You have a group 1 fluid. Now you have to determine if your fluid is "gas" or "liquid". Selection of the diagram for categorization depends on the vapour pressure of your fluid @ design temperature. If your fluid has vapour pressure @ 90C bigger than 0*5 bar g its considered as gas which means your diagram is No. 6. If your Group 1 fluid has vapour pressure @ design temperature lower than 0*5 barg* your diagram is No. 8. Example: water @ 120C. Your fluid is group 2. Vapour pressure of the water at 120C is bigger than 0*5 barg. This means your diagram is No. 7.