Abstract: Described herein is a system for monitoring arc-welding processes, comprising arc-voltage sensor means (21) and arc-current sensor means (22), means (23) for acquisition of voltage values (V) measured by said arc-voltage sensor means (21) and of current values (I) measured by said arc-current sensor means (22), and processing means (25) configured for processing said voltage values (V) and said current values (I) for calculating one or more vectors of time values (Ton[j]; TonV[j), TonI[j]) corresponding to a state of arc of the arc-welding process, According to the invention, said processing means (25) are configured for executing the operations of: calculating reference values (TssupV, TsinfV, TssupI, TsinfI) of arc time (Ton[j]; TonV[j), TonI[j]) via the steps of: calculating a statistical distribution of respective arc-time vectors (Ton[j]; TonV[j), TonI[j]) obtained from voltage values (V) and from current values (I), measured during execution of one or more reference welds; and calculating as referen