Process Diagram Symbols

Process diagram is divided into two major categories: Process Fow Diagrams and Process & Instumentation drawing(P&IDs), sometimes called piping and insrtumentation drawings
A flow diagram is a simple illustration that uses process symbols to describe the primary flow path through a unit.
A process flow diagram provides a quick snapshot ofthe operating unit.Flow diagrams include all primary equipmeent and flows.
A  technician can use this document to trace the primary flow of chemicals through the unit.Secondary and minor flows are not included.Complex control loops and instumentation are not included.

A process and instrument drawing is more complex.
The P&ID includes a graphic representation of the equipment, piping , and instrumentaion. Modern process control can be clearly inserted into the drawing to provide a process technician with a complete picture of electronic and instrument systems.

Process operators can look at their process and see how the engineering department has automated the unit. Pressure, temperature - flow an level control loops are all included on the unit P&ID.

**Key Terms**
**Electrical drawings** --> It shows symbols and diagrams that depict an electrical process.

**Elevation drawings** --> It is the graphical representation that shows the location of process equipment in relation to the existing structures and ground level.

**Equipment location drawings** --> They show the exact floor plan for location of equipment in relation to the plans physicals boundaries.

**Flow diagram** --> It is a simplified sketch that uses symbols to identify instuments and vessels and to describe the primary flow path through a unit.

**Foundation drawings** --> They concrete, wire mesh, and steel specifications that identify width, depth, and thickness of footings, support beams, and foundation.

**Legends** --> It is a document used to define symbols, abbreviations, prefixes and specialized equipment.

**Process and insrtument drawing (P&ID)** --> It is a complex diagram that uses process symbols to describe a process unit; also called piping and instumentation drawing.

Process technicians use P&IDs t identify all of the equipment, instruments, and piping found in their units. New technicians use these drawings during their initial training period. Knowing and recognizing these symbols is important for a new technician. The chemical processing industry has assigned a symbol for each type of valve, pump, compressor, steam turbine, heat exchanger, cooling tower, basic instrumentation, reactor, distillation column, furnace, and boiler. There are symbols to represent major and minor process lines and pneumatic, hydraulic or electric lines and there is a wide variety of electrical symbols.
The following figure shows basic Process and instrument Symbols

**Flow Diagrams**
 New technicians are required to study a simple flow diagram of their assigned operating system. Process flow diagrams typically include the major equipment and piping path the process takes through the unit.As operators learn more about symbols and diagrams, they graduate to the much more complex P&IDs.
 Some symbols are common among plants; others differ from plant to plant. Some standardization of process symbols and diagams is taking place.

Process flow diagram
Figure shown below is a PFD that shows the basic relationships and flow paths found in a process unit.It is easier to understand a simple flow diagramif it is brokendown into sections: feed, preheating, the process, and the final products.This simple left-to-right apporach allows a technician to identify where the process starts and where it will eventually end.
The feed section feed tanks, mixers, piping and valves. In the second step, the process flow is gradually heated for processing. This section includes heatexchangers and furnaces.In the third section, the process is included.Typical examples found inthe process section could include distillation columns or rectors.The process area is a complex collection of equipment that works together to produce products that will be sent to the final section.

Process and Instrument Drawings
A P&ID is a complex representation of the vaious units found in a plant, as shown below.It is used by people in a variety of crafts. The primary ousers of the document after plant startup are process technicians and instument and electrical, mechanical, safety and engineering personnel.
In order to read P&ID, the technicians needs an understanding of the equipment, instrumentation and technology.The next step in using a P&ID is to memorize ypur palnts process symbol list.This information canbe found on the process legend.Process and instrument drawings have a variety of elements, including flow diagrams, equipment locations, elevation plans, electrical layouts, loop diagrams, title blocks nad legends, and foundation drawings. The entire P&ID provides a three-dimentional look at the various operating units in a plant.

The following figure shows the major legends used in Process

Foundation Drawing
The construction crew pouring the footers, beams and foundation uses foundation drawings(Shown below). Concrete and steel Specifications are designed to support equipment, integrate underground piping, and provide support for exterior and interior walls.Process technicians do not typically use foundation drawings, but these drawings are useful when questions arise about piping that disappears under the ground and when new equipment is being added.

Elevation Drawing
Elevation drawings (Shown Below) show the location of process equipment in relation to existing structures and ground level.In a multistory structure, the elevation drawing provides the technician with information about equipment location.This information is important for making rounds,checking equipment, developing checklists, catching samples, and performing startupsand shutdowns.


Electrical Drawing

Electrical drawings include symbols and diagramsthat depict an electrical system.Electrical drawings show unit electricians where power transmission lines run and places where power is stepped downor up for operational purposes.

A process technician typically traces power to the unit from a motor control center(MCC).The primary components of an electrical systems are the MCC, motors, transformers, breakers, fuses, switchgears, starters, and switches.Specific safety rules are attached to the operation of electrical systems.The primary safety system is the isolation of hazardous energy lock-out, tag-out.Process technicians are required to have training in this area.

The following figure shows the basic symbols and flow path associated with an electricaldrawing. Electrical lines are typically run in cable trays to switches, motors, ammeters, substations and control rooms.

A transformer is a device used by industry to convert high voltage to low voltage.The electric department always handles problems with transformers.Electric breakers are designed to interupt curren flow if design conditions are exceeded.Breakers are not switches and should call for an elctrician.Fuses are devices designed to protect equipment from excess current.A thin strip of metal will melt if desig Specification are exceeded.During operational rounds, technicians check the ammeters inside the MCC for current flow to their electrical systems.Voltmeters, Electrical devices used to monitor voltage in an electrical system, are also checked during routine rounds.

Equipment Location Drawing
Equipment location drawings(plot plans)show the exact location of equipment in relation to the plants physical boundaries(Shown below).One of the most difficult concepts to explain to a new process technician is the scope and size of modern chemical procesing.Most chemicalm plants and refineries closely resemble smallcities; they have well-defined blocks and areas connected by a highway of piping and equipment.Equipment location drawing provide information about the neighbourhood



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