Sand blasting and laser combined derusting and desalting method for coastal heavy-corrosion steel structure

Abstract

The invention provides a sand blasting and laser combined derusting and desalting method for a coastal heavy corrosion steel structure. The method comprises the steps that S1, the thickness H1 of a rust layer on the surface of a to-be-cleaned steel structure is measured; s2, quartz sand is selected as a sand blasting grinding material, and the gravel particle size spraying pressure P is determined according to the rust layer thickness H1; s3, abrasive materials are sprayed according to the sand blasting parameters in the S2, and a main body rust layer is stripped; step S4, measuring the thickness H2 of the residual rust layer on the surface treated in the step S3; s5, pulse laser parameters are determined by referring to the thickness H2 of the residual rust layer; s6, the surface is cleaned according to the laser parameters in the S5, and a residual rust layer and soluble chlorine salt embedded into micropores / cracks on the surface of the steel structure are removed; and step S7, measuring the concentration C of chloride ions on the surface treated in the step S6. According to the method, a thick and heavy rust layer and deep salt on the surface of the steel can be effectively removed, sand blasting and laser are combined, cleaning is conducted in stages, the cleaning efficiency is effectively improved, and a high-cleanliness surface is provided for coating of a coating.

Description

Technical Field

[0001] This invention belongs to the field of metal surface treatment technology, and specifically relates to an efficient cleaning method for heavily corroded steel structures serving in high-salt and high-humidity environments such as coastal and marine areas. Specifically, it is a rust and salt removal method that combines sandblasting and laser treatment. Background Technology

[0002] In coastal infrastructure, offshore platforms, and cross-sea bridges, steel structures are exposed to harsh atmospheric environments with high salinity and humidity for extended periods. Corrosive media such as chloride ions cause electrochemical corrosion with the steel substrate, leading to the formation of a thick, porous, and crack-rich rust layer on the steel surface. Even more serious is the fact that these corrosive media (such as soluble chloride salts like NaCl and MgCl2) can penetrate the coating and reach deep into the micropores and cracks of the substrate surface. At this point, traditional mechanical surface cleaning methods (such as wire brushing or simple sandblasting) can remove surface rust through macroscopic physical action, but they are insufficient to effectively remove soluble chloride salts anchored deep within microscopic defects. These residual chloride ions act like "latent corrosion seeds," which, under subsequent coating coverage, can initiate and accelerate coating blistering, peeling, and continued corrosion of the substrate—a typical phenomenon known as "under-coating corrosion"—seriously threatening the safety and service life of the structure.

[0003] To ensure the long-term protection and safe operation of coastal steel structures, thorough surface cleaning during regular maintenance is a crucial step in surface treatment before painting, achieving the dual goals of "rust removal" and "salt removal." Currently, the surface cleaning methods widely used in engineering projects mainly include traditional sandblasting (shot blasting) and the emerging laser cleaning.

[0004] Traditional shot blasting uses compressed air to propel hard abrasive particles at high speed onto the surface to be treated, using kinetic energy to peel away rust and old coatings. Its advantages lie in its high processing efficiency and strong ability to remove thick rust layers. However, its mechanism based on macroscopic mechanical impact also brings significant limitations. First, its desalination capacity is severely insufficient. Due to the macroscopic scale of shot blasting, it is difficult to effectively remove soluble chloride salts embedded deep within the micropores and microcracks of the steel substrate, resulting in chloride ion residue and failing to fundamentally eliminate the hidden danger of "under-coating corrosion." Second, shot blasting carries the risk of substrate damage. Improper selection of blasting pressure and abrasive can easily cause excessive impact on the steel substrate due to its enormous kinetic energy, even inducing microscopic plastic deformation and altering the surface stress state of the material.

[0005] Emerging laser cleaning technology utilizes the interaction between a high-energy laser beam and surface contaminants, causing them to instantly vaporize and peel off. This is a "non-contact, non-abrasive" green cleaning technology. Its advantages include high precision, no dust, minimal thermal impact on the substrate, and the ability to handle complex geometric surfaces. Crucially, the high energy of the laser can directly vaporize or decompose chloride salts, effectively removing soluble salts embedded in microscopic defects in the substrate, demonstrating unique potential in desalination. Simultaneously, the laser treatment forms a thin, dense oxide film on the clean substrate surface. This film effectively inhibits "flash rust" on steel before subsequent coating, providing a longer processing window for the application. However, single laser cleaning technology faces severe challenges in terms of cleaning efficiency when dealing with heavily corroded steel structures: when dealing with heavy rust layers hundreds of micrometers thick, relying solely on laser cleaning not only requires extremely high energy density, but also suffers from a sharp attenuation of laser energy during the penetration of the surface rust layer due to the "coating shielding effect," resulting in insufficient effective energy at the interface between the rust layer and the substrate. Often, multiple repeated scans are required to achieve the desired cleaning effect, which directly leads to low cleaning efficiency, high energy consumption and time costs, and significantly reduced economic benefits.

[0006] Simply combining sandblasting and laser cleaning technologies without systematic parameter coordination and process integration results in a mere functional superposition rather than organic fusion. For example, excessively thick or thin rust layers after sandblasting directly impact the efficiency and effectiveness of subsequent laser cleaning; if sandblasting causes microscopic damage to the substrate, it can even exacerbate the risk of thermal stress concentration during subsequent laser treatment. Therefore, achieving precise parameter matching and functional complementarity between the two processes to form a standardized, closed-loop controllable composite cleaning process for "high-salt, high-humidity, heavily corroded steel structures" has become a pressing technical challenge in this field. Summary of the Invention

[0007] The purpose of this invention is to propose a combined sandblasting and laser cleaning method for rust and salt removal of heavily corroded steel structures in coastal areas. By combining the advantages of sandblasting and laser cleaning technologies, it can efficiently remove rust layers from the surface of heavily corroded steel, while thoroughly eliminating corrosive media from the substrate surface, providing an ideal surface for subsequent coating application. The combined sandblasting and laser cleaning method provided by this invention is suitable for steel or metal surfaces with rust layer thicknesses ranging from 100 to 1000 μm.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A combined sandblasting and laser rust removal and desalination method for heavily corroded coastal steel structures includes the following steps; Step S1: Measure the rust layer thickness H1 (unit: μm) on the surface of the steel structure to be cleaned. Step S2: Select quartz sand as the abrasive for sandblasting, and determine the grit size (unit: mm) and jet pressure P (unit: MPa) according to the rust layer thickness H1. Step S3: Spray the abrasive according to the sandblasting parameters in S2 to strip the main rust layer. Step S4: Measure the residual rust layer thickness H2 (unit: μm) on the surface after the treatment in S3. Step S5: Determine the pulsed laser parameters according to the residual rust layer thickness H2. Step S6: Clean the surface according to the laser parameters in S5 to remove the residual rust layer and the soluble chlorides embedded in the micropores / cracks on the steel structure surface. Step S7: Measure the chloride ion concentration C (unit: mg / m 2 ) on the surface after the treatment in S6.

[0009] Further, in Step S1, the rust layer is a mixture of deteriorated coating and iron rust. When the coating and the rust layer are significantly delaminated, the thickness of the iron rust area is taken as H1.

[0010] Further, in Step S2, the sandblasting pressure P and the rust layer thickness H1 satisfy a linear relationship P = k1×H1 + b1, where the value range of the coefficient k1 is 0.0004 MPa / μm to 0.0006 MPa / μm, and the value range of the constant term b1 is 0.15 MPa to 0.25 MPa.

[0011] Further, in Step S2, the particle size of the quartz sand is selected in segments according to the rust layer thickness H1: when H1 ≤ 400μm, the corresponding particle size range of the quartz sand is 1.0mm to 1.8mm; when H1 > 400μm, the corresponding particle size range of the quartz sand is 1.8mm to 2.5mm.

[0012] Further, in Step S3, the angle between the sandblasting jet direction and the normal of the surface to be cleaned is not greater than ±45°, and the sandblasting cleaning speed is 5 mm / s to 15 mm / s.

[0013] Further, in Step S4, the residual rust layer thickness H2 should not be greater than 30μm; if H2 does not drop below 30μm, repeat Step S3 for sandblasting treatment, and re - execute Step S1 and Step S2 before each repetition to ensure that conditions are created for subsequent laser treatment on the premise of avoiding damage to the substrate by grit impact.

[0014] Further, in Step S

[0015] Furthermore, in step S5, the laser scanning speed is 5000 mm / s to 10000 mm / s, the laser repetition frequency is 200 kHz to 4000 kHz, the laser pulse width is 100 ns to 300 ns, and the laser cleaning speed is 1 mm / s to 5 mm / s.

[0016] Furthermore, in step S7, the chloride ion concentration C should not exceed 20 mg / m³. 2 If it does not drop to 20 mg / m³ 2 For samples of 10 and below, step S6 is repeated for laser cleaning, and step S5 is re-executed before each repetition to avoid damage to the substrate caused by excessive laser power selection.

[0017] This invention proposes a combined sandblasting and laser cleaning method for rust and salt removal of heavily corroded steel structures in coastal areas. By organically combining sandblasting with pulsed laser cleaning technology, it achieves efficient and thorough removal of rust and chloride contamination from the surface of heavily corroded steel. The method first utilizes a parametrically controlled sandblasting process to rapidly peel off the main rust layer, significantly improving processing efficiency. Subsequently, by precisely matching laser parameters to the rust layer thickness, it achieves fine removal of residual rust and soluble chloride embedded in micropores / cracks in the substrate. This staged, parametrically coordinated process design not only fully leverages the advantages of both technologies but also forms a complete quality control closed loop through post-sandblasting thickness detection and precise matching of laser parameters. Ultimately, the treated surface cleanliness reaches Sa 3 or even higher standards, while controlling the surface chloride ion concentration below 20 mg / m², providing an ideal surface condition for subsequent application of high-performance anti-corrosion coatings. This technical solution effectively overcomes the limitations of traditional single cleaning methods in terms of efficiency, desalination effect, or cost, and has broad application prospects in the field of anti-corrosion maintenance of steel structures for infrastructure such as coastal areas, offshore platforms, and cross-sea bridges.

[0018] Compared with the prior art, the present invention has the following advantages: 1. This invention rapidly removes the thick rust layer from the main body through sandblasting, greatly reducing the workload of subsequent laser cleaning and effectively overcoming the efficiency bottleneck of single laser cleaning of heavy rust layers. This collaborative model fully leverages the high efficiency of sandblasting in treating macroscopic thick rust layers while retaining the advantages of laser in fine processing, significantly improving overall cleaning efficiency and making it particularly suitable for large-area engineering applications.

[0019] 2. The combined process of this invention not only achieves surface cleanliness standards of Sa 3 or even higher, but more importantly, it can stably control the surface chloride ion concentration at an advanced level below 20 mg / m². Sandblasting exposes the microscopic defects of the substrate, creating favorable conditions for subsequent laser removal of embedded soluble chloride salts. This fundamentally solves the technical problem of traditional cleaning methods' inability to completely remove salt, providing a truly clean and pollution-free ideal substrate for subsequent coatings. Attached Figure Description

[0020] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments: Figure 1 This is a schematic flowchart of the laser cleaning method for corroded rust layers according to the present invention; Figure 2 This is a morphological image of the corroded steel plate surface before cleaning; Figure 3 This is a surface morphology image after two passes of single sandblasting cleaning; Figure 4 These are surface morphology images after two passes of single laser cleaning; Figure 5 This is a surface morphology image after one cleaning cycle using the sandblasting and laser combined cleaning method provided by the present invention. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention. It is understood that the accompanying drawings are provided for reference and illustration only, and are not intended to limit the present invention.

[0022] like Figure 1 As shown, the present invention provides a sandblasting and laser combined rust removal and desalination method for heavily corroded coastal steel structures, which mainly includes the following steps; 1. Measure the rust layer thickness H1 (unit: μm) on the surface of the steel structure to be cleaned using a coating thickness gauge. During measurement, at least 5 evenly distributed test points must be covered on the corroded steel structure surface. The arithmetic mean is taken as the final rust layer thickness H1. The rust layer can be iron rust or a mixture of deteriorated coating and iron rust. If there is a clear separation between the coating and the rust layer, the rust area should be used as the rust layer test point, such as... Figure 2 The image shows a corroded steel plate with an average rust layer thickness H1 of 300 μm.

[0023] 2. Set the sandblasting parameters according to H1. The sandblasting abrasive is quartz sand with a Mohs hardness of 7, which is not easy to cause secondary pollution while ensuring the cleaning effect and the cost is controllable. The sandblasting pressure P and the rust layer thickness H1 satisfy a linear relationship P = k1×H1 + b1, where the value range of the coefficient k1 is from 0.0004 MPa / μm to 0.0006 MPa / μm, and the value range of the constant term b1 is from 0.15 MPa to 0.25 MPa. The particle size of the quartz sand is selected in segments according to H1: when H1 ≤ 400 μm, the corresponding quartz sand particle size range is from 1.0 mm to 1.8 mm to prevent excessive kinetic energy of the grit from damaging the substrate surface; when H1 > 400 μm, the corresponding quartz sand particle size range is from 1.8 mm to 2.5 mm to ensure the efficiency of sandblasting cleaning.

[0024] 3. Spray the abrasive according to the sandblasting parameters determined by H1. The spraying distance is controlled to be 80 to 200 mm, the spraying angle is perpendicular to the surface to be cleaned at ±45°, and the sandblasting cleaning speed is 5 mm / s to 15 mm / s. The main rust layer is peeled off by the impact of the abrasive, and the micropores and microcracks on the surface of the steel structure substrate are exposed, and it is ensured that there are no obvious scratches or abrasions on the substrate during the peeling process.

[0025] 4. Measure the residual rust layer thickness H2 and confirm that H2 ≤ 30 μm to create necessary conditions for the subsequent effective action of the laser on the substrate surface. If H2 is not reduced below 30 μm, repeat step 3 for sandblasting treatment, and re-measure H1 and determine the sandblasting parameters before each repetition. Thus, conditions are created for laser treatment while avoiding excessive damage to the substrate.

[0026] 5. Determine the laser cleaning parameters according to H2. The type of the laser beam is a flat-top pulsed laser. This laser beam not only has a high instantaneous energy density of pulsed laser to efficiently peel off pollutants and embedded soluble chlorides, but its flat-top energy distribution can also ensure uniform action. It can generate a dense and uniform oxide layer with a thickness of 1 to 3 μm on the substrate surface while completely removing the residual rust layer, effectively delaying the occurrence of flash rust. The laser power is set in segments according to the residual rust layer thickness H2: when H2 ≤ 15 μm, the laser power range is 100 to 300 W; when 15 μm < H2 ≤ 30 μm, the laser power range is 300 to 500 W. The laser scanning speed is 5000 mm / s to 10000 mm / s, and a spiral scanning path is recommended. The laser repetition frequency is 200 kHz to 4000 kHz, the laser pulse width is 100 ns to 300 ns, and the laser cleaning speed is 1 mm / s to 5 mm / s. Perform laser cleaning according to these parameters.

[0027] 6. Measure the chloride ion concentration C (unit: mg / m²) on the surface after laser cleaning using a soluble salt detector. The chloride ion concentration C should not exceed 20 mg / m², which is the safe threshold for subsequent anti-corrosion coating adhesion on steel structures in high-salt and high-humidity environments. If C does not drop to the threshold or below, repeat the laser cleaning process, re-measuring H2 before each repetition and adjusting the laser power accordingly. This cycle effectively avoids excessive laser power causing ablation damage to the substrate. If C meets the requirements, the entire cleaning process is complete.

[0028] Example 1: Example 1: A corroded steel plate with a surface size of 15mm × 7mm, which had been corroded in a coastal atmospheric environment for 8 months and had a rust layer thickness of 300μm, was subjected to two sandblasting cleanings. The abrasive was quartz sand with a particle size of 1.5mm. The sandblasting pressure was calculated according to the linear relationship P = k1 × H1 + b1, with k1 = 0.0005MPa / μm and b1 = 0.2MPa, resulting in P = 0.0005 × 300 + 0.2 = 0.35MPa. The spraying distance was 150m, the cleaning speed was 10mm / s, and the angle between the jet direction and the surface normal was approximately 45°.

[0029] The surface appearance after sandblasting is as follows Figure 3 As shown, the thickness of the residual rust layer was measured to be 5 μm. Macroscopic observation showed that the main body of the rust layer had been peeled off, and yellowish-brown rust traces remained in the micropores and microcracks. The cleanliness level only reached Sa2 level, and the chloride ion concentration C = 120 mg / m² was detected by the soluble salt detector.

[0030] Example 2: Example 2 involves performing two pulsed flat-top laser cleanings on the corroded steel plate under the same conditions as in Example 1. The laser power is 500W, the laser scanning speed is 8000mm / s, the laser repetition frequency is 500kHz, the laser pulse width is 300ns, the laser cleaning speed is 3mm / s, and the laser beam is at a 90° angle to the surface to be cleaned.

[0031] Surface appearance after laser cleaning Figure 4 As shown, the thickness of the residual rust layer was measured to be 150 μm, a large amount of residual rust could be observed on the surface, the cleanliness was only Sa 1, and the chloride ion concentration C = 150 mg / m² was detected by the soluble salt detector.

[0032] Example 3: Example 3 is an embodiment of the sandblasting and laser combined rust removal and desalination method for heavily corroded coastal steel structures proposed in this invention, using corroded steel plates under the same conditions as in Examples 1 and 2. The surface of the corroded steel plate was subjected to one sandblasting cleaning and one laser cleaning according to the cleaning steps described in the above specific embodiments.

[0033] The abrasive used for sandblasting was quartz sand with a particle size of 1.5 mm. The sandblasting pressure was calculated using the linear relationship P = k1 × H1 + b1, with k1 = 0.0005 MPa / μm and b1 = 0.2 MPa, resulting in P = 0.0005 × 300 + 0.2 = 0.35 MPa. The blasting distance was 150 m, the cleaning speed was 10 mm / s, and the angle between the jet direction and the surface normal was approximately 45°. After one sandblasting cleaning, the thickness of the residual rust layer H2 on the surface was 15 μm.

[0034] The laser power is 100W, the laser scanning speed is 8000mm / s, the laser repetition frequency is 500kHz, the laser pulse width is 300ns, the laser cleaning speed is 3mm / s, and the laser beam is at a 90° angle to the surface to be cleaned.

[0035] Surface appearance after cleaning Figure 5 As shown, the residual rust layer on the surface is less than 1 μm thick, the cleanliness level is only Sa 3, and the chloride ion concentration detected by the soluble salt detector is C=5 mg / m².

[0036] Three examples clearly demonstrate that sandblasting alone cannot solve the problem of incomplete desalination, and laser cleaning alone has the drawback of low efficiency. However, combined sandblasting and laser cleaning can give full play to the synergistic advantages of the two technologies and achieve the best treatment effect on steel plates with 300μm rust layer.

[0037] Some features of the present invention are described in different embodiments for clarity; however, these features may also be described in combination in a single embodiment. Conversely, some features of the present invention are described only in a single embodiment for brevity; however, these features may also be described individually or in any suitable combination in different embodiments.

[0038] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and substitutions can be made without departing from the technical principles of the present invention, and these improvements and substitutions should also be considered within the scope of protection of the present invention.

Claims

1. A combined sandblasting and laser rust removal and desalination method for heavily corroded coastal steel structures, characterized in that: It includes the following steps; Step S1: Measure the thickness H1 of the rust layer on the surface of the steel structure to be cleaned, unit: μm; Step S2: Select quartz sand as the abrasive for sandblasting, determine the grit size, unit: mm, and the jet pressure P, unit: MPa, according to the rust layer thickness H1; Step S3: Spray the abrasive according to the sandblasting parameters in S2 to peel off the main rust layer; Step S4: Measure the thickness H2 of the residual rust layer on the surface after the treatment in S3, unit: μm; Step S5: Determine the pulsed laser parameters according to the residual rust layer thickness H2; Step S6: Clean the surface according to the laser parameters in S5 to remove the residual rust layer and the soluble chlorides embedded in the micropores / cracks on the surface of the steel structure; Step S7: Measure the surface chloride ion concentration C after treatment in S6, unit: mg / m³ 2 .

2. The method for combined sandblasting and laser rust removal and desalination of heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S1, the rust layer is a mixture of deteriorated coating and iron rust. When the coating and the rust layer are significantly delaminated, the thickness of the iron rust area is H1.

3. The method for combined sandblasting and laser rust removal and desalination of heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S2, the sandblasting pressure P and the rust layer thickness H1 satisfy a linear relationship P = k×H1 + b, where the value range of the coefficient k1 is 0.0004 MPa / μm to 0.0006 MPa / μm, and the value range of the constant term b1 is 0.15 MPa to 0.25 MPa.

4. The method for combined sandblasting and laser rust removal and desalination of heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S2, the particle size of the quartz sand is selected in segments according to the rust layer thickness H1: when H1 ≤ 400 μm, the corresponding particle size range of the quartz sand is 1.0 mm to 1.8 mm; when H1 > 400 μm, the corresponding particle size range of the quartz sand is 1.8 mm to 2.5 mm.

5. A method for combined sandblasting and laser rust removal and desalination of heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S3, the angle between the sandblasting jet direction and the normal of the surface to be cleaned is not greater than ±45°, and the sandblasting cleaning speed is 5 mm / s to 15 mm / s.

6. The method for combined sandblasting and laser rust removal and desalination of heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S4, the thickness H2 of the residual rust layer should not be greater than 30 μm; if H2 is not reduced below 30 μm, repeat Step S3 for sandblasting treatment, and re-execute Step S1 and Step S2 before each repetition to ensure that, on the premise of avoiding damage to the substrate by grit impact, conditions are created for subsequent laser treatment.

7. A combined sandblasting and laser rust removal and desalination method for heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S5, the type of laser beam used is a flat-top pulsed laser, and its power is set in segments according to the residual rust layer thickness H2: when H2 ≤ 15 μm, the laser power range is 100 to 300 W; when 15 μm < H2 ≤ 30 μm, the laser power range is 300 to 500 W.

8. A combined sandblasting and laser rust removal and desalination method for heavily corroded coastal steel structures according to claim 1, characterized in that: In Step S5, the laser scanning speed is 5,000 mm / s to 10,000 mm / s, the laser repetition frequency is 200 kHz to 4,000 kHz, the laser pulse width is 100 ns to 300 ns, and the laser cleaning speed is 1 mm / s to 5 mm / s.

9. A combined sandblasting and laser rust removal and desalination method for heavily corroded coastal steel structures according to claim 1, characterized in that: In step S7, the chloride ion concentration C should not exceed 20 mg / m³. 2 If it does not drop to 20 mg / m³ 2 For samples of 10 and below, step S6 is repeated for laser cleaning, and step S5 is re-executed before each repetition to avoid damage to the substrate caused by excessive laser power selection.

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