6.12　Coating

6.12.1　Before coating，the derusting grade of the steel surface shall meet the requirements of the design document.The coating shall meet the relevant requirements of the current national standard GB 8923 Rust Grades and Preparation Grades of Steel Surfaces before Application of Paints and Related Products when there is no requirement in the design document.The treated steel surface shall be free of welding slag，craters，dust，oil stains，water and burrs，etc.

6.12.2　The pretreatment of steel plate shall be conducted on special rust removing equipment by abrasive cleaning at the plant.The welds welded on the installation site，and the damaged and scratched parts of the coating may be subject to manual derusting or mechanical derusting.

6.12.3　The ambient temperature and relative humidity during coating shall meet the requirements of the design document and the product manual.When there is no requirement in the design document，the ambient temperature shall be 5℃-38℃and relative humidity shall not be larger than 85%.The surface of the element shall be free of moisture condensation during coating，and shall be avoided from rain within 4h after coating.

6.12.4　The first layer of primer shall be coated before rusting the surface for the steel，of which the action of rust removing by abrasive cleaning is qualified.When storing in the plant，the primer shall be coated within 16h；and when storing out of the plant，the primer shall be coated on duty.For the steel，of which the action of rust removing by abrasive cleaning is qualified，the dust removal shall be performed again when it rusts before coating the primer.

6.12.5　The time and thickness of coating shall meet the requirements of the design document or the product manual.When the design has no requirements for the thickness of the coating，the total thickness of the dry paint film of the coating shall be 150μm outdoors and 125μm indoors.The allowable deviation is-25μm.The allowable deviation of the thickness of the dry paint film of each round of coating is-5μm.The coating interval shall be from forming the dry film of the previous coating to the next coating.

6.12.6　The variety，specification，performance and coating technical requirements of the heat-resisting anticorrosive paint on the surface of the blast furnace，hot-blast stove，uptake duct，downcomer，three-way pipe or five way ball shall meet the requirements of the design document and the product manual.

6.12.7　Coating may be brush coating，roll coating，air spraying，and high-pressure airless spraying.The appropriate coating method should be selected according to the condition of the coating site，the dimension of the coated matters，the variety of paint and the requirements of the design document.

6.12.8　The coating quality shall be in accordance with the following requirements:

1　The coating thickness shall meet the provisions of the design document.The coating shall be uniform and its color shall be consistent.

2　Paint film shall be attached firmly and be free of shedding，wrinkling，bubbles，pin holes and other defects.

3　The coating shall be complete and be free of damage and flow.

4　The element surface shall be free of error coating and missing.

5　The distance of painting color rings shall be uniform and the width thereof shall be consistent.

6.12.9　In the course of fabrication in plant，the following parts shall not be coated:

1　The range of 50mm-100mm to two sides of the welding seams as well as 50mm to hole on the installation site.

2　Joint surface of high-strength bolts.

3　Concrete clinging or covering surface.

6.12.10　After completing coating in plant，the logo，mark and serial number of the element shall be clear and complete.

6.12.11　After installing the process steel structure，the following parts shall be subject to repair coating:

1　Welding part of installation site，burned and scratched parts.

2　Parts of assembling or installing serial number and character.

3　Exposed part of combination or connection.

4　Fastener.

5　Coating missing part.

6　Part damaged in installation.