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Reliability, reliability, reliability!

Published:  07 February, 2014

Paul Frost, manager of Atlas Copco Systems Hemel Hempstead, spoke to ODEE’s Aaron Blutstein about why oil-free is generally the preferred choice within the offshore oil and gas market and why it’s likely to stay that way.

Compressed air is such an integral part of the offshore oil and gas sector that it could easily be perceived as just another necessary expense or perhaps, “the cost of doing business”.

Paul Frost told ODEE that compressed air in an offshore environment is a bit like the nervous system of a plant - you’ve got the main power generation, which are like the muscles, and then you’ve got the compressed air system, because without compressed air, valves and instruments don’t operate, and many other sub systems need it to function.

The offshore market explains Frost, is extremely competitive, and is relatively conservative in a positive sense. The industry is not looking for new unproven inventions, it’s almost the opposite – they are looking for well-established technology that they know works. They like experience of similar reference installations. He explains: “Offshore is not a place to be taking risks with new unproven technology - of course there is a place for R&D, but there is not a quantum leap – it’s more evolution than revolution within the compressed air offshore market.”

In the Upstream sector, Frost says that oil-free screw compressors are the most popular: “They were the machines, which we (Atlas Copco) sold in the early to mid- seventies, we pretty much still sell the same unit. Whatever else we change on the machine (which is a lot) - for example there are always efficiency gains with intercoolers and aftercoolers, and lowering pressure drops in the machine - the actual rotating components are fundamentally pretty much the same. That’s because it’s so robust and reliable, and that is of course the core of the machine.”

He highlights however there is still demand for oil-injected compressors within the industry (Atlas Copco makes oil-injected as well as oil-free), but because oil-injected compressors need regular oil filling and more frequent filter changes to prevent air contamination and shutdown conditions, oil-free compressors have dominated the market for Atlas Copco.

Frost explains that despite being simpler and easier to manufacture, the compressed air produced in oil-injected compressors needs to be a certain quality and to get that quality from an oil-injected machine you have to take out the oil you’ve introduced: “So there are some issues with this compressor type, as you’ve got to take it out somehow…Atlas takes the view that we’d rather not put it in, and instead use an oil-free machine so we can say there is absolutely no oil in it at all.”

Using oil-injected screw compressors plus filtration instead of oil-free screw compressors when oil-free compressed air is actually needed for the processes, also increases the potential risk of failure in the future, because using filters is just an initially cheaper alternative to receive oil-less compressed air.

Without proper maintenance or on-time replacement of filter elements, filters cannot work effectively and more oil will remain in the filtered compressed air. Frost warns that filter failure can be catastrophic. It is therefore understandable that the market generally thinks oil-free, despite it being a significantly more expensive technology. As Frost explains: “The number one priority after safety of course is reliability one, two and three.”


Reliability is dependent on both the technology and quality of servicing. In the Upstream sector, maintenance and servicing on compressed air systems are nearly always based on feedback signals, says Frost: “So you have pretty much real-time readings from these machines. Maintenance oil changes should take place annually for an oil free machine or subject to annual condition analysis - they’re not generally maintenance intensive. But you still have air filters and oil changes to do as with any rotating machine.”

The total lifetime cost, (over 20 years say) including investment cost, operation cost and maintenance cost of oil-free screw compressors are not higher than oil-injected compressors. Frost explains: “In general the oil-free machines tend to need less maintenance because on the oil-injected design you have the lubrication oil coming into contact with the incoming aspiration air. So over time the oil degrades, consequently there are more regular oil changes. By comparison, the aspiration inlet air and bearing lubricant are completely separate in an oil free compressor. Oil is in a closed loop system. Maintenance requirements tend to be less as a result.”

Frost concludes that ultimately the choice between oil-free and oil-injected is really very simple. Efficiency, price, physical space, weight are all important factors, but if you really whittle it down to one issue which the Upstream market values above all else, after safety, in a complete compressed air system, then it’s reliability every time. This is the ultimate holy grail of the sector, and is not going to change anytime soon.

Atlas Copco Compressors has completed delivery of its single largest-ever UK designed and built order, comprising instrument and process air compressor modules, worth in excess of £6m, to Kazakhstan where it will be used as part of a large project in the oil and gas industry. The physical size of the modules, which were custom-engineered at Atlas Copco’s Systems Division in Hemel Hempstead, required the chartering of an Antonov 124, one of the largest freight transporter aircraft in the world.

The four modules were flown by Antonov 124 to ensure that the client’s critical delivery schedule was met. The oversize modules had to be fitted with special “D” rings so that they could be pulled, with just millimetres to spare, into the front loading bay of the Russian-built Antonov 124 and then secured during flight.

The project, valued at over £6m, covers the supply of four containerised ‘plug and play’ modules. These include an Instrument Air module, weighing 42 tonnes and containing ZT55 oil-free screw compressors and desiccant dryers combined with pre-and after-filtration units. Three further Process Air modules were also supplied, each weighing 34 tonnes, containing ZT250 oil-free screw compressors, air handling units and desiccant dryers with pre-and-after filtration. All four modules have been specially designed to operate in extreme ambient temperatures of -40°C to +45°C.

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