EPA-450/2-78-047 

OAQPS NO..1.2-1 16 

Control of Volatile Organic 

Emissions from Petroleum Liquid 

Storage in External Floating 

Roof Tanks 

Emission Standards and Engineering Division 

. . 

U.S.'ENVIRONMENTAL PROTECTION AGENCY 

Office of Air, Noise, and Radiation 

Office of Air Quality Planning and Standards 

Research Triangle Park, North Carolina 2771 1 

December 1978 
OAQPS GUIDELINE SERIES 

Y 

The guideline series of reports is being issued by the Office of Air Quality Planning and Standards (OAQPS) to 

provide information to state and local air pollution control agencies; for example. to provide guidance on the 

acquisition and processing of air quality data and on the planning and analysis requisite for the maintenance of 

air quality. Reports published in this series will be available -as supplies permit -from the Library Services Off~ce 

(MD35).U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 277 1 I; or, fora nomrnal 

fee, from the National Technical Information Service, 5285 Port Royal Road, Springfield, Virginia 22 161. 

Publication No. EPA-45012-78-047 

OAQPS NO. 1.2-116 
Chapter 7.0 

1.1 

Chapter 2.0 

2.1 

2.2 

2.3 

Chapter 3.0 

. 3.1 

3.2 

3.3 

Chapter 4.0 

4.1 

TABLE OF CONTENTS 

Page 

Introduction ............ 1-1 


Need to Regulate ........... 1-1 


Sources and Types of Emissions ..... 2-1 


External Floating Roof Tanks . 2-1 


Primary Seals . ? . 2-3 


2.2.1 Mechanical Shoe Seal . 2-4 


2.2.2 Resilient Foam Seal ....... 2-4 


2.2.3 Liqufd-FilledSeal . 2-6 


References ............ 2-7 


Control Techno1 ogy .......... 3-1 
 w 

Rim-Mounted Secondary Seal . 3-1 


Wind Induced Emissions ....... i 3-3 


3.2.1 Shoe Seals on Welded Tanks ..... 3-3 


3.2.2 Liqufd-Mounted Resilient Foam and 

LiquSd-Filled Seals on Welded Tanks . . 3-5 


3.2.3 Vapor-Mounted Resilient Foam Seal on 

Welded Tank .......... 3-5 


3.2.4 Riveted Tanks ......... 3-7 


References ............. 3-10 


Cost Analysis ............ 4-1 


Introduction ............ 4-1 


4.1.1 Purpose ........... 4-1 


4.1.2 Scope ............ 4.1 

4.1.3 Use o f Model Storage Tanks . 4-1 


iii 
Chapter 

4.2 

4.3 

4.4 

4.5 

Chapter 5.0 

5.1 

5.2 

5.3 

Appendix A 

Appendix B 

Page 

4.1.4 Bases for Capital and Annualized . . . 4-5 Page 

Control of Emissions from External Floating 

Roof Tanks . . . . . . . . . . . . . 4-6 

4.2.1 Model Cost Parameters . . . . . . . 4-6 

4.2.2 Control Costs . . . . . . . . . 4-6 

Cost Effectiveness . . . . . . . . . 4-8 

Economics of Scale . . . . . . . . . . 4-13 

References . . . . . . . . . . . 4-15 . - 

Recommended Regulations, Compliance Test 

Method and Record Keeping . . . . . . . . 5-1 

Recommended Regulations . . . . . . . . 5- 1 

Compliance Test Method . . . . . . . . . 5-3 

Monitoring and Record Keeping . . . . . . . 5-3 

Selection of Experimental Tests for Wind 

Induced Emission Calculations . . . . . . . A-1 

A. Methodology of Selection . . . . . . . A-1 

B. Selection of Welded Tank with Shoe Seal and 

Rim-Mounted Secondary Seal . . . . . A-2 

C. Welded ,Tank with Shoe Seal and ShoeMounted Secondary Seal . . . . . . . A-3 

D. Riveted Tank with a Shoe Seal and RimMounted Secondary . . . . . . . . . A-3 

E. Resilient ~oam ~eai Mounted in Rim Vapor 

Space of Welded Tank . . . . . . . . A-6 

References . . . . . . . . . . . . . A-8 * 

Calculation of Wind Induced Emissions from 

Experimental Tests . . . . . . . . . B-1 YI 

A. Equation for Wind Induced Emissions . . . B-1 

B. EpforTestTank . . . . . . . . . B-1 
Page 

Appendix C. Emission Calculations . B-3 


C.l Primary Seal With and Without RimMounted Secondary ........ B-3 


C.2 Shoe Seal with Shoe-Mounted Secondary . 8-3 


References .............. B-6 

0 

LIST OF TABLES 

Page 

Table 4-1 Technical Parameters Used in Developing 

Gasoline Storage Tank Control Costs .... 

Table 4-2 Cost Parameters Used in Computing Control 

Costs. ............. 


Table 4-3 Control Cost Estimates for Model Existing 

Gasoline Storage Tank ........ 


Table 4-4 Cost Effectiveness of Control 1 ing Floating Roof Storage Tanks .......... 4-10 


Table 4-5 Factor for Estimating the Cost Effectiveness 

of Controlling Crude Oil Storage Tanks ... 4-12 

~p~eidix A 

Table A-1 Seal Gap Area in Inspected Welded Tanks with 

Shoe Seal Compared to CBI Experimental Tests . A-4 

A-2 Seal 

Shoe 

Gap 

Seals 

Area 

Compared 

in Inspected 

to CBI 

Riveted 

Experimental 

Tanks 

Tests 

with . A-5 a

A-3 Seal Gap Area in Inspected Welded Tank with 

Non-Metallic Seals Compared to CBI 

Experimental Tests .......... A-7 


Appendix B 

Table B-7 Ep versus Wind Speed ........ 8-2 


B-2 Emissions from 100 ft pl Gasoline Tank .... 8-4 

8-3 Emissions from 100 ft fl Welded Gasoline Tank 

with Shoe Mounted Secondary Seal ..... B-5 
LIST OF FIGURES 

Page 

Figure 2-1 External Floating Roof Tank (pontoon type) . - 2-2 

Figure 2-2 Primary Seals . . . . - . . , . . - 2-5 

Figure 3-1 Rim-Mounted Secondary Seals . . . . . . . 

Figure 3-2 Emissions from 100 ft Diameter Welded Gasoline 

Tank with Primary Shoe Seal at 16.1 kph (10 mph) 

Average Wind Speed . . . - . . . . . 

Figure 3-3 Emissions from 100 ft ~iametek Welded Gasoline 

Tank with Primary Foam Seal at l6.1 kph (10 mph) 

Average Wind Speed . - . . - . . . . 

Figure 3-4 Emissions from 100 ft Diameter Riveted Gasoline 

Tank with Primary Shoe Seal at 16.1 kph (10 mph) 

Average Wind Speed . . . . - . . . . . 
EPA policy is to express a1 1 measurements in Agency documents in metric 

units. Dual units are sometimes given in the text for clarity. Listed below 

are abbreviations and canversion factors for English equivalents of metric 

units. Frequently used measurements are also presented in dual units below 

for the reader's convenience. 

METRIC UNIT ALTERNATE UNIT CONVERSION. . , . .. 

ki 1 ogram (kg) pound (Ib) , ,, kgx2.205= 

ton kg x 1.1 x 10-YS= tons 

metric ton (m ton) or pound (Ib) Mg x 2205 = Ibs 

megagram (Mg) ton Mg x 1.102 = tons 

k i1 ometer (km) mile (mi) km x 0.621 = mi 

ki 1ometers per hour ' (kph) miles per hour (mph) kph x 0.621 = mph meter (m) foot (ft) m x 3.281 = ft 

centimeter (cm) inch (in) cm x 0.394 = in 

liter (1) gallon (gal) 1 x 0.264 = 

barrel (bbl) 1 x 6.3 x bbl : 

Pascal (Pa) atmospheres (aim) Pa x 9.9 x = atm 

pounds per square Pa x 6.7 x = psi inch (psi) 

atmospheres (atm) kPa x 9.9 x 10'~ = atm 

pounds per square kPa x 0.145 = psi inch (psi) 

FREQUENTLY USED MEASUREMENTS 

1,600,000 1 422,000 gal 10,000 bbl 

150,0001 40,000gal % 950 bbl 

10.5kPa c 1.52psi 

13.8 kPa 2.0 psi 

27.6kPa 4psi 9.7 kph 6 mph 

41.4kPa , 6psi 16.1 kph % 10 mph 

69.0 kPa 10 psi 22.5 kph % 14 mph 

viii 

Liquidmounted -. means a primary seal mounted so the bottom cf the seal 0 

covers the liquid surface between the tank shell and the floating roof. 

Vapormounted means a primary seal mounted so there is an annular vapor 

space underneath the seal. The annular vapor space is bounded by the L. 

bottom of the primary seal, the tank shell, the liquid surface, and 

the floating roof. J 

Petroleum liquids means crude oil, condensate, and any finished or 

intermediate products manufactured or extracted in a petroleum refinery. 

True vapor pressure means the equilibrium partial pressure exerted ' I 

by a petroleum liquid as determined in accordance with methods 

described in American' Petroleum Institute (API) Bulletin 2517, 

Evaporation Loss from Floating Roof Tanks, 1962. The API procedure 

may not be applicable to some high viscosity or high pour crudes. d 

Available estimates of true vapor pressure may be used in special 

cases such as' these. 

Vol ati 1 e Organic Compounds (VOC) means compounds which under favorable 

conditions may participate in photochemical reactions to form oxidants. 
This document is relat$ed to the control of volatile organic compounds 


(VOC) from the storage of petroleum liquids in external floating roof tanks. 
 -

Methodology described in this document represents the presumptive norm 


or reasonably available control technology (RACT) that can be applied to 
 . , 

existing external floating roof storage tanks. RACT is defined as the lowest 


emission limit that a particular source is capable of meeting by the application 

- . 

of control technology that is reasonably available considering technological 


and economic feasibility. It may require technology that has been applied 


to similar, but not necessarily identical, source categories. It is not 


intended that extensive research and development be conducted before a 


given control technology can be applied to the source. This does not, 


however, preclude requiring a short-term evaluation program to permit the 


application of a given technology to a particular source. The latter effort is 


an appropriate technology-forcing aspect of RACT. 


1.1 NEED TO REGULATE 


Control techniques guidelines concerning RACT are being prepared for those 


industries that emit significant quantities of air pollutants in areas of the 


country where National Ambient Air Qua1 ity Standards (NAAQS) are not being 

attained. Storage tanks for petroleum liquids are a significant source 

of VOC. A control techniques guideline (CTG) for storage of petroleum 1 iquids 

in fixed roof tanks (EPA-450/2-77-036) was published in December 1977, RACT 

for fixed roof tanks was defined as the retrofit with internal floating roofs 

or equival ent . 

The following recommended control measures apply to external floating 

roof tanks (EFRT) larger than 150,000 liters (950 bbls) storing petroleum 

liquids. They do not 'apply to fixed roof or tanks with or without internal 

floating roofs, nor do they apply to small production tanks. In general, 

RACT for external floating roof tanks (EFRT) is defined as follows: 

(I) A welded EFRT equipped with primary metallic shoe or liquidmounted seals is required to retrofit with a rim-mounted secondary seal 

if the TVP of the stored'l iquid exceeds 27.6 kPa (4 psi). 

(2) A welded or riveted EFRT equipped with primary vapor-mounted 

seals is required to retrofit with a rim-mounted secondary if the TVP of 

the stored liquid exceeds 10.5 kPa (1.5 psi). 

(3) A riveted EFRT equipped with primary metallic shoe or 1 iquidmounted seals is also required to retrofit with a rim-mounted secondary if' 

the TVP of the stored 1 iquid exceeds 10.5 kPa (1.5 psi ) .,: 

Specific reconunendations,for regulations, including'exemptions, are presented 

in Chapter 5.0. 

Estimated emissions from the affected EFRT's during 1978 were 65,000 

megagrams/year (71 ,630 tons/yr) . The proposed recommendati ons would reduce 

these emissions to 30,000 megagrams/year (33,060 tons/yr) . 

The emission estimates used in this document were calculated from data 

obtained by Chicago Bridge and Iron Company (CBI) on a 6.1 m (20 ft) 
diameter test tank. Data obtained by Pi ttsburgh-Des Moines Steel Company (PDM) 

on a 10.7 m (35 ft) diameter test tank were used to verify RACT for liquidmounted seals which are liquid or foam filled. An American Petroleum Institute 

(API) emission test program, scheduled for completion in 1979, is expected 

to provide verification of the val idi ty of the scal e-up techniques used 

herein. 

Cost effectiveness of retrofitting rim-mounted secondary seals to EFRT's 

is dependent on tank size, product type, product value, average wind speed 

and other factors. For example, the installed capital cost for retrofitting 

a rim-mounted secondary seal to a 30.5 m (100 ft) diameter welded tank 

equipped with a primary shoe seal is about $77,000. The net annual cost 

after credit for recovered product is $3,140 when storing gasoline at a 

TVP of 41.4 kPa (6 psi) and an average wind speed of 16.1 kph (10 mph). A 

welded tank having a vapor-mounted primary seal and a riveted tank having 

a primary metal 1 ic shoe seal can be retrofitted with a rim-mounted secondary 

seal for the same capital cost. However, in these two cases under the same 

storage conditions the emission reductions are larger and the net annual 

cost is $1 930 for the welded tank with the vapor-mounted seal and $1 750 for 

the riveted tank with the shoe seal. The cost effectiveness for the above 

th&e cases is $373, $1 17, and $99 per megagram of emissions controlled, 

resbectively. At lower wind speeds and vapor pressures, the cost effectiveI 

nesb would be higher. At higher wind speeds and vapor pressures, the cost I 

effbctiveness would be 1 ower. 

I 

SOURCES AND TYPES OF EMISSIONS 

There are an estimated 13,800 internal and external floating roof tanks 

' storing petroleum liquids at refineries, terminals, tank farms and along 

pipelines. ' Of these, 10,700 are storing liquids whose vapor pressures equai 

or exceed 10.5 kPa. Data are not available to establish how many of these are 

. external floating roof tanks. 

2.1 EXTERNAL FLOATING ROOF TANKS 

An external floating roof tank consists of a steel cylindrical 

shell equipped with a deck lor roof which floats on the surface of the stored 

liquid, rising and falling with the liquid level (Figure 2-1). The liquid 

surface is completely covered by the floating roof except in the small annular 

space between the roof and the shell. A seal attached to the roof contacts 

the tank wall and covers the remaining area. The seal slides against the tank 

wall as the roof is raised or lowered. The primary route of VOC emissions is 

by this seal. 

When a conmercial fit between the seal and the tank wall is maintained, 

most losses by the seal are attributable to the wind. 293,4,5y6 Wind induced 

losses occur when air flow across the tank creates pressure differences around 

* the floating roof, causing air to flow into the annular vapor space on the leeward side and air plus VOC to flow out on the windward side. Improper or loose fit 

,.. . 

* Unless the primary seal is liquid-mounted, the vapor space bounded by the 

sliding seal, wall, roof, and liquid surface defines an annular vapor space. 
- - - .--

Figure 2-1. External floating roof tank (pontoon type). 
of the seal creates gaps or openings between the seal and the tank wall. 

These gaps expose the liquid surface directly to the wind and sun, which 

combine to increase emissions. The wind flows across the tank, scouring 

the vapor space and sweeping away VOC. In addition, leakage through holes , . 

in the envelope (the fabric cover that is used to bridge the space between + 

the seal and the floating roof) or around the envelope attachment bolts can 

a 
 be a significant source of loss from shoe seals. 

Other causes of emissions are: (1) release of dissolved air saturated 

with VOC because of barometric pressure changes; (2) solar heating of liquid 

in the rim space which increases liquid vapor pressure and VOC migration; 

(3) evaporation of the liquid which clings to the tank wall when the tank 

is being emptied (wetting 10sses)~; (4) breathing of the vapor space due 

to changes in the ambient temperature or barometric pressure; or (5) changes 

in the bulk liquid temperature. Wind-induced losses are larger than all of 

these. 

2.2 PRIMARY SEALS 

There are basically three types of primary seals; mechanical shoe seals, 

resilient foam seals, and liquid-filled seals. Although there are other 

designs, these three comprise the vast majority of primary seals in use today. 

A weather guard is often installed over primary seals to protect the 

seals from deterioration caused by dust, rain or sunlight. Typically, a 

weather guard is an arrangement of overlapping thin metal sheets pivoted 

from the floating roof to ride against the tank wall. This helps protect 

the product from contamination, but its effect on gaps and hence wind-induced 

emissions is variable. Some weather guard designs could do little to curb 

emissions where other tighter designs may be reasonably effective over certain 

types of primary or secondary seals. Because of the uncertainties associated 

2-3 
------- - - I 

with emissions contt~ol, the weather guard is not usually considered as 

effective an emission control device as a secondary seal. Q ----_ _ . -

2.2.1 Mechanical Shoe Seal 

The mechanical shoe seal is characterized by a 75 to 130 cm (30" to 51" ) 

high metal sheet (the "shoe") held against the vertical tank wall (Figure 2-2a). 

The shoe is connected by braces to the floating roof and is held tight against 

the wall by springs or weighted levers. A flexible coated fabric (the 

"envelope") is suspended from the shoe seal to the floating roof to close 

the annular space between the roof and the primary seal. 

Emissions from the mechanical shoe seal occur from the exposed liquid 

surface in the gap spaces between the shoe and the tank wall, and 

through openings in the envelope or shoe. Close fitting primary shoe seals 

effectively reduce emissions from the liquid surface in the gap space, as 

do shoe-mounted secondary seals (Figure 2-2a) .8 Shoe-mounted secondary 

seals are discussed in Chapter 3.0. Emissions are also affected by the 

envelope and shoe conditions. Holes, tears, or other openings in the 

envelope or shoe allow direct communication between the annular vapor space 

and the atmosphere. Through these openings, the wind can scour the vapor 

space, exiting with VOC laden vapors. -

2.2.2 Resilient Foam Seal 

As illustrated in Figure 2-2c,d, resilient foam primary seals fill the 

annular space between the floating roof and tank wall with a continuous 

compressible foam log encased in a protective tube. The resiliency of the 

foam log allows the seal to adapt itself to some imperfections in tank 

dimensions and even to fill or partially fill some protrusions. The foam 

log may be vapor-mounted (Figure 2-2c) or 1 iquid-mounted (Figure 2-2d). 
--- 

TANKi 

METALLIC WEATHER GUARD, ,

~21y 


LIQUID FILLED TUBE 

a. Metallic shoe seal with shoe-mounted 

secondary. 

- , ,METALLIC WEATHER GUARD. 

/ /

TANK, TANK 

WALLs WALL 

RESILIENT FOAM LOG' 

c. Resilient foam seal with weather guard 

(vapor-mounted). , 

Figure 2-2 Primary Seals 

2- 5 
(D
 When a foam seal is vapor-mounted emissions can be much higher than when 


liquid-mounted. A gap between a vapor-mounted foam seal and the wall allows 


direct comnunication between the atmosphere and the vapor space bounded by 


the seal, the roof, the tank wall, and the product 1iquid. 


When a foam seal is liquid-mounted, the vapor space is eliminated and 


losses are comparable in magnitude to those for the shoe seal. 


2.2.3 Liquid-Filled Seal 

A liquid-fil led seal may be a tough fabric band or envelope filled with 


a liquid, or it may be a 20-25 cm (8-10" ) diameter flexible polymeric tube 

filled with a liquid and sheathed with a tough fabric scuff band (Figure 2-2b). 


The liquid is comnonly a petroleum distillate or other liquid that would not 


contaminate the stored product if the tube ruptured. Liquid-fi1 1ed seals are 


mounted on the product liquid surface with no vapor space. They are usually 
 (0 

protected by a weatherguard. 


Losses from tanks equipped with 1iquid-mounted 1 iquid-fi1led primary 


9
 seals are comparable in magnitude to shoe seals and liquid-mounted foam seals. 

2.3 REFERENCES 

1. Eva1 iration of Hydrocarbon Emissions fry Petrol.eum' ti.quid Storage, 

EPA-450/3-78-012, March, 1978. 

2. SOHIO/CBI Floating Roof Emission Program, Interim Report, October 7, 1976. 

3. SOH,IO/CBI, Fl oating Roof Tank Emission- Program, Final Report, 

November, 1976. 

4. Western Oi 1 and Gas Association, Metal 1 ic Seal ing. Ring. Emission 

Test Program, Interim Report, Chicago Bridge & Iron Company, January, 1977. 

5. Western Oi 1 and Gas Assqciation, Metallic Sealing R,ing- Emission 

Test Program, Final Report, Chicago Bridge & Iron Company, March, 1977. 

6. Western Oil and Gas Association, Metal 1 ic Sea,ling Ring Emission 

a Test Program, Supplemental Report, Chicago Bridge & Iron Company, June, 1977. 

7. SOHIO/CBI Floating Roof Tank Ernissi0.n'Test ' Prog,ram, Supplemental 

~eport, Chicago Bridge & Iron Company, February 15, 1977. 

8. Floating Roof Seal Development - Emission Test Measurement on 

Proposed CBI Wiper-Type Secondary Seal for SR-1 ,Seals, Chicago Bridge & Iron 

Company, February 23, 1977. 

R 9. Measurement of Emissions from a Tube Seal Equip-ped Floating Roof 

Tank, Pittsburgh-Des Moines Steel Company, October 9, 1978. 

3.0 CONTROL TECHNOLOGY 

Recomended control technology for existing external floating roof tanks 

with primary foam, liquid-filled, and metallic shoe seals is retrofitting 

with a rim-mounted secondary seal. A rim-mounted secondary seal is defined 

as a continuous device extending from the floating roof to the tank wall, 

and instal led over the primary seal. 

3.1 RIM-MOUNTED SECONDARY SEAL 

A rim-mounted secondary seal is continuous and extends from the floating 

roof to the tank wall, covering the entire primary seal. Installed over a 

mechanical shoe seal, this secondary seal can effectively control VOC that 

escape from the small vapor space between the shoe and the wall, and through 

any openings or tears in the seal envelope which would permit direct 

communication of the seal system vapor space with the atmosphere (see 

Figure 3.1.a). 

Rim-mounted secondary seals are effective in controlling emissions from 

the liquid and vapor-mounted primary seals shown in Figure 3.1. 1,2,3,4,5 

The secondary seals can often be rendered inoperative by cooling and 

hardening of waxy, heavy pour crude oils. These crudes cause a deposit on 

the tank wall which is scraped onto the roof when the tank is worked, 

damaging the secondary seal. 

Another type of secondary seal that is commonly installed on external 

floating roof tanks is a shoe-mounted secondary seal. A shoe-mounted 
TANK! 

-~'--WALLI 

RIM-MOUNTED SECONDARY SEAL 

- IL / 

VAPOR SPACE- . 

-

a. Shoe seal with rim-mounted secondary secondary seal. r 

RlMMOUNTED 

SEAL ,SECONDARY SEAL 1L/,sryARy 


TANK' WALL^ 

SEAL FABRIC, 

RESILIENT FOAM LOG' 

VAPOR SPACE: 

Resilient foam seal ~va~ormounted).~ 

with rim-mounted secondary 

Figure 3-1 Rim-Mounted Secondary Seals 
seal extends from the top of the shoe to the tank wall (see Figure 2-2a). 

Shoe-mounted seals do not provide protection against VOC leakage through 

the envelope. Holes, gaps, tears, or other defects in the envelope can 

allow direct communication between the saturated vapor under the envelope 

and the atmosphere and the wind can enter this space through envelope 

defects, flow around the circumference and exit with saturated or near 

saturated vapors. 

Three 30.5 m (100 ft) diameter tanks were chosen as base cases for 

emission calculations; a welded tank with a primary shoe seal ,a welded tank 

with a vapor-mounted resilient foam seal, and a riveted tank with a primary 

shoe seal. The emission reduction that would occur from installing a 

secondary seal over each of these base cases is discussed below. 

3.2.1 Shoe Seals on Welded Tanks 

When storing a 27.6 kPa (4 psi) vapor pressure product, a rim-mounted 

secondary seal installed over a primary shoe seal reduces emissions from 11.2 

megagrams per year (Figure 3-2a) to 2.8 megagrams per year (Figure 3-2d)- 

A shoe-mounted seal installed on a primary shoe seal reduces emissions from 

11.2 megagrams per year to 5.3 megagrams per year (Figure 3.2~) for the 

same product. Emission reductions for various seal configurations are best 

illustrated over a range of product vapor pressures by Figure 3-2. 

The amount of emissions curbed for each progressively stricter control 

option increases as the TVP of the stored liquid increases. For example, by 

subtracting (d) from (a) in Figure 3-2, the emission reduction for installing 

* The emission rates throughout this chapter are calculated for a 30.5 m 

(100 ft) diameter tank storing 41.4 kPa (6 psi ) vapor pressure gas01 ine with 

an average wind speed of 16.1 kph (10 mph). The average vapor molecular . weight was assumed to be 65, typical for gasoline- Emission rates may be 

scaled according to' Appendix B, 
24 

a - Primary shoe seal, no secondary seal I 


I

b - Primary shoe seal with gapped shoe-mounted 

secondary seal 

c - Primary shoe seal with tight shoe-mounted 

secondary seal 

d - Primary shoe seal with tight rim-mounted 

secondary seal 

2 2 

VOC 

Emi s s i0-ns 

(megagrams/yr) 

psi 

kPa 

True Vapor Pressure of Stored Product 

Figure 3-2. EMISSIONS FROM 30.5 rn (100 ft) DIAMETER WELDED GASOLINE 

TANK WITH PRIMARY SHOE SEAL AT 16.1 kph (10 mph) AVERAGE 

WIND SPEED 

8 
a a rim-mounted secondary seal over a primary shoe seal is only about 5.1 

meyagrams per year for s-toring a 27.6 kPa (4 psi) product, but the reduction increases to 18 megagrams per year if the stored 1 iquid has a TVP 

-- - -- - -- . -

of 69 kPa 110 psi). 

Emissions from a tank equipped with a shoe seal and shoe-mounted 

secondary seal storing 41.4 kPa (6 psi) vapor pressure product are 5.3 

megagrams per year. Retrofitting this tank with a rim-mounted secondary 

seal would reduce emissions by only 2.5 megagrams per year. Thus, tanks 

now equipped with a primary shoe seal and a shoe-mounted seal are controlled 

reasonably well and need not be retrofitted with a rim-mounted secondary 

seal. Nevertheless, the susceptibility of this system to envelope leaks 

and gaps make good inspection and maintenance practices imperative. A shoe 

e seal without any secondary seal should not be retrofitted with a shoemounted secondary. 

3.2.2 Liquid-Mounted Resilient Foam and Liquid-Filled Seals on Welded Tanks 

Liquid-mounted resilient foam and liquid-filled primary seals have 

approximately the same emission rates as primary shoe seals and exhibit the 

same emission reduction trends with control (see ~igure 3-2,c); ow ever 

in some cases the stored liquid may be harmful to the seal, making liquidmountina im~ractical. 

3.2.3 Vapor-Mounted Resilient Foam Seal on Welded Tank 

As discussed in Section 2.2.2, this primary seal has the potential for 

high emissions when vapor-mounted. These emissions can be effectively controlled by retrofitting with a rim-mounted secondary seal provided the gap 

between the secondary seal and tank wall is carefully controlled. This is 

@ illustrated in Figure 3.3 

C 
-


500 -

400 -

-

- 300 -

-

- 200 -

-

-

V 

h 

45 - a - Foam seal mounted in the vapor space, gapped, 

no secondary seal 

40 - b - Gapped foam seal with gapped rim-mounted 

secondary seal 

VOC 

Emissions 

(megagrams/yr) 

35 - d no secondary seal 

- Gapped foam seal mounted in the vapor 

30 - space with tight rim-mounted 

secondary seal 

e - Tight foam seal mounted in the 

25 - vapor space with a tight rimmounted secondary seal 

20 -

15 -

2 3 4 5 6 7 8 9 10 11 psi I I I I I I I 

10 20 3 0 40 50 60 70 

True Vapor Pressure of Stored Product 

Figure 3.3. EMISSIONS FROM 100 FT DIAMETER WELDED GASOLINE TANK WITH 

PRIMARY FOAM SEAL, 16.1 kph (10 mph) AVERAGE WIND SPEED 

3- 6 
Emissions from a tank storing a 41.4 kPa (6 psi) vapor pressure product 

equipped with a vapor-mounted resilient foam seal are 18.6 megagrams per 

year, if the primary seal has a tight commercial fit (Figure 3-3c) and 212 

megagrams per year if the primary seal is slightly gapped (Figure 3-3a). 

With a tight rim-mounted secondary seal, emissions from a gapped primary 

seal are reduced from 212 megagrams per year to 4.3 megagrams per year 

(Figure 3-3d). When instal led over a tight primary seal, emissions are 

reduced from 18.6 megagrams per year to 2.2 megagrams per year (Figure 3-3e). 

With a gapped primary seal and a gapped secondary seal, emissions are 95.3 

megagrams per year (Figure 3-3b). 

3.2.4 Riveted Tanks 

~iveted'tanks present special problems regardless of primary seal design. 

The primary seal must ride over the protruding rivet heads when the tank is 

being worked, creating gaps. If the primary seal stops or is riding on a 

row of rivet heads,the gaps can be nearly continuous and the wind-induced 

emissions extremely high. The portion of the seal riding on the rivets 

(and the riveted members) depends on design, and varies with location in 

the tank. Emissions based on experimental tests conducted to evaluate a 

shoe seal in contact with a "worst case" simulated rivet row are shown in . . 

Figure 3-4a. '6 

Installation of a rim-mounted secondary seal over this primary shoe seal 

reduces emissions from 39.9 to 22.3 megagrams per year based on one test and 

to 7.1 megagrams per year based on another (the only difference being the 

rivet row design with which the, secondary seal was in contact), At more . , 

favorable roof locations in a riveted tank, emissions will be lower. Emissions 

from a welded tank with a rim-mounted secondary were 2.8 megagrams per year. 
loo " a - Shoe seal, no secondary seal 

b - Shoe seal with rim-mounted secondary 

90 - seal, Position I 

- c - Shoe seal with rim-mounted secondary 

80 seal, Position I1 

d - Welded tank with shoe seal and rimVOC Emissions 70 mounted secondary 

(megagrams/yr ) 

60 -

50 -

40 -

30 -

20 -

10 , 

I I I I I I I I 1 

1, 

2 3 

I 

4 I 5 6 

I 

7 I 8 9 I 10 1 11psi 

10 20 3 0 40 50 60 7 0 kPa 

True Vapor Pressure of Stored Product 

Figure 3-4. EMISSIONS FROM 30.5 m (100 ft) DIAMETER RIVETED GASOLINE 

TANK WITH PRIMARY SHOE SEAL AT 16.1 kph (10 mph) AVERAGE 

WIND SPEED 
Rivet heads are particularly harsh on primary seals, and seal condition 

may deteriorate more rapidly. Frequent inspections and good maintenance 

practices must be followed to control emissions from riveted tanks. 
3.3 REFERENCES 

1. SOHIO/CBI Floating Roof Emission Program, Interim Report, 

October 7, 1976. 

2. SOHIO/CBI. Floating Roof Tank Emission Program, Final Report, 

November, 1976. 

3. Western, Oil and Gas Association, Meta,lic ,Sealing Ring Emission 

Test Program, Interim Report, Chicago Bridge & Iron Company, January, 1977. 

4. Western Oi 1 and Gas Association, ~eta1,ic ' Sealf ng-'Ring. EyJssi on 

Test Program, Final Report, Chicago Bridge & Iron Company, March, 1977. 

R
 5. Measurement of Emissions,from a Tube. Seal Equipped Floating Roof 

Tank Pittsburgh-Des Moines Steel Company, October 9, 1978. -3 

6. Western Oi 1 and Gas Associ,ation, Metallic Seal ing Ring Emission 

Test Program, Supplemental Report, June, 1977. 
4.0 COST ANALYSIS 

4.1.1 Purpose 

The purpose of this chapter is to present estimated costs for control 

of volati 1 e organic compound (VOC) emissions from existing external floating 

roof petroleum liquid storage tanks. 

4.1.2 Scope 

Estimates of capital and annualized costs are presented for controlling 

emissions from existing external floating roof storage tanks. The estimates 

pertain to welded and riveted steel tanks used for storing gasoline. Current 

standards for floating roof tanks require the use of single closure (primary) 

seals, so the cost of control is limited to the additional cost of installing 

(retrofitting ) a secondary seal on existing tanks. Control costs are ., 

developed for a model existing external floating roof tank with a diameter 

of 30.5 m (100 ft) , a height of 12.2 m (40 ft) and a storage capaci ty of 

8,910,000 liters, A range of cost effectiveness ratios are presented for 

storing gasoline that allow for varying operating conditions, locations, 

and control costs of tanks, 

4.1.3 Use of Mode1 Storage Tanks 

Gasoline storage tanks vary in size with typical diameters ranging 

from less than 9.1 m (30 ft) to more than 91.5 m (300 ft). Since it would 

be impractical to determine costs for all tank sizes, a middle size model 

was selected for this cost analysis. Table 4-1 presents the cases evaluated 

4- 1 

Tab1 e 4-1. 

+ TECHNICAL PAMETERS USED IN DEVELOPING GASOLINE STORAGE TANK CONTROL COSTS 

I.Storage Tank Size: 

Di ameter : 30.5 m (100 ft) 

Height : 12.2 m (40 ft) 

Capacity : 8,910,000 liters 

8,910 m3 (55,000 bbls) 

11. Wind Speed and Vapor Pressure 

9.7 kph (6 mph) 13.8 kPa (1.52 psi) 

16.1 kph (10 mph) 27.6 kPa (2.0 psi) f 

N 

22.5 kph (14 mph) 41.4 kPa (6.0 psi ) 

69.0 kPa (10.0 psi) 

III. VOC Control Efficiencies: (see Table B-2, Appendix B) 

Rim mounted secondar-y seals on floating roof tanks: 

a. Case I- Welded tank with the following primary seals - shoe seal, liquid-mounted foam 

seal, or 1iquid-mounted 1 iquid-fi 1 led seal - (75%) 

b. Case I1 - Welded tank with the following primary seal - a vapor-mounted foam seal - (84 - 88%) 

C. Case 111 - Riveted tank with the following primary seal - a metallic shoe seal - (45%) 
w a I 4

0 a 

Table 4-1 (Continued) TECHNICAL PARAMETERS USED IN DEVELOPING SASOLINE STORAGE TANK CONTROL 

a 

IV. Emissions Before Control (Mg/yr) :, 

CASE 

Wind Velocity 

True Vapor 

Pressure 

13.8 kPa 

f 

CJ NOTE: All cases - primary seals - no secondary 

V. .Emission After Control (Mg/yr) : 

a 

CASE 

Wind Velocity 

True Vapor 

Pressure 

NOTE: A1 1 cases - A rim-mounted 1 secondary was used over the specified primary seal. 
Table 4-1 (Continued) TECHNICAL PARAMETERS USED IN DEVELOPING GASOLINE STORAGE TANK CONTROL COSTS 

VI . Emissions Control led (Mg/yr) : 

a 

CASE 

Wind Velocity 

True Vapor Pressure 

- aReference Appendi # -A and B . 
and the technical parameters used in the analysis. The parameters were 

selected as being representative sf average annual wind speed on the 

United States Gulf Coast, East Coast and West Coast, respectively, and 

expected ranges of product true vapor pressure at stored temperatures. 

Emissions and emission reductions are based on extrapolations from a 

6.1 m (20 ft) diameter test tank to the full size model tank (see Appendix 

A and B). ' It will be noted from Table B-2, Appendix B, that Cases I1 

and I11 do not represent predictions of maximum achievable emission 

reductions. .Accordingly, cost effectiveness for these cases (see Section 4.3) 

are conservatively high. 

4.1.4 Bases for Capital and Annualized Cost Estimates 

Capital cost estimates represent the total investment required to 

purchase and retrofit the control systems on existing storage tanks 

including the cost of cleaning and degassing tanks. Costs for research 

and development, lost time during installation and start-up, and other 

highly variable costs are not included in the estimates, These costs vary 

so widely from case to case and from situation to situation that it is 

virtual 1y impossible to real istical ly quantify these costs. A1 1 capital 

costs reflect second quarter 1978 dollars. 

Annualized control cost estimates include operating labor, maintenance, 

credits for petroleum savings, and annualized capital charges. Cost 

estimates were obtained from an EPA contractor, equipment vendors, tank 

service companies, local air pollution control reports, and an API contractor. 

Credits for gasoline savings due to emission control have been calculated 

from the emission reductions projected from the experimental tests. 
The annualized capital charges are sub-divided into capital recovery 

costs (depreciation and interest costs) and costs for property taxes, 

insurance, and administration. Depreciation and'interest costs have been 

computed using a capital recovery factor based on a 10 year secondary seal 

life and an interest rate of 10 percent per annum. Costs for property 

taxes, insurance and administration are computed at 4 percent of the 

capital costs. All annualized costs are for one year periods commencing 

with the second quarter of 1978. 

4.2 CONTROL OF EMISSIONS FROM EXTERNAL FLOATING ROOF STORAGE TANKS 

4.2.1 Mode1 Cost Parameters 

Cost parameters used in computing secondary seal control costs are 

presented in Table 4-2. These parameters are based on actual cost data 

from an oil industry journal ,* a National Energy Information Center 

monthly publication ,3 an EPA c~ntractor,~seal vendors ,5y6 tank service 

cmpani es ,7 y8 1 ocal air pol 1 uti on control reports, 9y10 an API contractoP, 11 

and EPA estimates, 

4.2.2 Control Costs 

Table 4-3 shows the estimated costs of controlling VOC emissions from 

the model floating roof storage tank. The estimates pertain to existing 

welded and riveted floating roof petroleum liquids tanks that are equipped 

with primary closure seals. The installed capital costs are average industry 

costs of retrofitting a secondary seal on the model storage tank. The 

annual operating and maintenance costs are estimated based on normal 

maintenance and inspection programs. The annualized capital charges consist 

of the capital recovery costs using capital recovery factor with 10 percent 

annual interest rate and 10 year secondary seal life plus 4 percent of 0 

4- 6 
Table 4-2. COST PARAMETERS USED IN COMPUTING CONTROL COSTS 


I. Gasoline valuea 


II. Secondary Seal Value : 

A. Installed (Retrofit) Capital Costs: b 


Tank with primary seal : $176 per 1inear m. 

B. Annual Maintenance cost:' 

5% of installed capital cost plus annual inspection charge of $200. 


C. Replacement ~ife:'~ 10 years 


b~verage instal led cost of retrofitting secondary seal per References 4,5, 


6,7,8,9 and 10. 


'~nnual maintenance cost per EPA estimate and annual inspection charge per 


Reference 12. 


d~xpected replacement life per References 4 and 8. 

installed capital cost for property taxes, insurance and administration. 

The total annual control system costs are the sum of the annual operating 

and maintenance costs and annualized capital charges. Annual petroleum 

credits from control 1 ing (reduci ng) emissions are not i ncl uded i n these costs. 

From Tab1 e 4-3, it can be seen that the average instal 1 ed capital cost 

of a secondary seal on a 30.5 m (100 ft) diameter tank is $16,900 and the 

total annual control system cost average is $4,400. 

4.3 COST EFFECTIVENESS 

Table 4-4 presents the cost effectiveness ratios of controlling gasoline 

emissions from the model existing floating roof tank. The $100.64/m 3 price ' 

for gasoline was established by averaging the per barrel prices of regular, 

premium and no-lead gasoline from three different areas. The per barrel 

price was then converted to a $/m 3 . The cost effectiveness ratios for crude 

oil may be approximated by mu1 tiplying the cost effectiveness ratios in 

Table 4-4 by 1.38. For the development of this factor see Table 4-5. 

This factor reflects the different average values and emission rates of the 

two liquids. The amount of emissions control led (reduced) varies with wind 

velocity, absolute vapor pressure and control efficiency. Higher wind 

velocity, greater vapor pressure and higher control efficiency will result 

in a greater quantity of controlled emissions and larger petroleum credits; 

opposite (low) values will result in a smaller quantity of emissions controlled and lesser petroleum savings. Since a range of the above controlling 

factors is needed to cover the typical range 0.f tank operating conditions 

and locations, cost effectiveness ratios have been determined using various 

vapor pressure and wind velocity values for the factors and control system 

costs. 

4-8 
Table 4-3. CONTROL COST ESTIMATES FOR ~ ..MODEL - EXISTING GASOLINE STORAGE TANK 

Facility Size: 30.5 m diameter (100 ft) 

12.2 m height (40 ft) 

8,910,000 1 iteG-sii%i-ty (55,000 - .bbl --- )--. - -

Faci 1 ity Type: External Floating Roof Tank 

Control Device: Rim Mounted Secondary Seal 

Type of Primwy Closure Sea! : CASE-I CASE 'II CASE 111 . -

Instal led Capital Cost ($000) :a 16.9 

, Annual Operati g and Maintenance 1.I 

Cost ($000) :

6 'f 

a 
Annual ized Capital Charges ($000) : 3.3 

Total Annual Control System Cost 4.4 

(Not including petroleum 

credits)($000) :d 

+ 

a~verage instal led cost of retrofitting secondary seal on existing floating roof tank per References 4,5,6,7,8, and 9. 

I 

b~nnual operating and maintenance cost per EPA estimate and annual inspection charge per Reference 12. 

'capital recovery costs (using capital recovery factor with 10% annual interest rate, 10 year secondary seal life) 

plus 4% of installed capital cost for property taxes, insurance, and administration. 

d~um of annual operating and maintenance cost plus annualized capital charges; but, does not include petroleum 

credits (savings). 
0 

Table 4-4. COST EFFECTIVEMESS OF COlNTROLLIF(G FLOATING ROlOF GASOLIJE-STORAGZNKS 


5 SEAL. LIQUID-MOUNTED koAM StALs LIQUIbMOUNTED LIQUID-FILLED SEAL 

Wind Velocity ! 9.' kph 16. koh 

True Vapor Pressure --13.8 kPa. 27.6 kPa 11.4 kPa 59.0 -

kPa 13.8 kPa 27.6 -

kPa It,) kPa 159.0 kP

VOC Emissions Controlled 


(Reduced) (Mg/yr)a 1 1 .I6 ( 2.53 4.15 8.84 2.36 5.12 

Annual Petroleum ~avi 


(Credits) ($00,0/yr) 1 (1.33) (.35) (-77) 

Total Annual Control system 


Cost ($000/yr) I 4.4 4.4 4.4 4.4 4.4 4.4 

Net Annual Cost (credit) . .

)c 1 1 1 4.24 1 (bO~0Olyr 
 4i2 3.77 3 .O7 4.05 3.68

Cost (credit) per Mg of 


Control ed Emissions 3655 1589 908 347 1716 709
 a (BIMg) 
 I I 

I1 - WELI D TANK - RIMARY F iM SEAL J _ -.- --. . d 
 !

Wind Velocity <ph 

True Vapor Pressure $1.4 kPa 13.8 kPa 


VOC Emissions Controlled 


(Reduced) (Mgl~r)~ 


Annual Petroleum ~a;i gs 


(Credits) ($000/yr) 1 

Total Annual Control 


System Cost 


($000/yr 


Net Annual gost (credit) 


($000/yr 


Cost (credit) per Mg 


of Contr lled Emissions 


($lW~ 


QR-MOUNTED. . 
-- -- 

Tab1.e 4-4 (continued). COST EFFECTIVENESS OF CONTROLLING FLOATING ROOF GASOLINE STORAGE TANKS 
 ..... - ...... -

CASE 111 - RIVETED 2%WXITPRIMARY-SHOE-SEAL -

I 

Wind Velocity I 9.7 kph kph I I I 

True Vapor Pressure 1 13.8 k~al 27.6 k~al 41.4 kPa (6 11.4 kPa 

VOC Emissions Contr;l led 


(Reduced) (Mg/yr) 


Annual Petroleum Savi gs 


(Credits) ($000/yr) ! 

Total Annual Control System 


Cost ($000/yr) 


Net Annual gost (credit) 


($000/~r) 


Cost (credit) per Mg of 


Controlled Emissions 


($/~g Id 


"per Table 4-1. 


b(~missions Before Control) x (VOC Control Efficiency) x (Recovered Petroleum Liquid Value) t (Average Liquid Density) 

'sum of Annual Petroleum savings (Credits) and Total Annual Control System Cost. 


d(#et Annual Cost (credit) ) t (VOC Emissions Controlled (~educed) ). 

For the model existing gasoline floating roof tank, it should be noted 


from Table 4-6 that the cost effectiveness ranges from a cost of $3,665 


to a credit of $66 per Mg of controlled emissions. The corresponding cost 


effectiveness ratios of crude oil emission controlled using the 1.38 factor, 


vary from a cost of $5,044 to a cost of $25 per Mg. Thus, due to the higher 


value and emission rate of gasoline, the cost effectiveness for crude oil 


ranges from $66 to $1389 higher per Mg of control led emissions than for gas01 ine. 


4.4 ECONOMICS OF SCALE 


The preliminary cost of retrofitting a secondary seal to existing 


floating roof tanks were also developed for a 10.7 m (35 ft) diameter tank 


and a 53.3 m (175 ft) diameter tank. These were developed to check the 


1ineari ty of the scaling effect on cost effectiveness developed for our 

model tank. As could be expected there were some dis-economies of scale 


in the cost effectiveness of the smaller tank. This resulted in the smaller 


tank cost effectiveness ($/Mg of emissions control 1ed) being approximately 


105 percent of the cost effectiveness of the 30.5 m (100 ft) diameter model 


tank. Also, as expected, the larger tank had some economies of scale. This 


resulted in the 1arger tank cost effectiveness ($/Mg of emissions control led) 


being approximately 85 percent of the cost effectiveness of the 30.5 m (100 ft) 


diameter model tank. 


I 
C O m L n N mm*-

a m -
4.5 REFERENCES 

1, "Meghods for Extrapolating Chicago- Bridge and Iron 6.1 M (20. Ft ,J. Test . .--- Tank Results to Full Sivze Tank,!' EPA--0APQS Draft Report, .- April, 1978. 

2. "Refined-products prices", Oil and Gas Journal, March 27, 1978. 

3. Monthly Energy Review, June 1978, office of ~nercj~Information and 

Analysis, National Energy Information Center, 

4. R. Bakshi, Pacific Environmental Services, Inc.; Santa Monica, Cal. 

Petroleum storage tank and seal cost data memo to file by P..A. Quaney, 

U. S. Environmental Protection Agency, dated November 2, 1977. 

5. J. Hunter, \iestsrn Petro-Chemical Co., Los Anyeles, Cal . Petroletini ~ 

storage tank seal cost. data memo to file by R.A. Quaney, U.S. Environniental 

Frotection Agency, dated November 2, 1977.- 6. K. J. Kol kmeier, Pittsburgh-Des Moines Steel Co., Pittsburgh, Pa. Petrolcim 

storage tank seal cost data memo to file by R.A. Quaney, U.S. Environri;mtal 

Protection Agency, dated November 2, 1977. 

7. H.R. Wiggs, Tank Service, Inc., Tulsa, Oklahoma. Letter to R. tl. Schippers,' 

U. S. Envi ronrzentai Protection Agency, dated May 18, 1977. 

8. J. Mulkey, Tank Service, Inc., blilniington, Del. 

seal cost data memo to file by R.A. Quaney, U.S. 

Agency, dated November 2, 1977. 

9. California Air Resources Board. Public hearing 

Rule 463 of SCAQHD, June 25, 1976. 

10. Cal iforiiia Air Resources Board. Pub1 ic hearing 

Rule 463 of SCAQMD, March 25, 1976. 

Petroleum storage tank 

Environmental Protection 

- Proposed Ammendnents to. 

- Proposed A~nnendicents to 

11. Dr. W. Sheppard, Battell e Columbus Laboratories , Col ulnbiis , Ohio. Petrol eun 

liquids transportation cost,data memo to file by R.A. Q~laney, U.S. Environmental Protection Agency, dated EIovei~lber 2, 1977. 

12. R. H. Schippers, U. S. Environmental Protee tion Agency. Me1i10 on Sscondar-y 

S2als on New Petroleum Product Storage Tanks, dated I4ay 25, 1977. 

5.0 RECOMMENDED REGULATIONS, COMPLIANCE 

TEST METHOD, AND RECORD KEEPING 

The affected faci 1 i ties are external floating roof storage tanks with 

aci ti es greater than 150,000 1 i ters (950 bbls) containing petroleum liquids 

with a true vapor pressure greater than 10.5 kPa (1.5 psi ) . 

5.1 RECOMMENDED REGULATIONS 

Recommended regulations for the storage of petroleum liquids in external 

floating roof tanks are: 

1. Except where specifi cal ly exempted (See 5.1.4), a1 1 external floating 

roof tanks with capacities greater than 150,000 liters shall be retrofitted 

with a continuous secondary seal extending from the floating roof to the tank 

wall (a rim-mounted secondary) if: 

(a) the tank is a welded tank, the true vapor pressure of the 

contained liquid is 27.6 kPa (4.0 psi) or greater,and the primary seal is one of 

the following: 

(i ) a metal li c-type shoe seal, a liquid-mounted foam seal, 

or a liquid-mounted liquid-filled type seal, or 

(ii ) any other closure device which can be demonstrated 

equivalent to the above primary seals. 

(b) the tank is a riveted tank, the true vapor pressure of the . -- - - - - - -

contained 1 iquid is 10.5 kPa (1.5 psi ) or greater, and the closure device is as 

described in 5.1.1 (a). 
(c) the tank is a welded or riveted tank, the true vapor pressure 

of the contained liquid is 5 10.5 kPa (1.5 psi) and the primary seal is 

vapor-mounted. When such primary seal closure device can be demonstrated 

equivalent to the primary seals described in 5.1.9 (a), the provisions of 

5.1.1 (a) apply. 

2. The seal closure devices shall meet the following requirements: 

(a) there shall be no visible holes, tears, or other openings in 

the seal (s) or seal (s) fabric. 

(b) the seal(s) must be intact and uniformly in place around 

the circumference of the floating roof between the floating roof and the tank 

wall. 

(c) the gap area of gaps exceeding 0.32 cm (1/8 inch) in width tiaween 

the secondary seal installed pursuafit to 5.1.1 (c) and the tank wall shall not 

exceed 6.5 cm2 per 0.3 m of tank diameter (1.0 i n2 per foot of tank diameter). 

3. All openings in the external floating roof, except for automatic 

bleeder vents, rim space vents,and leg sleeves, are to provide a projection 

below the liquid surface. The openings are to be equipped with a cover, seal 

or lid. The cover, seal or lid is to be in a closed position at all times 

except when the device is in actual use. Automatic bleeder vents are to be 

closed at all times except when the roof is floated off or landed on the roof 

leg supports and rim vents are to be set to open when the roof is being 

floated off the roof leg supports or at the manufacturer's recommended setting. 

Any emergency roof drain is to be provided with a slotted membrane fabric 

cover or equivalent cover that covers at least 90 percent of the area of the 

opening. 

4. The following are specifically exempted from the requirements of 

5.1.1: 
(a) external floating roof tanks having capacities less than 

1,600,000 liters (10,000 bbls) used to store produced crude oil and 

condensate prior to custody transfer. 

(b) a metallic-type shoe seal in a welded tank which has a secondary seal 

from the top of the shoe seal to the tank wall (a shoe-mounted secondary). 

(c) external floating roof tanks storing waxy, heavy pour 

crudes. 

5. External floating roof tanks with a closure or other devices 

installed which will control VOC emissions with an effectiveness equal 

to or greater than the seals requi red in 5.1.1 (a). 

L 


5.2 COMPLIANCE TEST METHOD 

1. Compliance for external floating roof tanks does not require 

measurement of the primary or secondary seal gap area, except as required 

to meet 5.1.2 (c), and can be determined by visual inspection. 

2. For compliance with 5.1.2 (c), the secondary seal gap area can 

be determined by measuring the length and width of the gaps around the 

enti re circumference of the secondary seal. Only gaps' greater than or 

equal to 0.32 cm (1/8 inch) shall be used in computing the gap area. The 

area,of the gaps can be accumulated to determine compliance. 

5.3 MONITORING AND RECORD KEEPING 

It is recommended that the routine visual inspections be conducted annually 

or at shorter intervals, and that the secondary seal gap measurements be 

made annually. Evidence of any type of malfunction (as noted above) is to 

be recorded. 

When a liquid having a true vapor pressure greater than 7.0 kPa (1.0 psi) 

is stored in an external floating roof tank not equipped with a secondary seal 
01-
 a~proved a1 ternative control technology (see 5.1.5), a reco~dshould be 

maintained for no more than two years of the average monthly storage 


temperature, the type of liquid, and the Reid vapor pressure of the liquid. 


The true vapor pressure may be determined by using the average monthly 


storage temperature and typical Reid vapor pressure of the contained liquid 


or from typical available data on the contained liquid. Supporting analytical 


data can be requested if there is a question on the values reported. 

APPENDIX A 

SELECTIONOF EXPERIMENTAL TESTS FOR 

WIND INDUCED EMISSION CALCULATIONS 

An experimental 20' P) test tank at the Plainfield, Illinois, Research 

Center of Chicago Bridge and Iron Company (CBI) has been extensively used by 

industry to investigate the mechanisms causing hydrocarbon emissions from 

f 1 oating roof tanks. s233y495y6 A large number of tests were conducted on 

various types of seals to study the effect of parameters such as wind speed, gap 

between the seal and tank wall, and the leak rate of the shoe seal vapor 

space system on hydrocarbon emissions. Secondary seal efficiency was 

evaluated. Methods for extrapolating specific test results from the 20' P) 

test tank to full size tanks have been developed. This appendix describes 

the methodology used in selecting specific tests for extrapolation which 

are considered representative of average field tank conditions. 

A. METHODOLOGY OF SELECTION 

The selection of CBI tests on primary seals which represent the 

"average" primary seal gap in the field was based on EPA's analysis of 

r tank inspections made in 1976 by regulatory agencies in California. A total w 

of 398 tanks were included in this analysis; 163 welded tanks with primary 

shoe seals, 141 welded tanks with non-metallic seals of either the foam or 

liquid type, and 94 riveted tanks with shoe seals. Tanks equipped with a 

weather guard over the primary seal were included. Excluded were 47 tanks 

L 
which were reported to have either a "double" or "wiper" secondary seal. 

In the inspections, gaps between the primary seal and tank wall were 

measured with probes or rods of varying dimensions. The width and length 

of each gap was recorded. It was not possible to derive from the inspection 

data an average gap width in the field that was comparable to a specific 

CBI test, nor a range of gap width patterns which could be compared to one 

or several CBI tests. 

The final selection was made by comparing the gap areas in the tanks 

2 tnspected to the gap area in the CBI tests expressed as in /ft of tank 

diameter. 

B. SELECTION OF WELDED TANK WITH SHOE SEAL AND RIM-MOUNTED SECONDARY SEAL 

A number of tests were made with single shoe seals having gaps up to 

1 112 inches simulated by forcing the primary seal away from the tank wall with 

spacer bar arrangements. 73899 In all of these tests the leakage rate for the 

seal system (the space bounded by the shoes, the envelope, the rim space 

and liquid) averaged about 0.032 SCFM per foot of tank diameter at 1 112 inches 

of H20 pressure drop. A leakage rate of 0.50 SCFM at 1.5 inches of H20 is 

considered commerci a1 ly achievable. Further research was conducted by CBI 

to establish the relationship between shoe seal emissions and leak rate. The 

leak rate of seals inspected in California is unknown. The final determination 

of the base case for calculating wind induced emissions for a primary shoe seal 

was made by; (1) using the methodology described in (A), and (2) using a 

test that simulated a leak rate of 0.8 SCFM/ft of tank diameter at 1.5 inches 

of H20 pressure drop. This leak rate appears reasonable based on field test data 

and the California inspections which revealed relatively few tanks with openings 

or tears in the envelope. 

A-2 
- -- 

A comparison of the gap area in the inspected tanks with specific CBI 

tests is shown in Table A-1. Selected tests on envelope leak rate simulations 

are also shown in this table, 

It will be noted from Table A-1 that 89 percent of the tanks had gap 

areas (inZ/ft tank diameter) equivalent to tests whgre emissions remained 

relatively unchanged from a shoe seal with a tight commercial fit to one having a 

gap(s) up to one inch. 

. -

Test W-12 has a comnercial fit and simulates a seal system vapor space leak 

rate of 0.8 SCFM per ft of tank diameter at 1.5" H20 W-12 was selected as 

the base case for wind induced emission calculations. 

A rim-mounted sec0ndar.y over the W-12 primary seal was then judged to have 

at least a 75 percent efficiency based on numerous.secondary seal single seal 

combinations tested with var.ying gaps in the primary, secondary, or both, 

&ring the same test. ' 

C. WELDED TANK WITH SHOE SEAL AND SHOE-MOUNTED SECONDARY SEAL 

A secondary wiper seal mounted on the shoe was tested with a tight 

comnercial fit and with gaps.''' The efficiency of the wiper in each of these 

tests was used to estimate the base case (test W-12) emission reductions. 

D. RIVETED TANK WITH A SHOE SEAL AND RIM-MOUNTED SECONDARY 

Test W-28 was made with a single shoe seal in contact with simulated . -.- - -- :.. . .. - .-

horizontal and vertical rivet rows.!] Table A-2 gives a comparison of the gap 

area in the inspected tanks and the gap area in this test configuration, 

The gap area in a riveted tank will vary with the position of the roof in the 

tank and the rivet patterns in W-28 represent a condition where gaps may be 

expected to be at maximum. This is judged to be the reason why the inspected 
TAB'LE A-1. SEAL GAP AREA IN INSPECTED WELDED TANKS WITH 

SHOE-SEAL COMPARED TO CBI EXPERIMENTAL TESTS 

20 Ft. Diameter Experimental Test Tank 

Tanks Inspected Envelope Gaps in Seal 

Leakage 

Width T'otal ~rea~[nch' per Ft. Number Percent 

at 1 .5" Hz0 (inch) (inch 2, Tank Dia. 

0 

2 

2 

(% tank 

circ.) 

4 

0 

0 

0 

0 

a~apor pressure - 5 psia, wind speed - 10 mph. 

? b~ncludes area of tapers P 

0 7 1.75 in2/ft tank di meter 

d> 1.75 4.3 i n2/ft tank diameter 

e> 4.3 7 9.35 in2/ft tank diameter 

f> 9.35 7 14.7 i n2/ft tank diameter 

Includes only one tank > 14.7 

Continuous gaps this magnitude not recorded in inspections; these tanks are included in W-26 (%). 

gap areas, taken at random roof positions, are considerably lower than W-28. 

The inspected gap areas in the riveted tanks are substantially greater than in 

the welded tanks in Tab1 e A-1 . Also, the numbers of gaps in the riveted tanks 

were far more numerous than in the welded tanks and gaps in riveted tanks 

may exhibit the characteristics of the continuous gap in test W-6. 

A rim-mounted secondary over W-28 was tested in contact with two rivet 

patterns, tests W-29 and W-31. Emissions were calculated for both these 

tests and reductions obtained by subtraction from W-28. 

E. RESILIENT FOAM SEAL MOUNTED IN RIM VAPOR SPACE OF WELDED TANK 

Two tests were selected for the single seal. A single seal test with a 

"tight commercial fit" (Test 13, 16, 20, 21) and the same seal with gaps 

(Test 23). 12,13 

A rim-mounted secondary with a "tight commercial fit" was installed 

in each of the above tests. Emissions were then calculated for each (Test 32 

and 34A) and mission reduction obtained by difference. 

Inspection data for "non-metallic" seals are presented in Table A-3. 

The seals were not identified by type (liquid filled or foam) or location 

(rim vapor space or in the liquid surface). 

For comparative purposes emissions were developed for a secondary seal 

with gaps (Test 34B) installed over a primary seal with gaps (Test 23). 
ra, 

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REFERENCES 

1. SOHIO/CBI Fl.oat.ing Roof Etyission Program, Interim Report, 

October 7, 1976. 

2. SOHIO/CBI Floating Roof Tank Emission Program, Final Report, 

November, 1976. 

3. Western Oil and Gas. Association, Metallic Sealing Ring Emission 

Test Program, Interim Report, Chicago Bridge & Iron Company, January, 1977. 

4. Western Oi 1 and Gas Asspciation, Metal 1 ic Sea1.i.n-g Ring, ,Emission 

Test Program, Supplemental Report, Chicago Bridge & Iron Company, June, 1977. 

5. SOHIO/CBI Floating Roof Tank Emission Test Program, Supplemental 

Report, Chicago Bridge and Iron Company, February 15, 1977. 

6. Floating Roof Seal Development - Emissio~n Test Measurement on 

Proposed CBI Wiper-Type Secondary Seal for SR-1 Seals, Chicago Bridge & Iron 

Company, February 23, 1977. 

7. Mestern Oil and. Gas Association, Metallic Sealing Ring Emission 

Test Program, Final Report, Chicago Bridge & Iron Company, March, 1977. 

Reference 4, Op. C3t. 

Reference 2, Op. Cit. 

Reference 6, OP. Cit. 

Reference 4, Op. Cit, 

Reference 1 , Op. Ci t. 

Reference 2, Op. Cit. 
APPENDIX B 

CALCULATION OF WIND INDUCED 

EMISSIONS FROM EXPERIMENTAL TESTS 

A. EQUATION FOR WIND INDUCED EMISSIONS 4 


Emissions were extrapolated from the 20' fl test tank selected tests to 

u the 100' 0 model gas01 ine storage tank using the following equation:' y293 

Where: EF = Emissi'ons from full size tank, megagramslyr 

Ep = Emissions from test tank at 5.0 psi, lbs/day 

PF = Vapor pressure of stored product in full size tank, psi 

DF = Diameter of full size tank, feet = 100 

MHC = Molecular weight of full size tank hydrocarbon emissions 

(hydrocarbon vapor molecular weight), 1 bs/l b mole = 65 

B. Ep FOR THE TEST TANK 

In each specific test emissions were measured at varying simulated wind 

speeds. These results were then plotted to yield a smooth "Ep vs Windspeed" 

curve for each test.4 Ep values for the selected tests and various wind 

speeds read from these plots are given in Table B-1. 

i_ 
 In the 100' !il model tank analysis wind speeds of 6 mph, 10 mph, and 14 mph 

were used. These represent mean average annual wind speeds on the West Coast, 

Gulf Coast and East Coast, respectively. 

B-1 
-- 

TABLE B-1 - Ep (lbslday) vs Wind Speed (mph) 

(20' Test Tank - 5.0 psi) 

Sel ected Tests 

Welded Tank - Shoe Seal 

Single Seal (W-1 ,W-2 

W-1R) 

Single Seal (W-12) 

~im-~ountedSecondary 

(25 % W-12) 

ShoeSvlounted Secondarj 

Tight Fit (6-2) 

Shoe-Mounted Secondarj 

Gaps (C-1) 

Riveted Tank - Shoe Seal 

Single Seal (W-28) 

~im41ounted 

Secondary (W-29) 

Rim-Mounted 

Secondary (W-31) 

Welded Tank - 'Foam Seal 

In Rim Vapor Space 

Single Seal (13,16,20, 

21 1 

Single Seal (23) 

Rim -MOM ted 

Secondary (34A) 

Rim-Mounted 

Secondary (32) 

Rim -Mounted 

Secondary (34B) 
C. EMISSION CALCULATIONS 

1 , Primary Seal With and Witbut Rim-Mounted Secondary 

Using the equation in (A) emissions were calculated for each of the C 

selected tests at wind speeds of 6 mph, 10 mph and 14 mph, and stored gas01 ine 

c .vapor pressures of 2 psi, 4 psi, 6 psi and 10,psi. Emissions reductions 

are the difference between the single seal case (base case) and secondary 

seal case (control case). The results for a model 100' tank storing gasoline 

whose hydrocarbon emissions have a molecular weight of 65.0 1 bs/l b mole are 

given in Table 8-2. 

C.2 Shoe Seal With Shoe-Mounted Secondary 

The shoe mounted secondary was tested on -a primary shoe' seal with a 

vapor space leak rate of < 0.1 SCFM per ft of tank diameter, (Tests-C-1 , C-2, 

and W-1R). Emissions controlled in Test C-1 and C-2 were calculated at various 

wind speed and vapor pressure parameters. The emissions controlled were then 

subtracted from the emissions in the base case, Test W-12, to determine emissions 

from a shoe mounted secondary. The results are given in Table 8-3. 
TABLE 8-2 - WISSIDNS FM 1010' $ GASOLINE TANK (MEGAGWSIYR) 

Experimental Test 

Ielded Tank-Shoe Seal 

Shoe Mounted Secondary Adj .C-2 0.81 1.77 2.91 

AEmissions (SeeTab1e3) 0.74 1.59 2.62 

Shoe Mounted Secondarv 

AEmissions " 

Ad.1.C-1 

(see 3, 

1

1 1.07 

0.48 

1

1 2.33 

1.03 

1 

j 

3.84 

1.69 

:iveted Tank-Shoe Seal 

Rim Mounted Secondary 

AEmissions 

Rim Mounted Secondary 

AEmissions 5.78 12.33 1 20.28 

elded Tank-Resilient Foam 

eal in Rim Vapor Space 

Single Seal (with no gaps) i3,16,20,21 3.02 6.54 10.76 

Secondary Seal (no gaps) 32 0.35 0.76 1.25 

~~missions~ 2.67 5.78 9.51 

Single Seal (with gaps) 23 26.72 57.91 95.27 

Secondary Seal (no gaps) 

AEmissions 

34A 0.47 

25.25 

1.03 

56.88 1 

1.69 

93.58 

econdary Seal with Gaps 

ver Primary Seal with Gaps 34B 1.81 3.92 6.46 

Emission Reduction used in Chapter 4.0 

Extrapolated 
-- 

TABLE B-3 - EMISSIONS FROM 100' 0 WELDED GASOLINE TANK WITH - SHOE MOUNTED SECONDARY SEAL (MEGAGRAMSIYR) 

Wind Speed - MPH 

tored Product Vapor Pressure-PSIA 

Experimental Test Test Number 

hoe Mounted secondaryight Fit 

Base Case: Shoe Seal with W1, WlR, 

Leak Tight W2 

Envelope 

Base Case with Shoe C-2 

Mounted Secondary 

Controi ied by Secondary 

Shoe Seal with Envelope W-12 

Leak Rate 0.8 SCFMIft 

Tank 0 - 1 112" H20 

Control 1 ed by Secondary 

Shoe Seal with Shoe Adjusted 

Mounted Secondary C-2 

hoe Mounted Secondaryith Gaps 

Base Case: Shoe Seal with 

Leak Tight W1, W1R 

Envelope W2 

Base Case with Shoe C-1 

Mounted Secondary 

Control 1 ed by Secondary 

Shoe Seal with Envelope 

Leak Rate 0.8 SCFMIft W-12 

Tank $ - 1 112" H20 

Control 1ed by Secondary 

Shoe Seal with Shoe Adjusted 

Mounted Secondary ' C-1 
REFERENCES 

1. Su~aryof 20 foot Diameter Pilot Floating Rpof Hydrocarbo-n 

Emission Test Results, Chicago Bridge & Iron Company, December 28, 1977. 

2. Hydrocarbon Emission Lpss MeasuremeMs on a 2Q'- @. Floating Roof 

Tank with a Type SR-1 Seal for a Product at Various Vapor Pressures, Chicago 

Bridge & Iron Company, October 25, 1977. 

3. Methods for Extrapolating Chicago Bridge & Iron Company 20,' 

Test Tank Results to.Full Size Tanks, EPA, OAQPS Draft Report, April, 1978. 

4. Reference 1, Op Cit. 
TECHNICAL REPORT DATA 

(Please read Znshuctlons on the reverse before completing) 

REPORT NO. 2. 3. RECIPIENT'S ACCESSION NO. 

- - - - TITLE AND SUBTITLE 5. REPORT DATE 

Control of Volatile Organic: Emissions from December 

ORGANIZATION 

1978 

CODE -

Petroleum Liquid Storage in External Floating Roof T 

Richard K.Burr, ESED Jack G. Wright, SASD 

AUTHORE) 8. PERFORMING ORGANIZATION REPORT hlO. 

Kerri C. Brothers, ESED OAQPS NO. 1.2-116 

PERFORMING ORGANIZATION NAME AND ADDRESS 10. PROGRAM ELEMENT NO. 

U.S. Environmental Protection Agency 

Office of Air Qua1 ity Planning .and Standards 11. CONTRACT/GRANT NO. 

Emission Standards and Engineering Division 

Research Triangle Park, North Carolina 27711 

2. SPONSORlNG AGENCY NAME AND ADDRESS 

14. SPONSORING AGENCY CODE 

I 

5. SUPPLEMENTARY NOTES 

6. ABSTRACT 

This report provides the necessary guidance for development of 

regulations 1 imiting emissions of volatile organic compounds (VOC) from 

storage of petroleum 1 iquids in external floating roof tanks. Reasonably available control technology (RACT) is defined in this document; cost 

analysis for RACT is included for evaluating the cost effectiveness of 

controlling external floating roof tank sources. 

7. KEY WORDS AND DOCUMENT ANALYSIS 

DESCRIPTORS >.IDENTIFIEFWOPEN ENDED TERMS 

Air Pollution Air Pollution Control 

Storage Tanks 

Regulatory Guidance Stationary Sources 

Organic Vapors 

8. DISTRIBUTION STATEMENT 19. SECURITYCLASS (This Report)' 

Unclassified 

21. NO. OF PAGES 

64 

20. SECURITY CLASS (Thispage) 22. PRICE 

Unclassified 

€PA Form 2220-1 (Rev. 4-77) PREVIOUS .EDISIONI SOBSOLETE