The reason for poor reproducibility of the results obtained by two test methods for electric oil acid value detection

GB/T 264—1983(Petroleum products—Determination of acid number)and GB/T 28552—2012(Determination of acid number in transformer and turbine oils in service by BTB method(BTB method))

was analyzed.It finds out that

when the acid value of the oil is relatively high

within the color changing range of the indicator in above two standards

the pH value of the solution varied little with the alkali liquor volume

and no titration jump occurred

so the solution's color had no sudden change

resulting in difficult in judging the titration end-point.It suggests that

when using alkali bule 6Bas the indicator

the titration end-point be the point when blue color disappears;when using BTB as the indicator

the titration end-point be the point when yellow changes for yellowish-green;for the oil with heavy color which is difficult to determine the titration end-point

the sample weight should be reduced.After the above modifications

the poor reproducibility of the results has been greatly improved

which is beneficial to the electric oil quality supervision.