PFD vs P&ID Explained with a Practical Level Control Automation Example

PFD and P&ID comparison with a practical level-control loop.

Quick Summary

A Process Flow Diagram, or PFD, explains the overall process and its major equipment. A Piping and Instrumentation Diagram, or P&ID, provides the detailed information required to understand piping, valves, instruments, control loops and process-safety functions.

Process engineers, production teams, maintenance personnel and automation engineers frequently use PFDs and P&IDs. Although both drawings represent the same process, they are prepared for different purposes and contain different levels of detail.

In this article, we will compare a PFD with a P&ID and then examine a practical automatic level-control loop for a storage tank.

1. What Is a Process Flow Diagram?

A Process Flow Diagram, or PFD, provides a high-level representation of a manufacturing process. It normally shows the major process equipment and the principal flow paths connecting that equipment.

A typical PFD may show:

• Reactors, tanks, columns and vessels
• Pumps, compressors and blowers
• Heat exchangers, condensers and reboilers
• Main process and utility streams
• Flow direction
• Important operating conditions
• Major process-control loops

A PFD is particularly useful when someone needs to understand how raw materials move through the plant, where major process transformations occur and how the principal equipment items interact.

Simplified PFD Representation

Feed → P-101 Pump → TK-101 Tank → Product

The PFD communicates the main process route without showing every valve, instrument or signal connection.

2. What Is a P&ID?

A Piping and Instrumentation Diagram, or P&ID, is a detailed schematic representation of the process equipment, piping, valves, instrumentation and control functions.

The P&ID helps engineering and plant teams understand how equipment is physically and functionally connected. It is commonly referenced during detailed engineering, installation, commissioning, operation, troubleshooting, maintenance and safety reviews.

A typical P&ID may include:

• Equipment identification numbers
• Process and utility piping
• Line numbers, sizes and specifications
• Manual and automated valves
• Transmitters, indicators, controllers and switches
• Instrument and control-loop tags
• Electrical, pneumatic and digital signal connections
• Vents, drains, bypasses and sample points
• Relief devices and selected protective functions
• Interlocks and shutdown references, where applicable

Important: A P&ID is a schematic drawing. It normally does not represent the exact physical location, piping length, elevation or scale of the installed equipment.

3. PFD vs P&ID: Main Differences

Comparison	PFD	P&ID
Primary purpose	Explain the overall process	Show detailed piping, instrumentation and control
Equipment	Major equipment	Major equipment with connected components
Piping	Main process streams	Detailed process and utility lines
Valves	Only important valves, if required	Manual, control and protective valves
Instrumentation	Limited to major controls	Detailed instruments and loop identification
Main users	Process engineering and project teams	Process, piping, automation, operation and maintenance teams

4. Practical Automation Example: Tank Level Control

Consider storage tank TK-101. Feed enters the tank through pump P-101, and product leaves the tank through the outlet line. The objective is to maintain the liquid level near a defined setpoint.

Level-Control Loop

LT
101 → LIC
101 → I/P → LV-101

How the loop works

1. LT-101, the level transmitter, measures the liquid level in TK-101.
2. The transmitter sends the measured process value to LIC-101.
3. LIC-101 compares the measured level with the operator-defined setpoint.
4. Based on the control error and its configured control action, the controller calculates an output.
5. If a pneumatic actuator is used, an I/P converter converts the electrical control signal into a pneumatic pressure signal.
6. LV-101 changes its opening and adjusts the tank outlet flow.
7. The resulting change in outlet flow brings the tank level back toward the setpoint.

5. Understanding the Instrument Tags

Instrument tags combine letters and numbers. The letters describe the measured variable and instrument function, while the number identifies the relevant loop or device according to the project tagging convention.

Tag	Meaning	Function
LT-101	Level Transmitter	Measures and transmits tank level
LIC-101	Level Indicating Controller	Displays level and controls the loop
LV-101	Level Control Valve	Manipulates outlet flow
P-101	Pump	Transfers liquid into the system
TK-101	Storage Tank	Stores or provides hold-up for liquid

6. Common P&ID Instrument Letters

Letter	Typical meaning	Example
F	Flow	FT, FI, FIC
L	Level	LT, LI, LIC
P	Pressure or vacuum	PT, PI, PIC
T	Temperature	TT, TI, TIC
I	Indication	LI, FI, PI
C	Control	LIC, FIC, PIC
T	Transmit, when used as a succeeding letter	LT, FT, PT

7. Control Philosophy Considerations

A P&ID shows the functional control arrangement, but the automation engineer must still define the detailed control philosophy. For the tank level-control loop, the design team should consider the following points:

• Should LV-101 fail open, fail closed or fail in its last position?
• What should happen during loss of electrical power or instrument air?
• Is high-level alarm LAH-101 required?
• Is an independent high-high level switch LSHH-101 required?
• Should high-high level stop P-101 or close an inlet valve?
• Is the controller action direct or reverse?
• What are the operating, alarm and trip setpoints?
• Will the loop operate in manual, automatic or cascade mode?
• How should bad transmitter signals be handled?
• Does the function belong in the PLC, DCS or safety system?

Safety note: The required valve failure position and shutdown action must be selected from the process hazard assessment and approved control philosophy. A generic drawing should never be used as the sole basis for a safety-critical design.

8. Frequent P&ID Mistakes

1. Using inconsistent equipment or instrument tags.
2. Failing to define signal-line types in the drawing legend.
3. Showing a control valve without its actuator failure position.
4. Leaving obsolete instruments on the drawing after plant modifications.
5. Not matching the P&ID with the PLC or DCS control narrative.
6. Confusing a process control action with an independent safety function.
7. Using symbols without checking the project-specific legend.
8. Failing to update the as-built drawing after commissioning or modification.

Conclusion

A PFD gives the big picture of a production process. A P&ID provides the detailed engineering information needed to understand how the piping, valves, instruments and control functions work together.

In the tank example, the PFD may show only P-101, TK-101 and the main process streams. The P&ID goes further by showing LT-101, LIC-101, LV-101, the signal relationships and the complete level-control function.

Engineers should always read a P&ID together with its drawing legend, equipment data sheets, instrument index, control narrative, cause-and-effect document and applicable project standards.

Final takeaway

PFD tells us what the process does.
P&ID tells us how the process equipment, piping and control system are connected.

Further Reading

• https://www.isa.org/standards-and-publications/isa-standards International Society of Automation Standards

Overview of Piping and Instrumentation Diagrams

Disclaimer: The symbols and control arrangement in this article are educational examples. Always follow the approved project legend, company engineering practices, applicable standards and process-safety requirements.

How to draw isometric piping diagram using Excel

Isometric drawing presents three faces of an object and they all are equally foreshortened. It represents the concept from multiple angle. Professor William Farish (1759–1837) invented the concept 1^st. Isometric paper is available to draw isometric.

I always use excel for drawing piping concept to represent any process primarily and it really help me to get rid of using pencil eraser frequently. It also ease the drawing process by allowing copy and paste for same type of object. You can use different color to represent the drawing in your way. Moreover you can add automation by VBA later.

Here I will describe how I draw isometric in excel.

It is very simple you can 1^st draw isometric grid in excel by draw border manually and adjusting row height and column width as per your requirement.

Here you can get the sheet with the isometric grid. You can copy it and adjust the height and width if required. It can be copied easily to extent the drawing area. Just select the rows with existing grid, copy and paste to the required empty grid area and follow the same procedure for extending column area.

Click here to download isometric grid and sample drawing

Now you can start your drawing using the drawing tools,shape etc available in excel.

How to change color of open or close position for operating a valve with VBA.

Sub Valve_245()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant

    
    v = 1 ' Serial no which is maitained in column AE and need change for each sl no
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 245")) ' slection of the valve having collate 245 and need to change for every valve
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
Sub Valve_244()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 2
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 244"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
Sub Valve_235()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 3
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 235"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub


Sub Pump_221()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant

    
    v = 4
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Sequential Access Storage 221"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
Sub Pump_194()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant

    
    v = 5
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Sequential Access Storage 194"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub

 
Sub Valve_139()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 6
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 139"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub

Sub Valve_333()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 7
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 333"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
 
    

Sub Valve_159()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 8
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 159"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub

Sub Valve_94()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 9
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 94"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
 
Sub Valve_82()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 10
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 82"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub

Sub Valve_87()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 11
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 87"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub

Sub Valve_11()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 12
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 11"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
    End With
    

    ActiveSheet.Cells(v + 1, 33) = 0
    Range("D20").Select
    
    End If
    
    Application.ScreenUpdating = True
End Sub
 
Sub Valve_26()
Dim S As Variant
Dim v As Variant
Dim Obj As Variant


    

    
    v = 13
    Set Obj = ActiveSheet.Shapes.Range(Array("Flowchart: Collate 26"))
    
    
    Application.ScreenUpdating = False
    S = ActiveSheet.Cells(v + 1, 33).Value
    If S = 0 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
        .Solid
    End With
    With Selection.ShapeRange.Line
        .Visible = msoTrue
        .ForeColor.RGB = RGB(0, 176, 80)
        .Transparency = 0
    End With
    ActiveSheet.Cells(v + 1, 33) = 1
    Range("D20").Select
    End If
    
    If S = 1 Then
    Obj.Select
    With Selection.ShapeRange.Fill
        .Visible = msoTrue
        .ForeColor.ObjectThemeColor = msoThemeColorBackground2
        .ForeColor.TintAndShade = 0
        .ForeColor.Brightness = -0.5
        .Transparency = 0
        .Solid
    End With
     With Selection.ShapeRange.Line
        .Visible = msoTrue
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Accident and Incident

"The only certainty in life is death; uncertainty lies in when and how death occurs…… Man strives to delay its onset and extend the quality of life in the interim. Threats to these objectives involve risks, some natural, some man-made, some beyond our control and some controllable".
----- William Rowe

What Is an Accident?

An unplanned, unwanted, but controllable event which disrupts the work process and causes injury to people.

Most everyone would agree that an accident is unplanned and unwanted. The idea that an accident is controllable might be a new concept.
An accident stops the normal course of events and causes property damage or personal injury, minor or serious, and occasionally results in a fatality.


By dictionary definition: “an unforeseen event”, “chance”, “unexpected happening”, formerly “Act of God”
From experience and analysis: they are “caused occurrences”
Predictable - the logical outcome of hazards
Preventable and avoidable - hazards do not have to exist. They are caused by things people do -- or fail to do.

Hazard: It is a condition with the potential of causing injury to personnel, damage to equipment or structures, loss of material, occupational illness / disease, environmental pollution / damage etc. In short, hazards are capable of producing adverse effect on Safety, Health and Environment.


RISK: It is the probability of an event-occurring and the consequences if it occurs. It may be indicated by the probability of accidents, loss of lives and the damage of any operating unit.


Incident: An event or chain of events which could have caused injury, illness and/or damage (loss) to assets, the environment or third parties.

Dangerous occurrence: A dangerous occurrence can be defined as, “any incident that has a high potential to cause death or serious injury”.

Near-miss” incident: A “near-miss” incident can be defined as, “any event, which under slightly different circumstances, may have resulted in injury or ill health of people, or damage or loss to property, plant, materials or the environment or a loss of business opportunity.

Example: A window cleaner dropping a bucket from a height, which just missed a person standing underneath, would be classed as a “near-miss” incident. This incident did not cause an injury to a person but, under slightly different circumstances (the person standing nearer to the contact point) the person may have been injured.

Accident: An unintended and unplanned occurrence involving injury / loss of human life, damage to properties, loss of productivity etc. Accident is associated with number of losses-

• Loss of human life.
• Loss of plant, machinery and other properties
• Loss of production time
• Loss of confidence due to fear psychosis and panicky
• Loss due to compensation costs
• Loss of market goodwill

Causes of Accident:

Direct cause of injury and Accident – A harmful transfer of energy that produces injury or illness

Surface causes of accident – Specific hazardous conditions or unsafe behaviors that result in an accident

Root causes of accident – Common behaviors and conditions that ultimately result in an accident

UTILITY FLOW DIAGRAMS and P&ID

The Utility Flow Diagram shall be prepared as separate drawing titledas "Utilities Flow Diagram". The distribution of utilities for plant operation shall be shown on the drawing. The utilities for plant operation are generally classified as follows where applicable:

- Boiler Section;
- Condensate Recovery;
- Boiler Feed Water;
- Cooling Water;
- Raw Water;
- Plant and Potable Water;
- Fuel Tank;
- Dry and Plant Air;
- Nitrogen;
- Inert Gas;
- Hot Oil & Cold Oil System;
- Flare and Blow-down;

Utility Flow Diagrams shall be presented in accordance with the requirements stipulated in Standard P&IDs where applicable.

Utility Flow Diagrams shall show main distribution/collection headers and finger headers with their isolating facilities and instrumentation. The branch line and subheader arrangement shall be shown as practical as possible.



Indication criteria of connection between P&IDs and UFDs is according to the following general philosophy:

a) The indication of isolation valve shall not be duplicated on P&ID and UFD.


b) Valve and instrument which will be used for the normal operation shall be indicated on P&ID, such as:

• Block valves for water cooler inlet and outlet;
• Block valves for snuffing steam of heater;
• Globe valve for steam injection control;
• Control valves for fuel control.

c) Valves which will be used only for start-up and shut-down shall be indicated on the UFD such as:

• Header isolation valve for steam purge connection;
• Isolation valve for fuel gas or fuel oil.

Utility/common facility branch line header valves at the process Unit battery limit shall be shown. The Utility Flow Diagram shall also indicate any valve in utility/common facility individual branch lines required for process and maintenance operations even if these valves may be physically located in the pipe rack or the sequence of branches may allow in the future for a single valve to serve several branch lines.


Isolation facilities shall be indicated for:

• finger areas;
• process Unit block areas;
• at position of change from pipe rack to pipe rack.

The finger area is defined as being the area that serves a particular process area which may consist of one or more process Units. In addition to the equipment that is located alongside the finger pipe rack, the finger area also includes the equipment located alongside the main pipe rack.

Utility Flow Diagram shall be arranged to cover the whole refinery/plant area and these are divided into separate sheets each with corresponding match lines. Depending on the complexity and extent of the particular utility/common facility, sheets may be combined, extended or omitted as required.



All equipment that is supplying a particular utility common facility either from the system (e.g., steam boilers) or from a process Unit (e.g., waste heat boilers) shall be shown in a "box" in geographical location. This "box" shall give relevant equipment number(s), Unit number and sheet
number of the drawing in which the equipment is detailed.

Understanding Control loop in P&ID

About Control Loop:

Modern production systems use automatic control systems where control is carried out with minimal or without human intervention. The ‘Control loops’ used in a process industry in terms of a combination of two or more instruments or control functions arranged so that signals pass from one to another for the purpose of measurement and/or control of a process variable. The goal of process control instrumentation is to measure, monitor, and or control a process.


Following three tasks is associated with a control loop.

• Measurement
• Comparison
• Adjustment

Before we proceed it’s very essential to have a basic concept on the following terms which are needed to understand a control loop in P&ID:

1. Instrument and controller symbol and identification letter.
2. Different type of function symbols and their uses.
3. Symbol of different type of line and device  associated with control loop.
4. Instrument numbering.

To read out a control loop fro a P&ID first we have to identify the following things:

• Variable/variables are to be controlled by the control loop.
• Variables need to measure for functioning the control scheme.
• Type of instrument used for measuring variable.
• Type of controller, device and function used for controlling purpose.
• Type of signal and connection used for interlinking and transmission purpose.

EXAMPLE:

In the above example the tank is filling with the pipe line above the tank and emptying through the bottom pipe line.  The level of the liquid in the tank need to control for process purpose. So the control loop is designed here just to control the tank level. The level or height of the liquid is the process variable here and the level transmitter (LT) is used to measure the process variable continuously.A level controller (LC) is used as controller and a level control valve (LV) is used to control the flow inside the bottom pipe line.

Here the control loop is working in following steps:

• First the level transmitter (LT) is measuring the level.
• The measuring value is transmitted to level controller (LC) through electrical signal.
• The controller decide what to do depending on set or desired value.
• Then the controller send required command to the level control valve (LV) through a pneumatic signal.
• Finally the control valve increase or decrease the flow as per controller signal.

Instrument Tag or Number

An Instrument number or tag has two parts which is combination of letter and number.

• Identification letter for indicating the function and purpose of use.
• An individual tag number/Loop No./serial number.

Letter is used to classify the instrument by it's function and number is used to identify the loop/interlock. Identification letters on the ISA symbols indicate:

• The variable being measured (e.g. flow, pressure, temperature).
• The device’s function (e.g., transmitter, switch, valve, sensor, indicator).
• Some modifiers (e.g., high, low, multifunction).

In the instrument tag number in above figure the initial letter indicates the measured variable. The second letter indicates a modifier, readout, or device function. The third letter usually indicates either a device function or a modifier.

In that cases where the instrument is considered to be identified by it's location/area then the instrument tag number format will be as bellow: