If we consider the pellet properties in order of increasing importance, the hierarchy is as follows (figure). Metallurgical properties such as reducibility are important, but the chemical composition of the pellets and the physical characteristics (size, strength) are still of primary importance, since a highly reducible pellet with a low iron content, low strength and inappropriate size in a blast furnace and direct reduction plants will worsen the gas permeability of the bed and the efficiency of contact of the reducing gas with the charge material and will negate all the advantages inherent in its high reducibility. 

      The quality of the pellet should maximally correspond to the requirements of subsequent processing stages (blast furnace or metallization furnaces). The following tests are used to assess the quality of pellets for a blast furnace (figure and               ).

​    Taking into account the specifics of metallization furnaces, the following tests are additionally carried out to assess the quality of pellets: ISO 11256 - method for determining the conglomeration index, ISO 11257 - determination of the degree of destruction and metallization of raw materials for processing during direct reduction, ISO 11258 - determination of the degree of reduction and metallization of raw materials for processing during direct reduction in gas reduction processes. 

      Almost all tests require special equipment and can be performed only in specialized laboratories. Pellet factories conduct all types of physical tests of pellets and some factories have installations for testing LTD and swelling index. In addition to these definitions of pellet quality, an indicator of pellet yield was introduced. A certain pellet compressive strength limit was set for each pellet type and consumer requirement, below which pellets were considered substandard. By testing each pellet type and comparing yield, compressive strength, and LTD statistics, it is possible to determine with a high degree of probability the dependence of the LTD indicator on yield and pellet strength. For clarity, diagrams show the test results, where to obtain LTD+6.3mm of at least 70%, the pellet strength should be at least 275kg/pellet and the yield should be at least 67%. To work with this tool, it is necessary to develop statistics for each specific type of pellets with subsequent evaluation of the results.