Digital Solutions for Subsea Pipeline Cable Protection and Life Extension

Mimir Digital General
We live in a digital age of big data and device interconnectivity. Digital technology development continues at a rapid pace in both our personal and business lives, increasing in functionality and accessibility and supporting gains in productivity, efficiency, visibility, and informed decision making. With growing competition in energy markets and ever more demanding field development conditions, the offshore oil and gas industry is looking at advanced digital solutions to enable new efficiencies throughout the entire lifetime of a field.

Introduction

We live in a digital age of big data and device interconnectivity. Digital technology development continues at a rapid pace in both our personal and business lives, increasing in functionality and accessibility and supporting gains in productivity, efficiency, visibility, and informed decision making. With growing competition in energy markets and ever more demanding field development conditions, the offshore oil and gas industry is looking at advanced digital solutions to enable new efficiencies throughout the entire lifetime of a field. 

Subsea pipelines and cables are a critical part of fields and their continued reliable performance is essential to avoid costly repairs, replacement, or even abandonment. Digital solutions that provide insight through continuous monitoring can address existing design validation and performance assurance challenges, presenting new opportunities for the integrity management of these vital assets and the realization of new operating efficiencies.

Key existing challenges and opportunities in the design and integrity management of subsea pipelines and cables

It is estimated to be more than 100,000 kilometers of oil and gas pipelines and cables in service subsea today, and the desire is to extend their intended design life to maximize return on investment. 

For new offshore field developments, the performance demands on subsea pipelines are growing as the industry increasingly relies on cost-effective solutions such as long tiebacks for connections between new oil and gas reservoirs and existing offshore production facilities. In both brownfield and greenfield applications, if the key factors impacting the integrity of these pipelines can be  monitored, it provides owners and operators with extremely valuable visibility, enabling knowledge-based decision-making on aspects such as: reliability and safety, operational parameters, risk mitigation, life extension and inspection frequency; all with the end goal to reduce CAPEX and OPEX.

The key factors driving the design and longevity of a pipeline or cable can vary depending on its installation and service conditions. For example, if the pipeline or cable is being used in dynamic applications, such as for riser sections or flowline spans, then measuring motion and bending would quantify load and fatigue exposure, giving a realistic appreciation of the safety factors and system longevity. Similarly, if the pipeline is transporting corrosive or erosive materials, then measuring wall thickness degradation over time would also enable predictions of life expectancy. 

Typically, the design and service performance of subsea pipelines and cables have, for the most part, been verified by ROV/AUV surveys and pigging, in accordance with planned service schedules. These provide a snapshot on the condition of the pipe or cable but offer limited measurable data, only providing a single point of reference of what is happening, as opposed to a motion sensor that can provide millions of data points. 

Based on the levels of determined risk per pipeline, cable or per field, without the vast array of data points provided by a motion sensor, operations teams will need to set increased survey and maintenance schedules. This is a significant commitment in terms of cost considering the vessels, ROV and survey equipment required for deployment each time. In the case of pigging this can also include a potential need for permanent field infrastructure to be installed for pig retrieval.

Whilst continuous monitoring of key factors would provide the necessary insight to enable operators to gain reassurance or make informed decisions in relation to integrity management, it has not yet become commonplace on subsea pipelines and cables. Historical negative experiences of users include difficulty attaching and deploying the necessary hardware, limited battery life, data inaccuracy and the overall cost of monitoring hardware, which have hindered its wider adoption. 

A new approach to subsea pipeline and cable monitoring

Recognizing the value that monitoring provides, Trelleborg’s offshore operation is applying their in-depth knowledge and experience of pipeline and cable protection in harsh dynamic conditions to tackle the challenges holding back wider accessibility and adoption of monitoring on subsea pipelines and cables in critical locations, by simplifying the ROV  installation and increasing reliability and endurance. 

The operation is offering a new approach to pipeline and cable monitoring, by developing digital monitoring technology which can be either integrated into nearby ancillary protection products such as bend stiffeners or buoyancy modules, or attached via a standalone clamp system, negating the need for specialist support. Its goal at the outset was to engineer reliable, cost-effective sensing technologies which are easily accessible, deployable and recoverable, containing data which is easily validated and processed. 

Aligned to Trelleborg’s existing protection product functionality and application areas, the initial monitoring solutions released are designed to capture data on two key factors that commonly cause damage and fatigue of pipes and cables: motion and bending strain. Applications where pipelines and cables can experience motion and strain in a subsea environment are numerous, including: 

Vortex Induced Vibration (VIV) caused by current flow 
Slug Induced Vibration (SIV) created by variations in density of production fluid flow
Dynamic risers connecting to floating platforms, particularly towards topside terminations and touch-down points
Axial walking and buckling on High-Pressure High-Temperature (HPHT) flowlines
Pipeline and cable seabed stability

Trelleborg’s offshore operation is expanding their range of motion and strain monitoring devices within their Mimir Digital Intelligence product family. 

Application case study

In 2017, Trelleborg’s offshore operation collaborated with a major oil and gas operator to develop a solution to monitor motions of an existing flowline experiencing intermittent vibration. It was apparent from the ROV surveys that it was experiencing motion presenting an unforeseen risk to the operator. Unfortunately, due to its intermittent nature, the extent of motion was difficult to quantify as the ROV could only provide a snapshot in time unlike a motion sensor. 

Complex flow assurance and finite element analyses were performed in order to model the phenomena, however there were still uncertainties, leaving the operator with the decision of whether to slow down production, add mitigation methods, increase ROV inspection frequencies and duration, or to take a more novel, cost-effective approach.

Trelleborg’s Mimir MC (Motion Clamps) were retrofitted onto the flowline, to continuously and reliably record pipe motion data for subsequent processing and analysis.  As the nature of the pipeline motion was difficult to predict, it was important to have sensors capable of accurately recording data over a wide range of amplitudes and time periods. By working with advanced Microelectromechanical Systems (MEMS) sensor technology and validating data through testing, this was achieved. 
Power usage was also a key consideration as there was a requirement for a longer battery life (5 plus years) to support continuous monitoring, at the same time as ensuring the required sensor performance and sampling rate, whilst keeping the electronics and battery module as compact as possible. 

In this application, the requirement to measure small movements of the pipeline, increases sampling rate and power usage, altering the approach to data logging and communications. Due to the wireless bandwidth constraints subsea and the complexity of motion algorithms, which place a high demand on power usage, full data capture and physical recovery was the fastest and most efficient solution.

The clamp design itself was also a key consideration, with the application requiring ease of installation via an ROV, as well as continued, reliable clamping force throughout the service period, followed by a quick, easy and damage free recovery process to enable the technology to be repeatedly used over the life of the pipeline. 

Trelleborg’s offshore operation called upon their existing pipe clamping experience and product knowledge, working closely with ROV operators to develop a cost-effective clamping arrangement specifically to perform this function reliably.

The motion clamp general arrangement is presented in Figure 1 with key features highlighted below:

Mimir MC Motion Clamp 14


1. Advanced sensor technology
Modularly reconfigurable circuit board array with over 20 advanced sensors capable of monitoring all pipeline motions and strains, incorporating a wide range of use applications.

2. Independent, extended life: 
Designed as long-lasting, battery powered monitoring units, capable of continuous monitoring beyond five years due to the built-in selection of low power electronics and cutting-edge industrial MEMS sensors. 

3. Simplistic installation and removal: 
The motion clamp has been designed for attachment and removal via workclass ROV’s, being easily affixed to the pipeline by a manipulator jaw, in a single ‘locate-and-rotate’ actuation. 

4. Attachment assurance:
Reliable attachment to the pipeline was a vital consideration to ensure the clamp stayed locked in position under all design conditions, for the data recording to maintain a firm datum. Trelleborg applied existing clamping knowledge, considering variable parameters such as expansion, contractions, creep of coatings, temperature range, loadings and motions in the design.


5. Workflow based app: 
All clamp communication, operational documentation, including visual installation documents, material information, design assurance and factory acceptance testing were digitally provided to the operator directly via the Mimir Digital Technician App in a ruggedized tablet for ease of installation, removing the requirement for an onsite specialist technician to be present.

Mimir Digital Technician App resize

6. Electronic module pressure vessel: 
The pressure vessels protecting the electronics hardware were provided with safety and longevity in mind. The design also allowed repeated reuse to enable future swap-out of batteries and upgrade of the modular electronic boards.

Development of the motion clamp took place over a six-month period, with several units deployed onto the pipeline within a 12-month period. The data from the first deployment has since been recovered and processed by Trelleborg’s offshore operation, in open collaboration with the operator. Results so far have proven insightful, enabling the operator to make decisions on next steps.

Further developments

Since this application, Trelleborg’s offshore operation have further developed the performance and functionality of their Mimir Digital Intelligence monitoring devices to include ROV hot-swappable electronic modules, allowing the operator to retrieve the sensor or data only, negating the need to recover the entire clamp. Other developments include the further integration of Mimir Digital Intelligence technology within the existing product portfolio, alongside increasing the sensor portfolio and use cases.

Summary

By increasing the accessibility, reliability and cost-effectiveness of subsea monitoring, such systems can become more widely adopted within the oil and gas industry leading to insights and intelligent data, which can increase return of investment by enabling life extension of the field.  The increased knowledge that can be generated from sensors can allow fine-tuning of systems and processes, better quantifying an informing operators. Furthermore, their deployment can reduce the high OPEX costs associated with current ROV surveys. The data gathered provides key performance insight and modelling capabilities to support subsea asset integrity management, realizing value and carbon reduction opportunities through design and operational efficiencies and field life extension.