A large number of oil and gas pressure pipework failures in the North Sea are caused by corrosion under insulation (CUI), which in turn can lead to a high risk of loss of pressure containment (LOPC). In a sector where safety is absolutely paramount, this has to change.
However, it is often problematic to perform safety critical inspections such as corrosion detection around nucleonic level control systems using radiography, because the radiation exposure can interact with nucleonic detectors causing unplanned process upsets, typically called plant and equipment ‘trips’. Plant trips can result in an increased safety risk from interrupted process monitoring and substantial lost revenue.
Radiography is one of the most effective methods used to detect and measure CUI and other corrosion flaws but can the issue of plant trips ever be overcome?
The impact of non-destructive testing (NDT)
Radiography is one of the oldest NDT techniques and was developed in 1895, when the physicist Wilhelm Conrad Rontgen invented the X-ray, whic is a non-invasive method of seeing what is really going on inside the body, or a complex piece of equipment. Since then it has been applied to industries as diverse as security, art and forensic science.
Of course, now it plays a huge role in inspection, maintenance and risk management across the oil and gas industry. NDT is a broad area and an engineering discipline in its own right. However, at its core it refers to a wide group of proven approaches used to analyse the soundness of a material or component. Popular methods involve 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. This provides a huge benefit in an industry where efficiencies and production levels are crucial, but where safety and integrity are absolutely fundamental.
Corrosion under insulation (CUI)
The greatest benefit such methodologies provide is that equipment for transporting petroleum products (such as pipelines) can be inspected without making any structural changes. This means there is no reason to shut down nor to interrupt operations.
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.
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.
Inspection work scopes 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, and 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 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.
This is a massive issue affecting many aging assets and Oceaneering was determined to develop a solution. In collaboration with the suppliers of specialist ‘Pulsed’ X-ray systems and nucleonic instrumentation manufacturers, Oceaneering’s SME designed and implemented a procedure which has fundamentally changed how inspections are carried out while the plant is in-service. In essence it has eliminated the risk of radiography affecting production operations in and around nucleonics. The combination is a unique inspection offering called the Trip Avoidance X-ray Inspection (TAXI™) system, which reduces plant and equipment downtime while simultaneously improving process safety.
How it works
As an example, a separator used in petroleum production is a large, pressurised vessel designed to separate production fluids into their main constituent components of oil, gas and water. The hydrocarbons come up from the seabed through the risers and are carefully monitored while being processed.
Nucleonics are used to monitor the levels of each phase. This is important because when the vessel becomes too full or too empty, there is a risk of liquids “carry-over” into the gas system, or gas into the liquids which can cause severe safety and production problems. These systems work by measuring the amount of radiation that is able to travel from one side of the vessel to the other. As the fluids rise and fall, the radiation beam intensity varies when reaching the detector on the opposite side of the vessel, indicating the accurate fluid levels within the separator.
When radiography methods are deployed, the nucleonic detectors can become saturated, picking up radiation nearby, and creating the ‘false alarm’ that the fluid level has dropped significantly. When this happens, the detectors trigger an alarm which often leads to the complete shutdown of the plant or platform.
This problem has made operators very wary of using radiation NDT methods offshore, with the only other alternatives being either to turn off the nucleonic detectors while radiography testing takes place, leading to a ‘blind’ situation where levels cannot be measured, or to defer the inspections until a planned shutdown or turnaround.
TAXI neutralises this concern by creating unique pulses of radiation which the nucleonics detectors disregard avoiding the confusion completely, and doing it in such a way as to better meet the Ionising Radiations Regulation 2017. The system is field proven, having been trialled and now deployed on several North Sea offshore platforms as well as onshore process plants.
Following trials, one operator estimated TAXI could save them up to £5 million and 1,500 working hours per asset, per year, by avoiding production upsets, unplanned shutdowns and the ability to now carry out many more inspections in-service, reducing backlog.
The oil and gas industry is an environment where safety, environmental sustainability and regulatory compliance are prioritised, but often have to be balanced with ensuring continued security and operating efficiencies. The area of asset integrity and inspection management plays a huge part in providing that balance, providing measurable data that enables the safe and efficient operability of facilities.
The TAXI system is an industry breakthrough, enabling operators to carry out inspections around nucleonics while the plant is in-service. TAXI is revolutionising inspections, helping to assure the safety and integrity of oil and gas facilities globally.
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