Page 551 - Corrosion Engineering Principles and Practice

514 C h a p t e r 1 2 C o r r o s i o n a s a R i s k 515

permanent features along the pipeline route so that the two data sets can
be aligned and compared. The data should then be analyzed and indica-
tions of corrosion activity identified. The data analysis should reveal all
discrepancies in the two data sets, resolve these differences, and com-
pare the results to those obtained in the preassessment.
Direct Examinations
Direct examination requires excavating the pipe and performing
physical inspections and tests on the pipe surface and surrounding
soil/water electrolytes. Direct examination includes
• Ranking and prioritizing indications identified during
indirect inspections
• Excavating to expose the pipe and collecting data where
corrosion activity is most likely
• Measuring coating damage and corrosion defects
• Performing a root-cause analysis (RCA)
• Evaluating the process
Each indication obtained with indirect inspections is then
categorized for an action level as either
• Immediate action required
• Scheduled action required
• Suitable for monitoring
Subsequently, dig locations to expose the pipe are identified and
given a priority. At least one excavation and direct examination is
required for each ECDA region. When performed for the first time, a
minimum of two direct examinations are required. Before exposing
the pipe, the procedures for data collection and record keeping should
be defined to ensure consistency. The procedures should include [19]
• Photographic documentation
• Pipe-to-soil (P/S) potential measurements
• Soil and groundwater tests
• Coating assessment
• Undercoating liquid pH
• Mapping and measurement of corrosion defects
• Data for other analyses such as microbiologically influenced
corrosion and stress corrosion cracking
Once corrosion defects have been found, the remaining strength of
the pipe should be estimated using a standard calculation routine