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Environment:
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Offshore platforms
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Weather:
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Dry, Sunny, Rain squalls, Rain. Freezing fog. Gale force
winds. Airborne spray and sea salt.
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Temperature:
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- 4° to 86° F (- 20° to 30° C)
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Types of dust:
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Drilling cement dust. Barites. Drilling dust. Flare
carbon. Mud burning smoke. Grit blasts from platform maintenance
activities.
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Dust concentration:
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0.1 to 10 mg/m3
0.045 to 4.5 gr/1000 ft3
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Particle size (µm):
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0.3 to 100
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Potential damage to turbine:
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Erosion. Wet corrosion. Hot gas path
corrosion.
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Recommended Gas Turbine Inlet Air Filtration System
OPTION 1:
Relative humidity at platform level is expected to fluctuate above and below 60%.
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INLET WEATHER HOOD. (Inlet velocity < 3.5 m/s)
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ANTI-ICING, if located in arctic region
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SELF-CLEANING INERTIAL SEPARATOR
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PRE-FILTER COALESCER (Filter bank sloped and provided with drain
shelves and downspouts).
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FINAL STAGE FILTER. Fully potted hydrophobic medium barrier filter.
95% - 98% ASHRAE 52.1 Dust Spot Efficiency. (Filter bank sloped and
provided with drain shelves and downspouts to facilitate drainage of
deliquesced droplets).
OPTION 2:
Relative humidity at platform level is always expected to be above 60%.
- FIRST STAGE MARINE VANE WATER ELIMINATOR
- ANTI-ICING, if located in arctic region
- HIGH VELOCITY (5 m/s) POCKET TYPE PRE-FILTER. (Capable of filtering
sharp grit blast dust without damage to the filter medium)
- HIGH VELOCITY (5 m/s) POCKET TYPE FINAL STAGE FILTER. (Minimum
initial ASHRAE arrestance of 99% on SAE -Fine Dust)
- FINAL STAGE HIGH VELOCITY MARINE VANE SEPARATOR. (To protect against
droplet re-entrainmemt)
Notes applicable to both options:
- No implosion doors
- An integrated manometric drain system
- All internal materials must be capable of withstanding a marine
environment, with cautious use of dissimilar metals (i.e. insulate).
Material selection and joining is also of particular importance to coastal and offshore inlets. These inlets are fabricated from high-grade stainless steels, which contain chromium to make them corrosion resistant. When welding stainless material, chromium can leave solution and form chromium carbide at grain boundaries. This is defined as sensitization.
Sensitization generally occurs when the base metal is kept at a temperature of >500 degrees C for over 60 seconds (these numbers vary with carbon content). Sensitized stainless is prone to corrode due to chromium depletion. However, low carbon stainless (316L) will not form chromium carbides at grain boundaries unless carbon is included in the weld via gas shield breakdown, surface contamination, or improper electrode selection.
Chromium carbide is not visible to the unaided eye, but oxides of chromium cause the deep blue appearance of welded stainless steel. When welds have a black color, carbon has been included in the weld and corrosion will occur. In fact, passivating a weld which includes carbon will bring on corrosion.
Passivation creates a "passive" zone of chromium oxide which resists corrosion. But, passivation does not put chromium back into solution if sensitization has occurred. Thus, passivating "L grade" stainless steels is simply an aesthetic measure which adds no corrosion protection.
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