CORROSION INSPECTION IN OIL AND GAS PIPELINE Blessing Bamidele Ilugbusi (MSc, Applied Instrumentation and Control) Glasgow Caledonian University.An accident free pipeline operation is the dream of every player in oil and gas industry butcorrosion by nature is a contending issue in this regard. Corrosion has been around for allrecorded history (Durham and Durham, 2003), and causes the degradation of pipelinesystem due to chemical reaction with the operational fluid and environment. This reducesboth the static and cyclic strength of a pipeline (Cosham et al., 2007). Presently, theindustry is being faced with a wide variety of corrosive environments during the pipelinetransportation of oil and gas (Yahaya, 1999). Though corrosion rate is very slow, there is adanger that it will cause leakage of internal fluid in future (Hamona, 2006). To reduce theeffect of corrosion, active monitoring and frequent inspection are critical to maintainingpipeline health. However, the task is tedious and expensive when using the traditionmethod of visual inspection due to inaccessibility and hazardous environment in which thepipelines are deployed (Jong-Hoon et al., 2010).Corrosion inspection is an important means of detecting oil and gas pipeline defect. Thisplays an important role in the protection and of the safe operation of pipelines (Shufen etal., 2010; Hong, 1999). This has helped the industry in the management of pipeline. Theinspection is carried out by using an in-line inspection device that can measure the extentof internal corrosion (Yahaya, 1999), and cathodic protection (CP) system inspection forexternal corrosion.Cathodic protection is the process of forcing a metal to be more negative (cathodic) thanthe natural state (Durham and Durham, 2003). The cathodic protection systems are theimpressed current system and sacrificial anode. Impressed current can be achieved byapplying a current to the pipeline to be protected from electrical source (Bashi et al.,2003). The external monitoring requires periodic inspection and thorough analysis of thedata acquired. Southern (2008) revealed that multi-purpose, all-in-one, pipeline integrityautomation, wireless, data communication radios are available that monitor and report allcathodic protection rectifier operations, automate rectifier interruption, rectifier operationalstatus, and pipe-to-soil potential. This is done to ascertain the extent of corrosion anddamaged done to the pipeline.
In-line inspection in a pipeline operation is achieved by driving pipeline inspection gauges(PIGs) through a pipeline by the flowing fluid (Guo et al., 2005). Over the years internalcorrosion inspection has been dominated by intelligent pigs such as mechanical,electronic, ultrasonic or electromagnetic system and have been able to locate and detectanomalies in the pipe accurately (Lopez and Sadovnychiy, 2007). Some pigs candetermine the integrity of the pipeline in situ (Mathur et al., 2007) and other acquire andstore data for off-line analysis (Zhongwei et al., 2008). Yun et al. revealed that in-lineinspection is one of the most important ways to inspect pipeline safely. However,ultrasonic and electromagnetic in-line inspection is considered.The electromagnetic type of pigs make use of magnetic flux leakage (MFL) technique, it isa non-destructive in-line inspection of pipeline, involves the detection of defects andanomalies in the pipe wall and evaluation of the severity of these defects (Hari et al.,2007). The technique relies on using multi-transducer approaches to obtain greater defectsensitivity, high accuracy and reliable inspection system (Katrgadda et al., 1996). Thedifficulty with this method is the extent and complexity of the analysis of the MFL images(Khodayari-Rostamabad et al., 2009). Natural gas transmission pipelines are commonlyinspected using this method and the data obtained is processed to estimate an equivalentlength, width and depth of defects. The information is used to predict the maximum safeoperating pressure of the pipeline (Joshi et al., 2006).The ultrasonic in-line inspection is one of the important methods of inspecting the wall-loss defect on-line for crude oil pipeline as a result of corrosion. The device containscomplex mechanism and electronic instruments. It also exists as a multi-channel deviceconsisting of main and sub-structure. It has high precision for both inner and outer defects.The pipeline corrosion is judged by the residual wall thickness (Dai et al., 2007). This hasbecome the main pipeline online detection method because of the advantage of its fastspeed, reliability and economy (Shufen et al., 2010). Xu et al. revealed that ultrasonicdetection is affected by pipeline wall roughness, interaction between different echoesconstituting noise and branching-point geometry.In conclusion, corrosion inspection provides information on the state of pipeline andguides the operators to prepare adequate management programme. This will help inpreventing pipeline rupturing due to corrosion that can lead to product loss thereby causingenvironmental pollution and endangering human life.
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