Tiêu chuẩn Việt Nam TCVN 6486:2008 về Khí dầu mỏ hoá lỏng (LPG) - Tồn chứa dưới áp suất - Yêu cầu về thiết kế và vị trí lắp đặt

NATIONAL STANDARD

TCVN 6486 : 2008

LIQUEFIED PETROLEUM GAS (LPG) – PRESSURISED STORAGE – REQUIREMENTS FOR DESIGN AND LOCATION OF INSTALLATION

Foreword

TCVN 6486 : 2008 supersedes TCVN 6486 : 1999.

TCVN 6486 : 2008 is jointly compiled by the Technical Committee in charge of TCVN/TC 58 Gas cylinders and Gas Petrolimex Corporation JSC at the request of the Directorate for Standards, Metrology and Quality, and announced by the Ministry of Science and Technology.

LIQUEFIED PETROLEUM GAS (LPG) – PRESSURISED STORAGE – REQUIREMENTS FOR DESIGN AND LOCATION OF INSTALLATION

1. Scope  

1.1. This standard introduces requirements for design and location of installation of stationary liquefied petroleum gas ("LPG") containers of 0.15 m³ or more water capacity, used to store residential, commercial, and industrial LPG.

1.2. This standard shall not apply to:

- Storage of LPG for transportation;

- Storage in the course of gas distillation or separation;

- Refrigerated storage.

2. Referenced documents

The following referenced documents are indispensable for the application of this document. For dated referenced documents, the edition cited shall apply. For undated referenced documents, the most recent edition or revision shall apply.

TCVN 5684 Fire safety for petroleum and petroleum products facilities – General requirements.

TCVN 6008 Pressure equipments - Welds - Technical requirements and testing methods.

TCVN 6153 Pressure vessels - Safety engineering requirements of design, construction, manufacture.

TCVN 6154 Pressure vessels - Safety engineering requirements of design, construction, manufacture - Testing methods.

TCVN 6155 Pressure vessels – Safety engineering requirements of erection, use, repair.

TCVN 6156 Pressure vessels – Safety engineering requirements of erection, use, repair – Testing method.

TCVN 7441: 2004 Liquefied Petro gas (LGP) Compounds at Consumption Ends – Requirements in Design, Installation.

3. Terms and definitions

The terms and definitions used in this standard include:

3.1. Design pressure

The pressure to be used in determining the minimum permissible wall thickness of LPG bulk tank so that it is capable of handling the LPG pressure at the maximum operating temperature.

3.2. LPG bulk tank

A container used for storing LPG with a water capacity exceeding or equal to 0.15 m³.

3.2.1. Aboveground tank

A tank installed above grade and not covered with sand or earth.

3.2.2. Underground tank

A tank buried below the general grade and covered with sand or earth.

3.2.3. Mounded tank

A tank located above the general grade level and covered with sand or earth.

3.3. LPG system

A system is comprised of a tank and equipment such as pumps, compressors, piping, fittings, shutoff valves, control valves, connectors, etc. required for handling LPG.

3.4. Liquefied petroleum gas (LPG)

A hydrocarbon mixture composed predominantly of butane (C₄H₁₀) and propane (C₃H₈). These components account for at least 95% of the mixture by weight.

NOTE – “Khí dầu mỏ hóa lỏng” (LPG) is also called as “Khí đốt hóa lỏng” in National Standards announced before 2004.

3.5. Separation distance

The minimum distance between buildings or structures which must be kept to ensure the safety in case of LPG leakage or fire, minimize the possibility of damage and prevent gas dispersal.

3.6. Explosible area

The area where the mixture of LPG and air may cause fire or explosion.

3.7. Producer/ supplier

The entity that produces or supplies equipment and relevant services to meet the purchaser’s requirements.

3.8. Fire wall

A wall constructed of brick or concrete or another material with a fire resistance of at least 60 minutes and a height of at least 2m or higher than the top of the tank, and used to protect the tank from the heat radiation by an external fire and prevent the dispersal of LPG vapor to adjacent constructions or external ignition sources if the leakage of LPG occurs.

3.9. Excess-flow valve

A valve designed to close automatically when the LPG liquid or vapor passing through it exceeds a prescribed flow rate.

3.10. Emergency shut-off valve

A shutoff valve incorporating manual or combined means of closing installed to stop the supply of LPG immediately in an emergency.

3.11. Pressure relief valve

A valve designed to protect the LPG system in case of overpressure by mean of automatically discharging LPG to the outside of the system.

4. General requirements

4.1. LPG tanks must be used in compliance with applicable regulations adopted by competent authorities.

4.2. LPG tanks and systems must be designed, manufactured, installed, repaired, inspect, tested and maintained in accordance with national standards, including TCVN 6153, TCVN 6154, TCVN 6155, TCVN 6156 and TCVN 6008, and applicable regulations laid down in relevant technical standards.

5. Requirements for design of aboveground tanks

5.1. General requirements

5.1.1. A LPG bulk tank must be designed for storage of 100% of commercial propane at the highest temperature. The design pressure of the mixture must be selected with a consideration of mixture pressures that may occur in the course of tank operation.

5.1.2. Vacuum may be accounted for if the ambient temperature falls below the boiling point of LPG at the atmospheric pressure or where the selected speed of liquid release is very high but the corresponding vapor return line is unavailable.  

5.1.3. The selected maximum design temperature is the highest temperature of the product handed by the tank at normal operation plus a temperature differential to ensure that the safety valve does not lift in normal conditions.     

5.1.4. The selected minimum design temperature shall be -20°C, unless a lower temperature of a tank shell or the contents of the tank.    In such case, the lowest temperature shall be selected.

5.1.5. The minimum wall thickness shall include a corrosion allowance of 1 mm if the tank is made of carbon steel.

5.2. Tank connections, fittings and accessories

5.2.1. Any tanks shall have an access hole or inspection pit.  A tank’s access hole shall have an oval or circular shape of at least 400 mm x 300 mm in size or at least 400 mm in diameter respectively.  An inspection pit's size must be suitable for inspecting the inside of the tank.

5.2.2. A tank must be equipped with connectors, fittings and accessories suitable for the use of LPG and conformable with relevant standards.

5.2.3. A tank shall have at least the following appurtenances:   

- Pressure relief valve

- Liquid LPG filling valve

- Liquid LPG withdrawal valve

- Vapor LPG withdrawal valve

- Blowdown valve

- Liquid LPG level gauge

- Pressure gauge

5.2.3.1. Pressure relief valve

The pressure relief valve shall be installed to provide direct connection to the vapor LPG space of the tank and removed for regular inspection and testing by adopting suitable methods. The size of a pressure relief valve must correspond to the outside surface area of the tank in conformity with provisions laid down in TCVN 7441: 2004.
5.2.3.2. Liquid LPG filling valves

At least a check valve and a shut-off valve must be installed on the liquid LPG fill line.  A valve installed on a pipe joint with a nominal diameter of greater than 50 mm must be made of cast steel and be a ball valve with a working pressure at least equal to the Design Pressure of the piping system.

5.2.3.3. Liquid and vapor LPG withdrawal valves

An excess-flow valve and a manual shutoff valve or emergency shut-off valve must be installed on pipe joints at the outlet of the LPG withdrawal line. A ball valve installed on a pipe joint with a nominal diameter of greater than 50 mm must be made of cast steel. The emergency shut-off valve must be the one closed automatically by the operation of a heat-sensing metal cap or manually from a remote position, ensuring separation distance, by mechanical means or compressed air in case of emergency.

5.2.3.4. Blowdown valve

The blowdown pit of a tank must be located at the lowest portion of the section occupied by liquid; two block valves must be installed on the drain pipe outside the tank with the aims of preventing leakage; the minimum distance between these two valves shall be 500 mm so that the spilled liquid shall not freeze and make the valve obstructed.

5.2.3.5. Metering and gauging equipment

Each tank shall be provided with at least a liquid-level gauge with a range of levels indicating the tank capacity, and a pressure gauge which should be connected to the vapor LPG space.  The hole of the gauge used to measure the level of liquid LPG vented to atmosphere must be at least 1.5 mm in diameter. A temperature gauge, when fitted, must be installed in load-bearing pocket.

5.3. Tank supports

5.3.1. Tank supports must meet its design standards and be weld to saddle or V-shape plates already weld on the tank shell.  

5.3.2. The design of supports for tanks shall include provisions for expansion and contraction of the tank due to pressure and temperature. For tanks of less than 50 m³ capacity, the anchored structure may be employed to adjust the expansion level.

5.3.3. The design of the tank support must ensure that after installation, the tank has a downward slope of from 1 : 100 to 1 : 400 towards the tank discharge hole.

5.3.4. Tank foundations and supports must be capable of bearing loads when the tank space is completely filled with water.

5.3.5. Tank supports shall be designed so that the space underneath the tank is sufficient to install pipe lines and ensure safe operation and maintenance of equipment installed under the tank.

5.3.6. Steel legs and saddles of vertical or spherical tanks must be covered by fire-resistance materials. Appropriate methods must be employed to prevent standing water between support saddles or legs and fire-resistance materials.

5.4. Requirements for earthing

5.4.1. The lightning rod is not required but the LPG tank must be earthed with earth resistance of not exceeding 10 W.

5.4.2. Each tank is required to have at least two metal wires weld to the earthing system for the purposes of protecting the tank from lightning and static electricity.  Earth resistance of this system shall not exceed 10 W.

5.4.3. LPG tankers must be connected with the safety earthing system at the LPG loading position.

5.4.4. The safety earthing system must have an earth resistance of not exceeding 4 W. All of dead parts of electrical equipment and pumps must be connected to the safety earthing system.

This earthing system must be located at least 5 m far away from the earthing system for protection from direct lightning strike.

If a safety earthing system is connected to the earthing system for protection from direct lightning strike, total earth resistance shall not exceed 1 W.

6. Tank location

6.1. LPG tanks must be located outdoor and outside the house or building, and not located on the top or balcony or in the basement of a building.

6.2. Tanks should not be located beneath constructions such as eaves, bridges or overhead power lines.

The LPG tank must be located at least 1.5 m from the top view of the overhead power lines that are less than 1 kV. This required distance may rise to 7.5 m if the overhead power lines are over 1 kV.

6.3. If a LPG tank storage area is located adjoining doorways to the line of property occupied by hospitals, schools, shopping malls, etc., it must be protected by an enclosure with an open-type fence of at least 1.8 m high and located at least 1.5 m from a tank. There shall be at least two means of access to and exit from the fenced enclosure.  This is an outward opening lockable gate not less than 1 m wide.

6.4. A tank storage area shall be provided with appropriate safety precaution signs which must be kept in a legible condition such as danger signs, instructions for fire protection and alarming, and telephone number of fire agencies.

6.5. Pressure relief valves must be maintained in good conditions.   The relief valve discharge shall be located at the uppermost point of the tank, well-ventilated and directed upward. Any pressure relief valves installed on LPG piping system, LPG cylinders and LPG tanks shall not directed toward any tank, LPG piping and operators.  

6.6. Tanks must not be stacked one above the other. Aboveground tanks must be securely supported.  Tank supports must be flat and capable of supporting the weight of the tank filled with water.

6.7. The ground under a tank used to store LPG shall be graded to prevent the accumulation of any LPG liquid leaked from the tank.

6.8. Where the fire water system is applied, the drainage must be a consideration when determining the installation of this fire water system.  

6.9. Tanks should not be located in areas where there is a risk of flooding. Where an underground or mounded tank is located in an area where there is large volume of groundwater, it must be firmly anchored to prevent floating.

6.10. Minimum separation distances from storage tanks to nearest structures, buildings or office buildings and those between tanks are provided for in the following Table 1.

Table 1 - Separation distances from tanks to nearest structure, building or office building and between tanks

NOTES: Abovementioned distances are measured from the outside edge of an aboveground tank or from the filling connection or the relief valve of an underground or mounded tank.

6.11. Separation distances may be reduced by the provision of a fire wall in accordance with the following rules:

The minimum distance between the tank and the fire wall is 1.5 m.

Where a fire wall is constructed, the separation distance shall be calculated by adopting the following formula:

A = A + B (m)

Where:

D: minimum separation distance indicated in Table 1;

A: distance measured horizontally from the tank to the gable of the fire wall;

B: distance measured horizontally from the above-determined gable of the fire wall to the adjacent structure (housing or office building, etc.)

Figure 1. Separation distance from a tank with a fire wall

6.12. Fire walls are normally used on one side of a tank or tank grouping.  Fire walls should not be used on more than two sides of tank grouping or where the ventilation would be impaired.

6.13. LPG tanks and oxygen containers must be sited according to the separation distances in Table 2.

Table 2 - Separation distances between LPG tanks and liquid oxygen containers

The adjacent ends of the cylindrical tanks designed for horizontal installation shall be separated from each other in a row; they must be installed parallel with ends in line and must not be directed toward housing or service buildings. Aboveground tanks shall be installed in groups. The number of tanks in one group depends on the fire protection system and is provided for in Table 3.

Table 3 – Maximum number of aboveground tanks in one group

6.15. Separation distances from LPG filling facilities to adjacent buildings and to LPG tanks are provided for in Table 4.

Table 4 - Separation distances from LPG filling facilities to adjacent buildings and to LPG tanks

6.16. Separation distances between points of LPG transfer by road or rail tankers and adjacent buildings are provided for in Table 5.  

Table 5 - Separation distances between points of LPG transfer and adjacent buildings

6.17. Underground tanks must be protected from external loads on the tank shell, including loads from cars and other vehicles, etc.

6.18. Pumps and compressors shall not be located beneath tanks.

6.19. Vaporizing equipment of any types shall not be installed within the minimum separation distance of 1.5 m from the outer edge of the tank. Vaporizing equipment must be installed within a suitable electrical safety zone or to keep a regulated distance to the fixed ignition source.

7. Corrosion control

7.1. Each tank shall be protected against corrosion. Protective coatings must be tested for protection of tanks from the effects of corrosion at periodical intervals not exceeding 2 years.

7.2. Fireproofing coverings shall not be used to replace or support the fire water system, unless these fireproofing coverings are designed to allow the inspection of inner sides of tanks and measurement of thickness of the tank shell, and approved by competent authorities.

7.3. Fireproofting covering of a tank shall be tested at periodical intervals not exceeding 05 years which are same as those for testing for wall and shell thickness as well as inspection of inner side of a tank.

8. Labeling

A label must indicate the following information:

- Name of manufacturer;

- Date of manufacture;

- Manufacturing standard;

- Maximum allowable operating pressure;

- Minimum allowable operating pressure;

- Minimum operating temperature;

- Water capacity;

- Inspecting agency.

LIST OF REFERENCED DOCUMENTS

1) NFPA 58 : 2001 Liquefied Petroleum Gas Code.

2) AS 1596 - 1989 LP Gas - Storage and Handling / Australian Standard.

3) API 2510 - 2001 : Design and Construction of LPG Installations.