ISO 8222:2020 Petroleum measurement systems — Calibration — Volumetric measures, proving tanks and field measures (including formulae for properties of liquids and materials)

ISO 8222:2020 Petroleum measurement systems — Calibration — Volumetric measures, proving tanks and field measures (including formulae for properties of liquids and materials). Volumetric measures in glass are a category of cylinders or flasks with volumes less than 10 1. These are not covered by this document but may be used as additional volume measures for use in the calibration process. Standard sizes for glass measures are shown in Annex C. Specifications for such measures are given in ISO 4788. Measures can he top filled or bottom filled. Drainage of test measures can be by inverting the measure and pouring out the contents or by draining through a bottom connection and valve. Proving tanks are drained from the bottom. Volumetric measures are constructed of materials which should be resistant to corrosion by water and any other fluid which may be used, including cleaning fluids. Stainless steel is the most common material; however, other metals can be used, particularly in older measures. Carbon steel can be utilized for large secondary measures if internally protected from corrosion through coating with epoxy resin, phenolic or glass. The use of unprotected carbon steel should be avoided as it is subject to corrosion and deposition even if hydrocarbons are the only fluid to be used. A low or well-defined coefficient of expansion of the material is chosen, hence the use of materials such as aluminium and plastic is not normally acceptable (carbon fibre composite being the exception as it has a very low coefficient of expansion). The material used needs to be documented and the coefficient of expansion given in the design documentation and calibration certificates. This should also be engraved on the marking plate where possible. Suggested default coefficients of expansion of materials are given in AnnexA. Construction and design are such that there is minimal distortion of the measure when filled or emptied. This is achieved through adequate thickness of the materials. Strengthening bands and shaped end closures provide adequate stiffness to the measure. Measures are exclusively cylindrical in shape. The design and construction should ensure all liquid drains from the measure when it is emptied and all air is expelled when it is filled. The cylindrical section should he vertical or at a slope, with ends constructed with a domed or coned shape. Slopes on cones and cylinders should be approximately 30° to the horizontal. Standard proving tanks and test measures have...