Methods for detecting damage to the external anti-corrosion coating of pipeline fittings in power plants

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This post was last edited by Standing in the East on 2012-4-30 at 18:43. Power plant pipeline fittings are often exposed or buried underground; various external factors and environmental influences can over time damage these pipelines. Therefore, methods for protecting the outer layer of the pipelines from corrosion and for detecting any damage are essential. Below are some methods for inspecting power plant pipeline fittings as well as for protecting pipelines from corrosion. 　　I. Methods for detecting damage to the external anti-corrosion layer 1. Alternating current detection method The alternating current method is commonly known internationally as the Pearson detection method. It involves using the existing DC signal from cathodic protection or applying a DC signal temporarily to the pipeline; anomalies in the polarization voltage between the pipeline and ground at the point of damage to the anti-corrosion layer are then detected, thereby identifying the location and extent of the damage. Using the closely spaced potential method for comprehensive measurement helps to assess the overall cathodic protection of the pipeline. The combination of these two technologies represents the direction of development in this field, and it also meets the basic requirements of the International Corrosion Engineers Society standard RP0502—2002. 　　2. Close-spacing potential detection method The close-spacing potential method, CIPS, is primarily used to assess the effectiveness of CP systems, thereby providing an indirect indication of the condition of the anti-corrosion coating. The CIPS method collects data along the pipeline at intervals of 1.0–1.5 m, and generates a continuous graph of the open/closed pipe ground potential to reflect the cathodic protection potential throughout the entire length of the pipeline. When a defect exists in the anti-corrosion layer, the current density at that location increases, causing the protection potential to shift positively. When this shift reaches a certain level, it can be detected at the surface; when the potential falls below -850 mV, corrosion of the pipeline occurs. 　　The CIPS method cannot detect the exact location of coating damage; it is actually a pipe potential detection technique rather than a coating defect detection technique. The condition of the coating is determined through potential analysis, and therefore it is usually used in conjunction with DCVG. Using CIPS to determine insufficient CP or over-protection has its unique advantages.