There are two primary reactions possible at the cathode, the “hydrogen evolution reaction” and the “oxygen absorption reaction.” Other reactions are possible but are encountered less often. The electrons generated as the iron dissolves at the anode travel through the metal to the cathodic surface area. It is the site where chemical reactions absorb the electrons generated at the anode. The cathode is that portion of the metal surface that does not dissolve. The iron ion goes into solution and the two electrons are left behind in the metal. This loss of electrons is called oxidation.

The anodic reaction for iron would be: Fe → Fe 2+ + 2e.

The anode is the part of the metal surface that corrodes - that is, the metal dissolves in the electrolyte. They found that there were reductions in weights in the coupons after the observational period.Ĭorrosion reactions are electrochemical in nature and involve two types of reaction: anodic and cathodic. Similarly, reference, used average percent weight losses to determine corrosion of the coupons exposed to Bacilluscereus-SNB4 in wet and nutrient broth impregnated soils.

Reference ,in studying corrosion of stainless steel-304 in a brackish water environment, used weight loss analysis as well as open circuit polarization to determine corrosion in the steel. One method of determining corrosion in metals is by weight loss analyses. There is always a chance that pipelines could leak or rupture leading to hazardous failure which can inflict human fatality and also badly damage the environment and assets due to explosion and leakage. The study of the soil as a corrosive environment is necessary due to the large number of buried pipelines and tanks, as their deterioration can appear to be a real economic and environmental problem through the years. Generally, buried steel pipelines and tanks suffer from soil corrosion because of one or more of the following conditions: high moisture content, a pH value less than 4.5, a resistivity less than 1000 Ωcm, presence of chlorides, sulphides and bacteria, and presence of stray currents. The main types of bacteria associated with metals in terrestrial and aquatic habitats are sulfate reducing bacteria (SRB), sulfur-oxidizing bacteria, iron oxidizing/reducing bacteria, manganese-oxidizing bacteria, and bacteria secreting organic acids and slime. With regards to biological activity and soil corrosion, reference reported that incorporation of biocide in soil brought about a reduction in the numbers of bacteria present in the soil and subsequently, a reduction in the biocorrosion activity around and on steel coupons buried in the soil. The duration of exposure of steel to corrosive soil environment is also a factor in the rate of corrosion noticed in the exposed steel. Average and instantaneous corrosion rates in Q235 steel coupons buried in soils with different moisture content showed corrosion rate more in soil with 26% moisture than in soil with 12% moisture. A general trend is that corrosion rates in soil increases with increased moisture content. One critical factor in soil corrosion is the moisture content of the soil. Reference defined soil-corrosion as the deterioration of metal or other materials brought about by chemical, mechanical and biological action by soil environment. The corrosiveness of soil can be defined as the capacity of producing and developing the corrosion phenomenon. When metals are exposed to the soil, they begin to corrode.

It was observed that APWL increased by nearly the same ratio that CR decreased during the period of exposure of the coupons. This trend was observed in all three coupons and at both sites, except for a few excursions which did not significantly affect the established trend. It was observed that generally, there was an inverse trend between weight loss and corrosion rates in the coupons as the exposure period increased such that, while APWL values were seen to be increasing, CR values were decreasing. For the SS coupon, APWL and CR were 0.12% and 0.32 mpy, respectively from the water-logged soil and, 0.08% and 0.19 mpy, respectively for the sandy soil site. Similarly, APWL for the CS coupons from the water-logged soil and sandy soil sites were 4.5% and 3.6%, respectively while their CRs were 3.51 mpy and 3.67 mpy, respectively. The corresponding CRs were 5.58 mpy and 3.18 mpy, respectively. Post-exposure analyses of the coupons over the entire period showed that the APWL for the MS coupons retrieved from the water-logged soil and sandy soil sites were 5.4% and 2.8%, respectively. Average percentage weight loss (APWL) and corrosion rate (CR) were determined for mild steel (MS), carbon steel (CS) and stainless steel (SS) strip coupons buried in a water-logged soil (WL) and a sandy soil (SD)for a period of 190 days.

Exposure x7 coupon