prepared by: m.sirajudin (sr. static equipment engineer) july...

Prepared by: M.SIRAJUDIN (Sr. Static Equipment Engineer) July 29, 2010

Petrofac Saudi Arabia Ltd.

Introduction to Storage Tanks

July 29, 2010Storage Tanks ( basic info) Prepared by: M.SIRAJUDIN (Sr. Static Equipment Engineer)

To Give Basic Information on Storage Tanks used for Oil & Gas industry

OBJECTIVES

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• Tanks have been around since the beginning of hydrocarbon production.

• Tanks vary considerably, in the type and size, based on the type of

products to be stored and the volume involved.

• The failure of a tank can have several undesirable effects such as endangering personnel, affecting the environment and interrupting the Operator’s business.

• Companies therefore, require a consistent approach for assessing tank integrity and maintaining compliance with industry and regulatory standards, (that is community requirements). Such an approach must;

• Ensure tanks are not leaking and will not leak before next inspection

• Reduce the potential for releases

• Maintain tanks in safe operating conditions, and

• Make repairs and determine when replacement is necessary.

1. Background

Storage Tanks ( basic info) Prepared by: M.SIRAJUDIN (Sr. Static Equipment Engineer)

The primary function of a storage tank is to store liquid substance. This liquid substance may be:

a) Water b) Feedstockc )Finished products prior to shipping out to customersd) and Unfinished petroleum components awaiting for further - processing - blending

While in the storage tanks, these products may settle out undesirable substances such as; Water, Emulsions, Dirt etc. These undesirable substances can then be removed through draw-off devices. Products may also be mixed, blended and treated in storage tanks effectively, using the large capacity available in these tanks.

2. Functions of Tank


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• Broadly, the storage tanks can be divided based on internal pressure:

Atmospheric Tanks:

• Atmospheric storage is a term applied to tanks operating at or near atmospheric pressure.

• Although they are called atmospheric, they are operated at internal pressure slightly above atmospheric pressure ( pressure varies from atmospheric up to 0.5 psi above atmospheric.

Low Pressure Tanks:• Within the context of the tanks, low pressure means that tanks which

are designed for a pressure higher than atmospheric tanks. This means that these tanks are relatively high pressure tanks. These tanks are designed to operate from atmospheric up to 15 psig

Note: • Above types of tanks are used to hold liquid which will not vaporize at ambient

temperature. Tanks used in this category are primarily the open top, fixed roof (cone & dome) and floating roof.

• These tanks are most commonly used

3. Classification of Tanks


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Pressurized storage :

Pressurized storage applies to those vessels (mounded bullets) which are designed to withstand pressure sufficient to keep the liquid stored, from vaporizing. High vapor pressure hydrocarbons such as propane, butane, iC5 are the types of products requiring pressurized storage vessels (Mounded Bullets).

• Note: We will basically focus on aboveground vertical storage tanks of various types.

3. Classification of Tanks


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Above & below-ground tanks: There are many ways to classify the storage tanks. Most fundamental

classifications based on whether they are above ground or below ground tank.Above ground tank

• The above ground tanks have almost all their structure exposed. The bottom part of these tanks is placed directly above solid or concrete foundation.

• Advantages of these tanks are that they r easy to construct and can be built in for large capacities and cost less than underground tanks

Below ground tank• These tanks have less capacity than above ground tanks and are

usually limited to between 20k liters (20 cum) to 75k liters (75cum)• Can store fuel as well as variety of chemicals• They are subjected to severe corrosion

Note: We will mainly focus on aboveground, vertical storage tanks of various types

4. Types of Tanks


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Open Top tank:

This type of tank has no roof and shall be used for storing city water, fire water and cooling water

4. Types of Vertical Tank


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Based on Type of Roof

A. Fixed Roof Tanks: These tanks can be divided into cone and dome roof types and each can further

subdivided into non pressure, low pressure, high pressure & very high pressure fixed roof tanks.

•. Non pressure Fixed roof tanks are suitable at atmospheric pressure and are therefore provided with open vents. The design pressure/vacuum is ≤ 10/ ≤5 mbar (g)

•. Low pressure Fixed roof tanks are designed to work at low internal pressure or vacuum. The design pressure/vacuum is ≤ 25/ ≤8.5 mbar (g). They are provided with pressure/vacuum breather valves ser to be fully open at design pressure.

•. High pressure Fixed roof tanks are designed to work at higher internal pressure or vacuum and are also fitted with pressure/vacuum breather valves set to be fully open at design pressures. The design pressure/vacuum is ≤ 60/ ≤8.5 mbar (g).

•. Very High pressure Fixed roof tanks are designed to work at higher internal pressure or vacuum and are also fitted with pressure/vacuum breather valves set to be fully open at design pressures. The design pressure/vacuum is ≤ 500 / ≤ 20 mbar (g).

•. Can be used to store hydrocarbons as per product classification as given for example in the IP code.

4. Types of Vertical Tanks


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A. Fixed Roof TanksA1 Cone Roof :•. These tanks have vertical sides and is equipped with a fixed cone shaped roof

that is welded on the sides of the tank.•. Bottom is usually flat & the top is made in the form of shallow cone. •. They are economical to built ,These are the most widely used tanks for storage

of relatively large quantities of fluid.

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A. Fixed Roof Tanks :(A1) Cone Roof :

Self Supported Cone roof:

•. As per API 650, the slope angle of these tanks should be θ ≤ 37° (slope 9:12) , θ ≥ 9° (slope 2:12)

•. These are relatively smaller sizes of tank



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A. Fixed Roof Tanks :A1. Cone Roof : Supported Cone Roof•. As per API 650 Slope of supported cone Roof is 19mm in 300mm or greater θ approx 4 ° •. Support can be in the form of Truss, Column .•. For large diameter fixed roof tanks single or multi column supported roof are

used.



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A. Fixed Roof Tanks :(A1) Cone Roof : Single Column Supported Cone Roof ( construction of Roof)•.



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A. Fixed Roof tanks:A1 Cone Roof : Multi Column Supported Cone Roof•.



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A. Fixed Roof tanks

A2 Dome Roof :•. Dome approximates a spherical surface. These tanks are self supported



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A. Fixed Roof tanks

A3 With Internal Floating Cover (IFRT)•. In fixed roof tanks internal floating roof (IFC) can be installed to give a further

reduction of vapor losses . These tanks can be designed as non, low & high pressure tanks.

•. For safety & environmental reasons, internal floating covers shall be of full contact type.

•. In addition to cone roof the tanks has an internal floating roof pan is provided that floats directly on fuel surfece.



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A. Fixed Roof tanks

A3 With Internal Floating Cover (IFRT) : Internal Views•. These types of tanks can easily be identified with open vents in the

tank side walls just beneath the roof joint



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A. Fixed Roof tanks

A3 With Internal Floating Cover (IFRT) (Pictorial views)



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• Internal view of an internal floating roof tank



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B. EXTERNAL FLOATING ROOF TANKS (EFRT)•. Recommended for diameters of 15 m & above however can be used for small

diameters in special circumstances•. These types of tanks are designed to work at atmospheric pressure•. Diameters •. Common Types of Floating Roof Tanks are::

Pontoon Single Deck Floating Roof:•. A pontoon single deck type of roof consists of an outer pontoon ring divided by

bulk heads into liquid tight compartments with an inner section of ordinary steel plates acting as single deck membrane.

•. This type of roof is recommended for tanks diameters up to 48m.

Double deck Floating Roof: •. A double deck floating roof consist of an upper and lower deck extending over

entire area of liquid surface. •. The lower deck is separated from upper deck by circumferential rim plates and

radial bulk heads to form a liquid tight compartments.



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B. EXTERNAL FLOATING ROOF TANKS (EFRT) (site view)



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B. EXTERNAL FLOATING ROOF TANKS (EFRT)



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B. EXTERNAL FLOATING ROOF TANKS (EFRT) Diagrammatic View •.



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B. EXTERNAL FLOATING ROOF TANKS (EFRT)Details of Flexible Seal employed for Floating Roof Tank

•. The floating roof has mechanical seal attached to its full perimeter . The rim seal covers the space between the floating roof and the tank shell (side wall)



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B. EXTERNAL FLOATING ROOF TANKS (EFRT) Pictorial view



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B. EXTERNAL FLOATING ROOF TANKS (EFRT) Pictures from site

•. The purpose of using floating roof (internal/external) is that they minimize evaporation by covering the liquid surface



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COMMON INTERNATION ALSTANDARDS:

i. API 650 : (American Standard)•. Covers design fabrication, erection and testing requirements of vertical, above ground,

closed & open top welded steel storage tanks fro various sizes & capacities .•. For internal pressure approximating atmospheric, but higher internal pressure is permitted

when addition requirements are met and Appendix F is followed.

ii. API 620: (American Standard)•. Covers large field assembled storage tanks that contain petroleum intermediates (gas or

vapour) and finished products.•. The standard covers design & construction of large welded low pressure carbon steel above

ground storage tanks.

iii. API 579: (American Standard)•. is fitness for service standard and was developed to evaluate flaws & damage associated

with in service operation.

5. Design Codes/Standards used for Tanks


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a. COMMON INTERNATIONAL STANDARDS:

iv. BS EN 14015 ( British Standard)• Specification covers the design manufacturing of site built, vertical, cylindrical flat bottomed,

above f ground, welded steel tanks for storage of liquids at ambient temperature & above.

v. Shell DEP ( 34.51.01.31-Gen)

Covers the design requirement of shop assembled and site built, vertical, cylindrical flat bottomed, above ground, welded steel tanks

vi. Shell DEP ( 64.51.01.31-Gen)

This is extension of above DEP & covers the Erection & Testing of vertical tanks

vii. UL 142 ( Underwriter laboratory)•. Covers design & construction requirement of above ground storage tanks

viii. UL 52 ( Underwriter laboratory)•. Covers design & construction requirement of below ground storage tanks



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b. COMPANY STANDARDS:

1) 32-SAMSS-005 ( Manufacturing of Atmospheric Tanks)

2) 32-SAMSS-030 ( Manufacturing of Small Tanks)



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6. Question/ Queries?


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July 29, 2010

prepared by: m.sirajudin (sr. static equipment engineer) july...

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