GB/T 19780-2005Capacity calibration of spherical metal tanks - Total station external measuring method (English PDF)
球形金属罐的容积标定 全站仪外测法
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Issued by
General Administration of Quality Supervision, Inspection and Quarantine; Standardization Administration of the PRC
Level / Type
National · Recommended
Issue date
May 25, 2005
Implementation date
November 1, 2005
Scope
GB/T 19780-2005 is the English-translated version of 球形金属罐的容积标定 全站仪外测法.
China's national method for calibrating the capacity of a spherical storage tank by measuring it from the outside with a total station. It specifies the principle, the instruments, the measurement procedure, the calculation of the capacity table and the uncertainty for the external measuring method applied to spherical metal tanks.
A spherical tank holds liquefied gas under pressure - LPG, ammonia, ethylene - and the quantity in it is determined not by weighing but by measuring the level and reading the capacity from a table.
That table is the tank's legal measure: the custody transfer of everything that enters and leaves the vessel over its life depends on it, so the calibration is a metrological operation with commercial consequences.
Calibrating a sphere is harder than calibrating a cylinder. It cannot be filled with measured water, because a pressure sphere is not designed to carry the weight of a full water charge and because the vessel is in service.
It cannot be strapped like a vertical cylinder either, since a sphere has no constant circumference.
What can be done is to survey the shell from outside: a total station set up at defined stations measures a large number of points on the surface, and the true shape - which is never an exact sphere, since fabrication from formed plates and the settlement of the supports both distort it - is reconstructed from those points and integrated to give volume as a function of level.
The standard fixes the number and distribution of the measured points, the station geometry, the instrument accuracy required, the corrections for plate thickness, for temperature and for internal fittings that displace liquid, the calculation, and the uncertainty of the resulting table. Issued on 25 May 2005 and in force since 1 November 2005.
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Document preview — GB/T 19780-2005
National Standard of the People's Republic of China
- ICS
- 75.080
- Classification
- E 30
Issued by: General Administration of Quality Supervision, Inspection and Quarantine; Standardization Administration of the PRC
Contents
- 1 Scope
- 2 Normative references
- 3 Terms and definitions
- 4 Principle of the method
- 5 Instruments and equipment
- 6 Preparation before measurement
- 7 Measurement procedure
- 8 Calculation of the capacity table
- 9 Uncertainty of the result
- 10 Calibration certificate
1 Scope
This standard specifies the principle, the instruments, the measurement procedure, the calculation of the capacity table and the uncertainty for calibrating the capacity of spherical metal tanks by external measurement with a total station.
The table is the legal measure
A spherical tank holds liquefied gas under pressure, and the quantity in it is found by measuring the level and reading a capacity table.
Every custody transfer into and out of the vessel over its whole life rests on that table.
And a sphere cannot be calibrated the easy ways
It cannot be filled with measured water: a pressure sphere is not designed to carry the weight of a full water charge, and the vessel is in service anyway.
It cannot be strapped like a vertical cylinder either, because a sphere has no constant circumference.
So the shell is surveyed from outside
A total station at defined stations measures a large number of points on the surface, and the true shape is reconstructed from them and integrated to give volume against level.
True shape, not sphere - fabrication from formed plates and settlement of the supports both distort it, and that distortion is precisely what the calibration has to capture.
What has to be fixed
The number and distribution of measured points, the station geometry, the instrument accuracy, and the corrections for plate thickness, temperature and internal fittings that displace liquid.
Then the calculation and the uncertainty of the resulting table, without which the figure has no metrological standing.
......
This preview omits tables, figures, formulas and parts of the technical clauses. The complete document — 15 pages — is available in the English PDF.
Referenced standards
Similar standards
GB/T 13236-1991|GB/T 17286|JJG 168-2005|GB/T 19780-2005|GB/T 9251-2011|GB/T 21449-2008
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