Considerations for the Engineering and Design of

Aboveground Storage Tanks

Richard B. Garrett, PEMarch 2, 2011

Issues covered in this Presentation:Considerations for determining size of tank

desired.Owner’s perspective of what information

should be 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 FillDistance 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.

Tank Height 56 ftInternal Floating Roof 24 "Secondary Seal 15 "Damage / overfill from top of tank 42 " (using 3" safety factor) 52.5 ft

Tank Diameter

Shell Volume

(BBL)

Volume at Normal Fill

(BBL)Tank Heel

(BBL)

Working Volume

(BBL)High - High 6 " 52.0 ft 70 35,983 34,955 2,399 32,556High Level 6 " 51.5 ft 80 46,998 45,655 3,133 42,522Normal Fill 6 " 51.0 ft 90 59,482 57,782 3,965 53,817

100 73,434 71,336 4,896 66,441110 88,856 86,317 5,924 80,393

Working height 47.5 ft 120 105,746 102,724 7,050 95,675125 114,741 111,463 7,649 103,814

ft

Usable tank volume estimation

Volumes for various tank diameters

Floating Roof at low legs (Min) 42 " 3.5

Tank Design Data Bottom Design DataCode: API 650 Material Specification: A36Inside Diameter: 125'-0" Welding: Lap WeldedHeight: 56'-0" Corrosion Allowance: 1/16"Nominal Capacity: 114,741 BBL Slope: 1" in 10'-0" Shovel BottomMaximum Capacity: 111,463 BBLNet Work Capacity: 103,814Product: Gasoline Material Specification: A36Product Specific Gravity: 0.74 Welding: Double Butt WeldedDesign Specific Gravity: 1.0 Corrosion Allowance: 1/16"Design Liquid Level: 51'-0"Internal Pressure: AtmosphericExternal Pressure: Atmospheric Type: Two-Bay Rater Supported ConeMaximum Design Temperature: 200° F Material Specification: A36Maximum Operating Temperature: 200° F Welding: Lap WeldedDesign Metal Temperature: 58° F Uniform Live Load: 20 PSFWind Code: API 650, 11th Ed. Additional Dead Load: NoneWind Speed: 150 MPH Plate corrosion Allowance: NoneWind Check: As-Built Struc Corrosion Allowance: NoneWind Importance Factor: 1.0 Slope: 3/4" in 12"Earthquake Code: API 650, 11th Ed. Roof Insulation Thickness: NoneEarthquake Zone:Site Coeffi cient: Site Class DEarthquake Importance Factor: 1.0 Type: Internal Reverse SlopeTank Fill Rate: 6,500 BBL/Hr Outer Rim Corrosion Allowance: NoneTank Suction Rate: 5640 gpm Deck Corrosion Allowance: NoneShell Insulation Thickness: None

Annular Plate Data

Fixed Roof Data

Floating Roof Data

External RoofCone Roof vs. Geodesic Dome Roof

Design Considerations – perimeter railing vs. perimeter wind girder designed for access to inspection ports.

Maintenance of coating, vs. panel seamsOverall Cost Comparison

Overall Height – no real limitations, guided mainly by:Local codes, zoning restrictions on height limitationsConsider available water pressure height to fight firesAesthetics compared with other tanksManaging tank alignment if more than one live at same timeConsider Operators – if over 60’, may need intermediate

landing

Geodesic Dome vs. Cone Roof

48’ Geodome with perimeter walk/girder56’ High Cone with perimeter railing

Net Positive Suction Head RequiredNPSHR – 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 IssuesEmissions options – even though IFR may not be required for Distillate

(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 - NFPAFire 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.

CoatingsMany 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 crackingAvgas – 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 AlternativesExcavate & replace unsuitable soilsPiles –

Driven to refusal, can disturb nearby structureAuger cast – less disturbance

Both still require pile caps to transmit load from bottom to pilings.

Soil Stabilization – Low disturbance to nearby structuresReduces waste removalWith proper testing and documentation, binder

material can serve as remediation

Check for Requirements

Questions?

Richard B. Garrettrick0702@msn.com