Discovery™ is the world’s only field proven subsea CT scanner, and offers unparalleled information into pipeline integrity and flow assurance issues, without the need to remove coatings
As assets age, integrity issues tend to be of greater concern to operators. Ensuring that subsea installations are free from corrosion and/or flow assurance issues requires tight inspection and maintenance regimes, most of which require considerable time and money, and often lost production.
Subsea pipelines are no exception and can present an even greater challenge where lines are unpiggable, or are protected with coatings that must be removed and then replaced to ensure accurate measurements. In cases where traditional inspections cannot provide accurate information, operators may even be forced to estimate or model the pipeline, making key decisions without data that reflect the actual condition of the asset.
Tracerco specialises in providing technologies for real-time condition monitoring of subsea assets. One of its flagship innovations – Discovery™ – is the world’s only subsea computed tomography (CT) scanner, and offers a distinctive solution to the challenges of pipeline inspection.
First brought to market in 2015, Discovery remains unique in its use of CT technology to enable non-intrusive pipeline inspections. The system is the only technology able to scan through any type of protective coating and develop a complete tomographic image of pipe wall thickness, as well as the contents of the pipe, including waxes, asphaltenes, scales, hydrates, sand and lost pigs.
This technique also means that the system can be used on a variety of installations – including pipe-in-pipe, pipe bundles, caissons, risers and jumpers – all without ceasing production. Tracerco says that this offers savings of up to 35% over an inspection campaign compared to conventional techniques.
Yes we scan
As with a medical CT scanner, Discovery uses a radioactive source to pass a photon beam through the chosen material. In this case however, a high-energy gamma-ray source means the beam is able to pass through much denser material, enabling the system to be used on coated and concreted structures.
The unit is mobilised in two 6m ISO containers –a workshop and an equipment store – and can be deployed from any vessel of opportunity with a 5-tonne crane, ideally with active heave compensation (AHC). The total weight of the unit subsea is approximately 70kg. Once on the seabed, a work-class ROV is used to carry and manoeuvre the system over the desired pipeline. The system requires a 24V/5A DC supply, a maximum of 210 bar hydraulic pressure and Ethernet connections for operation, all made available through an integrated hot stab.
Once clamped onto the pipeline, the scanner spins around the full 360° circumference of the pipe to gather the CT data. Each image “slice” gathered covers around 15mm of pipe, and Discovery can move along the pipe automatically to build up a larger cross-section if required. It takes around one minute per revolution to produce a low-resolution scan, although more detailed images can be produced depending on the available time, and the pipe size, construction and circumference. Tracerco says more detailed scans usually average between 5-15 minutes.
The captured data is then transmitted to the surface and, using Tracerco-developed software, processed in real time to give a detailed picture of the pipe walls, its coating and its contents. Internal systems within the system also record data to ensure there is no loss of signal, and for added redundancy.
Using the real-time data, Tracerco’s inspection team will prepare an accompanying interim report detailing any urgent anomalies or areas of concern, allowing operators to address any serious issues immediately. Following this, a more detailed analysis is prepared by the company’s engineers and its wider Technology Group.
Although final processed results will depend on individual assets, Discovery has recently completed a Lloyd’s Register qualification programme, resulting in the technology being certified. This puts the accuracy of wall thickness measurements to within +/- 1.5mm, and density to within +/-50kg per cubic metre, with 80% confidence. It can also identify pitting or metal loss with a minimum depth of 1.2mm.
Suitable for both vertical and horizontal, Discovery can scan pipe diameters from 6 to 26 inches (152-660mm) and can clamp onto pipes of up to 675mm diameter, including coatings and other lines. It does require 360° access around these assets, which in the case of buried lines may mean some excavation is needed, but previous scans have successfully imaged even pipelines with high-density weighted concrete and rebar.
Bundles of information
As outlined, the key benefit of Discovery is its unique ability to scan through coated and concreted pipes, avoiding the considerable time and expense of removing coatings to check integrity. But the flexibility of the system means it is also the first tool capable of providing a complete picture of more complex pipe architectures. In the case of piggybacked pipes, typical inspections require full 360° access to each individual line to check integrity. Using external spacers, Discovery can clamp around the entire bundle, and perform a full scan of all lines simultaneously – another significant saving in time and cost. The scan also shows the bolts and pins securing the piggyback clamp itself.
The nature of pipe-in-pipe systems, often used to contain high-temperature products, also makes them a challenge to inspect. Tracerco notes that Discovery has proved to be “particularly adept” at scanning these lines, in that it can provide accurate wall thickness measurements for both inner and outer pipes, as well as displaying the integrity and alignment of the spacing between the inner pipes. The same goes for bundled pipes, where Discovery can offer clear integrity data on internal umbilicals, risers and even seam weld and rust accumulation.
In cases of hydrate and wax build-up, CT images will also provide insight into the size and formation of the deposits, and the ways in which they may be affecting fluid flow. In particular, it can also offer vital information on the presence and extent of under-deposit corrosion and localised pipe degradation underneath solid deposits – which are typically very hard to detect. In one deployment, Tracerco was able to identify hydrate formation and dissociation steps and accurately identify product pressure to within 0.1g/cubic cm, helping an operator devise a targeted solution to remove the build-up.
Following any remediation campaign, the system can also be used to confirm the removal of all deposits and verify whether pipe sections are completely clear.
Discovery has now been deployed successfully at depths down to 5,300ft/ 1,615m subsea, and has carried out in excess of 1,000 pipeline scans across the Gulf of Mexico, the North Sea and the Arabian Peninsula. Tracerco is currently considering the development of a larger unit, for lines of up to 42 inches (1,067 mm) in diameter.
Tracerco has recently announced the launch of a new fast scanning application for Discovery. Following customer feedback, the company completed further R&D work to develop a new method, specifically for detecting the presence of localised metal loss defects on subsea pipelines – up to 5 times faster than before.
The new development means that once a potential anomaly has been identified via the fast-scanning method, a more detailed and accurate scan to characterise it fully can be undertaken, simply by extending the duration of the fast scan. This eliminates the requirement of a separate scan and the need to deploy a secondary technology to validate the findings from the initial fast scanning inspection.
Operators can use this to screen subsea pipelines quickly and accurately to determine whether the integrity is within the acceptable tolerance specification. With non-intrusive inspection through any type of protective pipeline coating, defects can be fully characterised faster than ever, while again saving time, resources and the cost of an inspection campaign.
The first two inspection campaigns utilising Discovery as a fast-scanning technology have recently been completed on a large-diameter export pipeline in the Arabian Gulf and across a range of infield flowlines and jumpers in the Gulf of Mexico. The quality and volume of inspection data obtained provided the clients with sufficient statistical confidence that the fast scanning results were representative of the condition of their entire system, Tracerco told InnovOil. As such, both customers were extremely satisfied with the results, providing another testament to this impressive technology.