Leonard LeBlanc
Houston
- The plasma welding process developed by Cranfield University provides a stable arc for welding at water depths over 3,000 ft.
- The toroidal wind accelerator rotor platform (TARP) in smaller versions stacked to form towers or enlarged to encircle platform jackets, can generate more power offshore with less maintenance than conventional bladed generators or photovoltaics.
Plasma process effective for automated welding at 3,000 ft depths
Cranfield University's Underwater Welding Group (Cranfield, UK) has successfully carried out plasma welding for automated applications at pressures up to 100 bars, corresponding to a depth of about 3,000 ft. Theoretical projections indicate the technology can be extended even deeper without breakdown of the welding arc, although voltages would have to be increased dramatically.
Conventional welding processes, including TIG (tungsten inert gas), beyond depths of 1,500 ft or 50 bars pressures, become erratic and susceptible to disturbances that distort the weld. The plasma welding process prevents deviations of the weld path and instabilities produced by shearing of gas layers inherent in TIG processes. Gas flow in a plasma arc under pressure remains laminar.
Arc ignition was the major hurdle to be overcome in the plasma arc process, and that was achieved by developing a concentric electrode motion. This provides a low-energy route for ignition of the main arc.
High pressure welds exhibit low hardness (270 Hv in the hydrogen affected zone) and high tensile strength. Charpy values averaged above 50 J at 60°C.
Toroidal accelerator offers wind powergain for offshore
A toroid-shaped wind accelerator with small turbines can replace single-bladed, tower-mounted generators and photovoltaics on offshore platforms and effectively augment power needed to run downhole and multiphase pumps.
The designers say the toroid-shaped tunnels can be kept to a small diameter and stacked in the open or can be made as large as the perimeter of the platform and serve as reinforcement and actually reduce wind loading on the structure by up to 50%. In platform perimeter sizes, the toroid augments the wind flow field about the platform, so that the twin propellers on each side of the toroid need only be 3-5 meters in diameter.
The toroids or TARPs (toroid accelerator rotor platform) require much less space than conventional wind powered units, are easier to maintain, have a lower noise level, and reduce electromagnetic interference. Developers of the system include Eneco (West Simsbury, Connecticut, US) and Raytheon Engineers & Constructors (Cambridge, Massachusetts, US).
The toroid accelerates the wind, providing a omnidirectional flow field to two small diameter wind turbines located 180° from one another. The turbines rotate, aligning themselves to the wind and seek to equalize the thrust. When maintenance is required or destructive wind velocities develop, one of the turbines is stopped and the system rotates to place the turbines in stagnant or wake flow areas.
The blades operate in a fashion similar to a helicopter tail rotor with a simple flexbeam hub to reduce cyclic stress loading on the rotor blades. In addition, the rotors are not directly exposed to rainfall, which tends to reduce conventional turbine output by 10-20%.
Sub-seabed burial of nuclear wastes last resort for US
Although it will have to counter major international legal and political barriers, the US is once again looking at the issue of sub-seabed burial of nuclear wastes. Other countries are facing similar nuclear waste problems and have either opted for deep onshore burial or stockpiling, awaiting a solution later.
The two offshore areas of interest are deep abyssal plains - one northeast of the Hawaiian Islands and another northeast of Bermuda. Both areas are under 15,000 ft water depths and have a thick layer of seabed sedimentation. There are several attractive features of disposal in these areas. There has been no seismic activity in recent geological history. Very little marine life subsists on the seafloor, nor are there mineral deposits beneath.
Also, the seafloor sediments contain fine particles that are negatively charged. Radioactive metals are usually positively charged. There are two means of ocean bottom disposal:
- Wells could be drilled deep into the seabed using conventional drillships or semisubmersibles. Canisters of nuclear waste would then be stacked in the wellbores and a heavy protective grout is applied to seal the wells.
- The nuclear wastes would be contained in pointed cylinders with guide vanes. After free falling through the 3-4 miles of water column, the cylinders would sink hundreds of ft into the bottom sediment.
New developments in electronics, software:
- Wireless data: A wireless data network based on cellular digital packet technology to replace microwave and radio technology for SCADA systems offshore has been deployed by Petrocom Offshore Cellular Service of Harahan, Louisiana (US).
- Riser evaluation: A data evaluation hardware package has been set up on the Emerald Producer by BPP Technical Services of London and University College London to monitor the forces, configuration, loading cycles, and frequency spectra of the one of the vessel's eight risers.
- Inhibitor performance: In order to assess the performance of inhibitors and alloys in laboratory simulation of corrosion in multiphase pipeline flows, CLI International of Houston has developed a program entitled Multiphase Autoclave Pipeline Simulator.
- Air gun position: A pressure transducer that enables determination of the depth of seismic towed air guns to be determined with an accuracy of 1 cm has been developed by Scanor Technologies of Basingstoke, Hampshire (UK).
- Project evaluation: A distributed workgroup project evaluation tool package has been design by Technomation Systems of Houston to streamline preliminary engineering, cost estimation, project scheduling, risk analysis, and economic evaluation.
- Iceberg collisions: Lloyd's Register of London has developed an iceberg collision program to determine the survivability of a structure during an encounter with an iceberg.
- Compressor health: Southwest Research Institute of San Antonio, Texas (US) has developed an on-line system to sample cylinder pressures inside a reciprocating gas compressor at high speed.
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