A 42km/356mm diameter pipeline was built and commissioned in 1962 and is the primary source of sour gas to a sour gas processing plant. The pipeline has operated as a dehydrated sour gas/condensate pipeline, and was assessed as a candidate for an Internal Corrosion Direct Assessment (ICDA). This analysis came with the challenge of a lack of operational and inspection history. The decision was made to obtain as much history as possible by interviewing previous operators, and to perform an ICDA analysis based on this information. The ICDA analysis was performed by a technical specialist utilizing 1) wet sour gas corrosion methodology and 2) ICDA (critical angle) technology. The analysis was performed for one ICDA region. Nine assessment cases were identified as the operating criteria changed with time and each was assessed. On occasion the gas specifications had criteria below the minimum levels of influence, and analysis was also performed with these adjusted to force identification of potential internal corrosion locations. The results were presented identifying two locations of potential long-term corrosion, and one location susceptible to corrosion post 2000. Following a review of the ICDA analysis, it was felt that there was sufficient confidence to proceed with the direct assessments. The decision was taken to expose the three identified locations. The direct assessment at all three locations was performed using guided wave UT as the initial anomaly detector, and phased array UT was then utilized to confirm any anomalies, and was run along the bottom of the exposed line to confirm no anomalies were missed. The results of the NDE indicated no anomalies of more than 10%, and it was concluded that no significant internal corrosion of concern exists. The final phase of the ICDA (post assessment) concluded that the analysis was successful and that the ICDA project was a success. The re assessment intervals will be driven by any future changes in the transported product, and information obtained from on line corrosion monitoring.
On-Line Corrosion Monitoring of Plate Structures Based on Guided Wave Tomography Using Piezoelectric Sensors