corrosion inspection in oil and gas pipeline
TRANSCRIPT
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 but
corrosion by nature is a contending issue in this regard. Corrosion has been around for all
recorded history (Durham and Durham, 2003), and causes the degradation of pipeline
system due to chemical reaction with the operational fluid and environment. This reduces
both the static and cyclic strength of a pipeline (Cosham et al., 2007). Presently, the
industry is being faced with a wide variety of corrosive environments during the pipeline
transportation of oil and gas (Yahaya, 1999). Though corrosion rate is very slow, there is a
danger that it will cause leakage of internal fluid in future (Hamona, 2006). To reduce the
effect of corrosion, active monitoring and frequent inspection are critical to maintaining
pipeline health. However, the task is tedious and expensive when using the tradition
method of visual inspection due to inaccessibility and hazardous environment in which the
pipelines are deployed (Jong-Hoon et al., 2010).
Corrosion inspection is an important means of detecting oil and gas pipeline defect. This
plays an important role in the protection and of the safe operation of pipelines (Shufen et
al., 2010; Hong, 1999). This has helped the industry in the management of pipeline. The
inspection is carried out by using an in-line inspection device that can measure the extent
of internal corrosion (Yahaya, 1999), and cathodic protection (CP) system inspection for
external corrosion.
Cathodic protection is the process of forcing a metal to be more negative (cathodic) than
the natural state (Durham and Durham, 2003). The cathodic protection systems are the
impressed current system and sacrificial anode. Impressed current can be achieved by
applying 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 the
data acquired. Southern (2008) revealed that multi-purpose, all-in-one, pipeline integrity
automation, wireless, data communication radios are available that monitor and report all
cathodic protection rectifier operations, automate rectifier interruption, rectifier operational
status, and pipe-to-soil potential. This is done to ascertain the extent of corrosion and
damaged 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 internal
corrosion inspection has been dominated by intelligent pigs such as mechanical,
electronic, ultrasonic or electromagnetic system and have been able to locate and detect
anomalies in the pipe accurately (Lopez and Sadovnychiy, 2007). Some pigs can
determine the integrity of the pipeline in situ (Mathur et al., 2007) and other acquire and
store data for off-line analysis (Zhongwei et al., 2008). Yun et al. revealed that in-line
inspection 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 is
a non-destructive in-line inspection of pipeline, involves the detection of defects and
anomalies 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 defect
sensitivity, high accuracy and reliable inspection system (Katrgadda et al., 1996). The
difficulty 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 commonly
inspected using this method and the data obtained is processed to estimate an equivalent
length, width and depth of defects. The information is used to predict the maximum safe
operating 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 contains
complex mechanism and electronic instruments. It also exists as a multi-channel device
consisting 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 has
become the main pipeline online detection method because of the advantage of its fast
speed, reliability and economy (Shufen et al., 2010). Xu et al. revealed that ultrasonic
detection is affected by pipeline wall roughness, interaction between different echoes
constituting noise and branching-point geometry.
In conclusion, corrosion inspection provides information on the state of pipeline and
guides the operators to prepare adequate management programme. This will help in
preventing pipeline rupturing due to corrosion that can lead to product loss thereby causing
environmental pollution and endangering human life.
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