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Published Date

September 1997


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Quantity Calculations LPG and Chemical Gases, 2nd Edition

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It is essential to understand the differences in the various calculation procedures practiced if discrepancies between cargo calculated as loaded and cargo calculated as discharged are to be correctly recognised as either real or spurious. This new edition, which is completely revised, continues to assist the Chief Officer with this complex problem.

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Liquefied gases require commercial transportation and storage to be under pressure and/or refrigerated in a closed container. As a result, the quantification for custody transfer purposes of bulk liquid gas cargoes involves more complex considerations and procedures than other bulk liquefied gas commodities that can be carried and stored in “open”. Added to this is the availability and use of several calculation procedures that are valid within the present accepted levels of accuracy but with each having differences in the approach to the final value of the cargo transfer.

It is essential to understand the special considerations and differences of various calculation procedures between a cargo calculated as it is loaded and one that is calculated when it is discharged. Apart from inconvenience and cost of any reconciliation, spurious discrepancies produce doubt on the reliability of the equipment and shipboard cargo care.

 

SIGTTO recognised the need for a wider appreciation of these matters. This second edition contributes to a broader understanding of the situation. The information presented in the main text of this book can be used as general background by those in shippers’ and cargo receivers’ organisations who are concerned daily with liquefied gas custody transfer. The detailed appendices provide an aide memoire to those involved in the practical measurement and calculation of cargo quantities.

PREFACE

1. INTRODUCTION

2. VAPOUR/LIQUID EQUILIBRIUM

3. TERMS AND DEFINITIONS

3.1 GENERAL-DENSITY IN AIR AND DENSITY IN VACUO

3.2 TRUE DENSITY – APPARENT DENSITY

3.3 RELATIVE DENSITY (SPECIFIC GRAVITY)

3.4 APPARENT RELATIVE DENSITY (APPARENT SPECIFIC GRAVITY)

4. VAPOUR DENSITY

4.1 GENERAL

4.2 PERFECT GASES

4.3 REAL GASSES

5. LIQUID DENSITY

5.1 INTRODUCTION

5.2 PRACTICAL DENSITY METHOD: THE PRESSURE HYDROMETER (ASTM D1657)

5.3 DENSITY FROM COMPOSITIONAL ANALYSIS

5.3.1 ASTM D2598

5.3.2 THE FRANCIS FORMULA

5.3.3 THE COSTALD EQUATION

5.3.4 SPECIFIC DENSITY CALCULATION METHODS AND TABLES

5.4 LNG

6. VOLUME AND TOTAL QUANTITY DETERMINATION

6.1 TANK INVENTORY

6.2 THE LIQUID QUANTITY

6.3 SUMMARY

6.3.1 FROM LIQUID DENSITY AT OBSERVED TEMPERATURE

6.3.2 FROM LIQUID DENSITY AT REFERENCE TEMPERATURE

7. SHORE TERMINAL CONSIDERATIONS

7.1 COMPARISON BETWEEN SHIP AND SHORE FIGURES

7.2 FLOWMETERING

8. FUTURE DEVELOPMENT

9. CONCLUSION

APPENDIX 1 PROPERTIES OF COMMERCIAL GASES

APPENDIX 2 WEIGHT IN AIR CONVERSION

APPENDIX 3 THE FRANCIS FORMULA

APPENDIX 4 THE COSTALD EQUATION

APPENDIX 5 QUANTITY CALCULATION OF LPG – AN EXAMPLE

APPENDIX 6 MEASUREMENT REPORT FOR LIQUEFIED GASES

The purpose of SIGTTO is to promote shipping and terminal operations for liquefied gases which are safe, environmentally responsible and reliable. To fulfil this mission it will:

  • Proactively develop best operating practices and guideline

  • Sustain a learning environment by sharing lessons learned

  • Promote training and development of all within the industry

  • Foster mutually beneficial relationships with regulatory authorities and other stakeholders

  • Conduct its business with professionalism and integrity

Title: Quantity Calculations LPG and Chemical Gases, 2nd Edition
Number of Pages: 31
Product Code: 4400W050
ISBN: ISBN 13: 978-1-85609-144-2 (9781856091442), ISBN 10: 1-85609-144-9 (1856091449)
Published Date: September 1997
Binding Format: Paperback
Book Height: 300 mm
Book Width: 210 mm
Book Spine: 4 mm
Weight: 0.20 kg
Author: SIGTTO

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