In this paper, an equivalence relation on the class of t-norms induced by a T-partial order is provided and discussed. The equivalence classes linked to some special t-norms are characterized as well as some properties preserved by the introduced equivalence. Defining the set of incomparable elements with respect to the T-partial order, this set is deeply investigated. Finally, we give an answer to a recently posed open problem. (C) 2014 Elsevier B.V. All rights reserved.