Offshore companies with large, old oil rigs are considering replacing steel walls with glass reinforced plastic to withstand blasts from potential explosions.
Research funded by the Health & Safety Executive has found that current predictions of gaseous pressures on offshore platforms are too conservative.
This is due to the use of older tests that use statistical analysis and probability, and small scale models of offshore platforms.
A long term study, called the Joint Industry Project on Blast and Fire Engineering for Topside Structures, has instead used a 28m high steel platform owned by British Gas in Spadeadam to try out 25 controlled explosions.
The researchers discovered that over-pressure could reach 15 times the norm, or up to 5bar. This was far more than expected and has prompted a technical warning to the oil and gas industry from the Steel Construction Institute, the project’s manager.
Particularly affecting older platforms, the threats of a greater, though shorter, blast from the higher pressures have led offshore companies to consider improving the blast resistance of the walls protecting accommodation blocks in existing platforms.
Already separate since the Piper Alpha disaster of 1988, accommodation blocks are encased in several boxes of fire and blast resistant steel to protect human life in case of explosions.
But the new discoveries about over-pressures mean these are no longer considered adequate. Unfortunately, existing steel walls cannot be reinforced with more steel because the rig structure is not strong enough to take it.
TNO, a Dutch research organisation, has been trying out glass reinforced plastic instead. The material is strong enough to take twice the blast force of existing steel walls but half the weight.
‘You take a fire resistant panel,’ says Paul Mercx, a TNO scientist, ‘and cover it with layers of glass reinforced plastic. It’s the combination of fire resistance and blast resistance that is new.’
A series of prototype glass reinforced plastic panels measuring 2.5 x 2.5m sq passed a gas explosion test of an overpressure of 1bar.
However, a certain amount of debonding was noticed between the panel’s core and its outer skin. This meant that they did not live up to expectations when it came to a 120 minute hydrocarbon fire test.
But Mercx is optimistic. ‘We’re confident that these difficulties can be resolved by modifying the toughness characteristics of the adhesive used to bond the panel’s outer skin to its core.’