It confirms that exposure of carbon steel to soil containing chloride accelerates the corrosion; as a result pitting is observed. Figure 15a and b demonstrates cross-sectional EDS map of carbon steel sample exposed to soil containing 60 wt.% moisture and 5 wt.% chloride at site 1. A pit can be observed on carbon steel sample. Generally, α-FeOOH and γ-FeOOH are observed as corrosion products of steel buried in the soil environment. Shoaib et al. 15 examined the influence of moisture and chloride on the corrosion behaviour of SS400 carbon steel in the soil environment. The schematic diagram of the experimental test set-up is shown in Figure 2 In this figure, the specimen is represented by rectangular shape; was a carbon steel without coating, and with zinc- and copper-electroplated coatings, respectively; and was used as working electrode.
Applications: Oil Refineries, Petrochemicals, Power Generation (Nuclear/Thermal), Steel, Sugar, Boiler Equipments, Pressure Vessels and General Engineering Purposes. From the experimental findings of corrosion and then after carrying out microstructural analysis, a threshold value for moisture and chloride contents is determined beyond which no further addition of chloride and moisture contents can cause corrosion and deterioration of microstructure of carbon steel. galvanized tubing distributors
The presence of Cl element in the corrosion layer of carbon, zinc-coated, and copper-coated steels was obviously due to the addition of NaCl. From this figure corrosion pattern of granular and compact structure can be seen which is also reported in the literature 21 However, Figure 13 demonstrates EDS spectra of elements present in corrosion product of copper-coated steel, also listed in Table 3 From the table it can be seen that Br was present in trace amount in substrate metal. This indicates the occurrence of generalised corrosion mechanism 19 The EDS spectra of elements present in corrosion product of zinc-electroplated steel are shown in Figure 11 Three locations were selected for the determination of elements in corrosion product.
EDS analyses (wt.%) of carbon steel of selected spots in Figure 8. However, it has been reported in literature that the initial corrosion product formed on carbon steel is α-FeOOH which provides a shield to substrate metal against corrosion 17 , 18. Figure 8 shows the SEM micrographs of low and high magnifications of carbon steel.
Figure 7 shows the corrosion morphology of copper-electroplated and zinc-electroplated steel samples. Carbon steel sample exposed to soil containing 60 wt.% moisture and 5 wt.% chloride showed localised corrosion, while the samples buried in soil of 80 wt.% moisture and 10 wt.% chloride suffered general corrosion. Corrosion morphology of carbon steels tested in soil with 10 wt.% chloride (a = 20 wt.% MC; b = 40 wt.% MC; c = 60 wt.% MC; d = 80 wt.% MC).
Theoretically, carbon steel specimen buried in 60 wt.% moisture and 10 wt.% chloride should have more corrosion rate because of exposure of higher chloride content. The maximum corrosion rate was noticed for carbon steel exposed to soil containing 60 wt.% moisture and 5 wt.% moisture. Electrochemical results showed that the corrosion rate of SS400 carbon steel sample increased with increase in moisture content up to 60 wt.% and decreased after this value.