Designing Aboveground ASME Tank Installations

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Designing Aboveground ASME Tank Installations
A very important decision in designing a propane
distribution system with an aboveground ASME tank
is the selection of an acceptable and appropriate
location for the tank installation. Ensuring the
proper number and capacity of tanks is critical
to satisfactory system operation. Determining the
vaporization capacity of the supply container(s)
to meet gas appliance demand for any vapor system
is a fundamental design task.
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Designing Aboveground ASME Tank Installations

• In this module you will learn to
• Identify regulations that govern aboveground ASME
  tank site selection
• Identify steps to finalize an aboveground ASME
  tank location plan
• Identify factors that affect aboveground tanks
  vaporization capacity
• Select propane storage tanks by applying ASME
  tank vaporization guidelines
• Identify other considerations for selecting
  appropriate ASME tank sizes

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Designing Aboveground ASME Tank Installations

• In this module you will learn to
• Identify code requirements and components for
  aboveground ASME manifold tanks in vapor service
• Identify components for typical vapor service
  manifold tank installations with single regulator
  configuration
• Identify code requirements and components for
  manifold tanks supplying liquid to an auxiliary
  vaporizer

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Regulations that Govern Tank Location
Figure 1 presents, in table format, minimum
required distances and a brief purpose or
explanation of the requirement.
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Regulations that Govern Tank Location
Figure 1. Minimum Distance Requirements for
Stationary ASME Tank Installations
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Regulations that Govern Tank Location
Figure 1. Minimum Distance Requirements for
Stationary ASME Tank Installations
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Regulations that Govern Tank Location
Figure 1. Minimum Distance Requirements for
Stationary ASME Tank Installations
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Regulations that Govern Tank Location
Figure 2. Aboveground ASME Tank Location
Minimum Separation Distances
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Regulations that Govern Tank Location
The illustrations are presented as a guide or
reference only. Always check your companys SOP
and state and local codes.
The distance requirements above are based on
recommendations in NFPA 58. They do not replace
any requirements in your state or local codes.
Tanks should always allow space for maintenance.
Figure 3. Multi-Tank Installations
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Steps to Finalize a Tank Location Plan
Step 1 Mark the information on a worksheet and draw a simple sketch of the property.
Step 2 Explain to the customer the purpose in selecting a proper location for the tank.
Step 3 Determine that the customer prefers an aboveground tank.
Step 4 Determine the customers general preference for the tank location (in back of house, etc.). Explain that the final location will have to meet safety regulations.
Step 5 Select an area that has access for fuel delivery and fire fighting.
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Steps to Finalize a Tank Location Plan
Step 6 Based on the water capacity of the tank(s), select an area for the installation that meets the distance requirements. You may also refer to Table A (Figure 1) for an explanation of each distance shown in the illustration.
Step 7 When the final location for the tank has been selected, clearly outline the area with stakes or flags.
Step 8 Add the tank(s) location to the worksheet drawing/sketch of the property.
Some propane marketers have detailed procedures
for determining system layout. Always follow
local guidelines. Remember, a competent and
complete planning effort will produce a satisfied
customer.
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Sizing ASME Aboveground Tanks for Vapor Service
Factors Affecting the Vaporization Rate of Tanks
When a tank(s) is sized for vapor service, make
sure the vaporization rate of the tank(s), or
withdrawal rate, is equal to or greater than the
demand for propane.

• Outside Surface Area of the Tank The heat
  required to vaporize liquid is transferred
  through the walls of the tank. If the area of the
  tank wall which is in contact with the propane
  liquid (wetted surface area) is large, the total
  heat (Btu) that can be transferred to the liquid
  is high.
• Level of Liquid Propane in the Tank

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Sizing ASME Aboveground Tanks for Vapor Service
Figure 4. Effect of Decreased Liquid Level and
Wetted Surface Area on Vaporization Rate
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Sizing ASME Aboveground Tanks for Vapor Service
Factors Affecting the Vaporization Rate of Tanks

• Air Temperature Surrounding the Tank Because
  of propanes relatively low boiling point (-44F
  at atmospheric pressure) the heat needed for
  vaporization is usually available from the air
  that surrounds the propane storage tank. High
  summer air temperatures surrounding the tank
  create more available heat to be transferred to
  the liquid. As a result, the rate of
  vaporization is high. However, low outside
  temperatures in the winter reduce the tank
  vaporization capacity.

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Sizing ASME Aboveground Tanks for Vapor Service
Factors Affecting the Vaporization Rate of Tanks

• Location of the Tank. Certain ASME tanks are
  designed to be installed aboveground or
  underground. Aboveground tanks have maximum
  vaporization rates during exposure to high summer
  temperatures and direct sunlight. However,
  aboveground tanks may experience a drop in the
  vaporization rate in the winter due to low
  temperatures, sustained cloudy skies, and periods
  of rain, fog, sleet or snowfall.

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Sizing ASME Aboveground Tanks for Vapor Service
Factors Affecting the Vaporization Rate of Tanks

• Relative Humidity If the air is moist (high
  humidity), the air may cool down to a temperature
  where the moisture will condense on the wetted
  surface area of the tank freeze. The resulting
  "frost line" on the wetted surface acts as an
  insulator and drastically reduces the
  vaporization rate of the tank.

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Sizing ASME Aboveground Tanks for Vapor Service
Figure 5. Estimated Vaporization Rates for
Aboveground ASME Tanks
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Applying ASME Tank Vaporization Guidelines
Seven Sizing Factors The wide ranges of air
temperatures and relative humidity that are
experienced in different parts of the United
States dictate that the selection of storage
tanks be made using the following Seven Sizing
Factors

1. What is the lowest anticipated temperature for
   the installation?
2. What is the highest expected relative humidity?
3. What is the total gas system demand (Btuh load)?
4. What does the gas system customer profile tell
   about anticipated customer demand and critical
   service factors?
5. What are the operating characteristics of the
   connected gas appliances (appliance load
   factors)?
6. How does the installation compare to similar gas
   customers in the immediate area?
7. What are the propane company guidelines for
   delivery scheduling?

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Applying ASME Tank Vaporization Guidelines
Using Tank Vaporization Guides It is important
that persons who select propane tanks for
residential and small commercial installations
take the time to examine the assumptions and
conditions that apply to the tank vaporization
guide used.
Using a Rule of Thumb Guide (for Small to
Medium Propane Demand Systems and Moderate
Climate Conditions) The method uses ASME tank
dimensions, liquid level, and a constant value
for each 10 percent of liquid to estimate the
vaporization capacity of a given tank size at 0
F. Additional factors are used to calculate
available vapor at other temperatures. The method
does not consider relative humidity as a
variable, but yields fairly reliable vaporization
capacity estimates for moderate demand systems
for locations with moderate prevailing weather
conditions, such as the southern states and
Hawaii.
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Applying ASME Tank Vaporization Guidelines
Rule-of-Thumb Vaporization Capacity for ASME
LP-Gas Storage Tanks1
1 Engineered Controls International, Inc. REGO
Products LP-Gas Servicemans Manual
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Applying ASME Tank Vaporization Guidelines
Rule-of-Thumb Vaporization Capacity for ASME
LP-Gas Storage Tanks1
1 Engineered Controls International, Inc. REGO
Products LP-Gas Servicemans Manual
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Applying ASME Tank Vaporization Guidelines
Selecting Aboveground ASME Tank(s) for High
Demand Systems and Severe Climate Conditions
Using a Tank Vaporization Chart When the seven
sizing factors are applied to the gas customer
profile illustrated by Figures 7a and 7b, it is
apparent that a more detailed method for
aboveground tank selection is required for the
high-demand system.
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Applying ASME Tank Vaporization Guidelines
Figure 7a. High-Demand, Severe Service
Conditions Customer Profile
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Applying ASME Tank Vaporization Guidelines
Figure 7a. Example of a Gas Customer Profile
(Front)
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Applying ASME Tank Vaporization Guidelines
Figure 7a. Example of a Gas Customer Profile
(Front)
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Applying ASME Tank Vaporization Guidelines
Figure 7b. High-Demand, Severe Service
Conditions Customer Profile
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Applying ASME Tank Vaporization Guidelines
Figure 7b. Example of a Gas Customer Profile
(Back)
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Applying ASME Tank Vaporization Guidelines
Figure 7b. Example of a Gas Customer Profile
(Back)
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Applying ASME Tank Vaporization Guidelines
Tank Vaporization Chart Method for Selecting
Aboveground ASME Tank(s)
Step 1 Determine the total demand of all present and anticipated future appliances.
Step 2 Determine the effective load on the tank. Determining load-sizing factors is based on the way that gas appliances typically operate under normal circumstances.

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Applying ASME Tank Vaporization Guidelines
Figure 8. Determining Effective Load for Use
with the Tank Vaporization Chart Note
Calculations at bottom of chart are specific to
the Customer Profile in Figure 7.
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Applying ASME Tank Vaporization Guidelines
Figure 9. Average Appliance Load Factor Chart By
Customer Type
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Applying ASME Tank Vaporization Guidelines
Tank Vaporization Chart Method for Selecting
Aboveground ASME Tank(s)
Step 3 Determine the most severe weather conditions under which the tank must operate. The two most important factors affecting the vaporization rate of a propane tank are the temperature surrounding the tank during a gas demand and the humidity surrounding the tank.

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Applying ASME Tank Vaporization Guidelines
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Applying ASME Tank Vaporization Guidelines
Figure 11. Average Highest Relative Humidity for
the Month of January
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Applying ASME Tank Vaporization Guidelines
Tank Vaporization Chart Method for Selecting
Aboveground ASME Tank(s)
Step 4 Using the Estimated Vaporization Capacity Chart, select the proper size and number of propane tanks for the application.
Customer System Operating Factors Customer System Operating Factors Customer System Operating Factors
Vapor Distribution System Effective Load Severest Anticipated Operating Conditions Severest Anticipated Operating Conditions
Vapor Distribution System Effective Load Lowest Anticipated Ambient Temperature Highest Anticipated Relative Humidity
2,275,650 Btuh 0 F 80
Figure 12. Vapor Distribution System Operating
Factors (Example)
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Applying ASME Tank Vaporization Guidelines
Figure 13. Estimated Vaporization Rates for
Aboveground ASME Tanks NOTE Refer to Chart
Application Criteria for Use
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Applying ASME Tank Vaporization Guidelines
Tank Vaporization Chart Method for Selecting
Aboveground ASME Tank(s)
If the tanks listed in the tables do not provide
the vaporization rate to meet the effective load
of the appliances, there are four options that
might be used

1. Manifold two or more tanks together.
2. Install an underground tank.
3. Choose a larger capacity tank.
4. Change to liquid withdrawal and install a
   vaporizer.

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Other Considerations in Tank Selection
Frost Lines The first consideration for proper
tank sizing with regard to vaporization capacity
is to ensure that the tanks that are installed do
not develop a frost line under peak demand and
severe operating conditions. If the supply
tank(s) consistently develop a frost line when
the liquid level is above 20, the tank is too
small for the load, and larger tank(s) should be
installed. Efficient and Reliable Delivery
Schedule Figure 14 can be used to estimate the
initial frequency of required delivery scheduling
for a customer account.
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Other Considerations in Tank Selection
Figure 14. Example of a Delivery Scheduling
Chart
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Other Considerations in Tank Selection

• Summary of Sizing Considerations
• Proper selection of ASME tanks is one key to
  customer satisfaction.
• Tanks must be sized using the most severe
  anticipated conditions.
• Preparing a gas customer profile provides
  important information, and knowing how the
  customer gas appliances will be used are the
  basis for sizing and selecting propane supply
  tanks.
• Supply tank selection must consider any critical
  service factors.
• If the supply tank(s) are not capable of
  supplying sufficient volume of vapor at the
  minimum required supply pressure (10 psig),
  auxiliary vaporizing equipment should be used.
• Service technicians, and especially, delivery
  personnel should report the formation of frost or
  ice on customer propane tanks.

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Code Requirements for Manifold Tank Installations
Most propane system installers and jurisdictional
authorities interpret 2.3.3.2 (a)(4) as a
requirement for excess-flow protection in
manifold tank installations where the first-stage
regulator is connected to tank service valves
using vapor piping longer than the pigtail used
in typical single tank installations and where
the regulator is installed outside of the tank
dome.
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Selecting Components for Manifold Tank
Installations
Figure 16. Excess-Flow POL Fitting
Figure 15. Manifold Aboveground ASME Tanks
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Selecting Components for Manifold Tank
Installations
Figure 18. POL Back Check Tee
Figure 17. Manifold Underground ASME Tanks
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Selecting Components for Manifold Tank
Installations

• Special components for manifold underground tank
  installations
• Regulator vent pipe-away assembly
• POL back check tees
• Open-bottom water meter or valve box, or
  poured-in-place concrete vault with loose-fitting
  manhole cover

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Requirements for Manifold Tanks in Liquid Service

• If the actuated liquid withdrawal excess-flow
  valve (sometimes called an evacuation valve) is
  used for manifold tank connection, one of two
  forms of excess-flow protection must be provided
  
• A liquid transfer valve attached to an actuated
  liquid withdrawal excess-flow valve that is
  recommended by the manufacturer for continuous
  service or
• The actuated liquid withdrawal excess-flow valve
  must be removed and replaced with a liquid
  transfer valve equipped with an internal
  excess-flow.

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Requirements for Manifold Tanks in Liquid Service
Bottom Opening Liquid Withdrawal
Top Opening Liquid Withdrawal
Figure 20. Internal Valve with Excess-Flow and
Cutaway View
Figure 19. Excess- Flow Angle Valve
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Requirements for Manifold Tanks in Liquid Service
Liquid piping sections that can be closed at each
end must be protected by the installation of a
hydrostatic relief valve. Hydrostatic relief
valves should have a 400 to 450 psig start to
discharge rating.
Figure 21. Hydrostatic Relief Valve
Typically, liquid piping for manifold tanks is
comprised of threaded schedule 80 pipe sections
and heavy (2000 or 3000 pound) forged steel
fittings.
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Requirements for Manifold Tanks in Liquid Service
Figure 23. Slab for Manifold Liquid Service
Tanks
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Time to See If You Got the Key Points of This
Module

• Complete the Review on pages 30 - 33.
• See if you are ready for the Certification Exam
  by checking off the performance criteria on
  pages 34 - 36.

4.1.4 Student Book ? 2004 Propane Education Research Council Pages 30 - 36