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Natural Gas Transmission Business: Operations and Maintenance Aspects
Published in Pramod Paliwal, Sudhir Yadav, Natural Gas Transmission and Distribution Business, 2019
Survey of pipeline anti-corrosion coatings and evaluation of the condition of pipeline is important to ensure the pipeline integrity. Coating defect survey is carried out at about 5-year intervals to ensure an acceptable coating condition. A direct current voltage gradient (DCVG) survey is carried out above the ground to locate any areas of damaged coating.
Corrosion
Published in Mavis Sika Okyere, Mitigation of Gas Pipeline Integrity Problems, 2020
If the use of an internal in-line inspection tool is not feasible, then an external aboveground survey should be undertaken. The following external survey methods may be used. Close-Interval Potential SurveyThe CIPS survey determines the actual level of cathodic protection being experienced along the pipeline by measuring the pipe-to-soil potential and hence corrosion protection levels and quality of coating.Direct Current Voltage Gradient SurveyThe DCVG survey shall be used for a detailed assessment of the condition of the pipeline coating. DCVG shall be used for coating defect size evaluation, defect length evaluation, defect corrosion status, and defect influence regarding electrical interference.Pearson SurveyThe Pearson survey shall also be used to locate coating defects. It is very effective in tracing discontinuities or damage in buried pipelines’ coating, as well as loose electrical contacts and their exact site on the pipe, allowing the prevention of major failures.Visual inspectionDrone/robot technology
Assessing coating integrity and cathodic protection on buried pipelines under horizontal directional drilling conditions
Published in Corrosion Engineering, Science and Technology, 2022
Ying Huo, Bob Varela, Mike Yongjun Tan
The environmental and corrosion conditions around HDD pipelines are more complex than conventionally laid pipelines in many aspects, and therefore conventional techniques have major difficulties in assessing coating defects on HDD pipelines [6–8]. Such difficulty can be illustrated by analysing the case of the most widely used survey method for locating defects in the pipeline coating, direct current voltage gradient (DCVG) [9,10]. DCVG is widely used to identify the severity of coating damages on buried pipelines, however, it is unable to be sufficiently applied on HDD pipes because the technique has decreasing sensitivity with the depth of a pipe and therefore is of limited value for deeply buried HDD pipes. On the other hand, DCVG could not indicate the cathodic shielding areas because these areas shield the CP current and, therefore, there is no voltage gradient produced [6,7,11]. Another problem with most HDDs is that they are installed in locations that are often not accessible for DCVG surveys. Even in some cases, this technique was found useful, no general relationship between the voltage gradients measured and the defect size can be determined [6,11].