Red Book # 9105-4 Pontoon Floating Roof General Information

Red Book # 9105-4 ©Chicago Bridge & Iron Company. For Internal Use only. 1 __________________________________________________________________________________________________________

Horton Type 5 Pontoon Floating Roofs General Information Red Book Number: 9105-4 Revised: 29-05-2008 Issuing Authority: Ned A. Bacon/Plainfield/CBI Maintenance & Review: Plainfield Plate Structures Engineering 0.1 Scope: This standard furnishes engineering instructions and design specifications for Horton Type 5 Pontoon Floating Roofs which comply with API Standard 650, Appendix C. It includes references to written standards and standard drawings applying to the basic structure and its components. 0.2 Introduction: Standard designs for Horton Type 5 Pontoon Floating Roofs are shown in 9105-4-3 for diameters from 50' to 300' inclusive. 0.3 Description A Horton Type 5 Pontoon Floating Roof consists of a single center deck with a compartmented annular pontoon. See Figure 0.3 for a typical section through a Horton Type 5 Pontoon Floating Roof. The roof is designed to float directly on the product, thus reducing evaporation loss, corrosion, and fire hazard. The underside of the pontoon slopes upward toward the center of the tank to retain temperature generated condensable vapor under the center deck. The vapor insulates the liquid surface and is contained under the deck until the temperature lowers and it condenses back to product. The slope also provides proper flotation for the pontoon and an annulus of center deck attached to it assuring that rainfall will be directed to the center of the roof and not accumulate at the pontoon inner rim. The top deck of the pontoon slopes downward to the center to direct rainfall and melted snow onto the center deck where it can be removed by a drainage system. A seal is used to close the space between the floating roof and tank shell.

Figure 0.3 - Section Through Type 5 Pontoon Floating Roof Tank 0.4 Operating and Maintenance Instruction Booklet


An Operating and Maintenance Instruction Booklet is given to the purchaser for each tank. See 591-7 for instructions in making and issuing the booklets. 1.0 COMPONENTS OF THE TYPE 5 PONTOON FLOATING ROOF Pontoon and Center Deck: Pontoons can be either field assembled (KD) or shop built up (BU). 9105-4-3 provides basic information for detailing and covers the design for roofs up to and including 300'. ESTI E0744A describes the computer program which provides the pontoon dimensional details. Consult Plate Structures Engineering for diameters other than those covered by 9105-4-3 and for roofs with BU pontoons. Roof Supports: The floating roof is furnished with adjustable pipe supports. 9108-6 gives sizes, design procedures and permissible loads for the adjustable supports. 9105-4-3 provides information for locating the supports. Drainage System: A closed drainage system is used to remove water from the center deck. See 9202 for design and details. Drainage Plug: See 9202

for requirements.

Rolling Ladder and Rolling Ladder Runway: See 9203-3 . A rolling ladder is used to provide access to the roof from the gager's platform. Furnish the deck runway for the rolling ladder. A trussed runway which improves drainage of water towards the center sump can be sold; see 9203-3 (6.3). Furnish a vertical ladder if the tank height is greater than the tank diameter. Unless otherwise specified by the purchaser, a rolling ladder shall be supplied if the tank is to be certified as meeting API Standard 650. Center Deck Manhole: Provide one 24" diameter manhole located near the center of the roof. Pontoon Manhole: One 20" diameter vented manhole is required for each compartment of the annular pontoon. When the purchaser requires more than one manhole per compartment, only one requires a vent. Each manhole cover should include a gasket and be secured by a positive hold-down device. Use manholes B13B-C or B13A-C. Rim Vent: Rim vents shall not be required unless one of the following criteria applies: 1. Purchaser specifies that one or more rim vents be included; or 2. installation includes a mechanical shoe seal other than the CBI SR-1A or SR-1S and the shoe extends into the product more than 6 inches; or 3. whenever the Purchaser specifies a product vapor pressure in excess of the EPA recommended allowable of 11.1 Psia. Plate Structures Engineering shall be notified whenever vapor pressures may be in excess of 10.5 Psia or approach the EPA recommended allowable of 11.1 Psia. Additional rim vents may be warranted to eliminate excess vapor accumulation below the deck. The final decision on the number and size of rim vents shall be the Purchasers. Whenever rim vents are required they shall be 6" diameter. See Drawing. G6 for details. Locate o o individual rim vent approximately 180 from the inlet line and multiple vents 90 from the inlet line. Rim vents shall not be used on roofs with foam filled seals. Gage Hatch: One 8" gage hatch is supplied with each roof; see Drawing. 3200-R19. This gage hatch may be attached to a gage pipe as optional equipment specified by the purchaser. Gage Well: A gage well is furnished only when the Purchaser specifies an automatic gage. Both automatic gage and gage well are optional equipment.


Automatic Bleeder Vent: A minimum of two automatic bleeder vents are furnished on all Type 5 Pontoon Roofs. See 9208-4 . See 9105-4-3 for location. The automatic bleeder vent permits the release of all entrapped air-vapor mixture from under the roof while the tank is being filled and the roof is resting on supports. The vent closes automatically after the roof floats. When the tank is emptied, the vent opens before the roof lands. It is fully open when the roof is on its supports allowing air to enter and preventing a vacuum from forming under the roof. Automatic bleeder vents are not designed to release trapped product vapors from under the roof once the roof is floating and the automatic bleeder vent has closed. If excess product vapors result either from process upset conditions or due to ambient heating of high vapor pressure products, optional discretionary vents may be required to eliminate ballooning of the center deck. Ballooning of the center deck will effect operation of the primary roof drains and should be avoided. Note that if any discretionary vents are added, installation details must consider roof deflections under water loading conditions shown in Figure 2.6. Vertical riser must be high enough to eliminate product carryover under this loading condition. If the purchaser specifies that pressure-vacuum vents be substituted for the automatic bleeder vents, provide specific maintenance instructions for these vents in the O&M manual. Also provide a warning that the vents may open on a daily basis to relieve vapor generated from solar heating and/or barometric pressure changes. The set points of these vents must be confirmed at time of installation. See 761-1-2 . Guide Device: A guide pole prevents the floating roof from rotating in the tank during use and while resting on its supports. See 9201-6 for details. 1.1 Seal Between Roof and Tank Shell: Mechanical shoe (CBI preference) or foam filled seals may be used. Seals are described in 9204 . Nominal rim space is 8". Tanks over 320' require a 12" rim space. Tanks over 270' shall have a 12" rim space if the tank height exceeds 56' unless supported on a ringwall foundation. 1.2 Shell Inlet Nozzles shall have a nominal 5' inner extension. 1.3 Rims: See 9105-0-20

for rim plate configuration.

2.0 DESIGN BASIS Consult Plate Structures Engineering if design calculations are required by contract. 2.1 Specifications: API Standard 650, Appendix C "External Floating Roofs" and CBI requirements. 2.2 Material: See API Standard 650, Section 2, API 650 Appendix C, and 622-6-2

.

2.3 Design Loading Conditions: The dead weight is the metal weight (theoretical) plus the weight of the accessories. a. Roof on Supports: Members and attachments are designed to support the dead weight and a uniform live load of 25 psf. b. Roof floating on 0.7 specific gravity liquid: 1. Uniform live load of 25 psf. 2. Full retention of minimum 10" rainfall (no liquid leaks). 3. Buoyancy loss of center deck only. 4. Buoyancy loss of center deck and one peripheral compartment. 5. Buoyancy loss of center deck and two adjacent peripheral compartments. The dead weight is included in all 5 loading conditions. No rain water or live load is included with conditions 3, 4 and 5.


The roof is also designed to allow for air raising during construction. See 9105-4-3 (0.5)

.

2.4 Allowable Stresses: For design loading conditions 1, 2 and 3 above, the allowable average direct compressive stress is 20,000 psi in the effective participating plate area of the pontoon. For emergency design loading conditions 4 and 5 above, the average direct compressive stress may exceed 20.000 psi. Restraint against buckling is checked. The effective participating plate area in compression is as determined from the AISI Light Gage Cold Formed Steel Design Manual. The effective participating area in tension is as determined from the handbook of Astronautical Engineering, H.H. Koelle, McGraw Hill, New York, New York, 2.5 Flotation of Roof on 0.7 Specific Gravity Liquid: Sufficient pontoon volume is required to keep: a. the roof floating with the center deck and two adjacent pontoon compartments punctured. b. the roof floating without the center deck or any pontoon compartments punctured, while retaining a minimum 10" rainfall. 2.6 General Notes: Designs are made using CBI computer program E0716A. Standard designs based on 3/16" plate, except as noted, are given in 9105-4-3 . Consult Plate Structures Engineering for special thickness. See 9105-4-3 for designs with 1/16" corrosion allowance on the center deck and pontoon bottom deck and outer rim. Some large roof diameters may require a portion of the center deck to be double lap welded to resist tension in the deck with full water load. See 9105-4-3 for details. Consult Plate Structures Engineering for: a. Roofs floating on liquids of specific gravity higher than 1.0 or lower than 0.7. b. Type 5 Floating Roof Tanks to be constructed in locations of unusual wind conditions as described in 0.3 of 9105-4-3 . c. Roofs floating on product with a true vapor pressure in excess of 10.5 psia at normal storage temperature. Figure 2.6 shows Type 5 Pontoon Floating Roofs under various loading conditions.

Type 5 Floating Roof Floating on 58 pcf Product No Live Load

Type 5 Floating Roof Floating on 43.68 pcf Product No Live Load


Type 5 Floating Roof During Air Raise Operation Pontoon Rotated Counter Clockwise

Type 5 Floating Roof Floating on 43.68 pcf Product Holding a 10" Rainfall

Figure 2.6 Loading Conditions 3.0 DETAILS 3.1 Center Decks Center deck plates are detailed to extend to the outer rim. Type 5 bulkheads include a radius, see Figure 3.1(a and b), which provides a smooth transition from underneath the pontoon bottom to the center deck. The radiused bulkhead detail is preferred for all standard designs except those cases where shop BU pontoons are selected to facilitate overall project schedule. When shop (or site) BU pontoons are selected, the center deck plates will be detailed to extend to near the inner rim, where they lap weld to the bottom pontoon plates, as shown in 9105-4-3 , Figure 1.0. Stiffeners will hold the center deck horizontal for the first 6" inside the pontoon between bulkheads.


Bulkhead Length (BHL) CB

1’- 0”

6”

6”

Bulkhead Top Rise (BTR)

6”

Inner Rim (IR)

Outer Rim (OR) Bulkhead Bottom Rise (BBR) New Slope ∠ NSA

Radius “R”

RH

Summary of Radius Calculations • • • • •

CB = BHL - 1 ATAN(BBR/CB) = NSA (new slope angle) NSA/2 = ∠ AA 6 / Sin (AA) = RH Radius R = SQRT( RH2 - 62)

∠ AA

Where R = radius for bulkhead fabrication

Figure 3.1a Typical Layout of Radiused Bulkhead Outer Rim

6 x 6 clips Bulkhead

Bulkhead

6 x 4 ∠ Inner Rim Stiffener

Figure 3.1b Plan View of Pontoon (deck not shown) See 9100-1

and use Computer Program E0606A for center deck layouts.


3.2 Pontoon and Deck Shrinkage For tanks over 100' dia., extra material must be included for in the center deck layouts and the top and bottom pontoon plates to account for shrinkage due to welding. Calculate center deck plate dimensions by increasing the theoretical radius by the following: TANK DIAMETER

RADIUS INCREASE (Pontoon & Decks) 1/2" 3/4" 1" 1 1/4" 1 1/2"

100' - 150' > 150' - 200' > 200' - 250' > 250' - 300' over 300'

Calculate top and bottom pontoon plate dimensions based on the following: 1. 2. 3. 4. Note: rules.

Outside radius increase as given above. 1¼" lap between plates. Inner radius of top plate 1" less than inside radius of inner rim. Inner radius of pontoon bottom plate (if used) 3½" less than inside radius of inner rim. Computer program E0744A calculates pontoon top and bottom plate dimensions based on these

3.3 Drawing Details -- See Standard Form Drawing Data Classification 3220 Series 1 for available form drawings. 1. Show the theoretical nominal rim space and the outer rim radius (dimensions per 9105-4-3 unless otherwise indicated) on the roof field weld and assembly drawing(s). For tanks over 100', note on the drawing that these dimensions are "After Welding". Construction Manual #14 specifies the shrinkage allowance Construction is to add to this radius for erection and fit up. 2. Show 1" lap weld between adjacent pontoon deck plates for installations using shop (or site) BU pontoons only. This is not required for the preferred radiused bulkhead detail where the deck is extended to the outer rim. 3. Show 1" top deck plate overhang over inner rim. 4. Show the bottom deck plates projecting 3 ½" inside the inner rim. 5. The burn radius shown for the bottom pontoon plates or continous deck plates at the outer rim is the tangent radius computed using the the bottom pontoon slope. Note: the burn radius is different than the radius used to determine plate requirements using E0606A program.The radius used in E0606A is the total length (horizontal plus sloping) plus shirkage allowance.

******* ©Chicago Bridge & Iron Company, 2008. All Rights Reserved. For Internal Use Only. NOTICE: THIS DOCUMENT, AND ALL TEXT, DRAWINGS, DETAILS AND DATA SHOWN HERETO, IS THE SOLE PROPERTY OF CHICAGO BRIDGE & IRON COMPANY, AND SHALL NOT BE REPRODUCED IN ANY MANNER OR USED FOR ANY PURPOSE WHATSOEVER EXCEPT BY EXPRESS WRITTEN PERMISSION OF CHICAGO BRIDGE & IRON COMPANY.

Red Book # 9105-4 Pontoon Floating Roof General Information

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