JJG/API体积管标定方法差异及应对方法研究

Research on the difference of JJG/API for volume tube calibration and recommendation of countermeasures

体积管标定是流量计溯源的重要步骤,各国规范、标准有所不同这给用户使用带来诸多不便。本文首先比较国内JJG规程、国际API标准对体积管标定主要技术内容,接着系统分析体积管容积值、重复性计算模型,然后基于国外某油田活塞式体积管校准数据验证,表明两个标准(规范)所计算的标准容积值差异很小(1×10^(-6))、重复性差异较大(可达200×10^(-6));测量次数对重复性差异有着直接影响,API标准、JJG规程的测量次数的重复性差异分别达50×10^(-6)、179×10^(-6),分析指出重复性差异较大主要原因是JJG规程采用贝塞尔公式,API标准采用无极差系数且没有明确置信概率的极差法。通过理论推导及数据验证,将极差系数与置信概率还原到重复性计算公式中,获得普适性处理方法,在测量次数n≥5下API标准、JJG规程重复性差异小,可为以后规程修订、方法选择提供参考。

Volumetric tube calibration is an important process of the traceability of flowmeter,but the standards and benchmarks are different from each other in the countries,leading to the inconvenience for the users.In this paper the main technical contents between the domestic JJG regulations and international API standards for volumetric tube calibration are firstly compared.Then we systematically analyzes the volume value of the volumetric tube and repeatability calculation model.Based on the validation for the calibration data of the piston type volumetric tube in one foreign oil field,we demonstrate that the difference between the standard volume value calculated by the two standards(specifications)is very small(1ppm)but the repeatability has large difference(up to 200 ppm).The number of measurements has a direct impact on the repeatability.The repeatability differences of the API standard and the JJG standard are 50 ppm and 179 ppm,respectively.The analysis indicates the differences arise from Bessel formula of the JJG standard and the polarization method of the API standard free of the polarization coefficient and confidence probability.Through theoretical derivation and data validation,the coefficient of polarization and confidence probability can be reduced to the repeatability calculation formula to obtain a universal counteraction method.For the n≥5 measurements between API standards and JJG regulations,repeatability differences are small.This work can provide reference for the future revision of the regulations and method selection.