Case study: integrated integrity management

An integrated integrity management programme requires a full evaluation of in-line inspection reports, not just the final reports as received from the inspection vendors. The following case study is based on work done by Lamontagne Pipeline Assessment Corporation for a company that has been pigging since the mid 1990s, excavating those deemed immediately necessary then shelving the reports. The following illustrates the benefits of fully analysing the data on hand – the true form of integrity management.

The value of ILI evaluation and mid-cycle excavations

Without the ILI evaluation made by Lamontagne Pipeline Assessment Corporation for the following section of pipeline, four mid-cycle excavations would not have been made and leaks of hazardous liquids would possibly have occurred prior to the next in-line inspection.

An engineering evaluation was made on the NPS 12, 140-mile Eagle River to Bear Springs section based on the comparison of 2003 and 2006 MFL inspections. The initial run for this analysis was conducted on April 29, 2003 and identified 13,667 anomalies down to an estimated depth of 10 percent wall loss. The comparative run was undertaken in May 2006 and identified 30,170 anomalies down to a depth of 10 percent wall loss. Of the anomalies identified in 2003 and 2006, 10,254 anomalies were matched between the inspections. The majority of the unmatched features from the 2003 inspection were within the areas of high corrosion and therefore merged into groups in 2006. There were 365 external corrosion anomalies denoted in 2006.

It is evident that the internal corrosion growth is more rapid where product is being injected at Darby and Thesalon Stations. The run-to-run comparison as referred to above provided over 10,000 data points from which to extract growth information of the internal anomalies. In addition, the rate of growth of the internal anomalies was dependent upon the orientation of the anomaly. A varying growth rate with a confidence level of 95 percent is obtained when using the solid black line while the dashed line contains all of the most rapid values of growth.

Applying the appropriate growth rates based on orientation to the anomalies delineated in the 2006 inspection an excavation timeline based on pressure (1.0 ERF) and anomaly depth limits (70 percent) was established. This was done on a six-month interval over a 10-year period. As this evaluation was done in 2007, it may be seen in Table 1 that by including the growth rate eight more excavations had to be made to cover 2006 and another nine to cover the 2007 year period. It was in the initial eight excavations that the four locations were sand blasted through as the pipe was being cleaned for examination.

Based on the excavation estimates presented in Table 1 and further over the 10-year period, an economic assessment using net present value (NPV) may be made. A net present value assessment is generally used to optimise the mitigation plan by taking into account the future repair cost versus the cost of re-inspection. In this case, the underlying assumptions were an eight percent discount rate, US$22,000 per excavation and US$125,000 per in-line inspection. The corrosion growth rate employed is aggressive therefore a more reasonable set of limits (1.0 ERF, 70 percent depth) was used. The NPV demonstrates that some sweeping measures must be taken to address not only the corrosion anomalies within the pipeline but the root cause of the corrosive medium to lessen the aggressive attack on the pipe. In particular the product input at both Darby and Thesalon stations must be treated appropriately to prevent further aggressive attack.

The proposed re-inspection date would be on or about May 2008, as long as the excavations are made as outlined for the 2006 and 2007 time period.

In-line inspection evaluations pull together all the information gathered from previous ILI and excavations to provide a more definitive answer to dig scheduling and re-inspection intervals. The cost to an operator to have such evaluations completed for their whole system is negligible relative to the cost of one in-service failure. As a result of the case study examined here, four anomalies in different locations were actually highlighted and remediated just prior to failing in-service.

Table 1. Timeline for excavation of anomalies

About Marc Lamontagne
Lamontagne is the Principal of Lamontagne Pipeline Assessment Corporation (LPAC), a specialist in evaluation assessment and reporting, a crucial part of the integrity management programme. Proper assessment evaluation and reporting streamlines the costs and timelines associated with pigging, digging and repair. Through his experience and highly specialised education, Marc brings a wealth of knowledge to the table.