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ABSTRACT
The discovery of crude oil led to an industrial boost with other industries set up to benefit both directly or indirectly from the newly discovered oil and gas industry thereby creating jobs and earning foreign exchange for Nigeria. The safest and most economical way of transporting crude oil is the use of steel pipes. Pipeline Internal Gauge (PIG), is a machine that is used to monitor corrosion in steel pipeline. It measures specific parameters along the pipeline which is analysed for effective pipeline maintenance. However, pipelines have continually failed from corrosion as a result of the poor analysis of data recorded from the intelligent pigging of the pipeline. In this work, one magnetic flux leakage PIG and two ultrasonic PIGs were used to obtain data from three oil and gas pipelines. The first pipeline transported a three phase crude (carrying a mixture of crude oil, water and gas) from Mimbo to TMMP. The second pipeline transported crude oil from Ossu to Izombe and third pipelines transported gas from Mimbo to TMMP. All pipelines are located in the Niger Delta region of Nigeria. The Magnetic Flux Leakage (MFL) and Ultrasonic (UT) Intelligent Pigs were used to measure wall thickness and metal loss along the pipelines. Data obtained were analysed to ascertain the fitness for service (FFS) of the pipelines. A cleaning PIG” was first run through the pipelines to ensure that the pipelines were free of debris that may alter the signals and data collected by the intelligent PIGs (smart PIGs). The collected data from the smart PIGs runs were analysed using Dacon Technology Software and the results obtained were compared with the line pipe design data obtained from international standards and codes to determine the status of the service condition of the operating pipeline systems. The Estimated Repair Factor (ERF) results were the basis for determining the service condition of the pipeline. The analysis of the data obtained from the MFL intelligent pigging revealed a reduction in metal loss in the pipeline system transporting three (3) phase crude from Mimbo to TMMP by 17.11% between the data of year 2005 and year 2015. The metal loss peak data showed that the pipeline transporting three phase crude from Mimbo to TMMP passed through three separate environments which have different corrosion rate on the pipeline. The average ERF value for 3-phase pipeline is 0.237 while that of single phase pipeline is 0.653; this shows that pitting corrosion effect is more on a three phase pipeline. From the data collected and analysed, it was observed that the internal conditions of the pipeline have more effect on the ERF. It was observed from the data obtained that the points xiv on the pipeline from Mimbo to TMMP and the pipeline from Ossu to Izombe, both transporting liquid crude with ERF ≥ 0.2 have anomalies at the internal wall of the pipeline, while the pipeline from Mimbo to TMMP which transports gas have all its anomalies located at the external wall as well as ERF ≤ 0.2; indicating that pipelines with ERF ≥ 0.2 have anomalies at the internal walls while pipelines with ERF ≤ 0.2 have anomalies at the external walls. The ERF parameter is suitable for determining the acceptability of an anomaly.
