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　　The total painting area of steel box girder of a bridge in Huangpu River is more than 100000 m2. At the end of coating construction in 1995, according to the designation of the owner and the designer, the products of Shanghai Kailin paint factory were used at that time. See Table 1 for the matching scheme of outer coating of steel box girder.

　　According to the classification of atmospheric corrosion grade in iso12944-2 international standard, the steel box girder of the bridge is in C3 medium corrosion environment, that is, "urban and industrial atmosphere, medium sulfur dioxide pollution, low salinity coastal area". After exposed to C3 corrosion environment for one year, the mass loss rate of low carbon steel per unit area is 200-400g / m2, and the thickness loss is 25-50um.

　　At the same time, the system regulations of corrosion environment, service life and paint film thickness in ISO 12944-5 are also used for reference. See Table 2 for details.

　　The paint film on the outside of the steel box of the bridge should have a coating life of more than 15 years. However, in October 2005, Shanghai Pujiang Tunnel Development Co., Ltd. found that the corrosion level of paint film on the outside of steel box girder had exceeded the RI 3 level specified in ISO 4628-3 standard. According to ISO 12944 standard and advanced experience at home and abroad, the first overhaul is the most economical and effective. In order to ensure a good image of the bridge during the Expo, the company decided to renovate the steel box girder coating.

　　After a lot of investigation and analysis, the Technology Department of Shanghai Pujiang tunnel and bridge company decided to adopt the following coating design scheme, as shown in Table 3.

　　According to ISO 14713 standard (see Table 4), the coating matching system has a coating life of more than 20A.

　　Therefore, from April to October 2006, 8000m2 steel box girder was renovated according to the coating matching system in Table 3.

　　Supporting design scheme:

　　According to the two international standards of ISO 14713 and ISO 12944 and my understanding of heavy-duty anticorrosive coatings of major companies, the following two major supporting systems have been formulated, which have been provided to Shanghai Pujiang tunnel and bridge operation management company for reference.

　　Take the arc spraying zinc aluminum alloy as the primer, and see Table 5 for the matching design scheme with the sealing paint, intermediate paint and finishing paint.

　　According to ISO 14713 standard, the supporting system should have a corrosion resistance life of more than 20A. Compared with table 3, the following changes are made:

　　1. In order to ensure the stability of operation and reduce the porosity and roughness of Zn Al layer, the pseudo alloy of arc spraying Zn Al alloy was changed into Zn Al alloy. According to my investigation on the surface roughness of zinc aluminum coating of three domestic bridges, the roughness of zinc aluminum pseudo alloy coating is the largest;

　　2. The spray effect and penetration degree of the special epoxy sealer are better than that of the epoxy micaceous iron intermediate coat;

　　3. In order to increase the antirust ability of the coating, and to ensure the fullness of the coating, the epoxy micaceous iron coating is added;

　　4. It is not only for environmental protection reasons, but also for the better glossiness and weather resistance of polyurethane topcoat, which lays a foundation for future maintenance. According to the above supporting scheme, a lot of samples have been made with the corresponding heavy-duty anticorrosive coating of "Nippon", with good effect. The bridge headquarters has adopted zinc aluminum alloy coating.

　　See Table 6 for surface roughness value of zinc aluminum layer of steel box girder of bridge.

　　The above content is reproduced in "anticorrosive coating and coating" collected by Mr. Li Minfeng