A floating production storage and offloading (FPSO) vessel handling crude oil was scheduled to undergo an infrastructure reconfiguration from a turret mooring system to a spread mooring system. The proposed offloading system for this configuration was comprised of a catenary anchor leg mooring (CALM) buoy tied back to the FPSO through 20” twin looped oil offloading lines (OOLs).
The production fluid handled by the FPSO was predicted to contain large quantities of wax, with wax deposition likely, meaning that regular cleaning (dewaxing) of the OOLs was a requirement from a throughput perspective. Due to limited deck space on the FPSO, the operator proposed that pigging valves be installed to launch and receive cleaning tools in place of conventional launching and receiving facilities. ROSEN was asked to review a number of design options at the front end engineering design (FEED) stage to optimize cleaning effectiveness while minimizing operational risk. In addition to cleaning the OOLs, a primary concern surrounded the receiving and handling of the large volumes of wax and other debris through the pigging valves and transporting them back into the FPSO storage tanks.
ROSEN’s integrity specialists determined that an initial progressive cleaning solution was required in order to mitigate risk by limiting wax volumes until the wax deposits and associated debris could be more accurately quantified. In parallel to this, ROSEN identified a number of key areas for improvement, including:
- Internal bore transitions to increase pigging efficiency and mitigate stuck pig scenario
- Bypass lines to control the speed of the pig at launch and receive to prevent damage, reduce tool wear and increase cleaning efficiency
- Flushing configuration to enable blockage prevention in the event of wax buildup around the pigging valves and in the return line
- Pig tracking
High-level key performance indicators (KPIs) were also developed to enable optimization of the cleaning campaign. The monitoring of the actual vs. planned pigging frequency, along with observing the condition of the pigging returns, helped to provide a sufficient understanding of the system for the determination and optimization of subsequent pigging programs. These improvements would maximize the efficiency of the cleaning and minimize risk during the cleaning operations — resulting in less impact on operations and minimized associated costs.
By approaching ROSEN, the customer gained access to over 300 years of combined industry experience, incorporating world-renowned experts in pipeline integrity management, inline inspection, and cleaning tool design, manufacture and operation. During this project, ROSEN worked closely with the client to fully understand the operational and business drivers for the offloading system and its piggability.
The project aimed to determine the feasibility, based on the proposed design, of effectively cleaning the pipeline for the purpose of bore management, and to ensure that the maximum offloading flowrate could be maintained. This project was carried out during FEED, prior to detailed design, in order to identify limitations and system constraints that introduce risks that would compromise the ability to clean the offloading lines.
Benefits of the study include:
- Independent design review
- Identification of areas of risk in the design
- Identification of design improvements
- Provision of key recommendations
- Assurance that offloading flow rates can be effectively maintained
This allowed for the identification of key improvements to the OOL system design early on in the process, ultimately reducing operational costs and risk for the customer. ROSEN’s capability to launch and receive single body inline inspection tools through pigging valves assured that further inspection could be completed, should it be required, therefore enabling future assessments of the pipeline condition.