Analysis Of Corrosion Status Of Steel Components Outside Substations And Study On Adhesion Of Galvanized Steel Coating

The unique high temperature and humid marine atmosphere corrosion environment and industrial environmental pollution brought by industrial development in Guangzhou make the substation outdoor steel components easy to corrosion,leading a potential danger in the safe and stable operation of the substations.Therefore,it is necessary to investigate the on-site corrosion of the outdoor steel components of the substation,evaluate and explore the existing corrosion protection system.In view of the widespread problem of the poor coating adhesion to hot dip galvanized(HDG)steel in the substations,the surface of the zinc layer should be pre-treated by sand blasting or phosphating process.Although blasting and phosphating processes have be widely used in steel industry,a few papers of the study of blasting and phosphating process have been reported on the surface of zinc layer,and the reported technical process parameters are also different,affecting the application of blasting and phosphating in the coating on HDG steel,and at the same time,it also restricts the wide application of the duplex coating system on HDG steel with good corrosion resistance,mark ability and decoration.In this paper,an on-site survey of the corrosion status of outdoor steel components in the selected 39 representative substations was conducted and it is found that the corrosion problems of outdoor steel components in the substations are mainly concentrated in the corrosion of steel structure supports and accessories protected only by coating,the corrosion of bolts and nuts,and cracking and peeling of the coatings on the surface of HDG steel.In the corrosion protection systems commonly used in the substations,the coating adhesion of red dan primer and alkyds paint to HDG steel is too poor to be suitable for the protection of HDG steel,while the HDG steel surface with epoxy primer and acrylic coating or polyurethane coating has better adhesion,good salt spray corrosion resistance,sulfur dioxide resistance and ultraviolet aging properties.The results of the atmosphere corrosion tests on the site of 9 substations with typical corrosion conditions show that the atmosphere environment corrosion level of substations in Guangzhou area is usually in the level of C2 to C3.The outdoor steel components in the substations should be protected by hot dip galvanizing.Meanwhile,appropriately improving the thickness of hot dip galvanizing layer,and the correct choice of the coating system and construction methods,can significantly improve the service life of outdoor steel components in the substations.Based on the results of the micro-morphology observation on of the surface of the HDG layer treated by blasting or phosphating and the adhesion tests of the epoxy resin coating after treatment,the optimal blasting process parameters were determined to be:blast pressure 0.3MPa,blast angle 45^o,blasting time 30 s,sand particle diameter 300?m.The coating adhesion force to the surface of HDG layer prepared by this blasting process is 8.38 MPa,which is 3.25times higher than the coating adhesion force to the surface untreated.The optimal phosphating process parameters are:Zn O 1.0 g/L,H₃PO₃ 10 g/L,Na NO₃ 15 g/L,p H 2.8,and phosphating time t 30s.The coating adhesion force to the surface of HDG layer prepared by this phosphating process is 7.02 MPa,which is 2.71 times higher than the coating adhesion force to the surface untreated.The comparative study of the coating adhesion force to the surface of HDG layer multi-step treated by sand blasting and then phosphating shows that the coating adhesion force to the multi-step treated surface is up to 9.61 MPa,and higher than that of the coating of individual blasting or phosphating treatment.The surface of the multi-step treated zinc layer still maintains a rough surface with many pits and scratches,anchoring to the coating.The phosphating film,especially the thicker needle-like zinc phosphate at deeper pits and scratches on the rough surface of zinc layer,has the effect of nailing and biting on the coating,reduces the gap problems that may exist in blasting,enhances the bonding with the coating and the substation,and obviously improves the adhesion of the coating.On the other hand,the phosphate film has good anti-corrosion protection effect on the rough zinc layer after blasting.Subsequent painting can be carried out at longer intervals after surface treatment,making it easy to schedule production time flexibly.