The article discusses a methodological approach to ranking of main oil pipeline sections by the degree of corrosion hazard using smart pigging data.
Realization of monitoring of the anti-corrosion protection system status at the pipeline facilities of Transneft organizations, aimed at assurance of its efficiency, determines the necessity to develop and refine an appropriate methodological component.
As is known, the Transneft companies have been using a technique for technical inspection of the linear part of main pipelines with the help of pipeline intelligent pigs (PIP) for about 20 years. Use of high-resolution intelligent pigs makes it possible to detect defects, measure their parameters and classify by types.
In 2010 they performed in-line inspection of 45,000 kilometers of oil pipelines and 3,300 kilometers of oil product pipelines. In 2011 the scope of in-line inspection remained at the same level. Information on all detected defects and the repair work is stored and permanently added to the “Defect” database.
Ultrasonic flaw detectors WM utilized in the pipeline intelligent pigs make it possible to detect external corrosion damage of pipelines, development of which should be prevented by the cathodic protection system (CPS).
Taking the above stated into consideration, it is necessary to correctly use the data received with the help of the in-line inspection to assess the current corrosion status of sections of the main pipelines in order to design compensating actions aimed at assurance of the CPS efficiency.
For this purpose, it is recommended to use the accepted system of pipeline sections ranking by the degree of corrosion hazard.
Thus, sections of high corrosion hazard (HCH) include pipeline sections in which there were detected corrosion pits and cracks having depth exceeding 15 percent of the pipe wall thickness, or corrosion rate exceeds 0.5 mm a year .
Sections of increased corrosion hazard (ICH) include pipeline sections in which there were detected corrosion damages with the depth exceeding 10 percent of the pipe wall thickness or corrosion rate is in the range from 0.3 to 0.5 mm a year .
Relative depth of the external corrosion defect Hотн (percent) is calculated by the formula
where Hk – corrosion defect depth by the in-line inspection data, mm; δ – pipe wall thickness, mm.
Rate of corrosion defect development Vk, mm/year, is determined by the expression
where H1 – defect depth registered during the previous in-line inspection, mm; H2 – defect depth registered during the current in-line inspection, mm; ∆T – period of time between these two measurements, year.
To assess the changes of depth and rate of the corrosion damage over time, specialists retrieve values of the corrosion damage depth Hk of the last and next to last in-line inspection of the main oil pipeline done by flaw detectors WM from the database “Defect”.
Software “Expert 2” developed by the Flaw Detection Center Diascan is used for connection to the servers of the database “Defect”.