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Plastic linings are used extensively to protect metal (e.g. steel) and concrete substrates from corrosion and, in doing so, perform a very important role in people’s everyday lives. Corrosion control technology complies with the same strict standards as electric insulating technology and engineering, and significant progress has been made recently in the field.
(Published on July-August 2008 – JEC Magazine #43)
KANEMASA NOMAGUCHI PRESIDENT PLASTIC LINING ASSOCIATION
Composite materials are used successfully to protect substrates from corrosion. Even if this type of technology and engineering is spreading worldwide, we still need to learn more to gain a better grasp of it. At the JEC 2008 Forums in Paris, Plastic Lining Association (PLA) President Kanemasa Nomaguchi presented a paper on the subject.
What is corrosion?
As time goes by, steel and concrete substrates tend to lose their quality. One way to keep them in good condition is to keep corrosion under control (figure 1).
With electric insulation technology the aim is to eliminate any leakage of electric current. Similarly, in corrosion control, the thicknesses of the protective layers in liners are carefully designed to prevent leaks. An example (sectional view) is shown in figure 2.
For both steel and concrete substrates, a “pinhole” detector (figure 3) is used on site to ensure that layers are leaktight. This patented method, called “Pinhole test method of lined films for corrosion prevention” (European Application No.00203450.2, Japanese Patent 3505638, U.S. Patent 6,636,031 Bl) is JIS K 6766:2008 certified (Japanese industrial standard).
Table 1 shows typical corrosion-control applications using composites in the building and construction sector.
To satisfy customer and end-user expectations, the linings should meet quality control criteria (satisfactory design, quality and safety), quality assurance criteria (performance, reliable operation, periodical health monitoring) and economic criteria (sufficiently long service life, commercial operability) according to ISO 9001, 14001 and 26001. Some case studies are proposed below.
Table 2 shows the materials and processes used.
Case study A: electric power stations Electric power stations are very important to society and industry. Even though power supply sources such as windmills and solar cells are developing, thermal power sources are still the most common, representing nearly a third of total generating power. Thermal power stations need desulphurizers to prevent sulphur dioxide (S02) emissions, and these desulphurizers need to be protected from the highly corrosive S02
Coal-burning steam turbine systems are one type of thermal power station requiring a flue-gas desulphurizer that is coated with an anticorrosion flake lining.
Case study B: wastewater treatment facilities
Wastewater systems used to be designed for relatively noncorrosive natural water so steel and concrete pipes could be used. However, wastewaters have become much more corrosive, especially in city areas – mostly due to the presence of sulphuric acid (H2SO4) (figures 4 to 5). In Europe, America and Asia, plastic linings are used to protect the pipes from corrosion. Many different processes are available, and the problem is to reach a trade-off between cost and performance (service life).