Failure Analysis of API 5L Grade B Underground Crude Oil Transfer Pipe †

An underground transfer pipe was utilized to deliver crude oil from the BDA gathering station to the A main gathering station. The transfer pipe made of API 5L grade B has a diameter of 6 inches and a length of 18,000 m. The pipe has a design life of 20 years, but after being operated for five years, 41 points of leakage were found in the area of KM 14 to KM 16. Visual inspection of the leakages in the pipe indicates general corrosion as the main issue. Nevertheless, failure analysis is required to investigate the root cause of the problem in this area. Several characterization methods were performed, including ultrasonic testing, to measure the distribution of pipe thickness. SEM and EDS testing were conducted to understand the hole formations that led to leakage and study their elemental changes around the leakage point. XRD and FTIR characterization were carried out on the deposit found on the inner diameter of the pipe. The ultrasonic thickness measurement indicates gradual pipe thinning until a hole was formed. Deposit analysis revealed wax composition at the upper level of the pipe formed due to transferred crude oil, while the bottom deposit where leakage was identified consisted of corrosion products such as FeO₂ (geothite), Fe₂O₃ (hematite) and Fe₃O₄ (magnetite). The leakage failure in KM 14 and KM 16 was discovered to be where the pipe was at its lowest elevation point of underground pipe installation. This situation causes the pipe to be submerged by produced water at the 3 o’clock to 9 o’clock position, which initiates the occurrence of oxygen-influenced corrosion and the formation of hydroxide ions (OH⁻). The formation of hydroxide ions (OH⁻) triggers the Under Deposit Corrosion (UDC) mechanism.