Dear Durate,
the ferrography test is a detaild test to know more about the wear causes utilizing the quantitve and qualitative informations and especialy the size, shapes, color, of wear debries. the cost of the test is relatively up, therefor the test is used after you remark an increase in the the level of wear metal in the oil, another thing is that you nead the know more about the oil such as viscosity, VI, FP,TBN, TAN... witch can not be delevred by ferrography. you take in considiration also that it is more reliable to do all the test in one laboratory and get one report than to do some tests in a laboratory and another tests(may be for the same machine)in another tests.
A nother question is how much time you need for redemption the prise of your laboratory.
Noureddine.T
Condition Monitoring Engineer.