FLOW VELOCITY REQUIRED FOR SOLIDS MOVEMENT IN OIL AND GAS PIPELINES JOHN S SMART JOHN SMART...
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Transcript of FLOW VELOCITY REQUIRED FOR SOLIDS MOVEMENT IN OIL AND GAS PIPELINES JOHN S SMART JOHN SMART...
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FLOW VELOCITY REQUIRED FOR SOLIDS MOVEMENT IN OIL AND
GAS PIPELINES
JOHN S SMARTJOHN SMART CONSULTING ENGINEERS
HOUSTON TX
BLACK POWDER
IN PIPELINES
JOHN S. SMARTJOHN SMART CONSULTING ENGINEERS
HOUSTON, TX
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What is Black Powder?
• A mixture of fine particle corrosion products and other solids found in both liquid and gas pipelines
• Can be all iron sulfide, all iron carbonate, or all iron oxide
• It is called “black powder” because the presence of iron salts makes it black.
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What it is N0T !
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SEM Photomicrographs of Black Powder
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Sulfides
• Pyrrhotite – Fe1-.85xS normal corrosion product from H2S in gas, strongly ferromagnetic, pyrophorric
• Mackinawite – semi-stable form of FeS that forms under low H2S activity (slightly sour)
• Greigite – formed by sulfate reducing bacteria
Industry Amount H2S Allowed, Grains/100SCF
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Oxygen Contamination
• Oxygen acts as cathodic depolarizer, accelerates other corrosion reactions
• Air contact converts FeS to Fe304 and elemental sulfur
• Inhibitors lose their effectiveness
Oxygen Allowed, ppm or Vol%
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Water Allowed in Natural Gas
• There must be liquid water to have corrosion
• 7 lbs/MMSCF:– Dew point = 12oF at 600 psi – Dew Point = 32oF at 1000 psi – Dew Point = 43oF at 1500 psi
• 3 lbs/MMSCF specified in Europe – higher pressures and colder environments Industry Allowed Water in
Natural Gas, lbs/MMSCF
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GLYCOL IN BLACK POWDER• Gas Transmission Lines
carry some glycol as mist for a short distance, most carry as vapor (very small amount) from glycol dehydration
• Concentration of TEG is 97.66% at 7 lbs/MMSCF
• Will make a black sludge instead of a dry powder
• Bacteria can metabolize TEG at lower concentrations
• Can remove with a slug of methanol followed by pig
Ref: Van Bodegom et al, CORR. 1987
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SOURCES OF BLACK POWDER
• Producing wells• Corrosion product• Off-specification produced fluids (e.g.salt)• Powder Movement in line• Hydrotesting: sand and clays• Plant turnarounds and upsets water• Construction debris, millscale, rouge
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CALCULATION OF MINIMUM VELOCITY FOR SOLIDS MOVEMENT IN WATER, OIL, AND GAS PIPELINES
• Hydraulic Model used to calculate minimum velocity for solids movement in pipe by viscous drag
• Applied to sand and iron compounds in water, oil and gas
• Sets a minimum velocity for possible solids movement
• Erosion by solids occurs at much higher velocity
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HYDRAULIC MODEL
• Model of Wicks (Shell, 1969)
• Particles must be “rolled” out of a bed to start movement
• For level flow, must add extra 10-15% for uphill movement
• Shape factor for particles required (1.5-2.0 for PL solids)
• No interaction between particles (dry, non-magnetic)
• Round particles roll• Long thin particles slide• Rough particles bounce along,
called “Saltation flow”• Flake like particles move like
leaves in the wind
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FLUID VELOCITY TO MOVE IRON SULFIDE IN 40oAPI OIL
• Velocity to move FeS in 40oAPI Crude Oil much higher than sand in water
• Approximates FeCO3, Fe2O3, Fe3O4 movement velocity
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Velocity to Move Iron Sulfide in 20oAPI Oil vs. Pipe Size
• Higher velocity to move solids due to thickness of laminar boundary layer over particle bed used in model
• High viscosity fluids will result in significant time for particle to settle after bouncing
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Movement Velocity for FeS in No. 2 Diesel vs. Pipe Size
• Diesel often used for pigging as it can be recovered and sold
• When #2 Diesel used in pigging, FeS will settle out in front of a pig running at 5 ft/sec, possibly accumulating and sticking the pig.
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Bed Height of Solids in No. 2 Diesel in a 24 Inch Pipeline
When the pipeline fluid is
moving less than the entrainment velocity, sediment can build up to a steady state level that can be calculated by Wicks Model
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Accumulation of Solids in Pipelines
• CASE HISTORY– 20” Crude Oil
Pipeline– 0.5” iron oxide = 22
ft3/mile = 2 tons/mile
– 1.0” iron oxide = 9 tons per mile
– Must be removed for ILI Inspections
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Sticking Pigs• CASE HISTORY
– Pipelines can plug with sediment during pigging
– 200 feet of pipe had to be cut out and replaced in this 12 inch line
– Need to use pro-gressive pigging and jetting in front of pig in low velocity lines
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Velocity to Move Black Powder in Natural Gas at 1000 psi and 60oF
• Entrainment Velocity from 9-14 ft/sec depending on pipe size at 1000 psi
• Lines cleaned of black powder frequently show black powder again after a short time.
• Pigging upstream can cause black powder to move downstream
• Filter Seps needed ahead of centrifugal compressors
• Lines with “No Black Powder” problem may be just operating at low velocity
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Gas Velocity to move Black Powder Constituents in a 24 Inch Pipeline at 1000 psi
0
2
4
6
8
10
12
14
16
salt sand BentoniteClay
IronCarbonate
FeCO3
Iron SulfideFeS
magnetite(mill scale)
Fe3O4
hematite(rouge)Fe2O3
iron metal
Mineral
Ve
loc
ity
, ft
/se
c
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0 200 400 600 800 1000 1200 1400 16000
200
400
600
800
1000
1200
1400
1600
Flow Rate (MMSCFD) of Natural Gas at 60oF to Move 1 micron Iron Sulfide Black Powder
vs. Pressure and Nominal Pipe Diameter
8" Pipe
16" Pipe
24" Pipe
36" Pipe
48" Pipe
Pipe Line Pressure, psi
Flo
w R
ate,
MM
SC
FD
48"
36"
24"
8”
16”
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IRON SULFIDE FRACTURES INTO FINE POWDER
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FINE ROUGE IN NATURAL GAS FUELED DIESEL ENGINE
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Movement of Wet Powder
Dry powder
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PROBLEMS WITH BLACK POWDER
• Pyrophoric• Inaccurate ILI Inspections from
ferromagnetic iron sulfide in internal pits• Lowers Flow Efficiency• Abrasive
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Iron Sulfide is Pyrophoric
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Flow Efficiency - I
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Flow Efficiency - II
4
6
8
10
12
0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000
Fu
el c
ost
(th
ou
san
d d
olla
rs/ d
ay)
PIPE LINE ROUGHNESS EFFECT ON FUEL COST STA BBB-1 TO STA BBB-2 (Fuel cost based on $ 3.19/MCF)
<---------------Ratio Out Of Station Limit------------------------------>
Before Pigging
3 months after pigging
5 months after pigging
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Abrasiveness
• Black Powder in gas compressor, 24 hours
• Compressor rotated at 28,000 rpm
• Cause was an increase in pipeline velocity resulting in 6 tons per day black powder into station
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Abrasiveness
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Ceramic Coated Gas Cooled Gas Turbine Blade
• Ceramic coating fluxed by black powder
• Caused by adding a second generator onto gas supply line
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Solving Black Powder Problems
• Physical Stuff– Chemical cleaning– control contamination– Internal coating – Cyclone separator– Submicron filters– Analyze pipeline for
black powder– Glycol Injection to
control dew point– Corrosion Inhibitors
• Management Stuff– Operators, engineers and
managers need to cooperate, no-one can do it alone
– Managers need to recognize problem, direct effort, provide budget, and use analysis for forward planning
– Operators, engineers need to learn to speak economics to managers.
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END