Subsea flowline monitoring for asset integrity

Deepwater operators must manage subsea integrity, as pipelines and flowlines can gradually move over their lifetime, especially across slopes and transitions. Monitoring this behaviour is essential to protect connectors, reduce intervention risk, and maintain safe, uninterrupted production. Learn how Fugro partnered with Sonardyne to address a complex flowline termination assembly (FTA) movement monitoring challenge offshore Australia.

The challenge

FTA movement is a common subsea integrity challenge in deepwater gas fields, driven by pipeline walking and buckling. Hot flowlines on soft seabeds can experience axial walking of 1–5 m over field life due to thermal expansion, pressure cycling and seabed friction.

Walking concentrates at FTAs, risking jumper spool stress, connector unlock or seal failure—even with engineered mitigations like sleepers or anchors. Actual movement rates vary with soil stiffness, slugging and life-extension, and unmonitored walking can lead to costly shutdowns for jumper re-termination.

At an Australian offshore gas field, two seabed FTAs were suspected of moving. On behalf of the operator, Fugro wanted to implement precise monitoring to protect flowline integrity and maintain safe production.

Fugro came to us with a number of key requirements:

Accurate positioning: Monitoring axial and lateral movements of the FTAs relative to end stops during all operational states.
Data collection and storage: Measurements at 2-hour intervals, with subsea data storage for at least six months and data recovery planned at intervals of up to six months.
Long-term deployment: A monitoring system able to operate reliably for an initial three-year period, with minimal disruption to production.
Cost efficiency: A solution that avoided costly field shutdowns or extensive subsea infrastructure redesigns.

Red cylindrical equipment bundled on pallets next to large yellow pear-shaped buoys on pallets in a warehouse.

The solution

Fugro, in collaboration with Sonardyne, developed and implemented a robust monitoring solution tailored to the project’s unique requirements.

Our Acoustic Monitoring Transponders (AMTs) were selected as the core technology due to their ability to deliver accurate, repeatable position measurements with minimal operational impact.

AMTs measure pipeline walking by acting as acoustic nodes attached directly to the pipeline. Installed as an array, they continuously range between each other to monitor relative distances along the structure. By tracking changes in these inter-range measurements over time, the system can detect axial movement, quantify its magnitude and direction and identify localized sections of displacement.

Their long-life battery powered design enables long-term, absolute displacement data without introducing additional interfaces or complexity to the pipeline system.

Wireless acoustic communications capability also means they can be left in situ, but data can be collected on-demand, offering a low-risk, low-maintenance option. They can also be wired into existing infrastructure, to provide a continuous data-feed, if required.

Planning and Engineering:

Array planning was carried out to ensure that the acoustic geometry would deliver the required positioning accuracy and repeatability during the monitoring period.

This provided confidence that measured position changes reflected true pipeline movement, rather than measurement uncertainty.

It also aligned with allowing for data harvesting during routine survey and IMR operations.

Installation:

In November 2016, deployed a 10-unit AMT array at the site. This included:

Five AMTs in seabed stands (pictured).
Four AMTs in collars on the FTAs.
One AMT on the pigging manifold.

An ROV-mounted ROVNav 6 and a Dunker transceiver used from the surface (i.e. a vessel) were used to calibrate and communicate with the AMT array.

ROVNav 6 is a transceiver designed for use on ROVs to support subsea positioning and telemetry operations.

Data Collection and Analysis:

The AMTs were configured for hourly measurement cycles, capturing pressure, temperature, sound velocity and baseline travel times.

Data was harvested in April, May and October, analyzed and presented to the client as time-series graphs, enabling engineers to assess axial and lateral movements of the FTAs.

Real-Time Monitoring Enhancement:

In October 2017, a SMART (Subsea Monitoring, Analysis and Reporting Transponder) was added to the system, connecting to a Subsea Control Module (SCM). This enabled real-time data recovery, via the existing subsea infrastructure, reducing the need for data harvesting missions and allowing quicker decision-making.

By 2022, the operator had the data they needed and in June that year the array was recovered.

The results

The monitoring project delivered significant benefits to the client, ensuring the safe and efficient operation of the offshore gas field.

Accurate monitoring: The AMT array provided precise measurements of FTA movements, enabling the client to identify and address slow but significant axial and lateral shifts caused by varying temperature and pressure conditions.
Cost efficiency: The introduction of the SMART system reduced the frequency of data harvesting missions, minimizing operational costs while maintaining production.
Operational longevity: The monitoring system operated successfully for over three years, with batteries updated and AMTs replaced as needed to extend the deployment.
Enhanced decision-making: Real-time data access allowed the client to make informed decisions, avoiding the need for expensive field shutdowns or infrastructure redesigns.
Collaboration and Expertise: Fugro’s local expertise and collaboration with Sonardyne ensured the project’s success, from planning and installation to data analysis and remediation.

Conclusion

Fugro’s innovative monitoring solution, supported by Sonardyne technology, enabled the client to maintain production safely and cost-effectively while addressing critical movement issues in the FTAs.

The project demonstrated the value of precise subsea monitoring, real-time data access, and collaborative problem-solving in managing offshore infrastructure challenges.

Subsea asset monitoring in action

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Keeping production flowing by understanding subsea asset movement – wirelessly

Copilot said:

Wireless subsea monitoring helps operators track asset movement, vibration and fatigue, enabling safer production, longer asset life and better-informed integrity management decisions.

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Monitoring slugging events and spool piece fatigue

Deepwater asset monitoring made smarter. Wireless edge analytics and acoustic communications deliver continuous subsea data, helping operators assess fatigue, predict asset life and reduce monitoring costs.

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Rising to the challenge: riser tower monitoring

When Petrobras’s Cascade and Chinook development went into production in 2010, it claimed two major milestones. It was the first floating production, storage and offloading (FPSO) facility used to accept production from the fields in the Gulf of Mexico, at 2,600 m. It was also the world’s deepest operating FPSO.

Observer

System

SMART

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AMT

System

TL;DR: Fugro used Sonardyne’s Acoustic Monitoring Transponders to track suspected movement of two subsea flowline terminal assemblies offshore Australia. The long-term acoustic monitoring system provided accurate displacement data, reduced the need for intervention, and later enabled real-time data recovery through existing infrastructure—helping the operator protect asset integrity, avoid unnecessary shutdowns and make better-informed decisions.

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