LPG is an environmentally friendly, clean, safe and certified alternative fuel source widely used in residential, commercial and industrial applications.

Household liquefied gas tanks for residential purposes are primarily used for home heating systems and in commercial and industrial places also include a wide range of industries and in many processes such as heating, construction, cooking and It is used for commercial cooking, cleaning, product drying, fuel storage, etc

Definition of liquefied gas according to NFPA 58:

Any substance that does not have a vapor pressure exceeding the commercial propane limit and is mainly of the following hydrocarbons (except propylene) or a mixture of them. These hydrocarbons are: propane, propylene, butane (normal butane or isobutane) and Butylenes.

Pure propylene has a vapor pressure of 132.8 psig at 70°F (21.1°C).

The vapor pressure of commercial propane at 70°F (21.1°C) is 124PSIG. Although commercial propane may contain some propylene, pure propylene does not meet the definition of a liquid gas. Pure propylene is usually used as an industrial fuel gas.

The highest grade of commercial propane is the HD-5 grade, which has a minimum propane content of 90%

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Design parameters of liquid gas fixed tanks:

Definition of design pressure (DESIGN PRESSURE):

UG – 21

It states that tanks should be designed for the worst pressure and temperature conditions expected in normal operation. This law also states that the pressure difference between inside and outside or between the chambers of a tank, during work and testing, should be considered as the maximum pressure.

Beyond the guidelines stated above, no standard provides a specific definition for design pressure.

In general, the design pressure is determined by the maximum internal or external pressure of the tank during its normal operation. The design pressure must be sufficiently higher than any anticipated operating conditions for all components to perform satisfactorily against the overpressure.

Maximum Allowable Working Pressure (MAWP):

For a tank, the maximum allowable pressure is defined at the top of the tank in its normal operating position at a specific temperature (usually the design temperature).

Difference between design pressure and MAWP:

Let’s assume that the minimum sheet thickness of t is obtained by using the tank design formula and the design pressure P (for example, with a pressure of 10 times, a thickness of 7.2 mm is obtained, because there is no sheet with this thickness in the market, instead of a sheet with a higher thickness, for example, 8 mm It is used, now by subtracting this number that is 8 in the design formula, we get the equivalent pressure, which will definitely be a number higher than 10 bar pressure (design pressure). This number is the same as the maximum allowable working pressure or MAWP. greater or equal to the design pressure.

According to NFPA58 TABLE 5.2.4.2 code, the maximum allowable working pressure (MAWP) for tanks built according to the ASME standard is 250 PSI, provided that the maximum vapor pressure at a temperature of 37.8 degrees Celsius is 215 PSI. Therefore, the design pressure for a fixed liquid gas tank can be It should be less than 250 PSI. In fact, the maximum design pressure for a tank made according to ASME and containing pure propane is 250 PSI and for a tank containing pure butane is 100 PSI (NFPA 58 D.2.1.3)

Design parameters of liquid gas tanks (CARGO TANKS):

In liquefied gas transport tanks, in addition to NFPA58, ASME regulations, compliance with DOT regulations is also required. According to DOT (ICC) regulations, the temperature standard for safe filling of transport tanks is 46 degrees Celsius, with the explanation that for tanks with a volume of more than 1200 gallons, the vapor pressure Gas at 115°F (46°C) is designated by the DOT as the minimum tank design pressure.

The vapor pressures of CP propane and commercial propane at 115°F (46.1°C) are 211PSig and 255PSig, respectively. Normal butane and commercial butane have a vapor pressure of 51 psig at 115°F (46.1°C).

Liquid gas tanks are divided into fixed and mobile categories in terms of transportability, and fixed tanks are divided into two types, aboveground and underground, according to the conditions of use.

For domestic use, tanks are usually used with low capacities (normally up to 2000 gallons) under the name domestic lpg tank.

In areas where there is no access to city gas, the use of these tanks is more evident. Due to compliance with design and construction standards, accuracy in purchasing these tanks is important.

On the other hand, the existence of second-hand (used) tanks – due to the lack of control of the market of these tanks by the relevant bodies – requires more accuracy from customers when buying and using.

The existence of many technical and specialized points in these reservoirs requires the use of the opinions of experts in this field. The best method is to use technical inspection companies in the field of pressure vessels.

The transport tanks are designed and built in various types of cargo tank or fixed tank or portable tank with a capacity of 3000 liters to 48000 liters (according to the specifications of the truck and road transport regulations).

Standards for the design and construction of liquefied gas tanks:

ASME SEC 8 DIV1, 2, 12, ADR, DOT, EN12493, EN13445, ADMERKBLATT

Determining the size of liquid gas storage tanks for use:

To determine the size of the required tank, the effective factors in vaporization and evaporation of liquid gas must be determined. For this purpose, heat transfer formulas are used, and it can be applied when the tank is used continuously, and if the tank is used intermittently, the tank has a chance to compensate for the heat lost during use.

But the incorrect selection of tank capacity will cause pressure drop in winter and related problems. The experts of this company are ready to advise our dear customers to choose the correct tank size.

 Characteristics of liquefied gas tanks of Vera Makhzan Khazar Company:

• Tank capacity from 1000 liters to 200,000 liters
• Designed, manufactured and inspected in accordance with the latest ASME SEC VIII DIV I code
• Comply with the requirements of NFPA 58
• They comply with the requirements of Iran’s national standard 841The tanks are equipped with REGO valves (made in America) and Rochester level gauges
• They are designed with a pressure of 250 PSi and a temperature range of -20 to +50 degrees Celsius.
• After welding, all tanks are radiographed with X-rays and hydrostatically tested under water pressure
• The steel used in the construction of these tanks is compatible with liquefied gas (mainly SA516 Gr.70 steel).The tanks are controlled and approved by the technical inspection company approved by the National Standards Organization of Iran.