Manual of Petroleum Measurement Standards Chapter 19.2

Evaporative Loss from Floating-roof Tanks

MPMS CHAPTER 19.2

FOURTH EDITION, AUGUST 2020

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Contents

Page

1. Scope 1

2. Normative References 2

3. Symbols 2

4. Procedure for Estimating Loss 3

   1. General 3

      S

   2. Standing Loss L 4

      W

   3. Working Loss L 22

5. Sample Problems 23

   1. General 23

   2. EFRT Sample Problem 23

   3. IFRT Sample Problem 27

   4. Domed EFRT Sample Problem 30

6. Equipment Descriptions 34

   1. Components 34

   2. Types of Floating-Roof Tanks 59

7. Loss Mechanisms 60

   1. General 60

   2. Standing Loss 61

   3. Working Loss 63

8. Development of Estimation Methods 63

   1. General 63

   2. Standing Loss 63

   3. Working Loss 68

Annex A (informative) Development of Rim-Seal Loss Factors 70

Annex B (informative) Development of Rim-Seal Relationship Between Airflow Rate and Wind Speed 74

Annex C (informative) Development of Diameter Function 76

Annex D (informative) Development of Deck-Fitting Loss Factors 78

Annex E (informative) Development of Vapor Pressure Function 85

Annex F (informative) Development of Product Factors 87

Annex G (informative) Development of Clingage Factors 89

Annex H (informative) Development of Fitting Wind-Speed Correction Factor 90

Annex I (informative) Development of Deck-Seam Loss Factors 93

Annex J (informative) Documentation Records 95

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Contents

Page

Annex K (informative) SI Units 96

Bibliography 97

Figures

1. EFRT with Pontoon Floating Roof 36

2. EFRT with Double-deck Floating Roof 37

3. IFRT with Noncontact Deck 38

4. Domed EFRT 39

5. Vapor-mounted Primary Seals 41

6. Liquid-mounted Primary Seals 43

7. Mechanical-shoe Primary Seals 44

8. Secondary Seals 46

9. Access Hatch 47

10. Fixed-roof Support Column 47

11. Gauge Float (Automatic Gauge) 48

12. Gauge Hatch Sample Ports 49

13. Vacuum Breaker 50

14. Deck Drains 51

15. Deck Leg 52

16. Rim Vent 53

17. Vertical Ladder 54

18. Unslotted (Unperforated) Guidepole 55

19. Slotted (Perforated) Guidepole 56

20. Ladder/Guidepole Combination 57

C.1 Calculated Losses as a Function of Diameter Exponent 77

D.1 IFRT Deck Fitting Emission Factors—Effect of Ladder Sleeve on Emission Reduction 83

Tables

1. Symbols 2

2. Rim-Seal Loss Factors 6

3a Deck-Fitting Loss Factors—Other-than-guidepole Deck Fittings 9

3b Deck-fitting Loss Factors—Unslotted (Unperforated) Guidepoles 13

3c Deck-fitting Loss Factors—Slotted (Perforated) Guidepoles 14

fc

1. Typical Number of Columns N for Tanks with Column-Supported Roofs 15

2. Typical Number of Vacuum-Breakers N

   fvb

   fdd

   and Deck Drains N

   for API 650 Annex C Decks (EFRTs and

   Domed EFRTs) 15

3. Typical Number of Deck Legs N

   fdl

   for API 650 Annex C Floating Roofs 16

   d

4. Deck-Seam Length Factors S 18

   L

5. Clingage Factors C for Steel Tanks (bbl/1000 ft2) 22

   C

6. Effective Column Diameter D for Typical Column Construction 23

1. Summary of Deck Fittings Selected for Data Regression, and Associated Loss Factors for Each 81

2. Net Liquid Surface Area for a Ladder/Guidepole Combination 82

3. Emission Factors for IFRT Ladder Sleeves 83

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   Contents

   
   

   Page

4. IFRT Emission Factor Comparison for a Ladder/Guidepole Combination 84

1. Assumed Distribution of Time for a Floating Roof in Each Height Range 91

2. Assumed Floating Roof Height Distribution versus Survey Results 91

1. Noncontact Deck Seams 94

2. Contact Deck Seams 94

J.1 Documentation Records 95

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Evaporative Loss from Floating-roof Tanks

1 Scope

This standard contains methodologies for estimating the total evaporative losses of hydrocarbons from external floating-roof tanks (EFRTs), freely vented internal floating-roof tanks (IFRTs), and domed external floating-roof tanks (domed EFRTs).

The methodologies provide loss estimates for general equipment types based on laboratory, test-tank, and field-

tank data.

Types of floating roofs, rim-seal systems, and deck fittings are described for information only.

The equations estimate average annual losses from floating-roof tanks for various types of tank construction, floating-roof construction, rim-seal systems, and deck fittings, as well as for various liquid stocks, stock vapor pressures, tank sizes, and wind speeds (EFRTs).

The equations were developed for:

1. stocks with a true vapor pressure greater than ~0.1 psia;

   
   

2. average wind speeds ranging from 0 miles per hour (mph) to 15 mph (EFRTs); and

   
   

3. tank diameters greater than 20 ft.

The estimation techniques become more approximate when these conditions are not met.

When this standard is used to estimate losses from non-freely vented (closed vent) internal or domed external floating-roof tanks (tanks vented only through a pressure-vacuum relief vent, blanketed with an inert gas, vented to a vapor processing unit, or otherwise restricted from being freely vented), refer to the methodology in API TR 2569 [7].

The equations are not intended to be used in the following applications.

a) to estimate losses from unstable or boiling stocks (i.e. stocks with a true vapor pressure greater than the atmospheric pressure at the tank location) or from petroleum liquids or petrochemicals for which the vapor pressure is not known or cannot readily be predicted;

1. to estimate losses from tanks in which the materials used in the rim seal, deck fittings, or deck seams have either deteriorated or been significantly permeated by the stored stock;

   
   

2. to estimate losses from storage tanks that do not have a floating roof (API MPMS 19.1[53] addresses this);

   
   

3. to estimate losses from landing floating roofs (API MPMS 19.6.1 [8] addresses this);

e) to estimate losses from cleaning storage tanks (API MPMS 19.6.2 [9] addresses this).

The estimation procedures were developed to provide estimates of typical losses from floating-roof tanks that are properly maintained and in normal working condition. Losses from poorly maintained tanks can be greater. Because the loss equations are based on equipment conditions that represent a large population of tanks, a loss estimate for a group of floating-roof tanks will be more accurate than a loss estimate for an individual tank. The estimation can be improved by using detailed field information, including climatic data and operational data for the appropriate time period.

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