 32.28%, Scandium (Sc) 0.48%, and the remainder is nickel (Ni) and unavoidable impurities. The preparation process begins with vacuum induction melting, where the raw materials are fed into the melting furnace according to the desired ratio, and the tapping temperature is controlled above 1600°C. The molten steel is then refined in an argon oxygen deoxidation furnace (AOD). Aluminum is then added for deoxidation, and alloying elements are added to adjust the composition to the target values. The molten steel is then remelted in an electroslag remelting furnace to produce a pure steel ingot. Next, die casting is performed, using argon gas and mold slag for casting. After casting, the die is cooled to produce the steel ingot. Finally, the steel ingots are finished and subjected to high-temperature homogenization treatment at 1200°C, and then rolled into 2.8mm coils at a temperature ≥900°C.

[0042] Welding process: Welding material: ERNiCrMo-3 welding wire (PRE value ≥ 50); welding current: 130A, voltage: 24V, welding speed: 6cm / min, interpass temperature: ≤ 90°C. Before welding and sealing, nitrogen (purity ≥ 99.99%) was injected into the gap, and the oxygen content was tested to be < 0.1%. Finally, the hole was sealed to ensure that the weld area was tight and leak-proof. After sealing, a mass spectrometer leak detector was used to test for a leak rate of < 1×10 -6 Pa·m 3 / s. The weld area was ground and polished to remove surface debris such as weld spatter, and the weld was coated with 12% nitric acid solution for 20 minutes at room temperature. After rinsing with clean water, it was neutralized with 3% sodium carbonate solution and finally rinsed with pure water to form a passivation film with a surface roughness of Ra ≤ 0.8μm.

[0043] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the surface of the stainless steel cover plate has no pitting, cracks or discoloration, and the surface of the protected carbon steel pile inside has no corrosion, see Figure 4 .

[0044] The neutral salt spray test (ASTM B117) is an accelerated corrosion test that simulates a harsh corrosive environment through a high-concentration salt spray (5% NaCl, 35°C). The accelerated corrosion factor allows for an approximate estimate of a material's corrosion life in a seawater environment. A 24-hour spray test is generally considered equivalent to one year's worth of corrosion in a seawater environment. Based on this, it is estimated that a 100-year service life requires approximately 2400 hours of salt spray testing. This conversion requires the material to exhibit primarily uniform corrosion and that the seawater environment meets typical conditions. It also incorporates material properties and environmental classification to compensate for limitations of the salt spray test, such as its inability to replicate dry-wet cycles and biological attachment. Therefore, I used a 3000-hour salt spray test to infer a 100-year corrosion life.

[0045] Comparative Example 1

[0046] The difference from Example 1 is that commercial UNS S31254 austenitic stainless steel is used as the cover plate material. Other conditions are the same as those in Example 1, specifically: UNS S31254 austenitic stainless steel cover plate with a thickness of 2.5 mm is selected. Welding process: welding material Hastelloy C-276 welding wire (PRE value ≥ 40). Welding current 120A, voltage 22V, welding speed 8cm / min, interlayer temperature ≤ 100°C. The stainless steel cover plate is divided into sections (each section is 1.2m long) and covered with carbon steel piles, and then welded longitudinally. A 2.5mm center gap is reserved between the cover plate and the steel pile. Before welding and sealing, nitrogen (purity ≥ 99.99%) is filled into the gap, and the oxygen content is detected to be <0.1%. Finally, the hole is sealed to ensure that the welding area is dense and leak-proof. After sealing, a mass spectrometer leak detector is used for detection, and the leakage rate is <1×10 -6 Pa·m 3 The weld area is polished to remove surface debris such as weld spatter, and a passivation treatment is performed. Apply 12% nitric acid solution to the weld seam and allow it to sit for 20 minutes at room temperature. Rinse with clean water, then neutralize with 3% sodium carbonate solution. Finally, rinse with pure water to form a passivation film.

[0047] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the anti-corrosion effect deteriorates, see Figure 5 .

[0048] Comparative Example 2

[0049] The difference from Example 2 is that the welding process is as follows: the welding current is 110A, the voltage is 20V, the welding speed is 10cm / min, the welding material is ordinary E309L welding rod, and the other conditions are the same as Example 2, specifically: the original size of the carbon steel pile used in the experiment is φ50mm×500mm, of which the size of the covering section is 300mm, and 100mm exposed sections are reserved in each of the two sections for comparison.

[0050] The cover plate is made of UNS S32053-0.5Sc duplex stainless steel with a thickness of 3.0mm. The welding process is as follows: welding current 110A, voltage 20V, welding speed 10cm / min, and welding material is ordinary E309L welding rod. Before welding and sealing, argon gas (purity ≥99.99%) is filled into the gap, and the oxygen content is tested to be less than 0.1%. Finally, the hole is sealed to ensure that the weld area is dense and leak-proof. After sealing, a mass spectrometer leak detector is used to test the leak rate, which is less than 1×10 -6 Pa·m 3 The weld area was polished to remove surface debris such as weld spatter, and the weld was coated with 12% nitric acid solution for 30 minutes at room temperature. After rinsing with clean water, it was neutralized with 3% sodium carbonate solution and finally rinsed with pure water to form a passivation film.

[0051] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the anti-corrosion effect deteriorates, see Figure 6 .

[0052] Comparative Example 3

[0053] The difference from Example 1 is that no inert gas is used for protection and welding is performed directly. Other conditions are the same as those in Example 3. Specifically, the original size of the carbon steel piles used in the experiment is φ50mm×500mm, of which the size of the coated section is 300mm, and 100mm exposed sections are reserved in each of the two sections for comparison.

[0054] A UNS S31254-0.35Sc austenitic stainless steel cover plate with a thickness of 2.5mm was selected. Welding process: Hastelloy C-276 welding wire (PRE value ≥ 40) was used as the welding material. The welding current was 120A, the voltage was 22V, the welding speed was 8cm / min, and the interpass temperature was ≤100°C. The stainless steel cover plate was divided into sections (each section was no less than 5 times the diameter of the protected steel pile) and then covered with the carbon steel piles and welded longitudinally. The welded area was polished to remove surface debris such as weld spatter, and a passivation treatment was performed. The weld was coated with a 12% nitric acid solution and allowed to react at room temperature for 20 minutes. After rinsing with clean water, it was neutralized with a 3% sodium carbonate solution and finally rinsed with pure water to form a passivation film.

[0055] Salt spray test conditions: According to ASTM B117 standard, 5% NaCl solution, 35℃ continuous spray for 3000 hours, the anti-corrosion effect deteriorates, see Figure 7 .

[0056] As can be seen from the above embodiments and comparative examples, the core of the present invention's anti-corrosion technology lies in using a stainless steel cover plate that is resistant to seawater corrosion to cover the steel structure. The cover plate is then welded to isolate the steel structure from the corrosive environment, and an inert gas (nitrogen or argon) is filled into the middle hollow space. Specifically, an austenitic stainless steel cover plate with a thickness strictly controlled between 2 and 3 mm is first selected. The austenitic stainless steel is UNS S32053-Sc, UNS S31254-Sc, or UNS N04400-Sc alloy, and the scandium content is controlled between 0.3 wt.% and 0.5 wt.%. The above stainless steel has excellent corrosion resistance and can be used for a long time in harsh environments such as seawater. Then, the stainless steel and the ordinary carbon steel piles are welded together using welding technology. Hastelloy with a high PRE value is selected as the welding material. Parameters such as current, voltage, and welding speed are strictly controlled to reduce welding heat input and prevent changes in metallographic structure caused by overheating. During the welding process, the stainless steel and ordinary carbon steel piles are welded together at both ends, leaving a 2-3mm gap in between. Finally, when the weld is sealed, an inert gas (nitrogen or argon) is injected into the space between the stainless steel cover plate and the carbon steel pile to completely remove oxygen from the space and ensure that no oxygen remains in the inner layer. Finally, the hole is sealed to ensure that the weld area is dense and leak-proof. Salt spray test data indicates that the single-use anti-corrosion life is greater than 100 years, greatly reducing the frequency of anti-corrosion construction and avoiding the waste of manpower and material resources caused by multiple constructions, as well as the impact on facility safety.

Claims

1. A method for coating and anti-corrosion of seawater stainless steel in the splash zone of marine engineering facilities, characterized by: The steel structure is covered with seawater-resistant stainless steel cover plates by welding, and inert gas is filled between the seawater-resistant stainless steel cover plates and the steel structure to achieve corrosion protection.

2. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 1 is characterized in that: The seawater-resistant stainless steel cover plate is made of austenitic stainless steel containing rare earth element scandium (Sc). The thickness of the cover plate is 2-3 mm, and the austenitic stainless steel is UNS S32053-Sc, UNS S31254-Sc, or UNS N04400-Sc alloy.

3. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 2, characterized in that: The composition of UNS S31254-Sc is C≤0.03%, Si≤0.40%, Mn≤0.50%, Cr: 19.00%~21.00%, Ni: 17.00%~19.00%, Mo: 5.50%~7.50%, Cu: 0.50%~1.00%, scandium (Sc) 0.3%-0.5%, and the rest is iron (Fe) and unavoidable impurities; The composition of UNS S32053-Sc by mass is: C≤0.03%, Si≤1.00%, Mn: 4.00%~6.00%, Cr: 22.00%~24.00%, Ni: 24.00%~26.00%, Mo: 5.00%~6.00%, N: 0.17%~0.22%, scandium (Sc) 0.3%-0.5%, and the rest is iron (Fe) and unavoidable impurities; The composition of UNS N04400-Sc by mass is: C≤0.30%, Si≤0.50%, Mn≤2.00%, Cu: 28.00%~34.00%, scandium (Sc) 0.3%-0.5%, and the rest is nickel (Ni) and unavoidable impurities.

4. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 1 is characterized by: The seawater-resistant stainless steel cover plate is welded to both ends of the steel structure in the longitudinal direction to form a covering of the steel structure by the seawater-resistant stainless steel cover plate. The welding current is 110-130A, the welding voltage is 20-25V, the welding speed is 5-10cm / min, and the welding material is Hastelloy.

5. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 4, characterized in that: The seawater-resistant stainless steel cover plate is welded to both ends of the steel structure, leaving 2-3mm in the middle. Before welding and sealing, inert gas is filled into the gap between the seawater-resistant stainless steel cover plate and the steel structure to exclude oxygen. Finally, the hole is sealed to ensure that the welding area is dense and leak-proof.

6. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 5, characterized in that: After welding, the welding area is ground and polished to remove surface debris such as welding spatter, and passivation treatment is performed.

7. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 6, characterized in that: The passivation treatment is to apply 10% to 20% nitric acid solution to the weld, let it act at room temperature for 10 to 30 minutes, rinse with clean water, neutralize with 1% to 3% sodium carbonate solution, and finally rinse with pure water to form a passivation film.

8. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 1 is characterized by: The covering range of the seawater-resistant stainless steel cover plate is from 1 meter below the maximum low tide line to 2 meters below the maximum high tide line of the seawater tide level, and the covering length of a single section shall not be less than 5 times the diameter of the steel pile.

9. The method for coating and anti-corrosion of seawater-resistant stainless steel in the splash zone of marine engineering facilities according to claim 1, characterized in that: The inert gas is nitrogen or argon.

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