Designing in-house cathodic protection system to assess the long-term integrity of natural gas pipelines

The sustainability of energy supplies depends highly on the integrity of natural gas pipelines that often compromised by corrosion deleterious effects. The integrity commitment to safety is intuitively achieved by establishing robust protection systems, such as coating and cathodic protection (CP). The objective of this study is to predict failure indicators by identifying parameters that may adversely impact the pipeline protection. In this study, an in-house CP system and pipes network were designed to track the corrosion evolution. Pipe-to soil potential (P/S) measurement was proposed in this research as a monitoring strategy for judging whether a pipe is adequately protected. One of the National Association of Corrosion Engineers (NACE) International acceptance criteria recommending -0.850 V as a minimum instant-off potential for a pipeline to be considered protected was chosen as a baseline. The parameters evaluated in this study were the effect of the coating and the number of anodes of the ground bed. P/S of coated and bare pipes that have been installed since 1995 were measured at different conditions. Surprisingly, the comparative analysis conducted to assess the protection level of coated and uncoated pipes revealed that P/S potentials for both pipes were close and above -0.850 V. This indicates that the pipes were cathodically protected. The similarities in potential readings could be referred to the rust layer that accumulated on the bare pipes' surfaces and acts as a passive barrier similar to coating. Another interesting observation is that the P/S potentials increase gradually as the numbers of the anodes decreases. The results showed that decreasing the anodes numbers by 25-50% has little to no impact on the P/S potentials change, as the reading in the range of -1.473 to -1.666 V. However the P/S potentials reading abrupt to the range of -2.217 to -2.695 V when the number of anodes reduced by 75%. Although the increase in the P/S potentials appears to be beneficial, in fact, this increase can be considered as a negative indicator since the elevated potential implies that the anode discharges a high electrons influx which in turn shortens its lifetime.

Automated summary

The study aims to predict failure indicators by evaluating parameters of pipeline protection systems, revealing that the number of anodes has a significant impact on cathodic protection and decreasing anode numbers leads to an increase in P/S potentials. Additionally, the research shows that the rust layer on bare pipes can act as a protective barrier similar to coating.