This paper explores uplink communication in cell-free (CF) massive multiple-input multiple-output (MaMIMO) systems, employing semi-blind transmission structures to mitigate pilot contamination. We propose a simplified, decentralized method based on Expectation Propagation (EP) for semi-blind estimation challenges. By utilizing orthogonal pilots, we preprocess the received signals to establish a simplified equivalent factorization scheme for the transmission process. Moreover, this study integrates Central Limit Theory (CLT) with EP, eliminating the need for new auxiliary variables in the factorization scheme. We also refine the algorithm by assessing the variable scales involved. A decentralized approach is proposed to significantly reduce the computational demands on the Central Processing Unit (CPU).