Natural gas production in older United Kingdom North Sea gasfields is tailing off and energy companies are now having to finance major decommissioning works. Platforms and all their gas processing equipment are required by British and Norwegian law to be entirely removed after shutdown right down to the seabed.
Jet Edge abrasive waterjets are perfectly suited to steel cutting in volatile gas-laden atmospheres and an increasing number of offshore operators are turning to spark-free “cold cutting” to safely carry out the removal of redundant oil and gas production hardware.
Recently, Jet Edge’s UK distributor Aquablast safely cut up obsolete contactor towers on a live gas platform operated by the French oil company Perenco in the 40 year-old Indefatigable Gas Field off the Norfolk coast of England.
The towers, originally used for sweetening or dewatering produced gas under high pressure, were constructed of 70 mm heavy steel plate (2 ¾ inches thick) and weighed in at over 300 tons. So that the platform's own crane could lift the towers on its own, Perenco called in Aquablast to cut the towers up into smaller cylindrical sections.
A Jet Edge Spyder abrasive waterjet unit was used to make the deep circular cuts, but first a “mailbox” cut was made to allow internal inspection to decide exactly where to make the tower separations. Abrasive waterjet power came from a Jet Edge 55-260DXS diesel-driven mobile hydraulic intensifier pump with specially adapted engines for hazardous area operation.
The pressure compensated hydraulic intensifier – the heart of the Jet Edge system which can produce up to 55,000 psi operating pressures – has a major advantage over other systems in hazardous environments because safety relief valves and water dump systems are not required. In the unlikely event of a blockage, the Jet Edge intensifier simply holds its pressure until the reason for the stoppage is corrected or the pressure can be safely bled off.
Aquablast has modified a fleet of Jet Edge mobile intensifier pumps to comply with offshore oil and gas platform regulations by installing inlet air overspeed shutdown valves and other emergency shutdown provisions.
Donald Blair, Aquablast’s Managing Director and long time Jet Edge support partner in Europe, commented:
Jet Edge UHP intensifiers are extremely reliable and this is totally critical when operating on remote offshore oil and gas platforms. Equipment cannot be quickly replaced in the middle of the North Sea for logistical and often weather-related reasons and our reputation for dependability and minimal downtime is therefore vital to our customer relationships.”
The 2 3/4 inch thick cuts were made at an average cutting speed of over 1 ¾ inches per minute with a consumption of almandite garnet abrasive of approximately 23 lbs per foot ( 29 Kgs per metre). According to Blair, Perenco (UK) Ltd declared themselves “very impressed” with the super-thick cut and how the work was carried out in a safe manner with only minor interference to other works on a live North Sea gas installation.
The Spyder system is highly portable and quick to set up; straight or flexible track sections are secured either by suction cups, magnets or ratchet straps to curved or vertical surfaces. The cutting nozzle transport unit is pneumatically driven, avoiding any risk of ignition in a volatile atmosphere. The tower sections were safely transported to shore in England for scrapping but the three-ton cap of one of the towers was donated to Aquablast by Perenco to enable more trials and development to be carried out in expectation of future cold cutting tasks for the Jet Edge Spyder abrasive waterjet system.
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