The method for cleaning chemical process and hydrocarbon processing apparatuses is performed by establishing a closed flow circulation loop, under specific operating conditions and in the presence of hydrocarbon-based fluids. The cleaning method is monitored by performing chemical/physical analysis. After cleaning the apparatus(es) can be immediately inserted back into the process. An optional degassing step can also be performed, in case the apparatus(es) has to be disassembled for inspection of maintenance.