2009HG/T 20519-2009 Specification on content and procedure of detail design for chemical plant
1993HG 20519.31-1992 Legends of equipment and machines in the pipeline and instrument flow chart
HG 20519.31-1992 Legends of equipment and machines in the pipeline and instrument flow chart was changed to HG/T 20519-2009 Specification on content and procedure of detail design for chemical plant.