Electrical conductivity is a rapid indicator of the ionic content of water. Chloride is one of the ions that can contribute strongly to conductivity, but conductivity is not a chloride-specific measurement.
Why compare them?
When samples come from a stable process stream, a local relationship may be established between conductivity and chloride concentration. Such a model can be useful as a screening tool and can reduce the number of wet-chemistry measurements.
Important limitation
The relationship depends on the water matrix, temperature, other dissolved ions and process conditions. A model developed for one refinery unit should therefore be validated before it is applied to another stream.
Practical workflow: measure conductivity at controlled temperature, determine chloride by the laboratory reference method, plot the paired results, evaluate linearity and residuals, then validate the model with independent samples.