Oil and its wide range of derivative products
make it one of the most important indicators of economic and social development globally. Therefore, it becomes necessary the storage of the product to ensure its production and reserves. The storage of such fluids is generally in vertical tanks, regulated by a specific legislation: American Petroleum Institute (API).
The dimensioning test area in such tanks is included in the API standard under the Manual of Petroleum Measurements Standard (API MPMS). The objective of these standards is to establish the methods for obtaining and making measurements and tests that determine the tank capacity chart showing the volume of fluid contained in each centimeter of height of the tank.
There are storage tanks whose service involves the movement of petroleum fluids between two independent parties, called tax measurement or custody transfer. The dimensioning of such tanks requires compliance with the standard and conformity under recognition or accreditation which guarantees the reliability and proper application of the test and adjustments and corrections of the rules by which it is regulated. These regulation requires the testing to be evaluated through external audits by the competent assessment bodies.
ENAC is the Spanish representative of the European co-operation for Accreditation (EA) and a signatory to the Multi-Lateral Agreements, concluded by over 60 countries. Its function is to evaluate, through audits, that the conformity assessment bodies (laboratories, inspection and certification bodies and verifiers) are technically competent.
Storage tanks should be calibrated at least once in a maximum time period of 15 years, as long as there hasn´t been any alteration both in the structure of the tank and its accessories, and in the service condition of the fluid, in which case it should dimension the tank before commissioning.
After performing these checks, and based on the result of these variables, we proceed to the recalibration or re-calculating of the capacity chart.
The test consists in obtaining optical measurements using a total station from the center of the tank. After the data is treated, the circumferences that make up the tank are obtained at different heights. Knowing the condition in which the contained fluid works, different corrections are made based on the temperature and hydrostatic pressure to the working equipment, and the nature of the fluid itself.
CubicApplus is the Applus+ activity intended to calibration of vertical cylindrical tanks for liquid storage.
Applus+ is regulated by the API MPMS 2.2A, 2.2B, 2.2C, 2.2D and 2.2G / and ISO 7507-1, -2, -3, and ISO 7507-4 standards, both in the operational method as in the pre-trial actions, and for the comprehensive calculation of the uncertainty of the method.
Applus+ has ENAC accreditation for the testing process for tanks measurements, meeting the API MPMS 2.2D and ISO 7507-4 standards. Thus, the laser scanner, a method outside the legal framework is not used. The Applus+ equipment, unlike the laser, measure directly in field.
As a guarantee of accuracy and uncertainty of the method, a pattern bar of invariable material is used to verify the EODR equipment (electro-optical method from inside of the tank). It also has a verification calendar, in addition to the corresponding external calibration of the equipment under recognized organisms by ENAC and the CEM (Spanish Metrology Centre).
The calculation of the uncertainty of the method is very rigorous and includes all the variables that are part of the test, as well as the variations that may arise during the verification of the optical equipment.
The final outcome is a chart showing the capacity in the tank every centimeter high, depending on the type of contained fluid and the working conditions, with a reduced associated uncertainty.