Measuring tanks or level measuring equipment do not need to be approved by the Norwegian Metrology Service before use, as long as they are calibrated and in accordance with the requirements of the Regulation on calibration of measuring tanks used for financial settlement. Approvals issued before this remain valid for the specified period, provided that all conditions on the certificate are met. The owner or user of the tank is responsible for ensuring that the requirements of the regulation are met, while the Norwegian Metrology Service supervises compliance.
The regulation applies to both stationary and mobile tanks, but only tanks with a capacity of less than 20,000 m³.
A stationary measuring tank is permanently installed and secured in place so that its position and inclination remain constant. A mobile measuring tank can be moved between different locations, and may for example be mounted on a lorry, train or ship, or built into a frame structure.
For mobile measuring tanks, procedures must ensure that measurements remain correct when the tank is moved or its inclination changes – either by correcting the reading or the tank table, or by verifying correct positioning. Measures should also be in place to prevent deformation during transport, for example through physical protection.
Accuracy requirements must be considered when designing and constructing new tanks. It should be noted that the uncertainty requirement is based on the total capacity of the tank, meaning that higher uncertainty is accepted for larger tanks. Large tanks may therefore have unacceptably high uncertainty for their use, even if they meet the regulation.
Be aware that measuring tanks used in international trade (for example with petroleum products) may be subject to stricter requirements than the Norwegian regulation.
Level measuring equipment may include, for example, tapes, radar or laser. The regulation does not set accuracy requirements for level meters themselves, but they must be sufficiently accurate to ensure that combined measurement uncertainty does not exceed 0.5% of the tank’s capacity.
The Act relating to Units of Measurement, Measurement and Normal Time (20 December 2007 No. 1723) sets requirements for length measures, including conformity assessment, but these will not be detailed here.
The owner or user of the measuring tank is responsible for ensuring that the tank (and level measuring equipment) is calibrated.
Calibration must be documented by a competent body and show results in a tank table specifying volume at various levels in the tank. The division must be such that the uncertainty requirements can be met.
Calibration is normally carried out during construction, when scaffolding inside the tank allows for accurate and efficient measurement. All installations inside the tank (deadwood) must be documented, preferably with photographs, so that subsequent calibration is based on the same net geometry (as built configuration).
The tank must be recalibrated every ten years. This may be postponed for up to three years (a total of 13 years after the previous calibration) if other service is planned during that period.
Measuring tanks may be exempt from the recalibration requirement if:
Level meters must be calibrated every three years. This deadline may also be extended by up to three years (a total of six years) if other service is planned during that period.
The uncertainty in stated volume must not exceed 0.5% of the tank’s capacity. The uncertainty must be given with approximately 95% coverage probability (coverage factor k=2).
For smaller installations it may be sufficient to refer to the uncertainties given on calibration certificates for the tank and level equipment, but the Norwegian Metrology Service may require calculations to document combined measurement uncertainty.
For calculation of combined measurement uncertainty, see the PDF below.
Calculation of measurement uncertainty in tanks (In Norwegian)
The Norwegian Metrology Service supervises compliance with the requirements for calibration and use of measuring tanks and level meters in Norway. The following forms of supervision may apply:
During supervision, the user must be able to document:
During on-site supervision, the user must also document that any changes made to the tank since the last calibration have no impact on the measured volume.
If the requirements of the regulation are not met, the Norwegian Metrology Service may require corrections within a specified deadline. In more serious cases, the Service may prohibit use of the tank for financial settlement and impose administrative fines.
Supervision is subject to fees in accordance with the Regulation on Units of Measurement and Measurement.
General guidelines
The Norwegian Metrology Service offers on-request verification as one of our services. As a neutral third party, we can carry out verification and in-use inspections and issue documentation. We have the equipment and expertise to help your enterprise meet the requirements for measurements.
The Norwegian Metrology Service supervises that requirements for calibration and use of measuring tanks and level gauges are upheld in Norway. The following forms of supervision may apply:
1) The Norwegian Metrology Service requests documentation of calibration, etc.
2) On-site inspection of the tank.
3) Supervision of the internal control system. This applies only to enterprises required by the Norwegian Metrology Service to have internal control.
Phone:
64 84 84 84
E-mail:
postmottak@justervesenet.no
Contact form:
Fill in our contact form, and we will respond as quickly as possible.
Go to contact form
