Inspections under pressure

Alternative methods for vessel testing can reduce time and lower costs

It is costly, and potentially dangerous, to inspect pressure vessels in the process industry. To view the inside of a vessel, inspectors have to enter a confined space. In doing so, the inspector is exposed to a range of potential hazards, reduced levels of oxygen, toxic residues, heat and noise. So great care has to be taken to enable the inspection work to be done safely. But in recent years, a number of non-intrusive inspection technologies have become available, that could make this type of work a thing of the past. It could also save large sums of money.

Pressure vessels in process industries need inspecting, usually every five years, or every time major work is undertaken. The inspectors mainly look for corrosion that might have weakened the vessel walls.

This is important work. Tanks, heat exchangers, boilers and other types of pressure vessels can work under high pressure and are designed to operate under specific parameters. If a parameter is changed, for instance by corrosion affecting the thickness of the vessel wall, then a goalpost has been moved. The consequences could be disastrous. Most major incidents start as leaks where the knock-on effects snowball into something much bigger.

So it’s not surprising that process industries are very diligent about inspecting their pressure vessels. However, on the downside, the inspection itself has major financial repercussions, as the plant has to be de-pressurized and then shut down for the duration of the inspection. This means there will be environmental impact, as some of the contents will inevitably escape into the atmosphere. All before the inspector can finally enter to work under difficult conditions.

So, not before time, non-intrusive inspection methods are now entering the market. The accuracy of these methods is growing year on year as the understanding of deterioration mechanisms improve and computing power increases. Technologies include ultrasonic, radiography and laser scanning, to name a few. These are used to measure the integrity of the vessel, without physically having to view its inside.

Cost savings range between 50 and 80 percent while the time saving can be up to one-third. However in some companies there is resistance to change, as well as a lack of knowledge about the capability of non-intrusive inspection. The detection methods measure properties that cannot be physically observed and so can be difficult to explain.

But even if the measured properties are invisible, the benefits are tangible. A survey undertaken in 2017 by the Oil & Gas Technology Centre (OGTC) and ABB found that non-intrusive inspections could deliver increased production and lower maintenance costs worth up to £242 million per year to the UK oil & gas industry.

With non-intrusive inspection, the equipment can remain in use during the inspection. This means less downtime, less environmental impact, less work in difficult conditions and reduced risks. With potential benefits like these being offered, there is no reason why the high hazard industry should not try to keep the internal inspection of pressure vessels to an absolute minimum.

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About the author

Andy Hollins

Andy Hollins is a Principal Consultant with ABB, with specific interests in the safe and reliable operation of mechanical equipment. He graduated from Cambridge University with a degree in Engineering. He is currently working with process industry clients to improve plant uptime and address issues with equipment deterioration and ageing.
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