Pipeline And Subsea Integrity Assessment Using Corrosion Direct Assessment And Local Area Inspection

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Product Number: 51321-16732-SG

Author: Y. Zheng; M. Mateer; W. J. R. Nisbet; J. Sonke; J.T. Martin; P. B. J. van de Camp

Publication Date: 2021

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In the oil and gas industry, the management of the integrity of all pipelines and associated equipment ensures safe operation and availability for production during their intended life. Pipeline integrity assessment is usually executed in three separate steps:
1. threats (e.g., corrosion) analysis including effectiveness and efficiency of mitigation;
2. verification by monitoring and inspection;
3. fitness for service analysis to determine integrity status, estimate remaining life, and identify
required follow up actions.
Typically, in-line inspection by intelligent pigs is used to inspect for corrosion covering the entire pipeline. However, this approach is not always practical for more remote non-piggable pipelines, where verification can be a challenge and monitoring at topsides is often not sufficient to provide reliable data on the corrosion threat and effective mitigation of the full pipeline length. Therefore, alternative approaches are sometimes necessary.
This paper describes a practical engineering approach that leverages the available expertise, consisting of the following steps.

1. This method starts with the corrosion analysis to determine a worst-case scenario of maximum expected wall loss. The analysis uses corrosion prediction software (that includes multiphase flow model, a verified oil-water wetting model) as well as an analysis of the mitigation measures by operations (including corrosion inhibitor injection availability) and the data available that supports the corrosion inhibitor performance. This analysis results in a flow and corrosion profile and identification and prioritization of critical locations for local area inspection. Wall loss at a different scenario with different confidence is also estimated based on both model and data limitations.
2. An inspection plan, including identification of the minimum required scope and inspection method, is developed and implemented. Fitness for purpose analysis is performed based on different limit states.
3. Local inspection results are extrapolated to the whole system using different statistical methods to give an updated corrosion profile. The confidence of the overall integrity assessment is established based on both corrosion confidence and inspection confidence.
4. The inspection results are analyzed, resulting in a pipeline integrity status determination, which includes remaining life/extension and next inspection due date. A case study illustrates the implementation of the approach for the analysis of multiphase flowlines in the Gulf of Mexico.