Electrical engineers should master these important knowledge points of PID.

As the technical core of factory production, whether it is an engineer of a design institute, an electrical technician or the chief operator of the central control room, it is an essential skill for an electrical person to understand the meaning of each letter and symbol on the PID diagram and clearly understand the functions and control methods of these components.

0 1

What is a PID diagram?

Process flow chart:

Process? Flow? The chart, abbreviated as PFD, is completed by the process specialty, including the main information of the whole device, operating conditions (temperature, pressure, flow rate, etc. ), material balance (the logistics table shows the nature, flow and operating conditions of each logistics point), heat balance (heat load, etc. ), design and calculation (overall size of equipment, heat transfer area, pump flow, etc. ), main control points and controls.

You only need to draw a device with the same functions and specifications.

Process piping and instrument flow chart:

Roll? Experiment? Figure, referred to as PID. On the basis of PFD, PID is accomplished through process, pipeline installation and automatic control.

It is necessary to draw all the equipment, instruments, pipes and their specifications, insulation thickness, etc. , which is the main basis for drawing the pipeline layout.

The first version of PID diagram was formed in the process package stage. With the deepening of the design stage, it is constantly supplemented, improved and deepened, and published by stages and editions respectively.

The release of each version of PID shows the progress of engineering design, and provides the design information of corresponding stages of technology, automatic control, equipment, electricity, telecommunications, piping, pipe machine, piping, equipment layout, water supply and drainage and other specialties in time.

PID is one of the main finished products of basic design and detailed design, which reflects the comprehensive results of process design flow, equipment design, equipment and pipeline layout design and automatic control instrument design.

02

What can PID diagram tell us?

1. Use the specified category graphic symbol and text code:

Identify all equipment, machinery and drivers of the factory process, including standby equipment and mobile equipment for production, and number and mark them.

2. Use the specified graphic symbols and text codes:

All necessary pipes, valves, main pipe fittings (including temporary pipes, valves and pipe fittings), utility stations, thermal insulation layers, etc. It shall be clearly marked, numbered and marked.

3. Please use the specified graphic symbols and characters instead.

Represents all instruments with detection, indication and control functions, including disposable instruments and sensors, and numbers and marks them.

4. Use the specified graphic symbols and text codes:

Represents all sampling points used for process analysis, and numbers and marks them.

5. Safety production, commissioning, start-up, shutdown and accident treatment need to be illustrated on the drawing:

Including the design requirements and key design dimensions of the process system of automation, pipeline and other related majors.

point out

PID chart is also called process flow chart with control points.

With the help of unified graphic symbols and text codes, all the equipment, instruments, pipelines, valves and main pipe fittings needed to establish petrochemical process devices are combined according to their respective functions, and the structure and functions of the process devices are described on the premise of meeting the process requirements and being safe and economical.

Therefore, it is not only the basis of design and construction, but also a part of the complete technical data needed for enterprise management, trial operation, operation, maintenance and start-up.

Through the process piping and instrument flow chart, we can know that:

Number, name and label number of the equipment.

Technological process of main materials.

Process flow of other materials.

Through the analysis of valves and control points, we can know the control situation of production process.

03

Four elements of PID design?

The process flow chart (PID) includes all the elements of the process. Next, the four most important elements in PID diagram are introduced in detail: equipment, pipeline streamline, valve and instrument.

1

equipment

Use graphic symbols and text codes of specified categories? All equipment, machines and driving machines that represent the process of the factory.

According to the process from left to right, the outline and internal characteristics of the equipment (such as packing and tray of the tower, agitator and heating pipe of the container, etc.). ) are represented by thin solid lines, and the outline of the equipment should be drawn according to a certain proportion.

For equipment and machine legends not listed in the table, they can be simplified according to the actual shapes, but the shapes of similar equipment should be consistent in the same flow chart.

General equipment legend

Design concern

① Name and tag number of the equipment.

Every equipment, including spare equipment, must be marked. For expansion and reconstruction projects, the existing equipment should be represented by thin solid lines and expressed in words.

② Complete sets of equipment

For complete sets of equipment (such as fast-loading boilers, refrigeration units, compressor units, etc.). ), the box line of the complete set of supply scope should be drawn and marked with dotted lines. In general, all ancillary equipment within this range should be suffixed with "X", which means that this part of the equipment is provided with the host computer and does not need to be ordered separately.

(3) equipment project number and equipment specifications

The PID shall indicate the equipment position number, main specifications and design parameters of the equipment, such as the flow Q and lift H of the pump; The container shall be marked with diameter d and length l; Heat exchanger should fill in the heat exchange area and design data; The storage tank shall be filled with volume and relevant data. Different from PFD, the equipment specifications and parameters marked in PID are design values, while PFD is marked with operation data. ?

④ Connection and connection mode

The nozzle size, flange surface shape and flange pressure rating shall be specified in detail. Generally speaking, if the size, flange surface form and pressure grade of the equipment nozzle are consistent with the size of the connected pipeline and the flange surface form and pressure grade specified by the pipeline grade, there is no need for special marking; If not, comments should be added near the nozzle to avoid flange mismatch during installation design.

⑤ Parts

In order to understand the process flow, the tray adjacent to the nozzle, the tray number and other internal components of the tower (such as baffle, weir, internal separator, heating/cooling plate) should be expressed in PID.

⑥ elevation

Equipment with installation height requirements must be marked with the lowest elevation required by the equipment. Towers and vertical containers shall be marked with the actual distance or elevation from the ground to the tangent line under the towers and containers; Horizontal containers should indicate the height of the bottom inside the container or the actual distance from the ground.

⑦ drive device

The driving devices of pumps, fans and compressors shall be marked with the driving type and sometimes the driving power.

(8) Emission requirements.

PID shall indicate the emptying and emptying destination of vessels, towers, heat exchangers and other equipment and pipelines, such as discharging to atmosphere, pressure relief system, dry gas system or wet gas system. If it is discharged to the sewer, it shall be separately indicated that it is discharged to the domestic sewage, rainwater or oily sewage system.

2

Pipeline streamline

Use the specified graphic symbols and text codes? Detailed description of all required pipelines, valves, main pipe fittings (including temporary pipelines, valves and pipe fittings), utility stations and heat insulation, etc.

The pipeline streamlines in the flow chart are all represented by thick solid lines.

For auxiliary pipelines and public system pipelines, only a short section connected with equipment (or main process pipeline) is drawn.

For the pipeline flow chart with instrument control points, the streamline of all pipelines, that is, various materials, should be drawn, and the material code and the drawing number of the flow chart where the auxiliary pipeline or the public system pipeline is located should be marked on the pipeline.

For the pipeline connected to each flow chart, the drawing number of its continuous chart and the equipment number or pipeline number coming (or going) should be indicated at the beginning (or end).

In the pipeline process, in addition to drawing the flow arrow and indicating the source or destination with words, each pipeline should also be marked.

The pipeline on the construction flow chart shall be marked with three parts, namely, pipeline number, pipe diameter and pipeline grade (see relevant standards).

Pipeline legend

Design concern

① Pipe specifications

In PID, all process material pipelines and utility pipelines required for normal production, start-up, shutdown, accident maintenance, sampling, standby and regeneration shall be marked. All pipes shall be marked with pipe diameter, pipe number, pipe grade and medium flow direction. The pipe diameter is generally expressed by nominal diameter (DN), and English (inch) can also be used according to engineering requirements.

If different grades of materials are used in the same pipeline, the demarcation point of pipeline grade shall be indicated on the drawings. Generally speaking, the direction of medium flow is indicated in the direction of pipeline change in the pipeline instrument flow chart.

② Intermittent pipeline

The pipes used intermittently shall be marked with the words "Start", "Stop" and "Normal No Flow (NNF)". ?

③ Valve parts

The words "normally closed (N.C.)", "lead seal open (C.S.O)", "lead seal open (C.S.C)", "lock open (L.O.)" and "lock (L.C.)" shall be marked on the valve parts that are frequently closed during normal operation. All valves (except instrument valves) are located at P & amp； ID shall be indicated, and the valve type shall be indicated according to the legend; If the valve size is inconsistent with the pipe size, please indicate.

When the pressure grade of the valve is inconsistent with the pressure grade of the pipeline, it should be clearly marked; If the pressure grade is the same, but the flange surface forms are different, it should also be marked to avoid the installation failure caused by the wrong flange installation design.

④ Connection of pipelines

When the pipeline enters and exits PID, which picture is pointed by the arrow on the diagram, and the name and position number of the connected equipment should be clearly explained. In order to find the connected drawings and equipment. ?

⑤ Two-phase flow pipeline

Two-phase flow pipeline is prone to "plug flow", which causes pipeline vibration, so "two-phase flow" should be marked on PID. ?

⑥ nozzle

Ventilation, purging, steam purging, flushing and fire extinguishing steam ports used for start-up, stop and commissioning shall be clearly marked on the PID. ?

⑦ Heat tracing tube

Steam tracing pipes, electric tracing pipes, jacketed pipes and insulation pipes shall be clearly marked in the pipeline instrument flow chart, but the insulation thickness and insulation material type need not be marked (which can be found in the pipeline data sheet).

8 Buried pipeline

All buried pipelines should be marked with dotted lines, and the starting point and ending point should be marked.

Pet-name ruby pipe fittings?

All kinds of pipeline accessories, such as compensator, hose, permanent filter, temporary filter, reducer, blind plate, steam trap, detachable short pipe, non-standard pipe fittings, etc., should be marked on the drawing. Sometimes it is necessary to indicate the size, and the pipe fittings required by the process should be numbered.

Attending sampling point

The location of sampling point and whether there is a sampling cooler shall be indicated, and the size and quantity of connecting pipes shall be indicated.

? special requirements

The pipeline slope, symmetrical layout and liquid seal height requirements must be marked.

? Complete equipment takeover

The PID shall indicate the connection point with the complete set of supplied equipment, and the demarcation point between the pipeline and valve accompanying the equipment and the engineering design pipeline. The engineering design part must be marked on PID, which is consistent with the drawings provided by the equipment. ?

? Expansion pipeline and original pipeline

When the expanded pipeline is connected with the existing equipment or pipeline, the demarcation point shall be marked. Existing pipelines are indicated by thin solid lines.

? Internal and external piping of the device

When the pipeline inside the device is connected with the pipeline outside the device, a "Pipeline Connection Diagram" shall be drawn. List: pipe number, pipe diameter and medium name; The device is connected to a screen and which device; The outside of the device is connected with the pipeline at the boundary of the device. Where does this pipeline come from or go?

? Special valve element

Double valve and bypass valve should be clearly marked on PID. ?

? Coke cleaning pipeline

When the catalyst in the reactor is regenerated; The pipeline to be decoked shall be clearly marked.

three

Valves and other pipe fittings

Valves and other fittings on pipes? Thin solid lines should be drawn in corresponding positions according to the symbols specified in the standard, and their specifications and codes should be marked.

Legend of common valves

four

Instrument control

In the process piping and instrument flow diagram? Instrument control points are symbolically drawn on the corresponding pipes with thin solid lines.

Symbols include graphic symbols and letter codes, which are combined to represent the measured variables and functions processed by industrial instruments, or to represent the names of instruments, equipment, components and pipelines.

① Graphical symbols

The graphic symbol of instruments (including instruments used for detection, display and control) is a thin solid circle with a diameter of about10 mm. Allow the circle to break if necessary. When necessary, detection instruments or components can also be represented by pictograms or graphic symbols.

② Alphabetic code

Alphabetic codes indicating measured variables and instrument functions.

Ordinary letter code

Examples of letter combinations of measurement variables and instrument functions

③ Instrument tag number

In the detection and control system, each instrument (or component) that constitutes the loop should have its own instrument position number. The instrument tag number consists of letters and Arabic numerals. The first letter indicates the measurement variable, and the subsequent letters indicate the function of the table. Usually, three or four digits are used to indicate the equipment number and instrument serial number.

Design concern

① Online instrument

If the interface dimensions of on-line instruments such as flow meters and regulating valves are inconsistent with the pipeline dimensions, please indicate the dimensions.

② Instruments attached to the equipment.

If the instrument on the equipment is provided as an accessory of the equipment and does not need to be ordered separately, it should be marked, and the instrument number can be suffixed with "X".

③ Instrument number

The connection between instrument number and electrical and pneumatic signals cannot be omitted, and it is compiled according to the lead table of legend symbols. ?

④ Interlocking and signal

Interlocking and acousto-optic signals should also be clearly expressed on PID. ?

⑤ Flushing and purging

The flushing and purging of the instrument shall be displayed.

⑥ Complete equipment

The scope of supply of complete sets of equipment shall be indicated. Instruments within the manufacturer's complete range of supply should be marked, and the suffix "X" can be added after the number. ?