Comparison that shows the differences between a PFD and P&ID : PFD P&ID Used during construction? No Yes* Shows all process and service piping? No Yes Indicates presence of all controls? No Yes Shows all motors? No Yes Shows thermal insulation? No Yes Shows major equipment? Yes Yes Shows flow quantities? Yes No Shows stream compositions? Yes No This the most revealing distinction. The P&ID on a job site is probably one of the most used documents. Everyone working on piping has one in pocket, and it is constantly spread out during discussions. PFDs, on the other hand, are never seen on a job site. They are available, in the files, but not used. The PFD is a drawing needed early in the project. Indeed, the PFD is the most important drawing while the mass balance is being prepared. Later, the PFD guides the preparation of the P&ID. Finally the P&ID supplants the PFD, totally eclipsing it. Both PFDs and P&Ids can be characterized as Communication tools Records Aids to thought processes
FLOW DIAGRAMS 1.0 TYPES OF FLOW DIAGRAMS There are four main types of flow diagrams - Process Flow Diagram (PFD) - Process Piping and Instrument Flow Diagram (P&ID) - Utility Balance Diagram - Utility Piping and Instrument Flow Diagram (UFD) 2.0 PROCESS FLOW DIAGRAM 2.1 The PFD is meant be a description of the process. It serves the following functions : - Shows the basic processing scheme - Shows the basic control concept - Shows process information from which equipment can specified and designed - Provides the basis for development of the P&ID - Serves as a guide for the operation of the plant 2.2 The PFD includes the following information : - Material balance data (sometimes on separate sheets) - Flow scheme and direction of flow - Basic control instrumentation - Temperatures - Pressures - Vessel dimensions - Heat exchanger and fired heater duties 2.2 cont d Not all equipment is shown; spares and parallel equipment are often omitted. However, the are indicated by equipment numbering procedure 2.3 The information is presented as follows :
2.3.1 Some equipment is shown using standard symbols regardless of actual type. Examples : - Pumps and drivers - Compressors and drovers - Heat Exchangers - Filters 2.3.2 Other equipment is shown in elevation in a simplified rendering of the actual arrangement. Examples : - Heaters - Towers and columns - Reactors - Vessels and tanks - Dryers 2.3.3 Instruments are indication showing location of variable being controlled and location of acting device, usually a control valve. Variable type is indicated in the bubble (such as FC for Flow controller ) but r or I for recorder or indicator read-out is not shown, nor is the instrument number. Details are left to be shown on the P&I. 2.0 PROCESS FLOW DIAGRAMS 2.3 cont d 2.3.4 Valuing is generally omitted. A valve is only shown where it can clarify understanding of intermittent or alternate flows such as dryer regeneration or system bypass. 3.0 PROCESS PIPING AND INSTRUMENT FLOW DIAGRAM 3.1 The P&I provides a detailed definition of piping, instrumentation, and equipment. It serves the following functions: - Describes equipment - Shows all instrumentation - Shows piping and valuing - Defines the job scope - Provides the basis for detailed design
- Shows relationship of vendor supplied terms to contractor s work - Used to train personnel - Aids in trouble shooting during startup and operation. 3.0 PROCESS PIPING AND INSTRUMENT FLOW DIAGRAM con d 3.2 The P&I includes the following information : - All equipment with item number - Titles of towers, reactors, thanks and package equipment - Dimensions of tower, vessels and tanks - Vessel elevations - Pumps, compressors and their drivers according to equipment type - All piping with line numbers, sizes and specification. Indicate whether traced or buried - All valves shows according to type - All packaged equipment with tie-ins to lummus piping or instrumentation - Sample connections - All instrumentation with numbers function types and whether electronic or pneumatic - In-line instrument sizes - Control valve sizes and action on air failure - Relief values with size and set pressure 3.3 The information is presented as follows : 3.3.1 Tower, reactors, drums, tank and heaters are generally shown in line in the upper half of the P&I in approximately their relative proportions. 3.3.2 Pumps and compressor are shown in line in the lower quarter of the drawing 3.3.3 Other equipment should be located to represent as well as possible the actual physical relationships, such as overhead condenser above the reflux drum or reboilers adjacent to a tower.
3.0 PROCESS PIPING AND INSTRUMENT FLOW DIAGRAM 3.3 con d 3.3.4 Allow an ample amount of space for package systems equipment such as heaters and compressor so that the auxiliary equipment and instrumentation normally associated with such equipment can be properly shown. 3.3.5 Process lines generally enter and leave at the bottom of the drawing. 3.3.6 Utility lines enter and leave the drawing adjacent to the equipment they service. 3.3.7 A sheet is developed for each job showing legend, symbols and general notes. The P&I should be consistent with this sheet. Additional symbols added to the master sheet where no suitable symbols exist. 4.0 UTILITY BALANCE DIAGRAMS 4.1 The Utility Balance Diagram is s diagrammatic summary of a utility. It serves the following functions : - Shows utility usage for each piece of equipment serviced - Shows total usage so generating system can be specified - Allows related streams to be established (i.e blowdown, makeup, chemical treatment). - Shows interrelationships of various levels of the utility (i.e. high pressure and medium pressure steam). 4.2 Utility Balance Diagrams are generally made only for the more complex systems. For example : - Steam and condensate - Cooling Water - Fuel gas/oil - Effluent systems 4.0 UTILTY BALANCE DIAGRAMS con d 4.3 The Utility Balance Diagram includes the following information : - Utility usage for each item of equipment. Two or more cases may be shown but one should be denoted as the design case.
- Total usage. This means simultaneous usage and may be less than the arithmetic total due to interactions or phasing of the operation. - Control concept for maintaining the relationship between different level of the utility. (i.e letdown control for steam systems). 4.4 The information is presented as follows : - Consumers are shown by item number in block arranged according to utility level - Actual physical layout is ignored ; in fact, it is generally undetermined when these drawing are begun. - The generating system portion shown in the manner of a PFD. 5.0 UTILITY PIPING AND INSTRUMENT FLOW DIAGRAM 5.1 The UFD defines the utility service system in much the same way a P&I defines a process system. The two types of UFD s are : - System UFD shows production of the utility (i.e., cooling tower, steam generator). - Distribution UFD shows headers, subheaders, utility stations, etc. 5.2 The UFD includes the same information a utility as a P&I does for the process.
NOT OIL TO (FROM E-2) COOLING WATER TO (FROM E-1) FLARE GAS FROM V-1 TI2 TI2 TI2 18 & CW 10 " 19 & CW 10 " 15A-2" 16A- 6" IH 17-6" IH 18ACW=10" 19ACW=10" 15A-2" 20 AIA = 1 1/2 " 21 AUA = 1 1/2 " 22 AIA = 1 1/2 " 23A5 = 2" IM 5.0 UTLITY PIPING AND INSTRUMENT FLOW DIAGRAM Con 'd 5.3 The information is presented as follows 5.3.1 For a system UFD, the presentation is the same as for a P &I. 5.3.2 For a distribution UFD, the piping is shown as if super shown schematically in the same sequence as the actual piping. 5.3.3 More than one utility system can be shown on single drawing if space permits. Systems frequently combined are. - Cooling water, quench water, utility and other miscellaneous water system - Plant air, instrument air, nitrogen or other miscellaneous gases - fuel systems 5.3.4 Utility generating systems and their distribution pipe may be shown on the same UFD when space permits.