原油贸易计量中净重量计算方法的差异分析

Analysis on Difference of Net Weight Calculation Methods in Crude Oil Trade Measurement

原油贸易计量分为动态计量和静态计量。油量计算先得到20℃毛体积,再计算出毛重量、20℃净体积和净重量。通过分析和研究这些标准发现,各类标准的计算顺序存在差异,一类是先计算出毛重量再计算净重量;另一类是先计算20℃净体积再计算净重量。两类计量方法均有相关理论支持,但贸易双方不知晓差异的存在。通过具体的计算实例,给出了采用不同方法计算净重量带来的差异。以一批100 000 m^3不同密度原油计量为例,20℃密度在850.0~950.0 kg/m^3、水的质量分数在0.25%~1.00%时,两种计算方法差异率为0.13‰~1.52‰。经过分析可知,当密度越小、水的质量分数越大时,差异率越大,与贸易双方规定的小于3‰差异率范围相比更为显著。建议贸易双方在拟定交接合同时应规定检验标准,规避因计算方法不同带来的争议。

Crude oil trade measurement is divided into dynamic measurement and static measurement. The gross volume at 20 ℃ is obtained first, then the gross weight, net volume and net weight at 20 ℃ are calculated. Through the analysis and study of the calculation standards, it is found that there are differences in the calculation order of various standards. One is to calculate the gross weight and then the net weight;the other is to calculate the net volume at 20 ℃ and then the net weight. The two kinds of measurement methods have relevant theoretical support, but the two sides of trade do not know the existence of differences. The difference of net weight calculated by different methods is given through a specific calculation example. Taking the measurement of a batch of 100 000 m^3 crude oil with different density as an example, when the density of the crude oil at 20 ℃ is 850.0~950.0 kg/m^3 and its water content is 0.25%~1.00%, the difference rate of the two calculation methods is 0.13 ‰ ~1.52 ‰. It can be seen from the analysis that when the density is smaller and the water content is higher, the difference rate is larger, which is more significant than the difference rate of less than 3 ‰stipulated by both sides of the trade. It is suggested that the trade parties should stipulate inspection standards when drafting the handover contract to avoid disputes caused by different calculation methods.