Methodology for the Evaluation of Cleaning Pigs on Sludge Deposits from Corrosion Pits

摘要

For decades pipelines have been operated in remote and environmentally sensitive areas as well as within populated locations. Proper maintenance of pipelines can prevent internal corrosion to a remarkable degree. The methods employed are primarily mechanical cleaning (pigging) and chemical treatment (corrosion inhibitors, biocides), often used in combination. Corrosion issues arise in areas of the pipeline typically under localized areas containing sediments that tend to be an agglomeration of solids, waxes and water. The resulting corrosion defects can then become ideal locations for sediment and water to continue to gather and create deep, dirt filled localized pitting that cannot be protected through chemical treatment without the aid of mechanical cleaning (pigging). In an effort to increase the knowledge of the cleaning efficiency of typical pig designs at removing sludge and debris from pre-existing corrosion pits, a novel test setup and method has been devised. A recirculating flow loop was constructed with the capabilities of launching a 102 mm (4") diameter cleaning pig using either crude oil or water as the pumped fluid. During the test, a pig would be passed through a test apparatus which housed flush mounted coupons with variously sized pits, packed with manufactured sediment (sludge). Following the pigging operation, the coupons were removed and analyzed via laser scanning techniques to measure sludge volume removal and maximum depth of cleaning. The pigs' cleaning abilities were compared based on both metrics and information was gathered based on the profile of the sludge's surfaces post pigging, as well as images of the pigs with adhered sludge.