Magnetic flux leakage (MFL) is a non-destructive testing method used to inspect ferrous materials. However, there are a variety of factors that can affect the MFL inspection tool’s ability to detect and characterize anomalies. An orthogonal experimental design (OED) method is applied to study the effects of apparatus parameters on MFL signals. Integration of OED method of analysis into a routine sample preparation technique could improve the repeatability and quantization capabilities of MFL tools. Three key apparatus parameters, namely permanent magnet (PM) height, magnetic concentrator (MC) length and backing iron (BI) length are chosen for the present study. The importance of each of these key parameters on MFL signals for different defects is determined by a series of experiments.