Custody transfer, alternatively known as fiscal metering, would occurs when fluids or gases are exchanged between parties.
Hence payment is usually made as a function of the amount of fluid or gas transferred, so accuracy is an utmost priority. Even a small error in measurement can add up fast leading to financial exposure in custody transfer transactions.
Since errors in measurement for custody transfer can be so expensive custody transfer and fiscal metering are regulated in most countries and involve government taxation and contractual agreement between involved custody transfer parties.
Another point to look at when discussing custody transfer are also influenced by a number of industry associations and standard organizations such as
- American Gas Association (AGA)
- American Petroleum Institute (API)
- US National Institute for Standards and Technology (NIST)
- Physikalisch-Technische Bundesanstalt (PTB) in Germany
- China Metrology Certificate (CMC)
- Gosudarstvennyy Standart (GOST) in Russia
Custody transfer applications require more than an accurate flow-meter.
There are a number of critical components that comprise a complete metering system including :
- Multiple meter runs (or at times called ‘meter streams’) in parallel
- Temperature and Pressure Transmitter (TT,PT)
- Flow computers
- Quality Measure – Online sampling equipment and/or analysis
- For gas energy content – Online gas chromatography
- For liquids – Sampling systems and water monitoring (BS&W)
- In-situ calibration and proving mechanism using either prover loop or master meters. Different arrangement would require different maintenance procedure.