Manual of Petroleum Measurement Standards Chapter 3.1B

Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging

FOURTH EDITION, OCTOBER 2021

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Contents

Page

1. Introduction 1

2. Scope 1

3. Normative References 1

4. Terms and Definitions 2

5. Design and Selection of ATGs 2

   1. General Precautions 2

   2. Use of ATGs for Custody Transfer or Inventory Control 2

   3. Accuracy 3

   4. Remote Readout 5

   5. Data Communication and Receiving 5

6. Installation of ATGs 5

   1. Manufacturer’s Requirements 5

   2. Mounting Location of Ullage-ATGs 5

   3. Mounting Location of Innage-ATGs 6

   4. Avoiding Turbulence 6

   5. Proximity to the Gauging Hatch 9

   6. Multiple Gauging Hatches 9

   7. Slotted/Perforated Still Pipe Design 9

   8. Mounting of ATGs 11

7. General Procedures for Initial Setting and Initial Verification of ATGs in the Field 11

   1. General Information 11

   2. General Precautions 11

   3. Initial Requirements 11

   4. Reference Manual Level Measurement Procedure 12

   5. Reference Measurement Tape and Weight Certification 12

   6. Initial Setting of ATGs in the Field 12

   7. Initial Verification 13

8. Operation and Maintenance 16

   1. General Operating Considerations 16

   2. Subsequent Verification of ATGs 16

9. Recordkeeping 17

Annex A (informative) Safety Precautions: Physical Characteristics and Fire Considerations 18

Bibliography 19

Figures

1. Example of an ATG (Contact or Non-contact) Mounted on a Still Pipe Supported by Tank Bottom 7

   Contents

2. Example of an ATG (Contact or Non-contact) Supported by a Bracket Hinged to the Lower Tank Shell

   Page

   Plate 8

3. Example Installation of a Top Mounted ATG on a Fixed Roof Tank Without Still Pipe (this installation may

   not be suitable for custody transfer) 9

4. Example Installation of a Top Mounted Innage-ATG on a Fixed Roof or Floating Roof Tank Without Still Pipe (this installation may not be suitable for custody transfer) 10

Tables

1 Accuracy Requirements and Verification Frequencies for ATGs by Tank Service 4

Standard Practice for Level Measurement of Liquid Hydrocarbons in Stationary Tanks by Automatic Tank Gauging

1. Introduction

   
   

   This standard presents both metric (SI) units and U.S. customary units and may be implemented in either system of units. The presentation of both units is for the convenience of the user and is not necessarily an exact conversion. The units of implementation are typically determined by contract, regulatory requirement, the manufacturer, or the user’s calibration program. Once a system of units is chosen for a given application, it is not the intent of this standard to allow arbitrary changing of units within this standard.

   
   

   Safety precautions are listed separately from general precautions that affect accuracy or performance.

   
   

   NOTE Precautions are given in addition to any existing federal, state, or local regulations (for example, the Occupational Safety and Health Administration) that govern practices described in this standard. Users of this standard should be familiar with all applicable safety and health regulations.

   
   

2. Scope

   
   

   This standard covers the level measurement of liquid hydrocarbons in stationary, aboveground, atmospheric storage tanks using automatic tank gauges (ATGs). The standard discusses automatic tank gauging in general, accuracy, installation, commissioning, calibration, and verification of ATGs that measure either innage or ullage. It covers both intrusive and non-intrusive ATGs used for either custody transfer or inventory control. The standard also covers the requirements for data collection, transmission, and receiving.

   
   

   This standard does not cover the following:

   
   

   1. hydrocarbons having a Reid vapor pressure above 15 pounds per square inch (in.) absolute (100 kPa);

      
      

   2. measurement of weight or mass with ATG equipment (this is covered in API MPMS Chapter 3.6 and Chapter 16.2);

      
      

   3. measurement of the level in underground tanks or in pressurized tanks storing liquid hydrocarbons;

      
      

   4. conversion of the tank level to liquid volume (this is covered in API MPMS Chapter 12.1);

      
      

   5. measurement of temperature, sampling, density, and sediment and water (S and W), which are discussed in API MPMS Chapters 7–10.

   
   

   Safety and material compatibility precautions should be taken when using ATG equipment. Manufacturers’ recommendations on the use and installation of the equipment should be followed. Users should comply with all applicable codes and regulations, API standards, and the NFPA National Electrical Code.

   
   

3. Normative References

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any addenda) applies.

API MPMS Chapter 3.1A, Standard Practice for the Manual Gauging of Petroleum and Petroleum Products