1
THE RED BOOK OF LPG ENGINEER
Contents
2
Basics of LPG – Effects of Pressure and Temperature
Flammability
Other Hazards
Vapor Pressures of Butane-Propane Mixtures
Properties of Propane and Butane
Properties of Hydrocarbon Gases
Viscosity of Liquid LPG
Flame Temperature and Flame Speed of Gases
Mollier Chart of Propane
Mollier Chart of Normal Butane
Mollier Chart of Isobutane
Calculating Motor Octane Number of a LPG Mixture
Calculating Vapor Pressure of a LPG Mixture
Unit Conversion Tables
Filling Ratio of LPG Tanks
LPG Tanks and Safety
Tank Design Codes
Certification Doesn’t Mean Same Quality
Pressure Vessel Steels
Periodic Inspection for LPG Tanks
Codes and Standards for LPG Installations
LPG Tank Accessories
Safety Relief Valves for LPG
LPG Level Gauges
LPG Pumps
LPG Compressors
LPG Vaporizers
LPG Regulators
Vapour Condensing in LPG Piping
Installation of LPG Storage Tanks Safety Separation Distances
Cathodic Protection for Underground LPG Tanks
3
4
4
5
6
7
8
8
9
10
11
12
13
14
18
22
23
25
26
30
31
32
35
37
38
40
41
42
44
45
47
Basics of LPG – Effects of Pressure and Temperature
3
LP-Gas or LPG ...
LPG or LPG stands for “Liquefied Petroleum
Gas”. It is the term widely used to describe
a family of light hydrocarbons called “gas
liquids”. The most prominent members of
this family are propane (C3H8) and butane
(C4H10). Other members of the LP Gas family
are ethane and pentane. These latter fuels
have their own distinctive markets and are not
further discussed here. C3H8 C4H10 kimya formülü
biçimi
Main source of LPG is natural gas; and
crude oil-gas mixtures which come out oil or
natural gas wells. The secondary supplies are
the various refining processes at petroleum
refineries.
The term “liquefied gas” may seem a
contradiction in terms since all things in nature
are either a liquid, a solid or a gas. Yet, it is the
unique character of LPG that makes it such a
popular and widely used fuel. LPG at normal
temperature and pressure is a gas. It changes
to a liquid when subjected to moderate
pressure or cooling. In liquid form the tank
pressure is about twice the pressure in
a normal truck tyre.
The reason LPG is liquefied is to make it easy
and efficient to transport and store. One unit
of liquid has the same energy content as
270 units of gas. If left as a gas the container
to hold the fuel would be 270 times larger than
what is required as a liquid. In other words,
LPG has density (compactness) for storage
and transportation, yet all the benefits of
a clean vaporous fuel when used.
LPG usually consists of a mixture of propane
and butane for standard heating and cooking
purposes. Propane starts vaporizing above
-45°C, so it is more versatile for general use.
Butane starts vaporizing above -2°C and
requires a propane/butane mixture in cold
environments as it will not vaporize as readily
as propane. LPG is also used in specialized
applications that require a more rigorous
specification. Such applications include
food processing, aerosol propellants and
automotive fuel (autogas).
Inside a storage container, LPG exists both
in liquid and vapor state. The LPG inside the
container is boiling; somewhat similar to boiling
water, but the boiling point of LPG is such low
that it can boil at ambient temperatures. Heat
is also required to boil LPG but generally, heat
removed from ambient air is sufficient.
When some vapor is consumed; a certain
amount of liquid evaporates to fill the space
and the pressure of the container doesn’t
change. Although this is not an everyday
practice, just imagine some vapor is added
to the container by using a compressor.
The vapor condenses, and the pressure of
the container doesn’t change. When vapor
is consumed at such a rate that exceeds the
heat transfer rate from ambient; then heat
is taken from the product itself. In this case,
removal of vapor decreases the temperature
inside the container, and the pressure
decreases.
The pressure inside the container is depending
to the temperature. When temperature rises,
more liquid evaporates and the pressure
rises. When temperature falls, some vapor
condenses and the pressure falls.
Flammability
Other Hazards
LPG is highly flammable when mixed with air in
the correct proportions. If the concentration of
LPG vapor in the air is between 2% to 9.5%;
then the mixture becomes flammable. 2% is
the LEL (lower explosive limit) which means,
below this limit the mixture is too lean to burn.
9.5% is the UEL (upper explosive limit) which
means, above this limit the mixture is too rich
to burn.
LPG vapor is nearly twice dense than
air. Therefore, when a leak occurs, the
leaking gases tend to flow downwards and
accumulate at ground level or somewhere
below ground level, like sewage or drainage
channels.
However, when an LPG leak occurs it doesn’t
homogenously mix with the surrounding air;
some objects may limit or create air currents
and flammable mixture may occur in some
spots.
LPG itself is odorless and colorless.
An odorant which is added to LPG gives its
characteristic, unpleasant odor and enables
to detect and locate leaks.
Since LPG vaporizes at low temperatures, skin
contact with LPG liquid may contact frostbites.
Effect of frostbite on body is similar to burns,
and medical treatment is also the same as
burns.
LPG is not toxic; but is a simple asphyxiant.
When a leak occurs in a confined space, LPG
vapors will displace the air, prevent the livings
inside from breathing oxygen and may cause
deaths.
LPG burning appliances shall be located in
well ventilated places. If the appliance has a
flue, this must be connected to a chimney.
When these practices are neglected carbon
monoxide poisoning may cause deaths. LPG
water heaters inside bathrooms or flueless
LPG stoves in living spaces poses a big risk
of carbon monoxide poisoning.
4
Vapor Pressures of Butane-Propane Mixtures
5
Figure 1
Vapor Pressures of
Butane-Propane
Mixtures
Properties of Propane and Butane
FORMULA
Boiling Point at 1.013 bars,°C
6
PROPANE
N-BUTANE
C3H8
C4H10
-42
-0,5
-43,7
+31,1
Relative density of gas (air=1.00) at 1.013 bars
(14.696 psia), 15,6°C/15,6°C (60°F/60°F)
1,55
2,07
Relative density of liquid (water=1.00) at 15,6°C (60°F)
0,508
0,584
Weight, kg/m³ at 15,6°C
lb/gal. at 60°F (**)
4,22
4,86
50,004
21,498
25,363
91,101
49,162
21,136
28,702
102,980
95,49
2,563
125,7
3,374
267
230
0,528
8,45
466
871
0,394
6,31
405
761
2,1
9,5
1,8
8,3
at 14.696 psi, °F
Heat of combustion of liquid
MJ/kg at 15,6°C
Btu/lb at 60°F
GJ/m³ at 15,6°C
Btu/gal at 60°F (**)
Heat of combustion of gas
MJ/m³ at 1.013 bars, 15,6°C
Btu/ft³ at 14.696 psia, 60°F
Ratio of vapor volume at 1 bar (14.696 psi) and 15,6°C
(60°F) to liquid volume at 15,6°C (60°F)
Vapor volumes
m³ vapor at 15,6°C/kg liquid at 15,6°C
ft³ vapor at 60°F/lb liquid at 60°F
Ignition temperature in air, °C (***)
°F
Limits of flammability, percentage of gas in air mixture
at lower point
at upper point
* From API Technical Data Book-Petroleum Refining. The values are for pure propane and butane and do not necessarily
apply to commercial products, which may have other hydrocarbons present in varying amounts.
** From GPSA Engineering Data Book
*** From AGA Gas Engineers Handbook
Table 1
Properties of
Butane and
Propane (*)
Properties of Hydrocarbon Gases
7
Table 2
Properties
of Several
Hydrocarbon
Gases
Viscosity of Liquid LPG
8
Table 3
Viscosity of
Hydrocarbon
Gases in
Saturated State
Flame Temperature and Flame Speed of Gases
Table 4
Flame
Temperatures
of Hydrocarbon
Gases
Mollier Chart of Propane
9
Figure 2
Mollier Chart of
Propane
Mollier Chart of Normal Butane
10
Figure 3
Mollier Chart of
Normal Butane
Mollier Chart of Isobutane
11
Figure 4
Mollier Chart of
Isobutane
Calculating Motor Octane Number of a LPG Mixture
12
When the composition of a LPG mixture is
given; the motor octane number (MON) of
this mixture can be calculated, following this
procedure.
The MON factors for hydrocarbon gases
are given on “Table 5 : MON Factors for
Hydrocarbon Gases”. The factors are given
as separate columns; for molar, volumetric
or mass percentage composition. Use the
appropriate column with the composition data.
For C2 and lighter hydrocarbons, use the MON
factor for Propane,
Table 5
MON
Factors for
Hydrocarbon
Gases
For C5 and heavier hydrocarbons, use the
MON factor for N-Butane,
Partial MON of a specific component in the
mixture is calculated by multiplying
[the percentage rate of component] x [MON
factor]
MON of the mixture is the sum of partial
MON’s of all components.
Sample Calculation:
The MON of a LPG mixture, with the following mass percentage composition :
Ethane : 2%
Propane : 35%
Iso-butane : 28%
N-butane : 34%
Pentane : 1%
Total MON = (0,02 x 95,9) + (0,35 x 95,9) + (0,28 x 97,1) + (0,34 x 88,9) + (0,01 x 88,9) = 93,786
Since the composition of the mixture was given in % mass, the factors are taken from the appropriate
column (% mass) of the table.
Calculating Vapor Pressure of a LPG Mixture
13
When the composition of a LPG mixture is
given; the vapor pressure of this mixture can
be calculated, following this procedure.
According to Dalton’s Law, the total pressure
exerted by a mixture of gases is the sum of
the partial pressures of the constituent gases.
According to Raoult’s Law, the partial pressure
exerted by the each component is the product
of the vapor pressure of each component, at
the existing temperature and the mol fraction
of the component.
A sample calculation, alongside with
explanation is given on “Table 6 : Calculating
Vapor Pressure of a Mixture”.
Table 6
Calculating Vapor
Pressure of a Mixture
Unit Conversion Tables
14
15
16
17
Table 7
Unit
Conversion
Tables
Filling Ratio of LPG Tanks
18
Heat input from the surrounding environment
will both increase the liquid volume, and the
vapor pressure inside the tank. Therefore,
LPG cylinders and tanks shall be filled up to a
limit. These limits can be determined by using
the following tables:
Table 8 : Maximum Filling Limit By Weight
Table 9 : Maximum Filling Limit by Volume;
which is prepared as 3 separate tables, for
above ground tanks up to 4.5 m³ (1.200 gal.)
for above ground tanks larger than 4.5 m³
(1.200 gal.) and for all underground storage
tanks.
Aboveground Containers
Specific
Gravity at 60o F
(15.6o C)
0 to 1200 gal
(0 to 4.5 m3)
Total Water
Capacity (%)
> 1200 gal
(> 4.5 m3)
Total Water
Capacity (%)
Underground
Containers
All Water
Capacities (%)
0.496 - 0.503
0.504 - 0.510
0.511 - 0.519
0.520 - 0.527
0.528 - 0.536
0.537 - 0.544
0.545 - 0.552
0.553 - 0.560
0.561 - 0.568
0.569 - 0.576
0.577 - 0.584
0.585 - 0.592
0.593 - 0.600
41
42
43
44
45
46
47
48
49
50
51
52
53
44
45
46
47
48
49
50
51
52
53
54
55
56
45
46
47
48
49
50
51
52
53
54
55
56
57
Table 8
Maximum Filling
Limit by Weight
19
Maximum Permitted LP-Gas Volume (Percent of Total Container Volume):
Aboveground Containers 0 to 1200 gal (0 to 4.5 m3)
Specific Gravity
C
0.496
to
0.503
0.504
to
0.510
0.511
to
0.519
0.520
to
0.527
0.528
to
0.536
0.537
to
0.544
0.545
to
0.552
0.553
to
0.560
0.561
to
0.568
0.569
to
0.576
0.577
to
0.584
0.585
to
0.592
0.593
to
0.600
–50
-45
-40
-35
-30
-45.6
-42.8
-40
-37.2
-34.4
70
71
71
71
72
71
72
72
72
73
72
73
73
73
74
73
73
74
74
75
74
74
75
75
76
75
75
75
76
76
75
76
76
77
77
77
77
78
78
78
78
78
79
79
79
79
79
79
80
80
79
80
80
80
81
79
80
80
80
81
80
80
81
81
81
-25
-20
-15
-10
-5
-31.5
-28.9
-26.1
-23.3
-20.6
72
73
73
74
74
73
74
74
75
75
74
75
75
76
76
75
76
76
76
77
76
76
77
77
78
77
77
77
78
78
77
78
78
79
79
79
79
80
80
80
80
80
80
81
81
80
81
81
81
82
81
81
82
82
82
81
81
82
82
82
82
82
83
83
83
0
5
10
15
20
-17.8
-15
-12.2
-9.4
-6.7
75
75
76
76
77
76
76
77
77
78
76
77
77
78
78
77
78
78
79
79
78
78
79
80
80
79
79
80
80
80
79
80
80
81
81
81
81
82
82
83
81
82
82
83
84
82
83
83
83
84
83
83
84
84
84
83
83
84
84
84
84
84
84
85
85
25
30
35
40*
45
-3.9
-1.1
1.7
4.4
7.8
77
78
78
79
80
78
79
79
80
80
79
79
80
81
81
80
80
81
81
82
80
81
81
82
82
81
81
82
82
83
82
82
83
83
84
83
83
84
84
85
84
84
85
85
85
84
85
85
86
86
85
85
86
86
87
85
85
86
86
87
85
86
86
87
87
50
55
60
65
70
10
12.8
15.6
18.3
21.1
80
81
82
82
83
81
82
82
83
84
82
82
83
84
84
82
83
84
84
85
83
84
84
85
85
83
84
85
85
86
84
85
85
86
86
85
86
86
87
87
86
86
87
87
88
86
87
87
88
88
87
87
88
88
89
87
87
88
88
89
88
88
88
89
89
75
80
85
90
95
23.9
26.7
29.4
32.2
35
84
85
85
86
87
85
85
86
87
88
85
86
87
87
88
85
86
87
88
88
86
87
88
88
89
86
87
88
88
89
87
87
88
89
89
88
88
89
90
90
88
89
89
90
91
89
89
90
90
91
89
90
90
91
91
89
90
90
91
91
90
90
91
91
92
100
105
110
115
120
37.8
40.4
43
46
49
88
89
90
91
92
89
89
90
91
92
89
90
91
92
93
89
90
91
92
93
89
90
91
92
93
90
90
91
92
93
90
91
92
92
93
91
91
92
93
93
91
92
92
93
94
92
92
93
93
94
92
92
93
94
94
92
92
93
94
94
92
93
93
94
94
125
130
51.5
54
93
94
94
95
94
95
94
95
94
95
94
95
94
95
94
95
94
95
94
95
95
95
95
95
95
95
Liquid Temperature
O
F
O
20
Maximum Permitted LP-Gas Volume (Percent of Total Container Volume):
Aboveground Containers 0 to 1200 gal (0 to 4.5 m3)
Specific Gravity
C
0.496
to
0.503
0.504
to
0.510
0.511
to
0.519
0.520
to
0.527
0.528
to
0.536
0.537
to
0.544
0.545
to
0.552
0.553
to
0.560
0.561
to
0.568
0.569
to
0.576
0.577
to
0.584
0.585
to
0.592
0.593
to
0.600
–50
-45
-40
-35
-30
-45.6
-42.8
-40
-37.2
-34.4
75
76
76
77
77
76
77
77
78
78
77
78
78
78
79
78
78
79
79
80
79
79
80
80
80
80
80
80
81
81
80
81
81
82
82
81
81
82
82
83
82
82
83
83
83
83
83
83
84
84
83
84
84
84
85
84
84
85
85
85
85
85
85
86
86
-25
-20
-15
-10
-5
-31.5
-28.9
-26.1
-23.3
-20.6
78
78
79
79
80
79
79
79
80
81
79
80
80
81
81
80
81
81
82
82
81
81
82
82
83
82
82
82
83
83
82
83
83
84
84
83
83
84
84
85
84
84
85
85
85
84
85
85
86
86
85
85
86
86
87
86
86
87
87
87
86
87
87
87
88
0
5
10
15
20
-17.8
-15
-12.2
-9.4
-6.7
80
81
81
82
82
81
82
82
83
83
82
82
83
83
84
82
83
83
84
85
83
84
84
85
85
84
84
85
85
86
84
85
85
86
86
85
86
86
87
87
86
86
87
87
88
86
87
87
88
88
87
87
88
88
89
88
88
88
89
89
88
89
89
90
90
25
30
35
40*
45
-3.9
-1.1
1.7
4.4
7.8
83
83
84
85
85
84
84
85
86
86
84
85
86
86
87
85
86
86
87
87
86
86
87
87
88
86
87
87
88
88
87
87
88
88
89
88
88
89
89
89
88
89
89
90
90
89
89
90
90
91
89
90
90
91
91
90
90
91
91
92
90
91
91
92
92
50
55
60
65
70
10
12.8
15.6
18.3
21.1
86
87
88
88
89
87
88
88
89
90
87
88
89
90
90
88
89
89
90
91
88
89
90
91
91
89
90
90
91
91
90
90
91
91
92
90
91
91
92
92
91
91
92
92
93
91
91
92
92
92
92
92
93
93
94
92
92
93
93
94
92
93
93
94
94
75
80
85
90
95
23.9
26.7
29.4
32.2
35
90
91
92
93
94
91
91
92
93
94
91
92
93
93
94
91
92
93
93
94
92
92
93
94
95
92
93
93
94
95
92
93
94
95
95
93
93
94
95
96
93
94
95
95
96
93
93
94
95
95
94
95
95
96
96
94
95
96
96
97
95
95
96
96
97
100
105
110
115
37.8
40.4
43
46
94
96
97
98
95
96
97
98
95
96
97
98
95
96
97
98
95
96
97
98
96
97
97
98
96
97
97
98
96
97
98
98
96
97
98
98
96
97
98
98
97
98
98
99
97
98
98
99
98
98
99
99
Liquid Temperature
O
F
O
21
Maximum Permitted LP-Gas Volume (Percent of Total Container Volume):
All Underground Containers
Specific Gravity
C
0.496
to
0.503
0.504
to
0.510
0.511
to
0.519
0.520
to
0.527
0.528
to
0.536
0.537
to
0.544
0.545
to
0.552
0.553
to
0.560
0.561
to
0.568
0.569
to
0.576
0.577
to
0.584
0.585
to
0.592
0.593
to
0.600
–50
-45
-40
-35
-30
-45.6
-42.8
-40
-37.2
-34.4
77
77
78
78
79
78
78
79
79
80
79
79
80
80
81
80
80
81
81
81
80
81
81
82
82
81
82
82
82
83
82
82
83
83
84
83
83
83
84
84
83
84
84
85
85
84
84
85
85
86
85
85
86
86
86
85
86
86
87
87
86
87
87
87
88
-25
-20
-15
-10
-5
-31.5
-28.9
-26.1
-23.3
-20.6
79
80
80
81
81
80
81
81
82
82
81
82
82
83
83
82
82
83
83
84
83
83
84
84
84
83
84
84
85
85
84
84
85
85
86
85
85
86
86
86
85
86
86
87
87
86
86
87
87
88
87
87
87
88
88
87
88
88
88
89
88
88
89
89
89
0
5
10
15
20
-17.8
-15
-12.2
-9.4
-6.7
82
82
83
84
84
83
83
84
84
85
84
84
85
85
86
84
85
85
86
86
85
85
86
86
87
85
86
86
87
88
86
87
87
88
88
87
87
88
88
89
87
88
88
89
89
88
88
89
89
90
89
89
90
90
90
89
90
90
91
91
90
90
91
91
91
25
30
35
40
45
-3.9
-1.1
1.7
4.4
7.8
85
85
86
87
87
86
86
87
87
88
86
87
87
88
89
87
87
88
88
89
87
88
88
89
90
88
89
89
90
90
89
89
90
90
91
89
90
90
91
91
90
90
91
91
92
90
91
91
92
92
91
91
92
92
93
91
92
92
93
93
92
92
93
93
94
50
55
60
65
70
10
12.8
15.6
18.3
21.1
88
89
90
90
91
89
89
90
91
91
89
90
91
91
92
90
91
91
92
93
90
91
92
92
93
91
91
92
93
93
91
92
92
93
94
92
92
93
94
94
92
93
93
94
94
93
93
94
94
95
93
94
94
95
95
94
94
95
95
96
94
95
95
96
96
75
80
85
90
95
23.9
26.7
29.4
32.2
35
92
93
94
95
96
93
93
94
95
96
93
94
95
95
96
93
94
95
95
96
94
94
95
96
97
94
95
95
96
97
94
95
96
96
97
95
95
96
97
97
95
96
96
97
98
95
96
97
97
98
96
96
97
98
98
96
97
97
98
98
97
97
98
98
99
100
105
37.8
40.4
97
98
97
98
97
98
97
98
97
98
98
98
98
98
98
99
98
99
99
99
99
99
99
99
99
99
Liquid Temperature
O
F
O
Table 9
Maximum Filling
Limit by Volume
LPG Tanks and Safety
What’s the key factor for success of a
business? Profitability, productivity, efficiency,
sales, cash flow? If we’re talking about LPG
business, the key factor, definitely is safety.
A minor leak may conclude an explosion which
will ruin a whole storage terminal, kill hundreds
of people and demolish the neighboring
buildings. The financial loss will be several
times of the value of the whole terminal.
Consider the legal compensation for deaths
and injuries and the cost will be even higher.
Any owner and operator of a LPG system is
taking the risk several million Euros; and all this
can happen within minutes.
Some real data from several LPG accidents in
the history, will show the importance of safety:
The “Mexico City Bleve” is considered among
the worst industrial disasters of 20th century.
The LPG storage terminal of PEMEX has
completely demolished within 5 hours. There
were 600 dead and 7.000 injuries. Everything
triggered by the failure of a 8” vapor line, and
the first BLEVE has occurred just within 10
minutes.
The “Feyzin Refinery Bleve” has occurred in
1966. A fire has began, involving 5 spherical
LPG tanks, with 1.200 to 2.000 m³ capacities,
and the result is 81 death, 130 injuries and
losses exceeding 125 million US dollars.
In “Viareggio Train Derailment” several LPG
22
tank wagons caught fire and the result is 32
death, 100 people left homeless and around
1.000 residents of the town were evacuated.
Looking from the safety aspect, tanks are
definitely the most important element among
the various other components of a LPG
system. Tanks are the elements which keep
highly flammable and hazardous gases “under
control”. A failure of a pump, carousel or
compressor may stop the production for some
time, and the operator will lose some money.
However, a failure of a tank means “10 minutes
to a disaster”. a tank failure means..
The tank may look “simple” but tank
manufacturing is definitely a complex business.
It requires the co-operation of several
engineering disciplines. Design, material,
welding, NDT’s, corrosion protective coating
are important topics of tank manufacturing.
Moreover, every single item and every step of
the process shall be tested, verified and these
shall be recorded to enable tracking. This is
a multiple aspect work, which requires high
technology, knowledge, experience and hard
working.
Tank Design Codes
Think of a pressurized nitrogen buffer tank.
Nitrogen is neither flammable, nor corrosive;
but a pressurized nitrogen tank may expose
serious health risks. Pressure, is a form of
stored energy and the sudden release of this
energy, as a result of vessel failure can be
destructive or fatal. Consider this pressure
is exerted by a liquefied gas, and the risk
is higher. This gas is also flammable, which
raises the risk even higher.
...era and the
invention..
The risks involving pressure vessels were
well known for more than 100 years. Since
the beginning of industrialization era, the
invention of steam machine, steam boilers
have became common. At the same time,
industrial accidents related with steam boilers
has appeared, in some cases causing deaths
of many people. The first examples of pressure
vessel design codes were prepared in those
days. Experience from several countries,
many installations and millions of different
application has distilled and forged into the
design codes; which form the basis for design,
manufacturing, operating, repairing and
maintaining pressure vessels.
Two worldwide adopted and widely accepted
design code throughout LPG industry are,
ASME Boiler and Pressure Vessels Code
(BPVC) of USA; and the Pressure Equipments
Directive (PED) of European Union. The reason
23
may be the leadership of USA in oil industry
and the leadership of Germany in chemical
industry.
ASME BPVC has organized in Sections on
different topics, e.g. Section III includes the
rules for nuclear facility components and
Section X is for fiber reinforced plastic vessels.
The whole Code is more than 16.000 pages.
Section VIII is the section which is most related
to LPG tanks.
Section VIII, Rules for Construction of Pressure
Vessels consists of three divisions. Division 1
is general rules, Division 2 is alternative rules.
Division 3, which gives alternative rules for
pressures above 10.000 psi (690 bar) is out of
our scope.
PED of Europe is a legislative framework which
is obligatory throughout the EU, covering the
equipment subject to a pressure hazard. This
directive doesn’t include as much details as
BPVC, and the “harmonized standards” takes
the role here. Some examples to harmonized
standards are AD Merkblatt of Germany,
BS5500 of UK, and CODAP of France. In fact,
these standards are older than PED and have
dominated the industry many years before the
appearance of PED.
AD Merkblatt is the most popular among those
and others still popular in their home country
and in the countries influenced by those.
There are not major differences between
the harmonized standards, since they are
conforming and harmonized to the same
framework directive. However there may be
some minor differentiation in details, between
AD Merkblatt, BS5500 and CODAP.
However, ASME BPVC and PED have different
approach. These can be considered as are two
different ways, going to the same destination.
The materials, methods, procedures and
certification of those are different for ASME
and PED. The difference in the approaches
of PED, BPVC Division 1, and BPVC Division
2 are given on Table 10 : Brief Comparison of
Design Codes.
An important regulation for tank vehicles
and vehicle mounted tanks, especially when
the vehicle will be used for transportation
inside the European Union is ADR. ADR is
the European Agreement Concerning the
International Carriage of Dangerous Goods by
Road. The recent version covers more than
1.000 pages.
It is a mandatory regulation, involving both
the technical and operational aspects of
transportation of dangerous goods. ADR’s
scope includes any type of dangerous goods,
24
ranging from nuclear wastes to cosmetic
products. ADR has some clauses relating
to the design, manufacturing, installation,
labeling, periodic maintenance and
re-qualification of LPG cylinders, vehicle
mounted tanks, ISO tank containers and
similar.
The requirements of ADR can be summarized
as follows; even the smallest part or detail, like
the installation method of a bumper, is required
to depend on an engineering design, to be
tested, approved and certified by an authority.
Brief Comparison of Design Codes
PED and European
Harmonized Standards
Wall thickness of tanks are smaller; light tanks, savings in materials
More comprehensive engineering, more detail in tests, higher cost of
engineering
Long term reliability depend on strict quality management and maintenance
ASME Division 1
Wall thickness of tanks are bigger, heavier tanks, higher cost of materials
Basic engineering, simpler tests, lower cost of engineering
Long term reliabilitiy depend on bigger safety factors
ASME Division 2
ASME’s interpretation of European approach.
Wall thickness of tanks are close to PED design; light tanks, savings in
materials
More comprehensive engineering, more detail in tests, higher cost of
engineering
Less certified manufacturer, less manufacturing experience
Table 10
Brief Comparison
of Design Codes
Certification Doesn’t Mean Same Quality
A LPG tank must be designed and
manufactured according to an applicable
design code. This is the “Step 1” of the quality
ladder. However, there can be a significant
difference in safety between two LPG tanks
designed and manufactured according to the
same design code. Let’s see how and why:
- The buyer shall pay attention to the coverage
and details of the certificate. The paperwork of
“full certification” may be quite similar in look to
“certification of surveillance to hydrostatic test”.
ten thousands of
- A design code, and the other codes,
pages of information.
standards and regulations it refers makes
ten thousands of pages information. Google
the technical forums on the web, and you’ll
see thousands of topics on design codes,
where engineers discussing “how to interpret
the Clause X of the code”. Here “specific
experience” matters.
- The information given in the design code
is open to anybody who buys and reads it.
Recent technological developments and
innovations, patented technologies and
processes, and similar information which pave
the road to the “excellence” don’t take place in
design codes.
- Design codes rather determine the “minimum
requirements for safety” than the “requirements
for highest quality”. The features which create
better safety, higher quality are above than the
code requirements.
25
Pressure Vessel Steels
European Standard “EN 10028-3 : Flat
products made of steels for pressure
purposes. Weldable fine grain steels,
normalized” covers a range of weldable,
fine grain steels supplied in the normalized
condition and intended for pressure purposes.
This is a very common pressure vessel material
when the vessel design and manufacturing
is made according to Pressure Equipment
Directive and harmonized European
Standards.
It has three steel grades; P275, P355, and
P460 which indicate each grade’s minimum
yield strength in MPa (for plates 16 mm thick
and below).
These are further subdivided on the basis of
impact testing (transverse) temperature:
N and NH indicate impact testing at -20° C or
above,
26
NL1 at -40° C or above, and
NL2 at -50° C or above.
Plates to EN 10028-3 are widely specified
in the manufacturing of pressure vessels
throughout Europe and the standard is
regularly seen in other parts of the world where
equipment has been originally designed by a
European company.
The designation EN 10028-3
P355NL1
shows that
P
: This is a grade of steel for pressure purposes
355 : Minimum yield strength is 355 MPa
NL1 : Impact tested in the transverse direction at -40° C
The designation EN 10028-3
P460N
shows that
P
: This is a grade of steel for pressure purposes
460 : Minimum yield strength is 460 MPa
N
: Impact tested in the transverse direction at -20° C
27
Chemical Composition of Steels According to EN 10028-3
hizalama
Table 11
Chemical
Composition of
Steels According
to EN 10028-3
28
US standard “ASTM A516 : Standard
Specification for Pressure Vessel Plates,
Carbon Steel, for Moderate- and LowerTemperature Service” covers carbon steel
plates intended primarily for service in welded
pressure vessels, where improved notch
toughness is important. This also is a very
common pressure vessel material when the
design and manufacturing is made according
to ASME Boiler and Pressure Vessel Code.
Chemical Composition of Steels According to ASTM/ASME
According to different strength levels, the
plates are available in four grades; Grade
55, 60, 65, and 70. The steel shall be killed
and shall conform to fine austenitic grain size
requirements. The mechanical properties
such as tensile strength, yield strength, and
elongation shall be determined by a tension
test for the plates.
köşelerdeki yeşil
noktalar
Table 12
Chemical
Composition of
ASTM/ASME
A516 Steels
29
Mechanical Properties of Steels According to ASTM/ASME A516
Table 13
Mechanical
Properties of
ASTM/ASME
A516 Steels
Periodic Inspection for LPG Tanks
30
Isısan recommends the following periodical
inspection for LPG storage tanks. However
local codes, regulations and standards may
require further tests and controls, or more
frequent checks.
Isısan recommends to have LPG tanks
re-qualified by a notified body, following the
test procedure given by this notified body and
hiring NDT services when necessary, every
10 years.
Period
Recommended Inspection, Test and Controls
1 year
•
•
•
•
•
•
External visual inspection
Leak test of flanged and screwed connections
Check temperature, pressure and level gauges are operating
Check excess flow valves, emergency shut off valves and similar are operating
Check cathodic protection is functional, for underground storage tanks.
Possible leaks, malfunctioning equipment, paint defects shall be fixed 5 years
•
•
Testing safety relief valves
Check start to discharge pressure and tight closure of valve when pressure is
released. Check for visual corrosion and defects on valve body and internals.
Safety relief valves shall be renewed when necessary
10 years
•
Re-qualification by a notified body, following their advices and hiring NDT
services when necessary.
The following inspection and tests are must, further shall be determined by the notified body according to the test results and operating conditions:
Internal visual inspection
Corrosion mapping by measuring plate thickness (ultrasonic measurement)
Hydrostatic pressure test at 1.3 times of design pressure
•
•
•
Codes and Standards for LPG Installations
NFPA 58, Liquefied Petroleum Gas Code,
prepared and published by National
Fire Protection Association of USA is a
well respected and worldwide accepted
guideline for LPG industry. This is a code,
not a standard and the diffence is, a code is
adopted by governmental bodies and enforced
by law. This is a comprehensive and useful
guide, which will answer most questions.
NFPA 58 also formed a base on many local
standards. However, the rules defined by
local authorities, -local codes, regulations and
standards- may differ from NFPA 58. In this
case, the owner shall consider to conform the
strictest rule, which will be the safe choice.
aynı şeyi yukarıda da yazmışım.
The difference between a code and a
standard is; code is adopted by one or more
governmental bodies and enforced by law.
A list of codes, standards and regulations
which may be helpful to LPG engineers are
given as follows.
ASME Boiler and Pressure Vessel Code
AD 2000 Code
ADR European Agreement concerning the International Carriage of Dangerous Goods by Road
EEMUA 190 Guide for the Design, Construction and Use of Mounded Horizontal Cylindrical Steel
Vessels for Pressurized Storage of LPG at Ambient Temperatures
API 2510 Design and Construction of LPG Installations
API 2510A Fire-Protection Considerations for the Design and Operation of Liquefied Petroleum
Gas (LPG) Storage Facilities
Model Code of Safe Practice Part 9: Liquefied Petroleum Gas.
Vol.1. Large bulk pressure storage and refrigerated LPG; by Energy Institute of UK
Codes of Practice(s) published by UK LPG
EN 12493 LPG equipment and accessories - Welded steel tanks for liquefied petroleum gas
(LPG) - Road tankers design and manufacture
EN 12252 LPG equipment and accessories - Equipping of LPG road tankers; German version EN
12252
... LPG road tankers.
EN 1442 Transportable refillable welded steel cylinders for LPG - Design and construction
EN 1440 Periodic inspection of transportable refillable LPG cylinders
EN 14678-1, 2 and 3 LPG automotive filling stations
31
LPG Tank Accessories
Table 14 :
The mandatory tank accessories determined
by the recent version of NFPA 58, published
in 2011, are given on Table 11 : Tank
Appurtenances According to NFPA 58.
One can easily see that the simpler forms
of safety equipment are for the smallest
tank (lower risk), and vapor connections
(less amount of leak, lower risk). The basic
approach is to establish more than one,
independent, reliable means of shutoff. There
are several options in the market, which
have certain strength and weaknesses when
compared with the other.
First of all, the design engineer must always
keep in mind that, only a manual shut-off valve
can offer a “positive shutoff”. Excess flow
valves, back flow check valves and internal
valves are very helpful safety equipment, but
may not offer complete sealing. In any case,
a manual shutoff valve must be installed in
series to these equipment.
It is inevitable to do some repairs or
maintenance on a LPG system, while isolating
this part from where there’s LPG. In this
case, there must be at least two means of
separation equipment in series; and preferably
one of those must be a blind flange or similar.
There are many instances that a valve seal,
which seem perfect before beginning the
there's yerine
contains
32
for the small tanks and vapor
connections; where the amount of
possible leak, therefore the risk is small
repair works, has failed during these works
and resulted a fire. The reason which leads
this failure may be an increase of temperature,
or pressure, or mechanical shocks during the
repair, welding, hydrostatic test works. When
not possible, the safest option, complete
decanting and gas-freeing shall be preferred.
Restricted orifice is the simplest and cheapest
form of safety precaution; among those
referred in “Table 14 : Tank Appurtenances
According to NFPA 58”. It is definitely fail-safe.
However, its application is only limited to small
LPG flows.
An excess flow valve is a purely mechanical
device. It shuts off automatically when the
gas flow exceeds a certain rate. When a LPG
line has ruptures or breaks off, there’ll be a
sudden increase of flow. Excess flow valves
enables flow in both direction, but controls
the flow just in one direction. However they
cannot offer a perfect sealing; there’s always
a small leak from an already shut off” excess
flow valve. Several sizes and models of excess
flow valves are available; which are designed
for installation inside the tank, onto the tank
nozzles and onto the pipe lines.
A backflow check valve, also a purely
mechanical device, allows flow in only
one direction. This can be used at inlet
connections of LPG tanks, which will prevent
any flow from the tank to outside. They
offer better sealing than excess flow valves,
especially the double check models. It is
allowed to use double check valves as a filler
valve for small LPG tanks. These incorporate
both a metal-to-metal seat check and a soft
seat check; combining the advantages of both.
Restricted... yeni
paragraf olarak
başlasın.
increase of flow,
which will trigger the
closure of excess
flow valve.
"already shut off"
veya tırnak işaretini
tümden kaldıralım.
Designers must
consider that excess
flow valves cannot
offer ...
33
Table 14
Tank Appurtenances
According to NFPA 58
34
Excess flow valves and check valves for LPG
tank service are designed so that, external
damages will not hamper their function. The
valve either completely remains inside the tank;
or has weakened shear points. An external
force will cause the valve to shear from this
point, keeping the critical sealing parts in place.
Emergency shut-off valves are remote
actuated shut-off valves which can be installed
onto a piping. These may be actuated via
cables, hydraulic or pneumatic operation;
and can be connected to a control system.
Emergency shut-off valves may be connected
to the fire alarm system, or gas leak detection
system for automatic closure.
Internal valves are equipment which “almost
completely” remain inside the tank when
Manual valves also have different models,
fitted. By this way, the valve is protected
any of which offers certain advantages on
from any type of external force, blast, fire, or
the others. Quarter turn ball valves offer good
similar. Internal valves may offer automatic
performance in most conditions. They have
closure function in cases of excess flow,
very small resistance to flow, therefore the best
fire or remote operation. These may be
choice for pump inlet lines. There are fire-safe
operated mechanically via cables, hydraulic
models of ball valves, which are designed to
or pneumatic actuators. Internal valves may
offer sealing under fire; which is an important
also function as an integral part of a control
safety feature. Fire safe valves have additional
system. For example, the internal valves on a
metal-to-metal seats which function when the
LPG tanker truck can be set to automatically
soft seals are destroyed by fire.
close when the parking brake is released. For
A fire safe valve has
example, internal valves may be connected to
additional..
a fire detection system, or gas leak detection
An other example is...
system for automatic closure.
Internal valves are robust equipment, but
eventually will need some repair. This can only
be done after the tank is completely decanted.
An other disadvantage is, they often require
modified flanges/coupling for installation;
which means an internal valve may not fit on
an existing LPG tank.
Safety Relief Valves for LPG
Safety relief valves are essential safety equipment
for LPG installations. Any closed system
containing liquid LPG is prone to the risk of high
pressures. Heat transfer from the surrounding
will increase the pressure to such levels that the
equipment will fail, releasing highly flammable
vapors to the environment. Safety relief valve is an
effective, controlled means of relieving dangerous
pressure and preventing BLEVE.
35
Pressure relief valves are also mandatory for
underground and mounded tanks, however the
relief capacity shall be 30% of an above ground
tank.
Safety relief valves must be “spring loaded”,
however pilot operated models with a springloaded pilot are allowed for tanks with > 151 m³
capacity. The safety relief valves suitable for LPG
service are pop-action, or full-lift types, which
means that the valve opens fully at once, not
gradually or proportional to the rate of pressure
increase.
The “start to leak” setting of the pressure relief
valve shall be 100% of the container pressure
BLEVE is the abbreviation of “Boiling Vapor
Expanding Liquid Explosion”. This is the most
dangerous fire accident which may happen to
a LPG tank. The fire in contact with the tank
makes the liquid to boil, increasing the pressure
and at the same time heating up the tank shell.
Increasing temperature weakens the tank shell,
and the failure of the tank results the whole
contents to release to the environment, a massive
explosive gas cloud and a heavy explosion.
The safety relief valves of a LPG storage tank
shall be sized and selected considering the fire
conditions. An empirical formula, which is based
on some experimental data in the past, which is
used for sizing safety relief valves is as follows :
F = 53,632 x A0,82
Where:
F = Discharge flow rate (SCFM air)
A = Total outside surface area of the container (ft²)
Figure 5
BLEVE
36
rating. The manufacturer of the relief valve has a
“plus” tolerance, not exceeding 10% of this set
pressure, marked on the valve.
Safety relief valves must be so installed that
to relieve vapors. No block valves are allowed
at installation, except the specially made SRV
manifolds, which prevents blocking of all SRV’s.
A common industrial practice, even further
the code requirements, is to have some extra,
backup relieving capacity. Depending on the size
of tank, the tank is preferably equipped with:
2 safety relief valves, one of which is spare (100% backup)
3 or 4 safety relief valves, one of which is spare (50% or 33% backup,
accordingly)
The outlets of SRV’s shall piped vertically upward
for tanks > 7,6 m³. Rain caps and/or drain holes
must be considered to protect the SRV against
accumulating water. For underground storage
tanks, the height of this piping shall be min. 2,1
meters (7 feets). Anything which will limit the
discharge, are not allowed on this pipe, e.g.
bends, obstructions, tight caps, etc.
Safety relief valves shall be checked and tested
every 5 years; and shall be replaced at 10 years
intervals. During inspection, the valve shall be
checked visually against defects and corrosion,
then the valve shall be connected to a suitable
test bench, including a calibrated pressure gauge.
At the test bench some pressure will gradually
applied to the valve to determine the “start to
leak” pressure. The “start to leak” pressure shall
be within 100% to 110% of the pressure valve
rating; and the SRV will close again, with no leak
after the pressure is released.
Every piece of piping or hose, in which liquid LPG
may be trapped between two isolation valves
shall be equipped with a hydrostatic relief valve.
Even looks similar, hydrostatic relief valves are
different types, which are suitable to discharge
liquid LPG.
LPG Level Gauges
37
Overfilling is an important risk for LPG tanks;
therefore LPG tanks shall be equipped with more
than one level gauge.
The mechanical movement of the internal
parts are conveyed to the outer part by using a
magnetic piece.
Fixed liquid level gauge, which is not more than
a bleeder valve/internal piping combination
is simplest and most reliable form of level
checking. It can be installed on above ground or
underground tanks, even applicable to smallest
sizes. A combination of fixed liquid level gauges
can be installed to check several levels.
The float follows the changes in liquid level and
this movement mechanically conveyed to the dial,
which shows the level as % full. Advantages of
float gauge are:
- Requires no source of energy
- Can be used on both underground and above
ground tanks. Can be installed at the centre or on
the top of the tank
A rotary level gauge is also a simple and reliable
mechanical device; consisting of a rotary hollow
tube dipping inside the tank, a bleeder valve
connected on the other end of this tube outside
- Doesn’t require operator access
the tank, and a dial to see the measured level.
The dial is prepared to show % full of the tank.
- Can be incorporated with a level transmitter,
The operator loosens the bleeder valve then
enabling remote reading or the level signal can be
slowly rotates the handle, while the end of tube
further processed as an input to a control system.
inside the tank moves from top of tank, slowly
There are several types of electronic level
to the bottom. While rotating the handle, the There are'dan
operator checks the level at which vapor flow itibaren yeni paragraf
replaces to liquid.
Rotary level gauges can be installed only on
above ground tanks. They’ll need a platform,
ladder or similar to enable operator access.
Magnetic float gauges or simply float gauges
consist of two pieces. The float-arm assembly
which works inside the tank and the dial
assembly which remains outside the tank.
Magnetic.. yeni
paragraf
gauges for LPG installations; but LPG is a hard
application. Low cost types don’t work properly
with LPG, and the models suitable for LPG
application are generally more expensive. This
makes electronic level gauges feasible for big size
tanks or specific applications.
For tanks up to 10 m³ there are filler valves
offering automatic over fill protection, with a float
operated mechanism. This can be done for
bigger sizes, using an electric signal, an actuated
valve and the control system. A pneumatic
actuated ball valve works fine for this application.
The level signal can be taken from the float
gauge, however it’s a better approach to use
a separate level detector for overfill protection.
Vibrating fork type level detectors offer a good
performance/cost ratio for overfill protection
applications.
a control circuit
Figure 6
Fixed Level (left) and
Rotary Level (right)
Gauges
LPG Pumps
38
Pumps are essential elements of LPG systems,
for liquid transfer in various applications. The main
challenge is; LPG is a fluid on saturated state.
This means, a slight difference of temperature,
a slight pressure drop, or a slight resistance to
flow will cause the liquid to evaporate rapidly.
flow rate combinations. The performance curve
of a centrifugal pump is such that, it can produce
higher pressure at low flow, and can handle
higher flow rates at low differential pressures.
When the pump rpm is increased, both the flow
rate and the outlet pressure increases.
Principally, pumps can only handle liquids and
not vapors. The most important feature of LPG
pumps is to handle some vapor when mixed with
liquid. It is essential for pump operation and can
be achieved by some special features.
There are several models of LPG pumps, but
mainly divided into two groups.
Cylinder filling or autogas dispensing operations
require very high differential pressure. The tank
being filled is so small, and the filling time should
be limited. Moreover, the flow must be forced
through narrow openings inside the cylinder
valve. The inside cross section of the multivalve
on an autogas tank is not much bigger. The
best option to fulfill this requirements is the multi
stage centrifugal pump. A variant of this model
is the side channel pump with open, radial
blade impellers which can handle some vapor
with liquid and called as “self priming”. These
pumps often have a centrifugal first stage, in
order to reduce NPSH (net positive suction head)
requirement.
Positive displacement pumps, in which the
liquid is encapsulated in a volume and forced to
move with the movement of this volume. These
may be reciprocating (piston), or rotary (vane or
gear pumps). In positive displacement pumps,
the outlet pressure and flow rate remains nearly
constant, independent of the inlet and outlet
conditions. When the pump rpm is increased, the
outlet pressure doesn’t change but the flow rate
increases.
Dynamic pumps are machines in which the
liquid gains a speed (kinetic energy), then this
is converted to pressure (potential energy). In
dynamic pumps, the outlet pressure and flow
rate depends on the inlet and outlet conditions.
Same pump can operate at different pressure/
Regenerative turbine pumps, which are also a
member of centrifugal pumps range, can achieve
such high differential pressures in a single stage
design. They have a single impeller, with open
radial blades. These models can be preferred for
small scale cylinder filling applications, autogas
dispensing and vaporizer feeding.
Gear pumps are used in some truck mounted
applications for bulk transfer; but are not
common.
The most common truck pumps are of rotary
vane design. These offer the high flow rate,
compact design, low to moderate pressure
and low rpm (since driven by the truck engine,
running at idle speed) advantages to bulk delivery
application. The physical contact of rotating parts
inside these pumps create some wear, however
these parts have a quite long service life and can
be replaced at reasonable cost.
Although not common, LPG tanks are installed
on the roofs of high rise buildings (higher than
100 m.) in some countries. In this case, a pump
with higher differential pressure is required for bulk
deliveries. Multistage, side channel pumps are the
solution for these applications.
these requirements
39
Net positive suction head-required (NPSHR) is the
minimum inlet pressure required at the pump inlet
to avoid cavitation. Net positive suction headavailable (NPSHA) by the system must be greater
than the required, for efficient pump operation.
In order to achieve this, the pressure drop at
the inlet piping of the pump must be kept to
minimum; by following these guidelines:
- the inlet piping shall be kept as short as possible
- bends and reducers shall be avoided
inlet strainer
- stainer shall be one or two size bigger
- full bore ball valves shall be preferred
- the inlet line shall be so designed that the flow
velocity is under 1 m/s
Figure 7
Operating Principle
of Regenerative
Turbine Pumps
LPG Compressors
40
Compressors are machines which transfer gases
and vapors, however liquefied gases may also
be transferred by using a compressor. Cavitation
is a big problem in pump operation; and in
some liquid transfer applications, the pump
inlet conditions may be too poor for an efficient
operation. In such cases, using a compressor
may be more efficient for liquid transfer.
An other advantage of compressor over pump
is, the ability to transfer vapors. This is a must
while gas freeing a tank before any repair. The
vapors in the tank may not simply vent into the
atmosphere, but must be transferred into an
vented
other storage tank.
In such trading applications where the buyer
already pays for the that the Compressor is
by far the best choice while evacuating a LPG
transportation tank after a road accident; and
transferring the liquid and vapors into a safe tank,
during haz-mat operations.
In evacuating transport tanks, using a
compressor is more efficient than using a pump,
and is generally the preferred method. During this
process, the liquid level continuously drops and
cavitation begins below a certain level. However,
the compressor may easily transfer all liquid, after
that even the product in vapor phase. Vapor
recovery takes a long time, and isn’t feasible
unless there is a financial loss.
Figure 8
Liquid Transfer by
Using a Compressor
How liquid is transferred by using a compressor
is shown on “Figure 10 : Liquid Transfer by Using
a Compressor”. Please note, that the direction of
flow for liquid is, reverse of the direction of flow for
vapor. The compressor reduces the pressure of
the tank being filled, and increases the one being
evacuated; thus creating a pressure differential
between two tanks. This pressure differential
drives the liquid flow.
How vapor recovery is made, is shown on “Figure
11 : Vapor Recovery.” The four way valve, back
flow check valve and isolation valves on the
piping enables quick swift from liquid transfer
to vapor recovery. As shown on the figure, the
vapors are introduced into the liquid phase of
the tank. The compression process adds some
heat to the compressed gas, which is useful
during liquid transfer. However, cooling the vapor
is necessary during vapor recovery, otherwise
the tank pressure will increase too high. The hot
vapor cools down while passing through the
liquid.
In case of using a
pump for this process
Figure 9
Vapor Recovery
LPG Vaporizers
LPG is stored in liquid state, and needs to be
evaporated before use. Evaporation either
occurs naturally, by absorbing heat from the
surroundings, or heat should be applied to LPG.
Natural vaporization, which depends on the heat
taken from the surrounding environment may
work for domestic applications and in moderate
climates. Applications with high gas demand,
and installations at cold environment will require
vaporizers.
Vaporizers are classified according to the medium
which gives heat energy.
Direct fired vaporizers burn LPG directly to
obtain heat. They’ve high performance/cost ratio
and compact, ready to use equipment. They
don’t need electricity, therefore applicable for
site, temporary or portable applications where
electricity is not available.
Electric operated models are generally used
for 25 to 300 kgs/hour LPG capacity. They’re
compact, safe and generally preferred for
domestic, commercial and light industrial
applications.
For higher demands; there are hot water or steam
operated models. These require an external
generator of steam or hot water, therefore either a
separate boiler shall be installed or the vaporizer
shall be connected to an existing boiler. These
41
models are cost effective when there’s some
extra boiler capacity.
In general, small scale installations rely on a single
vaporizer; however in most cases two vaporizers
are installed in parallel. In this case, one of the
vaporizers will have enough capacity to feed
the whole system and the other will serve as a
backup.
Different combinations with 3 or 4 vaporizers in
parallel, one of which is serving as backup, are
also possible.
LPG Regulators
Regulators are the essential equipment for bulk
installations, which reduces the gas pressure
and maintains a constant level of pressure for
proper operation of boilers, burners, stoves
and similar gas consuming appliances.
Typically a gas stove or burner requires a
gas pressure of 11 in. water column; which
is nearly equal to 300 mm. water column or
30 milibars. The regulator should maintain
this pressure regardless of the changes in
gas flow rate; whether a small pilot or several
appliances are operative. It must also protect
the appliances from excessive pressure,
especially when a faulty condition exists.
Regulator selection for a specific application
needs to analyze
42
only perform well under right conditions.
A drop of inlet pressure will seriously decrease
a regulator’s capacity.
Although single regulator may be used to
reduce container pressure directly to the
pressure which appliance needs; two stage
regulation has many advantages.
In two stage regulation; first stage regulator
is mounted on the storage tank. For high
capacity applications, first stage regulator
will be installed at vaporizer outlet. The outlet
pressure for first stage regulators may be up to
2 bar, but typically this value is 10 psi, which
equals to 700 mbar. Then the pressure is
reduced down to 30 mbar at the second stage
regulator. Several advantages of two stage
regulation are:
-since the outlet pressure of first stage
regulator is high, the pressure can compensate
pressure losses in pipe; therefore small pipe
sizes may be used.
- second stage regulator is closer to the
appliance, and pressure losses in second
stage piping don’t disturb the performance of
appliances.
- more uniform appliance pressure is obtained
- when high pressure gas expands to a lower
pressure, a chilling effect occurs inside the
- inlet pressure and variations due to climatic
changes, etc.
- outlet pressure demand,
- expected gas flow
- pressure losses in piping between the
regulator and the appliance
Figure 12 : Regulator Performance Diagram
shows the effects of inlet pressure and gas
flow to regulator performance. A regulator may
Figure 10
Regulator
Performance
Diagram
43
regulators. In case moisture is present in
the LPG; this chilling effect may cause the
regulator to freeze-up and be clogged. Since
pressure difference is not so high as in single
stage regulation, two stage regulation greatly
reduces the risk of freeze-ups.
- in general, capacity range of first stage
regulators are very wide. They allow to handle
capacity increases simply adding second stage
regulators.
An important, additional feature of the regulator
is, to prevent excess pressure in the low pressure
side. A relief valve is integrated in the regulators,
which, in such case, relieves the excess pressure
from the vent hole.
Regulators have adjusting screws and/or different
spring alternatives which allow to adjust the
outlet pressures within a range, to satisfy different
requirements.
- second stage regulator is closer to the
appliance, and pressure losses in second
stage piping don’t disturb the performance of
appliances.
- more uniform appliance pressure is obtained
- when high pressure gas expands to a lower
pressure, a chilling effect occurs inside the
regulators. In case moisture is present in the
LPG; this chilling effect may cause the regulator
to freeze-up and be clogged. Since pressure
difference is not so high like single stage
regulation, two stage regulation greatly reduces
the risk of freeze-ups.
- in general, capacity range of first stage
regulators are very wide. They allow to handle
capacity increases simply adding second stage
regulators.
bu bölüm yukarının
tekrarı olmuş.
Figure 11
Two stage
regulation
Vapour Condensing in LPG Piping
44
In general, 5 to 15 psi ( 350 mbar to 1 bar) is the
normal range of pressure setting for the first stage
regulators. The second stage regulators will offer
greater capacity when higher first stage pressures
are selected. However; if the intermediate
pressure is high enough, the gas may condense
in the piping, especially when the temperature
is low. Butane, or butane rich mixtures are more
prone to condensation and such risk begins for
propane at temperatures below -25 oC.
Vapour condensation will create safety and
operational issues, and therefore shall be
avoided. Selecting a first stage outlet pressure
below the values given on Table 15 : Dew Point
Pressures for LPG Mixtures, will overcome the
vapor condensation problem.
Table 15
Dew Point Pressures
for LPG Mixtures
Installation of LPG Storage Tanks
Safety Separation Distances
LPG tanks shall be fixed on concrete
foundations. The dimensions of concrete
columns shall fit to the size of tank. The
foundation design shall be made by a qualified
civil engineer, considering both the normal
operating conditions, and the extra weight
during hydrostatic testing of the tank. The
weight of tank accessories, ladders, platforms,
valves, instrumentation and piping; snow and
wind loads shall be taken into account.
In underground tank applications, the
customer shall prepare the tank basin and tank
foundation. The size of the basin shall fit to the
size of tank. The concrete foundation design
shall be made by a qualified civil engineer,
considering normal operating conditions; and
the anchorage to prevent floating. Since LPG
is less dense than water, heavy rains may
cause floating of the tank. The tank foundation
must be heavy and the anchorages must be
strong enough to prevent floating. The tank
basin may be surrounded by a concrete wall.
In this case, necessary openings shall be
made to ensure drainage of the tank basin.
The location and installation of LPG storage
tanks shall conform to local regulations
and standards. LPG storage tanks must be
separated from potential sources of fire, or
important buildings and structures which will
be protected against fire. The minimum safety
45
separation distances, according to NFPA 58
are given on “Table 16 : Safety Separation
Distances for LPG Tanks”.
3. The line of adjoining property
4. Main roads
5. Adjacent LPG storage tanks
The user must also conform to the local
regulations and standards.
LPG storage tanks shall be installed outdoors.
Tanks shall not be stacked one above another.
For above ground tanks, safety separation
distances are measured from the tank shell.
For underground tanks, the safety separation
distances are measured from any potential
point of LPG discharge; like safety relief valve,
LPG filling connection, and/or liquid relieving
type level indicators.
The recent version implies to
The safety separation distance between the
LPG storage tank and the following shall be
at least the figures given on “Table 16 : Safety
Separation Distances for LPG Tanks”:
The earlier versions
of NFPA 58 were
1. An important building
implying to measure
2. Group of buildings
safety separation
distances for
underground tanks
measure from the tank shell,
also for underground and
mounded tanks
Table 16
Safety Separation
Distances for
LPG Tanks
46
The distance from any part of an underground
tank to any building or the line of an adjoining
property shall be at least 3 m.
There should be minimum 3 m. distance
between the LPG tank and a potential source
of ignition, any opening to the buildings, and
openings to direct-vent appliances, mechanical
air intakes, sewer and drainage channels.
Electric devices shall be considered as a
potential source of ignition.
Loose or piled combustible material, such as
weed or long, dry grass shall be separated
3 m. from the tank. To ensure it, rounded
pebbles may be laid along the surrounding of
tank.
The horizontal distance between LPG tanks
above the ground and tanks that contain
liquids with a flash point lower than 90°C,
should be at least 6 m.
No part of any tank above the ground
should ever be located on a site that would
be horizontally 2 m away from an energy
transmission line with nominal voltage between
0,6 – 10,5 kW; and 7,5 m away from one with
nominal voltage greater than 10,5 kW, from all
directions.
Multiple underground tanks with a capacity of
1 m³ or higher, should be located such that
cranes and similar machines can easily access
their ends and edges.
For a single above ground tank, with less than
5 m³ water capacity; the safety separation
distance could be reduced up to 3 m. In order
to consider this as a single tank, its distance
from any tank with a capacity greater than 1
m³, should be at least 7,5 m.
In applying the distance between buildings
and LPG tanks of 125-gal (0,5-m³ or more
water capacity, a minimum of 50 percent of
this horizontal distance shall also apply to all
portions of the building that project more than
5 ft (1,5 m) from the building wall and that are
higher than the relief valve discharge outlet.
This horizontal distance shall be measured
from a point determined by projecting the
outside edge of such overhanging structure
vertically downward to grade or other level
upon which the container is installed. This
is not applicable to installations in which
overhanging structure is 15 m or more above
the relief valve discharge outlet.
Neighboring storage of other flammable or
hazardous materials, will result an increased
risk. Refer to regulations and standards, or
make a risk analysis in such cases.
The above ground tanks shall be grounded
and the performance of grounding shall be
checked annually. The resistance of the
grounding circuit (system to ground) shall be
less than 5 Ohm.
Cathodic Protection for Underground LPG Tanks
Cathodic protection is compulsory for
underground tanks. Otherwise, any possible
scratches or small defects of paint may cause
severe corrosion. Several methods for cathodic
protection are applicable, however most common
is the method of galvanic anode. The application
of cathode protection should be done as follows:
47
The performance of cathodic protection system
shall be checked annually. The potential
difference between the reference electrode, the
tank itself, every single anode, and the complete
system shall be measured and evaluated,
according to Table 17 : Performance Checking of
Cathodic Protection Systems.
cathodic
• The appropriate size and number of anodes are
determined according to the tank size and soil
conditions.
• The anodes shall be placed vertically at the
center-line of the tank, roughly 1,5 meter away
from the tank shell, and evenly distributed around
the tank.
Measurement
• The connecting cable should not be used for
the purpose of dangling the anode bag into the
hole.
• Each anode bag shall be soaked with 20-25 lt.
of water.
Nominal Value
Comments / Troubleshooting
-600 mV < Vref < -350 mV
Vref > -350 mV : Paint Defect
Vref < -600 mV : Measurement Error
Tank Connected to
Anodes
-1100 mV < Vref < -650 mV
Vref > -650 mV : Replace Worn-out
Anodes
Vref < -1100 mV : Disconnect
Excessive Anodes
Every Single Anode
-1600 mV < Vref < --1400 mV : perfect
-1400 mV < Vref < --1200 mV : OK
Vref > -1200 mV : Replace Worn-Out
Anodes
Tank Itself
• The excess of anode cables should not be cut
out, but kept as is and buried in the ground.
• The cable connection lug(s) on the vessel shall
be cleaned & grinded for good electric contact,
and the cable terminals shall be connected to
these lugs. After then, the connections shall be
isolated.
• The tank basin then filled by salt free, washed
and sieved sand.
Table 17
Performance Checking
of Cathodic Protection
Systems