2.5　Derusting and Primer Painting

2.5.1　When parts and steels need derusting,the blasting derusting,shot-blasting derusting,manual derusting and power tool derusting may be adopted.The steel surface after treatment shall be free from welding slag,overlap,spatter,dust,oil stain,water or burrs.After derusting and before painting primer,the surface of parts and steels shall meet the requirements of the current relevant standards of the Nation or design.

2.5.2　When adopting blasting and shot-blasting derusting on the surface of parts and steels,measures shall be taken to control environmental pollutions.The relative humidity of the construction environment shall not be larger than 85%,and the surface of parts and steels shall be free from dew.

2.5.3　When conducting blasting derusting,the compressed air used shall be free from visible oil,water and dirt.

2.5.4　The derusting grade of the surface of parts and steels shall meet the design requirements,and it shall be in accordance with those specified in Table 2.5.4 when there is no requirement of design.

Table 2.5.4　Derusting grade of surface of parts and steels

Note:The derusting grade is detailed in"Rust Grades and Preparation Grades of Steel Surfaces Before Application of Paints and Related Products"(GB 8923).

2.5.5　When painting primer on parts and steels,the ambient temperature and relative humidity shall meet the requirements stated in the technical documents of coating products.Where no requirement is stated in the technical documents of products,the ambient temperature should be 5℃~38℃,and the relative humidity shall not be larger than 85%.When painting,the surface of parts and steels shall be free from dew;within 4h after painting,the surface shall be protected against rain.

2.5.6　The surface of parts and steels shall be free from mistaken coating or lack of coating.The coating shall be even without such obvious defects as wrinkle,sagging,lifting,pinhole,re-rust and bubble.

2.5.7　The milled end face of parts shall be protected by painting varnish after milling.

2.5.8　Before painting primer,the mark shall be transferred;protective measures shall be taken for the weld joint before qualified inspection and for the surface of parts within 50mm at both sides of field joint.The following position shall not be painted with primer:

1　High-strength bolted connection friction surface.

2　Contact surface of column base plate and base.

3　Internal surface of totally enclosed parts.

4　Machining surface required by machinery installation.

5　Position that is not to be painted according to the design.