The Evaluation Methodology of Pipeline Coatings Based on AC Current Attenuation Survey

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by B. Liu, Engineer; Ph.D, R & D Center of Petro China Pipeline Company, Lang fang, Hebei Province, P.R. China,,
C. W. Qian, Senior Engineer; R&D Center of Petro China Pipeline Company, Lang fang, Hebei Province, P.R. China,
Q. Gao, Engineer; PetroChina Pipeline Company, Langfang, Hebei Province, P.R. China,
R. Y. He, Senior Engineer; Ph.D, China Special Equipment Inspection and Research Institute,

Document Type: Proceeding Paper

Part of: ICPTT 2009: Advances and Experiences with Pipelines and Trenchless Technology for Water, Sewer, Gas, and Oil Applications

Abstract: Pipeline External Corrosion Direct Assessment (ECDA) methodology published by NACE is intended to improve safety by assessing and reducing the impact of external corrosion on pipeline integrity. There are many kinds of inspection tools to support this methodology. AC current attenuation surveys are typically used to assess coating quality and to detect the discrete coating anomalies. Also, there are many tools that can be selected during indirect assessment step, such as C-Scan or PCM, which are based on AC attenuation surveys, the main difference between any two tools may be various frequencies of AC signal from their transmitter. Although the current in pipelines are easily detected by receivers of PCM or C-Scan, the relationship between coating quality and the current is highly difficult to be found. According to the electrical transmission line theory, Rg can be defined as the appropriate parameter that can indicate condition of coatings. However, the holiday density of coating was not considered in this theory. In this paper, Y (the AC attenuation rate) and holiday densities are considered as the effective parameters to assess the external corrosion of the pipeline with a coating. The evaluation methodology of pipeline coatings based on ac current attenuation survey is developed in this paper. Using this approach, Rg Value, Y value and holiday density play appropriate role on the assessment. Some new modules are presented in this approach, including current distributaries module, holiday module, and intelligent critical curve of AC attenuation.

Subject Headings: Coating | Pipelines | Surveying methods | Corrosion | Parameters (statistics) | Geomatic surveys | Power transmission lines | Safety | Professional societies |

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