Custody Transfer Meter Proving Services


Citadel Engineering Company’s products for metering system’s equipment, Instruments and special tools are listed in below:

  • Bi-Directional Pipe Prover (Stationary and Portable)
  • 4Way Valve (Hydraulic & Electrical)
  • Sampling System
  • Static Mixer
  • Basket Strainer, Straightener
  • Inflatable Seal, Inflation Pump, Removal Tools, Detector Switch


Flow Metering will be classified according to the purpose for which it is required. The classification requires five general levels of accuracy, along with defined rangeability, and calibration as follows:

  • Class I - Fiscal Metering (taxation and royalties)
  • Class II - Custody Transfer (invoicing for payment)
  • Class III- Internal Accounting /Performance Measurement
  • Class IV- Control and Protection
  • Class V – Indication



Any special requirements regarding taxation and royalties shall be achieved by this Class of metering; otherwise, the measurement for invoicing of payment shall be in accordance with Class II



The measurement shall be fully in accordance with the API Manual on Petroleum Measurement. The type of meter shall be determined according to the application and in agreement with the third party. All straighteners shall be provided in accordance with the API Manual on Petroleum Measurement Standards. Temperature and pressure compensation shall also be provided and shall use the tables in the API Manual on Petroleum Measurement Standards. The accuracy of the temperature and pressure transmitters shall be +/- 0.1% or better.

Turbine meters should be considered for any flow rates especially when exceeding (16,000 m3/d) and where the liquid metered has low viscosity and poor lubricity characteristics. The Ultrasonic Meter can be used the same as the Turbine meter if it has custody transfer approval. The distance between the meter and its prover shall be kept as short as possible. The meter shall be able to operate within linearity of +/- 0.15% or better throughout its normal range. The meter shall be able to reproduce its output within +/- 0.02% or better of meter reading under constant operating conditions.

P.D. meters to be sized to operate between 30% and 80% of nameplate rating. Turbine meters to be sized to operate between 10% and 80% of nameplate rating. Ultrasonic meters to be sized to operate between 5% and 90% of nameplate rating. Coriolis meters should be considered for meter run sizes less than 6".

Calculation shall be performed in a certified flow computer, and not in the DCS. All instruments shall be calibrated to standards traceable to NIST or other International Standards. The provision for meter proving in the site shall be provided unless agreed otherwise with the third party. One stand-by meter shall be installed. No bypass shall be permitted.



The measurement shall be as in Class II above except that meter proving is not required, and the calculation may be carried out in the FCS. No stand-by meter is required, a bypass valve may be provided, where tank inventory measurement is available or where agreed with the parties involved.



Orifice Plate may be used for this class of measurement as a primary flow element.



An orifice plate should be used for this class of measurement.


LACT units are designed for unattended custody transfer of crude oil from a seller to a buyer. The LACT design is determined by:

  • Flow rate
  • Operating pressure
  • Gravity
  • The temperature of the oil

Minimum pressure drop through the piping and components is desirable.

LACT units have traditionally been fitted with positive-displacement meters, but a turbine meter can be used with certain types of fluid. New units being built today utilize Coriolis meters because they have no moving parts and can offer a lower cost. 


Master Meter Proving System and In-Directional provers are fully portable to ensure timely and efficient scheduling. Our Prover Operators and Measurement Technicians are experienced in custody transfer measurement and will aid your team in solving even the most complex liquid measurement challenges in a safe and cost-effective manner.

  • Current Max Flow Rate 1700 BPH
  • ANSI 600 Pressure Rating
  • LACT Unit Meter Proving
  • Load Rack Meter Proving
  • Custody Transfer Metering Skids
  • Coriolis, PD & Turbine Meter Proving






The industry codes and standards referenced in and/or applicable to this document are listed below. The latest revision number and/or date of each referenced industry code or standards are applicable in effect at the start of the project. Any subsequent change shall be revised for further impact.


  • API MPMS, Ch. 1 Manual of Petroleum Measurement Standards Chapter 1 – Vocabulary
  • API MPMS, Ch. 4 Proving Systems
  • API MPMS, Ch. 5 Measurement of Liquid Hydrocarbons
  • API MPMS, Ch. 6 Pipeline Metering Systems
  • API MPMS, Ch. 7 Manual of Petroleum Measurement Standards Chapter 7 – Temp. Determination
  • API MPMS, Ch. 8 Sampling
  • API MPMS, Ch. 11 Physical Properties
  • API MPMS, Ch. 12 Calculation of Petroleum Quantities
  • OIML R117-1 Dynamic measuring systems for liquids other than water
  • Part 1: Metrological and technical requirements
  • ISO 5168:2005 Measurement of fluid flow - Procedures for the evaluation of uncertainties
  • ISO 3171:1988(en) Petroleum Liquids-Automatic pipeline sampling
  • ISO 10790 Measurement of fluid flow in close conduits-guideline to the section, Installation and use of Coriolis meters
  • ISO 17089 Measurement of fluid flow in close conduits.
  • IEC 61508 Functional safety of electrical/electronic/programmable electronic safety-related systems
  • IEC 61131-3 Basic software architecture and programming languages of the control program within PLC
  • 94/9/EC (ATEX 95) ATEX 95 Equipment Directive
  • 2006/95/EC Low Voltage Directive
  • 2004/108/EC Electromagnetic Compatibility Directive
  • SI 2006/3418 Electromagnetic Compatibility Regulations (encompassing the EMC Directive 2004/108/EC)
  • SI 1996/192 The Equipment and Protective Systems Intended for Use in Potentially
  • Explosive Atmospheres Regulations as amended by SI 2001/3766 (ATEX EU Equipment Directive 95 (94/9/EC))
  • API-MPMS 4, Chapter 4 - Proving Systems
  • API-MPMS 18, Chapter 1 8 - Custody Transfer
  • API-MPMS 21, Chapter 21 - Flow Measurement Using Electronic Metering Systems
  • API-RP-500, Recommended Practice for Classification of Locations for Electrical Installations in Petroleum Refineries
  • API-RP-500, Classification of Hazardous Area
  • API-RP-540, Electrical Installations in Petroleum Processing Plants
  • API-RP-552 Transmission Systems
  • API-RP-553 Refinery Control Valves
  • API-RP-554, Process Instrumentation and Control
  • API-RP-555, Process Analyzers
  • APT-RP-520, Sizing, Selection, and Instrumentation of Pressure-Relieving Devices in Refineries
  • API-STD-521, Guide for Pressure Relieving and DE pressuring
  • API-STD-527, Leak Tightness of Pressure Relief Valve
  • ASME/ANSI, B16.5 Pipe Flange and Flanged Fittings
  • ASME/ANSI, B31.3 Refinery (Mechanical Design)
  • IEC 60079, Electrical Apparatus for Explosive Gas Atmosphere
  • IEC 600529, Degrees of Protection Provided by Enclosure (IP code)
  • NACE MR 01-75, Sulfide Stress Cracking Resistance Metallic Material for Oil Field Equipment