Anti-corrosion treatment process for outer surface of ductile iron pipe

Abstract

The invention discloses a corrosion-resistant treatment process of an outer surface of a nodular cast iron pipe, particularly relates to a corrosion-resistant treatment process of an outer surface of a nodular cast iron pipe, and aims at providing the corrosion-resistant treatment process of the outer surface of the nodular cast iron pipe with the advantages of improvement of corrosion-resistant property of the outer surface of the nodular cast iron pipe and prolonging of the service life of a pipeline. The corrosion-resistant treatment process of the outer surface of the nodular cast iron pipe comprises the following steps of annealing, finishing and grinding, water pressure test, coating of a cement mortar lining, steam curing of the cement mortar lining, grinding of the cement mortar lining, preheating of the pipeline, treatment of the outer surface of the pipeline, spraying of a sacrifice anode protecting coating, sealing of holes and spraying of a finishing layer, solidifying of the finishing layer, spraying of markers, and packaging and shipping. The new process has the beneficial effects that the problems of damage to the sacrifice anode protecting coating in the production procedure and consumption of active metal of the coating caused by the steam curing are solved, the attaching capability of the sacrifice anode protecting coatings, such as zinc layers, is improved, the corrosion-resistant property of the outer surface of the nodular cast iron pipe is improved, and the service life of a pipeline is prolonged.

Description

technical field [0001] The invention relates to a treatment process for the outer surface of a nodular cast iron pipe, in particular to an anti-corrosion treatment process for the outer surface of a nodular cast iron pipe. Background technique [0002] In the prior art, in the anti-corrosion treatment process of the outer surface of the ductile iron pipe, the anti-corrosion coating such as pure zinc coating and other sacrificial anode protective coatings usually sprayed on the outer surface of the pipe can provide cathodic protection for the ductile iron pipe. At the same time, the corrosion products of these sacrificial anode protective coatings are dense and insoluble in water, which can protect the ductile iron metal in the damaged area of ​​the small area of ​​the coating from corrosion. The reason why the sacrificial anode protective coating can play a cathodic protection effect on the base of the ductile iron pipe is that the zinc and other substances in the coating in...

AI Technical Summary

Problems solved by technology

[0004] Although the traditional process meets the requirements of the current ductile iron pipe product standards, the biggest defect of the traditional process is that it reduces the active metal content of the sacrificial anode protective coating, and the probability of coating damage increases, which in turn affects its anti-corrosion performance. The reasons are as follows: First, there are multiple processes from spraying the sacrificial anode protective coating to spraying the finishing layer, and each process will cause local damage to the sacrificial anode protective coating. After coating, the follow-up process will easily lead to wear of the sacrificial anode protective coating sprayed on the outer surface of the pipeline, especially in the processes of finishing grinding, cement mortar lining coating, cement mortar lining grinding and other processes, because the supporting roller drives the pipeline to rotate at high speed And the vibration will cause serious damage to the sacrificial anode protective coating on the contact part between the pipeline and the supporting wheel. In addition, the coating will also be damaged to a certain extent during the transportation of the pipeline between processes; second, after spraying the sacrificial anode protective coating, after several Only one process can reach the process of spraying the finishing layer. The surface of the sacrificial anode protective coating will inevitably be polluted by dust or other foreign matter, resulting in poor adhesion between the sacrificial anode protective coating and the finishing layer, which will also be reduced to a certain extent. Corrosion resistance of the external anti-corrosion coating; third, especially in the cement mortar lining steam curing process, the sacrificial anode protective coating is in a high temperature and high humidity environment for a long time (about 8 hours), and electrochemical corrosion occurs on the coating surface The reaction consumes part of the active metal, which weakens the cathodic protection ability of the coating

Fourth, zinc layer, zinc-aluminum alloy coating and zinc-aluminum pseudo-alloy coating, zinc-aluminum rare earth alloy and zinc-aluminum rare-earth pseudo-alloy coating, zinc-aluminum-magnesium alloy and zinc-aluminum-magnesium pseudo-alloy coating, zinc-aluminum The anticorrosion performance of magnesium rare earth alloy and zinc aluminum magnesium rare earth pseudo alloy coating cannot meet the strong corrosive soil environment

[0005] Even so, those skilled in the art have not found the defects and hazards of the traditional process. The reasons are mainly in the following four aspects: first, most of the soil environment is weakly corrosive, and usually the outer surface of the ductile iron pipe is sprayed with a pure zinc layer The final finishing layer is added as an external anti-corrosion coating. The color of corrosion products (also called white rust) such as zinc hydroxide and basic zinc carbonate (also known as white rust) that appear on the metal zinc layer during the steam curing process is similar to that of the pure zinc layer. It is easy to find that the color of the metal zinc layer changes; second, ISO2531, GB / T13295 and other product standards only require that the quality of the zinc layer per unit area be checked in the process of spraying the zinc layer, that is, the unit is g / m 2 It is not required to check the active metal zinc content of the metal zinc layer before spraying the finishing layer, because there is no suitable online detection method for the active metal zinc content of the zinc layer on the outer surface of the ductile iron pipe; Third, this field does not require detection of the active metal zinc content of the metal zinc layer before the installation of ductile iron pipes. Similar to the second reason, in addition to laboratory testing, there is currently no suitable method before installing pipes on the construction site To detect the metal zinc content in the zinc layer on the outer surface of the ductile iron pipe

Fourth, the reason why the traditional process can be used until now is that after spraying the zinc coating, entering the steam curing process can play a role in preventing rust. Although some active metal zinc is lost, there is still some metal zinc in the coating. The corrosion potential of the zinc layer is still lower than that of the ductile iron matrix, and it can also play a certain cathodic protection effect on the ductile iron pipe matrix, so it can also play a certain anti-corrosion effect in the buried application environment; in addition, compared with other processes In terms of anti-rust methods, sacrificial anode protective coating such as spraying zinc layer is the most efficient method, which can fully meet the needs of fast production rhythm of ductile iron pipes, while other anti-rust methods are very inefficient and cannot meet the requirements of fast production rhythm.