Project Phase
Decommissioning EDC Concept Select & Pre-FEED
Disciplines
Study Management
Process and Flow Assurance Led Multidiscipline Engineering
Estimation
Location
UKCS
Service
Engineering Consultancy
Summary
We developed a clear, executable strategy to clean and disconnect an export pipeline system ahead of decommissioning, solving major late-life topsides utility constraints and identifying practical schedule and cost-saving opportunities to accelerate readiness.
Overview
Infinity were selected to carry out front end engineering for a late-life normally unattended installation (NUI) that was being preparing for decommissioning of a long-distance export pipeline, with a piggy-backed chemical line. The first decommissioning phase required an approach to achieve specified Oil-in-Water (OIW) cleanliness and implement a safe disconnection strategy—despite limited topsides utilities and constrained discharge capability.
Objective
- Define the optimal method to clean the pipeline system to a suitable OIW standard
- Develop a safe, practical approach to isolation and disconnection
- Produce an execution-ready methodology supported by risk screening, schedule logic and cost basis
- Ensure the solution worked within topsides utility and discharge limitations
km export line
inch pipeline
inch piggy back line
Key findings
- Utilities were the governing constraint: limited power/water/discharge on the late-life topsides required a constraint-led solution set and feasibility screening (including a coarse HAZID).
- Flow assurance defined the cleaning envelope: modelling identified liquid hold-up and enabled flushing simulations to define flowrates and durations for different OIW cleanliness levels (supporting emissions and operability assessments).
- Facilities and temporary systems were central to delivery: we designed practical topsides/terminal handling for flushing fluids using a blend of existing terminal equipment and low-footprint temporary packages, then supported layout, tie-ins, connections and installation planning.
- Vendor input improved realism and reduced scope: early engagement shaped the basis of temporary equipment, de-risked installation assumptions, and surfaced simplification opportunities.
Differentiator
A constraint-led, execution-focused methodology built around the realities of a late-life topsides facility. By integrating flow assurance, process/facilities design, temporary systems engineering and vendor input from the outset, we avoided standard solutions and developed a practical, low-footprint approach that simplified execution and unlocked both schedule and cost savings.
Outcome
We delivered clear recommendations for how to clean and disconnect the pipeline system safely—controlling gas, managing condensate and liquid hold-up, and treating flushing fluids—supported by a practical execution methodology plus schedule and cost estimates. The study also identified several ways to reduce scope and accelerate decommissioning readiness, including a new approach to flushing-water storage at the receiving terminal to work around restricted discharge capacity, the use of nitrogen as the driving medium for pig-train propulsion to remove the need for a temporary onshore water-treatment package, improved management of liquid hold-up that reduced reliance on terminal operations and lowered OPEX exposure, and an operating philosophy that allows topsides isolation and disconnection to progress in parallel with pipeline cleaning—decoupling dependencies and shortening the critical path.
Find Out More
Have questions about this project? Contact us to find out how Infinity can help to manage your subsea assets.
joao.conde@infinity-limited.com
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