Marathon Oil UK LLC was fined £1,160,000 in May following a high-pressure gas release on its Brae Alpha offshore platform on Boxing Day 2015. Aberdeen Sheriff Court heard that an eight-inch diameter high-pressure pipework in Module 14 of the platform suffered a catastrophic rupture as a result of CUI. This allowed more than two tonnes of high-pressure methane gas to be released almost instantaneously.
CUI is a severe form of localised external corrosion that occurs in carbon and low alloy steel pipe and equipment that has been insulated. This form of corrosion occurs when water is absorbed by or collected in the insulation. “The equipment begins to corrode as it is exposed to water and oxygen and temperature fluctuation, which is a common problem in the energy sector, both onshore and offshore,” says a spokesperson for Oceaneering, an engineered services and products provider primarily to the offshore energy industry.
Steve Drake, NDT market manager at Ashtead Technology, explains further. He says that the potential for CUI is greatest in marine environments, hot and humid environments, and in locations with high rainfall, aggressive atmospheres or steam tracing leaks. “Intermittent wet and dry conditions, or systems that operate below the dew point can encourage CUI. Some insulating materials may [also] contain contaminants, such as sulphides and chlorides, or may retain moisture, or be designed in a way that restricts moisture drainage,” he adds.
PREVENTION METHODS
The Brae Alpha offshore platform incident, which saw significant and widespread damage within Module 14, occurred while most of the 100 personnel on the platform were gathered in the accommodation block, in readiness for their Boxing Day meal, and away from the source of the blast.
An investigation by the Health and Safety Executive (HSE) found that Marathon Oil had failed to undertake any suitable and sufficient inspection of the pipework that would have allowed the company to identify the risk and prevent the hazard from materialising. These failures resulted in personnel being exposed to an unacceptable risk of serious personal injury or death from fire and explosion. It also led to HSE serving an Improvement Notice in January 2016, requiring Marathon Oil to implement an effective hydrocarbon pipework inspection and maintenance regime (www.is.gd/hugije).
The case serves as a reminder as to the importance of inspection and maintenance to pipework that could potentially suffer from CUI and corrosion. But what prevention methods are there?
The Oceaneering spokesperson explains that non-destructive testing (NDT) “plays a huge role in inspection, maintenance and risk management across the oil and gas industry”, with popular NDT methods involving visual inspections, ultrasonic techniques, radiography, thermography, laser shearography, eddy current testing, microwaves, and acoustics.
“The most effective NDT methods identify and address issues regarding safety, equipment reliability, environmental protection and regulations, without affecting the serviceability of the component – for example, pipelines and other high-risk pressurised plant and equipment. For more than 25 years, there was no reliable NDT method for detecting corrosion and CUI in the vicinity of nucleonics. That is until now,” the spokesperson says.
“Inspection work scope deferral has often been the case when the pipes, are close to nucleonics because of the risk of process trips. Visual inspections can be performed on uninsulated pipes, but can only give limited information about the equipment’s condition. Where facilities piping is insulated, the cost of removing, inspecting and then reinsulating equipment has to be taken into consideration, especially if the threat of CUI is unknown.
“Deferring inspections can leave operators open to safety and lost production risks from LOPC (Loss of Primary Containment) incidents. When deferment is not an option, operators often isolate nucleonics to prevent the risk of radiography sources ‘tripping’, but this leaves operators blind to potential process problems that could be developing, for example in vessel separators, and that is a potential safety risk in itself.”
Oceaneering was determined to develop a solution. In collaboration with the suppliers of specialist pulsed x-ray systems and nucleonic instrumentation manufacturers, Oceaneering’s SMEs designed and implemented a procedure. The procedure is said to eliminate the risk of radiography affecting production operations in and around nucleonics.
The combination is an inspection offering called the Trip Avoidance X-ray Inspection (TAXI) system, which is said to reduce plant and equipment downtime while simultaneously improving process safety.
FOR HIRE
Ashtead Technology hires out NDT technologies to its clients. Drake explains that by making this equipment available for hire, Ashtead provides access to the latest technology without the burden of capital cost, while a further advantage of instrument rental lies with the ability to call upon technology at short notice.
One solution is the Eddyfi Lyft, which employs Pulsed Eddy Current (PEC) in a portable, rugged, battery-powered NDT instrument with connect-anywhere wired and wireless communications. Designed to improve the speed, ease and quality of inspections with real-time C-scan imaging, the Lyft is said to offer fast data acquisition (up to 15 readings per second) grid-mapping and dynamic scanning modes. Three different sizes of standard probes and a specialised splash-zone probe enable the inspection of wall thicknesses up to 64mm, insulation up to 203mm thick (fibreglass, plastic wrap, concrete, or other non-ferrous materials), as well as stainless steel, aluminium, and galvanized steel weather jackets.
Olympus OmniScan phased array ultrasonic systems, meanwhile, are some of the most popular instruments in Ashtead’s entire rental fleet. The OmniScan MX2 (main image), for example, is said to increase testing efficiencies, ensuring manual and advanced performance with faster setups, test cycles, and reporting, in addition to universal compatibility with all phased array and ultrasound modules.
The Olympus HydroFORM corrosion mapping scanner has been designed for the detection of wall-thickness reductions due to corrosion, abrasion, and erosion. It is also said to detect mid-wall damage, such as hydrogen-induced blistering or manufacturing-induced laminations, and can easily differentiate these anomalies from loss of wall thickness.
Other systems available for hire include the Phoenix ISL Tracer freehand scanning system and the SilverwingScorpion, which is a motorised magnetic inspection tool, able to inspect vertical, curved and overhead surfaces. The Scorpion is a dry-coupled UT (ultrasonic testing) crawler that connects with a UT Lite data acquisition instrument via a 30-metre umbilical cord. When combined with the UT Lite, the Scorpion continuously records thickness measurements as it moves over the inspection surface. The recorded thickness information is presented in the software as an A-scan trace, a digital thickness measurement and a B-scan profile.
“Every tank, pipe or vessel is different; not just in age and material of construction, but also in build and maintenance quality. The environment can also have a significant impact on the quality and integrity of an asset, as can operational conditions. It is important, therefore, for inspection staff to deploy the most appropriate instrumentation,” concludes Drake.