Investigating Effects of Corrosion on Industrial-Coated Mild Steel Pipelines in Acidic Environment

Abstract

The importance of pipelines in the transportation of carbon-hydrates products in both developed and developing countries throughout the world can never be overstressed. So, the study of basic factors responsible for the smooth flow and sustainable delivery of essential products is continued. This study, therefore investigated the influence of corrosion on different coated mild steel pipelines in an acidic environment. Samples were obtained from Pipe Coaters Nigeria, Onne and prepared for experimentation. The sample was cut into pieces (coupons) of sizes, 3.5cm x 2.6cm x 0.8cm. A total of twelve samples in the subgroup of four per container were subjected to FBE, PP, and PE coating, while four samples were left uncoated. Also, 12ml, 8ml, 3ml and 0.5ml of concentrated tetraoxosulphate (vi) acid were used to dilute distilled water to obtain solutions of pH 3, 4, 5 and 6 for the study. Coupon retrieval was carried out periodically every five days. A weight loss test was conducted with an analytical weighing balance. Four coupons (uncoated and coated) were suspended in each of the four beakers containing H₂SO₄ solution of different pH (3, 4, 5 and 6) for an exposure time of 840 hours. During the process, seven measurements were taken at an interval of 120 hours exposure time to establish the final weight, W_f. The rates of corrosion of the respective samples were determined using a weight-loss approach. The experimental data were analysed with analysis of variance at a significant level of 0.05 {confidence level of 95%} with the aid of Minitab 16 software. The corrosion rates for the uncoated and coated samples are 0.993 mmpy, 0.0679 mmpy, 0.0510 mmpy and 0.0575 mmpy, respectively. The uncoated and coated coupons further reduced to 0.0658 mmpy and 0.0456 mmpy, 0.0372 mmpy, and 0.040 mmpy at the end of 600 hrs and thereafter pick up to 0.7061 mmpy, 0.0545 mmpy, 0.0403 mmpy, and 0.0428 mmpy.at the end of 840 hrs immersion time in Ph3 solution. This trend continued in all the environments and the minimum corrosion rate recorded in uncoated and coated specimens during the experimentation period are 0.4359 mmpy, 0.0295 mmpy, 0,0215 mmpy and 0.0266 mmpy, respectively. Interestingly the results showed that corrosion occurred and the rate of corrosion varied in the following trend: uncoated, FBE, PE and PP.