The problem with trying to use linear polarization resistance measurement for coating evaluation is that you have to pass a current through the coating, and you are then trying to measure the associated resistance.  If you are using LPR, then by definition you are only applying +/- 10 or 20 mV of perturbation and the resistance of the coating is very high, so if the coating is any good at all, the amount of current passing is infinitesimally small, so the technique does not provide useful results.

I would suggest that you read around the subject of coating evaluation to gain a broader understanding of the subject.  People use potential logging (to evaluate the change in potential associated with uptake of water and/or aggressive species) because changes in potential precede the onset of active corrosion.  People use electrochemical impedance measurements, because that technique can evaluate changes in the capacitance (initially) of a coating that are associated with the uptake of aggressive species and also can provide an indication of other processes (such as the onset of active corrosion) that may occur at the electrochemical interface.  However, the active corrosion condition may quickly modulate to a diffusion response, which is not very easy to interpret.  In consequence, people also use electrochemical noise analysis, because that technique is exceptionally good to evaluate the onset of localized attack and, generally speaking the onset of degradation and corrosion of coated samples commences at pores or 'holidays' in the coating.  So, whereas impedance measurements effectively provides an averaged response from the whole of the exposed area, electrochemical noise analysis addresses the electrochemical response resulting from the specific attack at active corrosion locations - i.e. just from the pores or holidays in the coating.  

What kind of coat do you use in your work? Next information later.

for this type of corrosion you focus on pitting corrosion , Electrochemical Impedance Spectroscopy would give a better results 

The problem with trying to use linear polarization resistance measurement for coating evaluation is that you have to pass a current through the coating, and you are then trying to measure the associated resistance.  If you are using LPR, then by definition you are only applying +/- 10 or 20 mV of perturbation and the resistance of the coating is very high, so if the coating is any good at all, the amount of current passing is infinitesimally small, so the technique does not provide useful results.

I would suggest that you read around the subject of coating evaluation to gain a broader understanding of the subject.  People use potential logging (to evaluate the change in potential associated with uptake of water and/or aggressive species) because changes in potential precede the onset of active corrosion.  People use electrochemical impedance measurements, because that technique can evaluate changes in the capacitance (initially) of a coating that are associated with the uptake of aggressive species and also can provide an indication of other processes (such as the onset of active corrosion) that may occur at the electrochemical interface.  However, the active corrosion condition may quickly modulate to a diffusion response, which is not very easy to interpret.  In consequence, people also use electrochemical noise analysis, because that technique is exceptionally good to evaluate the onset of localized attack and, generally speaking the onset of degradation and corrosion of coated samples commences at pores or 'holidays' in the coating.  So, whereas impedance measurements effectively provides an averaged response from the whole of the exposed area, electrochemical noise analysis addresses the electrochemical response resulting from the specific attack at active corrosion locations - i.e. just from the pores or holidays in the coating.  

The real problem is that even if you will measure any current passing through the coating (provided it is of dielectric nature) via LPR method, you will not evaluate corrosion current density, since for that you would have to measure what is the resistance associated with charge transfer at the metal-corrosive medium interface. When you describe such a system whereby a metal is coated by some dielectric (e.g. organic coating) which might contain defects you will measure not only charge-transfer resistance (if the medium penetrated up to the metal surface) but also a large resistance associated with ionic conduction in electrolyte solution inside the pores and defects.

Dr Mousa, you asked for recommend paper present comparison study on corrosion behavior of coated steel samples via linear polarization resistance. There are more than one based on such approach. The linear polarization resistance adopted form Potentiodynamic polarization was used to rank the protective property of each coating system, then the difference in the corrosion potential between each coating and bare steel substrate, and the anodic Tafel slope of the bare steel substrate in addition to the obtained linear polarization resistance were used to verify the percent of connected porosity (open pores) within the coating matrix. This approach seems to be able to present results even the connected porosity of < 0.073%. The link below presents the related article.

https://www.researchgate.net/publication/222425131_Corrosion_behaviour_of_magnetron_sputtered_a-_and_b-a_coatings_on_AISI_4340_steel_as_a_function_of_coating_thickness

Article Corrosion behaviour of magnetron sputtered α- and β-Ta coati...