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GENERAL ENGINEERING SPECIFICATION

ACCESSORIES FOR ATMOSPHERIC

STORAGE TANKS

GES D.02

Page 2 of 8

Rev 0 1999

INDEX

SEC TITLE PAGE

1.0 SCOPE OF SPECIFICATION 3

1.1 Introduction 3

1.2 Other NOC Specifications 3

2.0 DESIGN 3

2.1 Location of Attachments 3

2.2 Roof and Shell Manholes 4

2.3 Manual Gauging for Fixed Roof Tanks 52.4 Water Draw-off Connections 5

2.5 Flush Type Shell Connections 5

2.6 Fire-Fighting Facilities 5

2.7 Level Instruments 5

2.8 Temperature Instruments 5

2.9 Additional Requirements for Floating Roof Tanks 6

2.10 Fixed Roof Tanks with Internal Floating Covers 7

2.11 Tank Heaters 7

Figure 1: Location of Principal Connections and Attachments 8

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GES D.02

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Rev 0 1999

1.0 SCOPE OF SPECIFICATION

1.1 Introduction

1.1.1 This specification covers the general requirements for establishing the design, size, quantity and location of

accessories for atmospheric fixed roof and floating roof storage tanks and open top storage tanks.

1.1.2 This specification should be read in conjunction with, and as a supplement to, GES D.01, "Atmospheric

Storage Tanks (API 650)".

1.2 Other NOC Specifications

The following NOC Specifications are an integral part of this specification and any exception shall be

approved in advance by the Owner.

GES D.01 Atmospheric Storage Tanks (API 650)

GES H.07 Fire-Fighting Facilities on Storage Tanks

GES J.03 Level Instruments

GES J.05 Temperature Instruments

GES P.01 Piping Material Specification

GES W.01 Welding Procedures and Qualifications

GES W.05 Welding Materials

GES X.01 Surface Preparation and Painting Application

GES X.06 Factory Coatings for Electrical Equipment and Instruments.

2.0 DESIGN

In addition to the minimum requirements of the design code, the following shall be taken into

consideration.

2.1 Location of Attachments

The location of principal connections and attachments for fixed roof tanks shall be as per Figure 1. Unless

otherwise specified, the location of shell nozzles and manholes for floating roof tanks shall also be as per

Figure 1 at the end of this specification. The requirements for, and the location of other tank connections

and appurtenances, will be specified on the appropriate Data Sheets/Drawings.

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GES D.02

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2.2 Roof and Shell Manholes

Table 1. Number and Size of Manholes

The minimum number of size of shell and roof manholes shall be as per the following:

Nominal

Tank

Diameter

Number & Size of Manholes

Shell Roof

All Tank Types Fixed Roof

Tanks(1)

Floating Roof

Tanks

ft m No in mm No in mm No in mm

10-20 3-6 1 24 (600) 1 20 (500) 1 20 (500)

>20-40 >6-12 2 24 (600) 2 20 (500) 1 30 (750)

>40-60 >12-18 1 24 (600)

1 30 (750)

2 20 (500) 1 30 (750)

>60-90 >18-27 1 24 (600)

1 30 (750)

2 24 (600) 2 30 (750)

>90 >27 2 24 (600)

1 30 (750)

2 24 (600) 2 30 (750)

Notes

(1) Where internal floating covers are used, at least one manhole shall be fitted to the floating covers

of 24" (600 mm) diameter.

Gaskets for shell manholes to API 650 shall be coarse, woven fibre, impregnated with suitable synthetic

rubber. Gaskets shall be sized to fit the internal pitch circle diameter of the bolt holes, to enable them to be

fitted without having to cover the joint faces with adhesive. Gaskets for other shell and roof connections

shall be compressed non-asbestos fibre to ASME B16.21.

2.3 Manual Gauging for Fixed Roof Tanks

2.3.1 Fixed roof tanks (with or without internal floating covers) shall be fitted with a manual gauging sampling

well or a gauge hatch as indicated on the Tank Data Sheet.

2.3.2 Manual gauging sampling wells shall be floor mounted only, with no shell attachments.

If a manhole or a separate roof connection is used for gauging sampling purposes, it shall be located near a

roof support.

2.3.3 Gauging hatches shall be as per the following:

- the gauging hatch shall have a seal with corrosion resistant seats suitable for a pressure of 0.125

psig (0.86 kPag), or design pressure of tank whichever is greater, and a heavy stay-back cover;

- the gauging hatch shall be of 8" (200 mm) minimum diameter,

- the cover shall weigh at least 6 lb (3 kg).

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GES D.02

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Rev 0 1999

2.4 Water Draw-off Connections

Tanks in hydrocarbon service shall be provided with a minimum of one water draw-off connection using

the API Low Type shell nozzle. Water draw-off sumps shall be provided as follows:

- for tanks over 20 ft (6 m) in diameter, a water sump is required. The sump may be any shape

provided it has a volume at least equal to the volume of sump specified in API 650. End of draw-

off pipe shall be 4" (100 mm) above bottom of sump;

- if "apex down" cone bottom is specified, a sump is not required. The draw-off line shall be piped

to the centre of the tank, turned down and terminated 4" (100 mm) above the bottom;

- for tanks 20 ft or less in diameter, a sump is not required. The inlet end of the water draw-off pipeshall be 2" (50 mm) above the bottom, except in the case of "apex down" cone bottom tanks. In

such cases, the end of the pipe shall be 4" (100 mm) above the bottom;

- when flush type suction nozzles are used, the maximum size water draw-off connection shall be

NPS 6.

2.5 Flush Type Shell Connections

Flush type shell connections shall be provided with a flow guide box.

2.6 Fire-fighting Facilities

For fixed and floating roof tanks, refer to GES H.07 for the design requirements regarding fire-fighting

systems.

2.7 Level Instruments

(a) Gauge types and installation by the Owner or Vendor/Contractor will be specified. A minimum of

one level gauging instrument per tank, readable from grade, shall be provided.

(b) Level instrumentation shall generally be in accordance with GES J.03.

(c) Asphalt service. Provision shall be made to automatically shut off heaters when they become

exposed above the liquid level. The type of level control and installation requirements by the

Vendor/Contractor or Owner will be specified.

2.8 Temperature Instruments

Connections for temperature indication shall be provided as follows:

2.8.1 For fixed roof tanks without internal floating covers a NPS 1 threaded connection shall be furnished for a

thermowell installation (see Figure 1). Supply and installation of thermowell will be by the Owner or

Vendor/Contractor, as specified.

2.8.2 For floating roof tanks and fixed roof tanks with internal floating covers, the type and method of

installation of the temperature measuring device will be specified.

2.8.3 Temperature instruments shall generally be in accordance with GES J.05.

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2.9 Additional Requirements for Floating Roof Tanks

2.9.1 Gauge Well and Guide Pole

Gauge well and guide pole assemblies shall be provided as follows:

2.9.1.1 A combination gauge well and guide pole assembly shall be provided for each floating roof tank, whether

or not the tank is to be equipped with an automatic gauge. Gauge well and guide pole assemblies shall be

floor mounted only, with no shell attachments.

2.9.1.2 If an automatic gauge is installed in a combination gauge well and guide pole assembly, a manual gauging

sampling well shall also be provided.

2.9.2 Roof Drains

The design and use of roof drains shall be as follows:

2.9.2.1 Floating roofs shall be provided with drains fabricated from flexible metal hose or articulated pipe.

Chicksan swivel joints with Viton seals shall be provided for articulated pipe joints.

2.9.2.2 An automatic roof draining device shall be provided in addition to the primary drains, when tanks are

located in areas where rainfall is expected to exceed 10" (254 mm) in a 24 hour period.

2.9.2.3 Roof drains shall be sized per API 650 and shall permit the bottom of the pontoon or double deck to be

lowered to 15" (375 mm) from the tank shell bottom.

2.9.2.4 Proposals to use roof drains sized on other than the API 650 basis shall be submitted to the Owner for

approval. Such proposals shall be accompanied by calculations demonstrating that the primary drains are

capable of carrying off water at the specified rate with the roof in the lowest operating position.

2.9.2.5 If emergency drains are provided on double deck or pontoon floating roofs, they shall be of the open type

design.

2.9.3 Roof Vents

2.9.3.1 Each roof shall be equipped with a bleeder vent, designed to open automatically when the roof lowers to 3"

(75 mm) above its lowest operating position or lower leg setting, and to close automatically when the roof

raises more than 3" (75 mm) above its lowest position. Liquid withdrawal rates will be specified.

2.9.3.2 When flexible steel shoe-type seals are used, the roof shall be equipped with a vent or vents between the

roof rim and the seal shoe. These vents shall release excess air or non-condensable vapours entering the

tank through the filling line.

2.9.4 Ladders, Platforms and Walkways

2.9.4.1 If the tank diameter is equal to or greater than the height, a rolling type roof ladder shall be furnished

having a minimum angle of 30from the vertical. If the tank diameter is less than the tank height, it shall

have a vertical roof ladder.

2.9.4.2 For floating roof tanks, guard railings shall not be furnished for wind girders specified to be used aswalkways, except for tanks having an air foam system with multiple outlet foam stations, or if local

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procedures dictate fire-fighting from the wind girder.

2.10 Fixed Roof Tanks with Internal Floating Covers

2.10.1 Vents and Inspection Hatches

Tank shell air-circulation vents shall be located above the seal of the floating cover, i.e. above the upper

travel limit. Alternatively, the vents may be located on the tank roof, provided their inlet overhangs the

shell and they are designed such that the incoming air is deflected downward. Shell and fixed roof vents

shall be covered with a coarse mesh screen with " (13 mm) openings, provided with weather shields.

Locations where the use of air-circulation vents are not permissible, due to environmental considerations,

will be specified.

Inspection hatches shall be provided in the tank roof per API 650, Appendix `H', to permit visual inspectionof the seal region. A guard railing 30" high x 4 ft long (750 mm x 1200 mm) shall be installed at the

outside edge of each inspection hatch.

Designs which combine inspection hatches with tank shell vents (located on the tank roof) are acceptable.

2.10.2 Overflow Slots

Unless otherwise specified, overflow slots shall be provided to prevent over filling the tank above its net

capacity, and shall be sized for the maximum filling rate. The slots shall be covered with coarse mesh

screen with " (13 mm) openings, provided with weather shields.

2.10.3 Roof Ladder

If a permanent ladder is specified for a fixed roof tank with internal floating cover, for access from the roof

to the internal floating cover, it shall be designed to accommodate the full travel of the floating cover.

2.11 Tank Heaters

Tank heating coils and associated piping shall have all pressure joints welded in accordance with GES

W.05.

Internal heater support design shall take into account differential thermal expansion, shell radial

displacement and rotation of shell to bottom junction, at the heater nozzle.

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D-02.pdf