Oil and gas production pipelines are susceptible to internal corrosion at locations where flow conditions promote water accumulation and solid particles settlement (precipitation). These deposits form diffusion barrier between the produced fluids and underlying substrate, which results in water chemistry near the steel surface different from that in the bulk fluids. This can potentially lead to an accelerated localized corrosion through under deposit corrosion (UDC). Successful corrosion management of UDC is based on risk assessment, mitigation and monitoring. As a normal practice, mechanical scraping along with chemical treatment is commonly applied as the mitigation for UDC. However, for this case, installing a scraper facility was not economically viable for new pipelines connected to an ageing platform that was meant for temporary period. Therefore, an assessment was conducted to determine if solids deposition and associated corrosion risks could be completely eliminated or tolerated to an acceptable level for safe continuous operation before diverting the pipelines permanently and equipped with scraping facility. The assessment utilized a novel approach consisting of advanced precipitation modelling, UDC laboratory testing including solids characterization in addition to flow assurance and corrosion simulation. The results showed that the overall deposition and associated corrosion risk is low. By implementing the recommended measures, these pipelines can be operated safely without scraping facilities temporarily, after which the pipelines will be routed to future scraping facility
Pipeline under-deposit corrosion (UDC) is a localized corrosion phenomenon that develops beneath or around solid deposits, which settle at the bottom of low flow/intermittent flow pipelines. These deposits are complex mixtures of water, organic, inorganic, and biological materials, and their composition can vary significantly depending on the properties of the product being transported and the operating conditions in the pipeline.
The inorganic solid deposits can be transported from the formation, produced in the system due to corrosion, precipitate from the water, or debris/fragments from the degraded coating1. Whereas, the organic deposits, which can precipitate from the crude oil or being formed on the surface due to microbiological activity, are not considered in this paper for being ruled out in case study.
