Tracerco’s DiscoveryTM is the world’s only subsea CT scanner
Sitting on the bottom of the ocean, it can be easy to forget about pipelines. Once they are laid, it feels like they are out of sight and out of mind.
However, extreme undersea environments can take their toll on a pipeline’s integrity. Corrosion and cracks can cause catastrophic damage to a vital piece of infrastructure, resulting in supply interruptions and heavy environmental damage.
As such, quickly and effectively diagnosing any flaws in a pipeline is vital to ensuring its performance. Measurement and data-driven insights company Tracerco has developed and deployed a pipeline scanning system called Discovery to do just that.
InnovOil spoke to Tracerco’s business development manager for subsea applications, Mike Banks, about how they are unlocking the secrets of pipeline data.
Tracerco utilises a new fast scanning application for Discovery. Tracerco completed R&D work to develop a new method specifically for detecting the presence of localised metal loss defects on subsea pipelines up to five times faster than before.
“There was a need to see what was happening inside pipelines so that operators could diagnose potential blockages or restrictions accurately and effectively. There was also a need for inspecting unpigabble pipelines without removing any of the pipelines’ protective coating,” Banks said. “CT ticks both of those boxes in one instrument, so that’s the reason why we started looking into it.”
Discovery functions like a medical CT scanner, where a number of x-rays are taken of a subject from multiple angles. It can take accurate measurements of pipe wall thickness through any type of protective coating whilst simultaneously diagnosing and characterising flow abnormalities within subsea pipelines without interrupting normal pipeline operations.
“There’s a single radiation source, and a number of detectors mounted opposite that, which then rotate around the object under inspection, in our case a pipeline,” Banks explained. “From the data that we generate, we can reconstruct an image of the pipeline to find information about the integrity of the pipeline itself and find out what’s happening inside the pipeline.”
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.
“By employing the Discovery fast screening approach, pipelines can be inspected up to five times faster than before, meaning operators can save up to 80% of the inspection time,” Banks said.
“Since the introduction of the fast scanning approach, we have been able to scan 10 times the pipeline length in the same number of days offshore. This has brought a number of significant benefits to our customers in terms of resource and cost reduction for inspection campaigns.”
On the outside looking in
Pipeline inspection has largely been limited to the used of pigs to scan a pipeline from within. This limits the type of systems that can be scanned accurately. Discovery can offer its users the ability to scan a greater variety of pipelines than before.
“It gives them that opportunity to be able to inspect a pipeline that up until the advent of Discovery might not have been able to be inspected, such as a complex pipeline system,” Banks explained.
“If you can get an inline inspection tool in for the integrity of the pipeline, you’re probably going to use that because it’s going to give you 100% coverage of your pipeline. But if you’ve got a complex pipe system, pipe-in-pipe or a bundle or piggybacked pipelines or it’s heavily coated, then Discovery can then scan that.
“Imagine a pipe-in-pipe system: if you can’t get an inline inspection tool through, then you can’t inspect that inner production pipeline. Discovery can inspect both the outer and inner pipe in one single scan.
“Complex systems or even pipelines with other pipelines piggybacked onto them can also be inspected without having to decouple the piggybacked pipeline.
“For Discovery, the thickness of coating doesn’t really matter and the coating itself doesn’t need to be physically bonded to the pipeline, so there could be a gap there and it doesn’t affect the quality of the data.
“We’re able to make a judgement in real time if there are any metal loss defects there or not, and if there aren’t we can simply move onto the next scan.”
In the field
Discovery’s fast scanning technology was recently utilised on two inspection campaigns, one in the Gulf of Mexico and one in the Arabian Gulf.
In the Gulf of Mexico, Tracerco was able to identify some major defects on a number of flowlines, including jumpers, steel catenary risers and pipe-in-pipe flowlines, all of varying diameters.
In total, 50,000 feet (15,240 metres) of pipe were scanned at depths down to 4,200 feet (1,280 metres).
In the Arabian Gulf, Tracerco was called upon to scan a 24-inch (610-mm) gas export pipeline. “That was the first project we employed the fast screening on, so in that case the customer wanted to scan multiple four-metre sections,” Banks said.
“We were able to do each section in about 24 hours, whereas normally it would have taken us about four or five days.”
Seal of approval
Tracerco also recently received Lloyd’s Register (LR) recognition for Discovery.
LR and Tracerco performed the qualification trials of Discovery in a simulated subsea environment at Tracerco’s HQ in Billingham, UK. The trials were successfully able to determine the depth limit for reliable POD (probability of detection) and typical sizing tolerances for metal loss anomalies at the inner and outer positions of subsea pipes.
“As part of the qualification trial we performed well over 500 individual scans on real pipes with real defects,” Banks said.
“In addition to that, we performed approximately 2,000 simulations to see how Discovery would perform. From the scans we were able to clearly define our POD and sizing tolerances.”
Banks added: “For metal loss defects, we’re looking at a POD of the wall thickness in the region of 2 mm. For general wall thickness, we have a tolerance of about 1 mm. And for certain defects there’s a detection range of approximately +/-1.5 mm,”
Banks summarised by stating: “We are extremely pleased to have this qualification programme recognised by LR, who provided valuable technical input in terms of the specific NDT technique and the general qualification process. The results give our customers an assurance that the qualification was conducted in compliance with international standards and guidelines for offshore pipelines.”