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  In the field of metal anticorrosion treatment, sandblasting derusting is a widely used surface pretreatment technology aimed at comprehensively removing rust, old coatings, oil contamination, and other pollutants from the surface of steel materials, thereby providing an ideal substrate surface for subsequent coatings or anticorrosion treatments. Among the various standards, the Sa2.5 standard is particularly important in projects requiring high anticorrosion performance, such as marine and industrial environments, due to its stringent surface treatment requirements. This article will elaborate on the technical requirements, implementation steps, and significance of the Sa2.5 standard for sandblasting derusting.

  I. Overview of the Sa2.5 Standard

  The Sa2.5 standard is one of the steel surface sandblasting derusting grades established by the International Organization for Standardization (ISO), with specific standards referenced in ISO 8501-1:2007(E). This standard categorizes surface cleaning into four grades: Sa1, Sa2, Sa2.5, and Sa3. The Sa2.5 standard requires that the surface be free of visible oil, dirt, scale, rust, paint coatings, and impurities, allowing only slight discoloration in the form of spots or stripes as residue traces. This standard ensures that the steel structure surface achieves a high degree of cleanliness after sandblasting treatment, providing a good adhesion foundation for subsequent coatings.

  II. Technical Requirements of the Sa2.5 Standard

  1.Surface Cleanliness:

  The steel surface should be completely cleared of rust, old coatings, and other contaminants, with no visible oil, dirt, loosely attached scale, rust, or paint coatings. Residue traces are only allowed to appear as slight discoloration in spots or stripes, which must not exceed the limits specified in the ISO 8501-1 standard.

  2.Surface Roughness:

  Appropriate surface roughness facilitates the mechanical bonding between the coating and the substrate, enhancing the coating's adhesion. Although the Sa2.5 standard does not directly specify roughness values, practical operations require adjusting sandblasting parameters based on specific coating requirements to achieve the appropriate roughness.

  3.Surface Uniformity:

  The surface after sandblasting treatment should be uniform and consistent, avoiding locally over-processed or under-processed areas to ensure overall anticorrosion effectiveness.

（G16）

  III. Implementation Steps

  1.Pretreatment:

  Remove all thick rust layers, visible oil, and dirt from the surface. This step is crucial for achieving the Sa2.5 standard, as any residues may affect the final treatment outcome.

  2.Sandblasting Derusting:

  Using compressed air as the driving force, quartz sand or environmentally friendly alternative abrasives are sprayed onto the steel surface at high speeds. During the sandblasting process, parameters such as blasting pressure, blasting distance, and abrasive flow rate need to be adjusted based on the surface condition to achieve the desired derusting effect.

  3.Surface Inspection:

  After sandblasting treatment, the surface should be comprehensively inspected to ensure there is no visible oil, dirt, scale, rust, paint coatings, or impurities. Simultaneously, check if the residue traces meet the requirements of the Sa2.5 standard.

  4.Subsequent Treatment:

  If necessary, subsequent operations such as surface passivation treatment and primer coating can be performed after sandblasting derusting to enhance the anticorrosion effect.

  IV. Significance and Application Fields

  The Sa2.5 standard for sandblasting derusting holds a significant position in the field of metal anticorrosion treatment. This standard not only ensures a high degree of cleanliness on the steel structure surface but also provides a good adhesion foundation for subsequent coatings, thereby extending the service life of the steel structure. In projects requiring high anticorrosion performance, such as marine and industrial environments, the application of the Sa2.5 standard is particularly widespread. For example, steel structures like offshore platforms, bridges, tanks, and pipelines all require sandblasting derusting treatment that meets the Sa2.5 standard or higher to ensure their long-term stable anticorrosion performance.

  As an important technical specification in the field of metal anticorrosion treatment, the Sa2.5 standard for sandblasting derusting imposes strict requirements on the cleanliness of steel structure surfaces and the adhesion of subsequent coatings. By following this standard for sandblasting derusting treatment, the long-term safety of steel structures in harsh environments can be ensured.

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