Heavy steel structure corrosion characteristics and protective methods of the large steel structures such as Bridges, television tower, tower, high-pressure lightning tower, the lighthouse in the sea, large reservoir sluice, water towers, offshore oil facilities, tank car, spherical tank, storage tank, oil tank, carbonization tower, heat exchanger, chimney, container, ship hulls, offshore platform steel structure, etc., Are long in the Marine atmosphere, industrial atmosphere corrosion environment. If you want to use for a long time, and not a large area of maintenance, long-term coating protection is the best, the service life can reach 20-30 years, less maintenance costs, can obtain obvious economic benefits.

1. Corrosion characteristics of steel structure in Marine atmosphere and industrial atmosphere

The steel structure in atmospheric environment is affected by sunshine, wind and sand, rain and snow, frost and dew, and the change of temperature and humidity throughout the year. Among them, the oxygen and moisture in atmospheric environment are the important factors that cause the corrosion of outdoor steel structure, resulting in electrochemical corrosion.

Industrial gases contain SO2, CO2, NO2, CI2, H2S and NH3, etc. Although the content of these components is small, the corrosion damage to steel can not be ignored. Among them, SO2 has the biggest effect, and CI2 can destroy the passivation film on the metal surface. These gases dissolve in water and become acidic, forming acid rain that corrodes metal installations.

The ocean atmosphere is characterized by a large amount of salt, mainly NaCI, which is deposited on the metal surface. Due to its hygroscopic property and increasing the conductive effect of the liquid film on the surface, and the strong erosiveness of CI- itself, the corrosion of the metal surface is aggravated. Steel structures corroded more severely the closer they were to the coast, with corrosion rates many times higher than in the inland atmosphere.

2, large steel structure commonly used protection methods

Steel structure is often sprayed with zinc or aluminum, aggravating corrosion coating to form a long-term anticorrosive structure, or with supporting heavy anticorrosive coating protection. The metal zinc and aluminum have great resistance to atmospheric corrosion. Spraying zinc or aluminum on steel components, zinc, aluminum is negative potential and steel formation sacrifice anode protection so that the steel is basically protected. At present, aluminum spray coating is used to prevent the corrosion of industrial atmosphere and Marine atmosphere. Its characteristics are as follows:

(1) The bonding force between aluminum spray coating and steel matrix is firm, the coating life is long, and the long-term economic benefit is good;

(2) Flexible process, suitable for long-term protection of important large and difficult to maintain steel structure, can be constructed on site;

(3) spraying zinc or aluminum coating with anticorrosive coating closed, can greatly extend the service life of the coating, from the effect of theory and practical application, spraying zinc or aluminum coating is the best bottom layer of anticorrosive coating. The protective life of composite coating of metal spraying layer and anticorrosive coating coating is longer than the sum of the life of metal spraying layer and anticorrosive coating protection layer, which is several times of the life of single coating protection layer.

The heavy anticorrosive long-acting coating is composed of primer, intermediate paint and top paint.

From the long-term economic consideration, spraying aluminum coating is the most economical, but the one-time investment is large, the well-constructed coating can be in 10 years without maintenance. Epoxy zinc rich primer + epoxy iron intermediate paint and acrylic polyurethane long-acting protection system have better economy.