Subsea saturation diving, at depths down to 1000 feet (300 meters) below the surface, tests equipment and men to the limit. To protect divers from the cold in the diving bell, manufacturers Unique LLC turned to Trelleborg Offshore for an innovative syntactic foam insulation solution."The engineered Trelleborg syntactic foam insulation, and the company's 3D modelling design capabilities, provide us with high accuracy thermal and buoyancy properties," commented Shane Julias, Design Engineer, Unique System LLC. "This enables us to predict the thermal insulation thickness required, and the uplift of the bell for accurate system buoyancy control.
"The performance of previous insulation systems used was more difficult to predict. It was also susceptible to damage and water ingress, which could affect the thermal and buoyancy properties. In contrast, the Trelleborg polyurethane-based foam has a high impact resistance and is totally impervious to water ingress under pressure. It is designed to eliminate any requirement for maintenance, so that life cycle costs are minimized."
The Unique System diving bell is designed as a submersible decompression chamber for a three man saturation diving team. It transports them from a ship's live-in hyperbaric chamber down to working depths with typical sea temperatures of between 45˚F and 65˚F (9˚C and 20˚C). Typical subsea tasks include pipeline repair, maintenance and inspection, cable maintenance, platform installation and removal.
The Heliox (Helium/ Oxygen) breathing mixture, for the diving bell atmosphere is supplied via an umbilical from the support ship. Heliox has a higher thermal conductivity than air, so good thermal insulation is essential for the divers' comfort. As dive times in the bell are often 10 to 12 hours, and the divers remain under saturation conditions for up to 30 days, their well being is critical to mission success.
"Trelleborg used its Trident™ Insulation system, which is based on BASF's ZEROHg™ glass syntactic polyurethane foam technology, in a one pour, one lift foam application. The application technique ensured no insulation interface joints for complete integrity," explained James Vultaggio, Product Group Manager, Trelleborg Offshore, Houston. "This eliminates water ingress into the foam which could affect the thermal properties."
The diving bell shell is constructed of ABS approved carbon steel, welded in carefully designed sections; the total weight of foam poured around the shell was 1300 lbs (600kg). This is the first use of the Trident™ Insulation system with BASF ZEROHg™ polymer technology in a custom coating operation and the first diving bell insulated with glass syntactic polyurethane foam. It represents a significant advance in diver safety and reduced operating costs.
"A project like this is an ideal subject for Trelleborg's subsea problem-solving expertise," added James. "Working with polymers across a number of technologies and industries, we can offer insight and innovation to improve thermal performance and find best-value engineered solutions."
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