Considerations for the Engineering and Design of

Report
Richard B. Garrett, PE
March 2, 2011
Issues covered in this Presentation:
 Considerations for determining size of tank desired.
 Owner’s perspective of what information should be
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conveyed to tank design team.
Comparison of Geodesic Dome vs. Cone Roof tanks.
Issues to consider per NFPA 30.
Miscellaneous Safety considerations.
Maintenance considerations.
Options for foundation design.
Check Requirements – State Web Page
1. Establish product, whether or
not Internal Floating Roof will
be used and type / dimensions
of IFR
2. Determine Desired Working
Volume:
Daily Throughput x (Resupply
Interval + Safety Factor)
10,000 bbl/day, 7 day resupply,
3 day safety stock
Minimum Working Volume
= 100,000 bbl
Highest impact to available capacity is Internal Floating
Roof
Overfill or Damage level
(Approx. 3’ from top of tank)
High – High Alarm
High Level Alarm
Normal Fill
Distance between levels is based
on maximum fill rate x response
time (usually 5 minutes or 6”
minimum)
Bottom of tank minimum level
depends on floating suction
geometry to keep liquid from
falling below roof for emissions.
Normally set around 3’ - 4’.
Expect to lose about 7’ – 8’ total
height from volume with IFR.
Usable tank volume estimation
Tank Height
Internal
Floating Roof
Secondary Seal
Damage /
overfill from
top of tank
High - High
High Level
Normal Fill
Floating Roof at
low legs (Min)
Working height
56 ft
Volumes for various tank diameters
24 "
15 "
42
6
6
6
" (using 3" safety factor)
"
"
"
42 "
52.5
52.0
51.5
51.0
ft
ft
ft
ft
3.5 ft
47.5 ft
Tank
Diameter
70
80
90
100
110
120
125
Shell
Volume at
Working
Volume Normal Fill Tank Heel Volume
(BBL)
(BBL)
(BBL)
(BBL)
35,983
34,955
2,399
32,556
46,998
45,655
3,133
42,522
59,482
57,782
3,965
53,817
73,434
71,336
4,896
66,441
88,856
86,317
5,924
80,393
105,746 102,724
7,050
95,675
114,741 111,463
7,649 103,814
Tank Design Data
Code: API 650
Inside Diameter: 125'-0"
Height: 56'-0"
Nominal Capacity: 114,741 BBL
Maximum Capacity: 111,463 BBL
Net Work Capacity: 103,814
Product: Gasoline
Product Specific Gravity: 0.74
Design Specific Gravity: 1.0
Design Liquid Level: 51'-0"
Internal Pressure: Atmospheric
External Pressure: Atmospheric
Maximum Design Temperature: 200° F
Maximum Operating Temperature: 200° F
Design Metal Temperature: 58° F
Wind Code: API 650, 11th Ed.
Wind Speed: 150 MPH
Wind Check: As-Built
Wind Importance Factor: 1.0
Earthquake Code: API 650, 11th Ed.
Earthquake Zone:
Site Coefficient: Site Class D
Earthquake Importance Factor: 1.0
Tank Fill Rate: 6,500 BBL/Hr
Tank Suction Rate: 5640 gpm
Shell Insulation Thickness: None
Bottom Design Data
Material Specification: A36
Welding: Lap Welded
Corrosion Allowance: 1/16"
Slope: 1" in 10'-0" Shovel Bottom
Annular Plate Data
Material Specification: A36
Welding: Double Butt Welded
Corrosion Allowance: 1/16"
Fixed Roof Data
Type: Two-Bay Rater Supported Cone
Material Specification: A36
Welding: Lap Welded
Uniform Live Load: 20 PSF
Additional Dead Load: None
Plate corrosion Allowance: None
Struc Corrosion Allowance: None
Slope: 3/4" in 12"
Roof Insulation Thickness: None
Floating Roof Data
Type: Internal Reverse Slope
Outer Rim Corrosion Allowance: None
Deck Corrosion Allowance: None
External Roof
 Cone Roof vs. Geodesic Dome Roof
 Design Considerations – perimeter railing vs. perimeter wind
girder designed for access to inspection ports.
 Maintenance of coating, vs. panel seams
 Overall Cost Comparison
 Overall Height – no real limitations, guided mainly by:
 Local codes, zoning restrictions on height limitations
 Consider available water pressure height to fight fires
 Aesthetics compared with other tanks
 Managing tank alignment if more than one live at same time
 Consider Operators – if over 60’, may need intermediate
landing
Geodesic Dome vs. Cone Roof
48’ Geodome with perimeter walk/girder
56’ High Cone with perimeter railing
Net Positive Suction Head Required
 NPSHR – compare greater of NPSHR, tank outlet,
floating suction, bottom of tank roof to determine
minimum tank level.
 Remember to take into account all losses from the
point of suction to the pump inlet. This is especially
critical if using a floating suction for product quality.
Depending on the geometry of the swivel, you could
experience more loss through that one item than the
whole length of piping.
Random Design / Safety Issues
 Emissions options – even though IFR may not be required for Distillate
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(Jet, Diesel, Kerosene), including this control measure will reduce
calculated emissions and may keep you from needing a Title 5 permit.
Tank stairs are laid out for convenience, usually along the normal
operator walk path. However, from a safety standpoint, tank stairs or
walkways providing tank top access should not cross tank valves.
As indicated in previous presentations, incorporating a corrosion
allowance for bottom and shell, especially if prior experience shows
potential areas of corrosion in similar service tanks, can pay big
dividends down the road.
Tank Anchoring may be required for not only earthquake areas, but
also due to high wind (hurricanes), especially with diameter to height
ratio less than 1.5.
For product quality and to facilitate removal of water, consider using
single sloped bottom with deep sump.
Fire Protection - NFPA
 Fire Protection – As mentioned in previous presentations, NFPA sets
minimum requirements that local AHJ can increase at their discretion.
For example, Section 22.8.2 states that “…floating roof tanks containing
any liquid shall not require protection when installed in accordance
with this chapter.” However some local departments still require foam
protection for these type of tanks.
 Note – Requirements of Chapter 22 either require remote
impoundment, intermediate diking, or other engineered option.
 Spacing is essentially 1/6 sum of diameters of adjoining tanks, up to
150’ diameter. Larger diameter may require increase to 1/4 sum of
diameters.
 If required, you might want to consider the use of underground HDPE
for transmission lines. Alternative usually requires application of
sprinkler code, which requires supports at 15’ on center, designed to
support 5 x the weight of the lines plus 150 lbs.
Coatings
 Many municipalities now require blast media to be collected and
properly disposed of. On site, this can be difficult and costly.
One option would be to have shell plate primed before shipping
and installation.
 Bottom is likely to contact with water, consider good thin film
coating to extend life.
 Depending on product service, may want to coat inside of tank –
ie:
 Ethanol – potential corrosive stress cracking
 Avgas – tends to be more corrosive than other finished products.
 The best intentions mean nothing – a key quality control
measure is Coating Inspections – especially in smaller facilities.
Bring in early to have input into specification, such as surface
preparation, maximum humidity allowed, admixtures for
holding blast, recoat window, etc.
Foundation Alternatives
 Excavate & replace unsuitable soils
 Piles –
 Driven to refusal, can disturb nearby structure
 Auger cast – less disturbance
 Both still require pile caps to transmit load from bottom to
pilings.
 Soil Stabilization –
 Low disturbance to nearby structures
 Reduces waste removal
 With proper testing and documentation, binder material can
serve as remediation
Check for Requirements
Questions?
Richard B. Garrett
[email protected]

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