In-Line Inspection of Offshore Non-Piggable and Challenging 30" Subsea Flare Line

Abstract

The objective of the paper is to present the success story of carrying out an in-line inspection (ILI) on a 50 years old offshore subsea flare line. The project was particularly challenging because the 30" flare line had no pigging facilities, a reducer, a subsea tie-in connection, as well as other restrictions. The paper shall outline the approach and methodology adopted to conduct the inspection in a safe and successful manner while adhering to the company and government health, safety, and environmental regulations and meeting the shutdown window. The 1 km long 30" flare line runs from a collector-separator platform to a flare tower. A site survey was conducted to identify process, space, and rigging related requirements. The shutdown window was allotted and fixed by the production teams. The line was first flushed to remove the hydrocarbons using a pumping spread mounted on a support vessel. This was followed by various modification works in addition to rigging up the temporary pigging traps. The works enlisted the help of support vessels and scaffolding teams. Extra controls were implemented due to the low maximum allowable operating pressure and the dirty pigging water in order to safeguard the property and environment. Eventually, 22 cleaning pigs were launched a in a train fashion. An Ultrasonic (UT) ILI tool was then used to gather information on the pipeline. Finally, the pipeline was dried using foam pigs. The operation was a success mainly because of the planning factor. Many activities were integrated including the availability of a maintenance barge which played a huge role in the operation. This was the first pigging operation on the flare line which was commissioned in 1971 - a total of 185 kg of debris was collected. Moreover, the UT inspection provided quantitative data which enabled an accurate assessment of the subsea pipeline integrity status. It is estimated that USD 4 million were saved by completing the works mainly through efficient planning and utilization of in-house available resources. The inspection results will form a cornerstone in development of future asset replacement plans for this category of flare lines. The success has created potential savings for another 21 challenging flare lines planned to be inspected for the next 5 years. The approach highlights the steps taken to conduct the quantitative ILI of an aged flare line (50 years old), with various inherent challenges, to explore the possibility of accurately inspecting and extending the remnant life of aged assets that are un-piggable, in a safe and environmentally friendly manner. Thus, resulting in positive impacts in savings and further optimizations in the asset replacement plans