Abstract
Distributed control system (DCS) is available in most of the compressor stations of cross-country pipeline systems. Programmable logic controller (PLC) is used in all the intermediate pigging (IP) stations/sectional valve (SV) stations to collect the field data and to control the remote actuated valves. This paper presents how DCS or PLC can be used for cathodic protection of gas pipelines. Virtual instrumentation (VI) software is used here for simulation and real-time implementation purpose. Analog input channels available in DCS/PLC can be used to measure pipe to soil potential (PSP) with the help of half-cell and voltage transducer. Logic blocks available in DCS can be used as low selector switch to select the lowest PSP. Proportional-integral (PI) controller available in DCS/PLC can be used for taking the controlling action. PI controller output varies the firing angle of AC phase controller. Phase controller output is rectified, filtered, and fed to the pipeline as cathodic protection current. Proposed scheme utilizes existing infrastructure to control pipeline corrosion.
Highlights
Corrosion is a phenomenon by which metal is etched away naturally contributing to material loss
This paper deals with how Distributed control system (DCS)/Programmable logic controller (PLC) can be utilized for gas pipeline corrosion monitoring and control
Designed controller is checked with different pipe to soil potential (PSP) set points and it is controlling perfectly
Summary
Corrosion is a phenomenon by which metal is etched away naturally contributing to material loss. Underground metallic pipelines are primarily protected by coatings. Impressed current cathodic protection is used to protect pipelines from coating defects. By impressing current to the pipeline, the entire structure is made to become a cathode of the corrosion cell. Impressed current corrosion controller should be dynamic enough to protect pipelines from ill effects due to variation in coating defects, soil resistance, soil pH, temperature, and so forth. Impressed current cathodic protection and details on pipe to soil measurement and half-cell are available in [1]. Application of virtual instrumentation for cathodic protection stray current monitoring is reported in [8]. Virtual instrumentation for natural gas pipeline corrosion control is reported in [9] and its autotuning is discussed in [10]. This paper deals with how DCS/PLC can be utilized for gas pipeline corrosion monitoring and control
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