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The Engineer’s Guide to Tank Gauging 2017 EDITION What is tank gauging? Tank ga

The Engineer’s Guide to Tank Gauging 2017 EDITION What is tank gauging? Tank gauging technologies Engineering standards and approvals Volume and mass assessment Accuracies and uncertainties Temperature measurement Liquefied gases Additional sensors System architecture Overfill prevention Appendix: Typical tank gauging configurations References Legal disclaimer This book is designed to provide information on tank gauging only. This information is provided with the knowledge that the publisher and author are offering generic advice which may not be applicable in every situation. You should therefore ensure you seek advice from an appropriate professional. This book does not contain all information available on the subject. This book has not been created to be specific to any individual’s or organizations’ situation or needs. Every effort has been made to make this book as accurate as possible. However, there may be typographical and or content errors. This book contains information that might be dated. While we work to keep the information up-to-date and correct, we make no representations or warranties of any kind, expressed or implied, about the completeness, accuracy, reliability, suitability or availability with respect to the book or the information, products, services, or related graphics contained in the book or report for any purpose. Any reliance you place on such information is therefore strictly at your own risk. Therefore, this book should serve only as a general guide and not as the ultimate source of subject information. In no event will we be liable for any loss or damage including without limitation, indirect or consequential loss or damage, arising out of or in connection with the use of this information. You hereby agree to be bound by this disclaimer or you may return this book. All rights reserved. No part of this book may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording or by any information storage and retrieval system, without written permission from the author. 1. What is tank gauging? 1 2. Tank gauging technologies 7 3. Engineering standards and approvals 15 4. Volume and mass assessment 27 5. Accuracies and uncertainties 33 6. Temperature measurement 41 7. Liquefied gases 47 8. Additional sensors 51 9. System architecture 55 10. Overfill prevention 63 11. Appendix: Typical tank gauging configurations 71 12. References 89 Table of contents Abbreviations AOPS Automatic Overfill Prevention System API American Petroleum Institute ATG Automatic Tank Gauge ATT Automatic Tank Thermometer BEV Bundesamt für Eich- und Vermessungswesen BS&W Base Sediment & Water DCS Distributed Control System EMC Electromagnetic Compatibility EODR Electro-Optical Distance Ranging FMCW Frequency Modulated Continuous Wave FWL Free Water Level FWV Free Water Volume GOV Gross Observed Volume GSV Gross Standard Volume HTG Hydrostatic Tank Gauging IEC International Electrotechnical Commission ISO International Organization for Standardization LNE Laboratoire national de métrologie et d’essais LNG Liquefied Natural Gas LPG Liquefied Petroleum Gas LTD Level Temperature Density MOPS Manual Overfill Prevention System MPE Maximum Permissible Error MPMS Manual of Petroleum Measurement Standards MTBF Mean Time Between Failures NIST National Institute of Standards and Technology NMi Nederlands Meetinstituut NSV Net Standard Volume OIML International Organization of Legal Metrology OPS Overfill Prevention System PLC Programmable Logic Controller PTB Physikalisch-Technische Bundesinstitut R 85 Recommendation 85, a special procedure for testing of tank gauging equipment defined by OIML. RRF Risk Reduction Factor RTD Resistance Temperature Detector SAT Site Acceptance Testing SIF Safety Instrumented Functions SIL Safety Integrity Level SP Technical Research Institute of Sweden TCT Tank Capacity Table TOV Total Observed Volume VCF Volume Correction Factor WiA Weight in Air WiV Weight in Vacuum What is tank gauging? Topic Page 1.1 Tank gauging is a system science 2 1.2 Where is tank gauging used? 3 1.3 The purpose of tank gauging 4 1.3.1 Oil movement and operations 4 1.3.2 Inventory control 5 1.3.3 Custody transfer 5 1.3.4 Loss control and mass balance 5 1.3.5 Overfill prevention 5 1.3.6 Leak detection 6 1.3.7 Volume reconciliation 6 1 1 - What is tank gauging? 2 1. What is tank gauging? Tank gauging is the measurement of liquids in large storage tanks with the purpose of quantifying the volume and mass of the product in the tanks. The oil and gas industry generally uses static volumetric assessments of the tank content. This involves level, temperature and pressure measurements. There are different ways of measuring the liquid level and other properties of the liquid. The measurement method depends on the type of tank, the type of liquid and the way the tank is used. Storage tanks can contain large volumes of liquid product representing a significant value. The accuracy performance of a tank gauging system is of high importance when assessing the tank content at any given time. Tank gauging is used on large storage tanks in refineries, fuel depots, pipelines, airports, and storage terminals. Storage tanks usually come in four basic designs: Cylindrical fixed roof tanks, cylindrical floating roof tanks and pressurized tanks of either spherical or horizontal cylinder design. There are tank gauges available for all these tank types. Besides precision level gauging, temperature measurements are essential in assessing tank contents accurately. All liquids have a thermal expansion coefficient and proper volume compensation needs to be applied when transferring volumes at different temperature conditions. A pressure measurement of the liquid head is often added to provide a current assessment of the average observed density and to calculate the product mass. Modern tank gauging systems digitize the tank measurement and digitally transmit the tank information to a control room where the liquid volume and mass information is distributed to users of the inventory data. 1.1 Tank gauging is a system science The concept of tank gauging involves much more than just the precision instruments on the tank. Tank gauging requires reliable data communication over large field bus networks, often both wired and wireless. The communication solutions often need arrangement for redundancy in the field buses, the data concentrators, the network components and the network servers. Tank gauging systems must also be able to calculate product volumes and mass according to the industry standards. The tank gauging software/information system must perform 1 - What is tank gauging? 3 many different functions spanning from operator interface, batch handling, reporting, alarm functions, connectivity to host systems and much more. It is a system engineering science across many areas of technology. 1.2 Where is tank gauging used? Tank gauging is needed wherever liquids are stored in large tanks. Such storage tanks are found in: • Refineries • Petrochemical industry • Distribution terminals • Pipeline terminals • Fuel depots • Air fueling storage at airports • Chemical storage Storage tanks are often placed in clusters or tank farms. The tanks are atmospheric, pressurized or cryogenic. Atmospheric tanks are vertical cylinders with various roof designs. Most common are: • Fixed roof tanks, either cone roof or dome roof tanks. • Floating roof tanks with various designs. In a fixed roof tank there is a vapor space between the liquid surface and the external roof. In a floating roof tank the liquid surface is covered by either an internal or an external floating roof. There are many different designs of floating roofs depending on the service, the liquid and the size of the tank. It is common that floating roof tanks have one or more still-pipes that go from the bottom of the tank, through an opening in the floating roof to the top of the tank. This still-pipe is used to access the liquid for sampling, hand level gauging, hand temperature measurement and automatic tank gauging. With a good Automatic Tank Gauge (ATG) design, all these things can be performed in one still pipe. Figure 1.2: Fixed roof and floating roof tanks. Figure 1.1 : Tank gauging involves a substantial number of interdependent devices and functions. 1 - What is tank gauging? 4 Pressurized tanks are often of spherical or horizontal cylinder design. Hand gauging cannot be performed on pressurized tanks. For high accuracy automatic tank gauging a still-pipe inside the tank is normally required. In cryogenic tanks, automatic tank gauges are often of the same design as for pressurized tanks. The methods for proper automatic tank gauging are described in various engineering standards. The most commonly applied standards are the Manual of Petroleum Measurement Standards (MPMS) issued by the American Petroleum Institute (API). 1.3 The purpose of tank gauging The information from a tank gauging system is used for many different purposes. The most common are: • Oil movement and operations • Inventory control • Custody transfer • Loss control and mass balance • Volume reconciliation • Overfill prevention • Leak detection 1.3.1 Oil movement and operations The operation of a tank farm relies heavily on information regarding the situation in the tank farm. To operate the tank farm safely and efficiently it is important to know exactly what is going on inside the tanks. The tank gauging system must at any given time provide instant information about: • How much liquid is in the tank • How much available room is left in uploads/Geographie/ tg-guide.pdf