On the mechanism of corrosion resistance of cast iron pipes: theory and practice

Summary

The stages of gray cast iron corrosion are considered, that result in the process of many years of replacement by the graphite component, and the iron of the metal matrix actually remains a preserved layer of non-corroding graphite. Owing to this, the service life of cast iron pipes, even without additional anti-corrosion protection, can actually reach 100–150 years. The corrosion resistance of ductile iron compared to gray cast iron is higher in an average ratio of 0.76. In practice, ductile iron pipes are supplied with protective coatings that provide for additional corrosion protection of the pipeline walls for a long time. The international standard ISO 21053:2019 «Life cycle analysis and disposal of ductile iron pipes while used in water supply systems» (clause 6) indicates the generally accepted service life of ductile iron pipes of 100 years.

Key words

protection from corrosion , cast iron pipelines , ductile iron , corrosion resistance , graphitic corrosion zone

Specific features of sewer tunnel construction and rehabilitation in Saint-Petersburg

Summary

The basic facts about the construction of deep sewer tunnels in Saint-Petersburg are presented. The causes of gas corrosion in sewers and their structural components are considered. The methods of protecting sewer tunnels in the process of construction or rehabilitation from gas corrosion are suggested. At the stage of designing the construction of a new sewer or its rehabilitation the concentration of gases in the underroof space must be measured. On the basis of the calculation data the decision on the sewer design, elevation differences, gradient and other parameters that ensure trouble-free operation is made.

Key words

collector , sewer tunnel , gas corrosion , composite material , protection from corrosion