While Positive Material Identification (PMI) is a highly effective method for verifying metal composition, it does have certain limitations. One major drawback is that PMI primarily analyzes surface elements and may not detect variations within the deeper layers of a material. Additionally, some techniques, like X-ray fluorescence (XRF), struggle to identify light elements such as carbon, which is crucial in differentiating certain alloy grades. This can make PMI less effective for applications where precise carbon content analysis is required, such as in stainless steel and carbon steel differentiation.

Another limitation is that PMI equipment, especially high-precision devices like optical emission spectrometry (OES), can be costly and may require skilled operators for accurate results. Environmental factors such as surface contamination, coatings, or rust can also affect the accuracy of readings, necessitating proper surface preparation before testing. Furthermore, while PMI is excellent for alloy identification, it does not assess mechanical properties like hardness, tensile strength, or impact resistance, making it necessary to use complementary testing methods for a complete material assessment.