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Flare stack inspection carried out by our drone team in Trinidad

Our team based in Trinidad were recently contracted by client who was interested in exploring the possible use of drones for inspection of their live flares before a shutdown took place.

But what are the issues with flare stacks and how do you utilise drones?

Flare stacks go up several hundred feet in inhospitable environments and operate at extreme temperatures; therefore, manually inspecting a flare stack requires that it be shut down for a long period to allow inspectors to climb up to the top and give the entire structure a thorough examination. Shutting down the flare stack allows it to cool and the metal to contract, which not only may help conceal any microfractures in the structure, it may also cause more to develop once the flare stack is reheated to its optimal operating temperature and the metal re-expands. The reignition process is particularly dangerous for flare stacks, as any of a number of variables can cause the flare stack to deflagrate, as happened to Rohm & Haas when hot air was inadvertently added to the flare during reignition, which created a flashback (Desai, 1996). There is a lot of available literature on the dangers associated with flare stacks, such as Straitz (2006), which examines the ways flares can go wrong, how such situations occur, and the warning signs that such problems present before becoming critical issues. Helicopters offer an alternate means of inspection, but cannot get particularly close to an active stack and may have difficulty inspecting it from certain angles, due the risk of damaging the helicopter through taking flare stack exhaust gases into the engine’s air intake, collision or heat. This problem is particularly prevalent for flare stacks that do not go straight up, but come out at an angle. In addition, using a helicopter is expensive, and flight paths may be restricted in the flare stack’s area, which can often be the case around refineries.

Drones also known as Remotely Operated Aerial Vehicles (ROAVs) offer a cheap, expedient, safe alternative. As they run on batteries, they require no air intake that may be clogged by soot; in addition, they are both much cheaper than hiring a helicopter and they can operate closer to an active stack than a helicopter safely. Unlike an in-person inspection, an ROAV can perform a flare stack inspection without requiring that the stack is shut down, so they can even perform thermal imaging while the stack is operating as a means of investigating any damage through which gases may escape, and check that the stack is flaring at the optimal temperature and efficiency. They are able to perform full inspections expediently, frequently, and at minimal risk to human health. ROAVs performing a flare stack inspection can be fitted with a gas sensor, to look for leaks leading up to the top and to ensure that the ROAV is operating in a safe environment, as although they are generally battery powered rather than using liquid fuel, as any electrical spark can set off ambient explosive gas at sufficient density. Such a sensor can be used in conjunction with thermal imaging to analyse the efficiency of a flare stack in a method such as that of Blackwood (2000), which could be achieved using two ROAVs flying in tandem, which is possible with modern software that would enable one to maintain a specific relative position to the other across the exhaust gas of the flare stack.

                                   

Inclement weather can present a unique set of difficulties for inspections, as high winds and precipitation can make conditions unsafe for climbers and helicopters. However, ROAVs have a much higher acceptable limit, particularly in the hands of a competent pilot, and image stabilisation software can allow inspectors to gather clear information regarding the state of their flare stack, even when the ROAV is being buffeted around. Inspectors often rent ROAVs to perform inspections themselves, relying on automatic control software or the lack of personal risk involved with piloting an ROAV compared to a helicopter to operate the ROAV themselves. However, this has led to ROAVs being piloted into heated air or exhaust gases, or to ROAVs colliding with the flare stack, resulting in fees to repair or replace damaged or lost equipment and delays as fresh working equipment is procured. The problem is, inspectors are only interested in gathering data with the ROAV, and so have not spent time learning how to pilot them with the finesse required to gather data safely and in an optimally efficient manner.

An ROAV pilot can plot an optimal course and guide the ROAV through it, and live footage can be transmitted back to monitors while it is being recorded. Such a setup would allow inspectors to instruct their pilot to examine specific areas more closely, as possible defects come to their attention in the course of the flare stack inspection route that the pilot has plotted. Working practices such as these gives inspectors the optimal balance between safely operating the ROAV and having the flexibility to focus on the areas that may require more in-depth attention, and allow either the flare stack to continue operating, or require minimal shutdown time, minimising the overall costs of flare stack inspection, which in turn allows for more frequent inspections, resulting in damage being identified at an earlier stage of progression, so that it can be rectified sooner and more cheaply. Such schemes can safely extend the operational lifetime of flare stacks, according to Al Awadhi et al., by up to approximately 250% of the original lifetime estimation. 

For more information or to enquire about the services contact either Trinidad office (info@rectrixtt.com) or the UK office (info@rectrixas.com)

See the inspection and flare stack pages for more details

 

 

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