The results of your electrochemical tests provide an accurate indication of the corrosion rate.  However, this measurement is only accurate for the material, electrolyte and test conditions in your test.  I may or may not be a reasonable indication of the corrosion rate that would be experienced for that material outside of the laboratory.  Corrosion processes can be very simple or they can be extremely complicated.  It all depends upon the material, the environment and the effect that corrosion products and bi-products have upon the system.  It depends upon how well your test sample reflects the metallurgy and chemistry of the materials used outside of the lab.  So the only answer that can be given is that "it depends".  It depends upon how accurately your test simulates the real application.  It depends upon whether you have identified, captured and controlled all of the important parameters for your corrosion process.  It depends upon whether the acceleration process that you used for your lab test skewed the results too much.  It depends ...

So, for a general corrosion test design question such as this, the only answer that can be given is that the electrochemical measurement of corrosion provides a snapshot indication of the corrosion that is occurring on the metal that you have placed into a controlled environment in the lab.  Whether this provides an accurate assessment of the corrosion beyond that specific test is dependent upon far too many variables to discuss for such a general question.

Corrosion of a metal/alloy is the combination of chemical and electrochemical reactions occurring at the surface. When we conduct electrochemical experiments on any selected specimen (metal or alloy), it is designed particularly according to the corrosion in natural environments. The difference is that with electrochemical experiments, we can control the parameters and study the effects of different parameters, such as temperature, composition and concentration of the electrolyte, presence/absence of aggressive ions, synergistic/aggressive effects of binary salts, etc., separately or in combination. To get more realistic results, we select a slow scan rate. The slowest the better. Generally we select a scan rate slow enough to obtain a result in a real time scale so that it is possible to observe the changes occurring on the surface, such as passivation and pitting as in the case of stainless steels or the extent of uniform corrosion in the case of non-passivating materials. The scan rate should be relevant enough so that the chemical reactions must not compete with the electrochemical reaction; e.g., in case of magnesium, the chemical reactions are faster than electrochemical reactions. At the same time the electrolyte composition has to be simulated according to the study. 

polarization resistance obtained from one DC method will not agree with the other DC method.This is because of the kind of perturbation

AC method offers a polarization resistance completely different

DO NOT TRY TO COMPARE

but one method can be use to evaluate the inhibitors , coating performance

please see my papers on inhibitors  and theory there in

If you can get see my awarding winning paper on

Electrochemical methods of determining instantaneous corrosion rates

J electrochemical society of india 1975

I totally agreed with the above answers. Electrochemical measurement is very sensitive. So many variables such as the electrolyte concentration and other environmental conditions are factors that could cause variation in your measurement. However, if the simulated condition is carefully carried out, the variation would not be much.

Stephen's post gives you the information to answer this question. In theory if you have exactly reproduced the field condition in your experiment then the corrosion rates should be the same. However, a field condition (e.g. a pipeline) will in the majority of cases vary considerably from a laboratory experiment. Factors such as flow variations, solids, the metal surface and ranged parameters such as gas concentrations, salinity etc. will cause variation from the laboratory corrosion rate. In many cases the objective of the laboratory experiments is to establish an upper limit for the corrosion rate to allow a corrosion risk assessment. Designing experiments that reproduce a real system is very difficult. For this reason you need to be very careful when using laboratory data to make materials selection decisions.

there is a book by AILOR

corrosion testing procedures- please see

Well, thanks everyone for your Invaluable Information  provided to the given topic. I have a query inline to the discussion, Is there  any technique/method to asses to evaluate the approximate life time of component/Material  when it is exposed to a given environment  over a period of time (By assuming a static environmental  effect Viz. Conc, temp and etc..)?. Please through some light to my query.

The short answer is no, but you can approximate the life time of the metal if you performa a lab corrosion test with concentrations, temperature and so on quite close to your real environment assumed to be static. 

Gopal it is million dollar question

you cannot predict nature

hence we use accelerated tesTing

there is a corrosion map of india  prepared by CECRI KARAIKUDI India

please contact www.cecri.res.in

Many thanks Prof V.S Muralidharan for your valuable suggetion

corrosion as many other processes in nature are very complicated. In the lab we usually isolate very few parameters (sometimes only one) trying to understand an effect or a process but in real life time, temperature and other parameters changes in time, some parameters might change with temperature etc' etc' . so the answer in "never". Lab experiment though is a good simulation to show major effects and help to understand. It might get close, very close but will never match 100%.

The electrochemical  methods are very specific and accurate forms of corrosion analysis. Electrochemical analysis is time saving and very much less laborious. But the parameters that are to be used must be done with proper caution and  care. Any mistake made will lead to mistakes in results & improper conclusions. 

i am an electrochemist with 48 years experience still enjoy fellowships

only weight loss is a reliable method

electro chemical methods have numerous limitations

1994 i wrote a book modern aspects of corrosion and its control with prof SNBanerjee

it is from NISCOM- out of print

Respected prof. Muralidharan, The weight loss method or the gravimetric method is a precise method for corrosion analysis. there is no denying that. but sir being a current research scholar in the field of corrosion I find that current publications support more of electrochemical analysis. I personally find that weight loss analysis has more chances of human error. 

 weight loss should be done as per AILOR book

do all methods and discuss results

I agree with Prof. Stephen 

Gentlemen, I think you miss the question. please reread

Thanks all for valuable answers .. 

I agree with Prof. Muralidharan and Dr.Stephen N Smith .  There are limitations to the interpretation of electrochemical testing since the results are true only to that environment, and existing variables being controlled.  In real life multiple other factors can influence the test data.  At the same time EC testing  does give one the directions to pursue.  Weight loss, salt spray tests etc become important when all the environmental influences are considered.

Yes, the lab tests are great indicators of expected performance, but because the variables are so well controlled the results are not entirely reflective of actual service environments, which have countless uncontrolled or unforeseen variables.

For a sample run on e-chem set-ups the best thing you can say is that an ideal clean sample will corrode at this rate in this environment. IF you use the same exposure environment from the site you can say that an idea clean sample will corrode at this rate in this environment under controlled conditions. 

You can also say use field results such as % loss to extrapolate your results, if a sample in field service shows 35% loss in 15 years and you get a sample to 30% loss in 1000 hours you can say that your exposure conditions are reflect 12 years of exposure, this is your corrosion rate under these extrapolations.

I've seen fairly good matches for the PR plots with actual service, but you also have to consider that field exposures may develop patinas over time which will slow corrosion. Another reason why it is good practice to say that you are using extrapolations and ideal samples.

I agree. Good Point and well explained.

No method is ideal.Virtually every test has its own limitations rather have some merits and demerits.

So called accelerated conditions may partly simulate actual field conditions but can not mimic the real ones dye to limitations in labs.

The results of one test may not be comparable in numbers but will definitely give an idea on the overall rates and behavior.

Agree with Dr Muralidharan. weight loss tests give a fair first hand information but they can not throw any light on mechanistic information. On the other hand electrochem test probes suffer from unrealistic facts abd other issues and especially unreliable in actual plant operations.

It all depends on what kind of information you are looking for and which method / technique you have chosen.

It is not corrosion rates only you should be aiming at.

Parvatalu, you are absolutely right. In addition to your answer, electrochemical tests are rapid. in the laboratory tests, the conditions are controlled . But the conditions outside the lab are not controllable. And besides, pilot scale testing should be more closed to the real life scenario compared with the the lab scale

agreed.Thanks