ASTM D4940-15 (2020) pdf free.Standard Test Method for Conductimetric Analysis of Water Soluble lonicContamination of Blast Cleaning Abrasives.
Rinse the conductivity cell in reagent water until therinse water is a cleanliness of 5.0 umholcm or less.
Rinse the conductivity cell two or three times with thefiltrate then determine conductance in accordance with theoperating instructions of the instrument. Use successive por-tions of the sample until a constant value is obtained.
The calibration value of the cell constant (both asmeasured and as predetermined and supplied with the conduc-tivity cell), the date,and the name of the person checking thecalibration.The material, date,readings，and mean in umholcmalong with name of person conducting the tests and identifi-cation of the apparatus.On the basis of five replicate interlaboratory tests of this test method in which three operators in threelaboratories analyzed, in duplicate, six blast cleaning abrasives containing ionic contamination,the within-laboratory coeffi-cient of variation (after rejecting results from one set ofreplicate tests as outliers)，was found to be 1.7 % with 20degrees of freedom (df) and the between-laboratory standarddeviation coefficient of variation was found to be 7.4 % with 15df. Based on these coefficients, the following criteria should beused for judging the acceptability of results at the 95 %confidence level:Two results，each the mean of tworuns obtained by the same operator should be consideredsuspect if they differ by more than 5 % relative.Two results，each the mean of tworuns, obtained by operators in different laboratories should beconsidered suspect if they differ by more than 22 % relative.12.2 Bias:
Bias can be present because of the mobility ofvarious ions.The hydrogen ion has a much greater mobilitythan the hydroxyl ion or other ions so that at low pH’s theconductivity will be relatively higher than at high pH’s for thesame ionic concentration.However, the bias introduced by thisfactor is in the proper direction.That is., high conductivity dueto a lower pH of the contamination would normally indicategreater corrosion potential.A bias may be introduced by extraneous contamina-tion or from reduced sensitivity of instruments for low levels ofcontamination in the range of conductivity between 0 and 30umholcm.ASTM D4940 pdf download.