Understanding and Preparation of Cause & Effect Diagram

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Carrying out safety analysis is important to prevent accidents and help in the design of control and protective systems for process plants. Control and sensor devices and their related control actions can be presented in a Cause & Effect chart to help with the analysis process.

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Understanding and Preparation of Cause & Effect Diagram

  1. 1. Understanding and Preparation of Cause & Effect Diagram Sreejesh.S ©2012 QuEST Global Services Pte Ltd. The information in this document is the property of QuEST Global Services Pte Ltd. and may not be copied or communicated to a third party or used for any purpose other than that for which it is supplied without the written consent of QuEST Global Services Pte Ltd. j sreejesh.s@quest-global.com
  2. 2. About this Document ©2012 QuEST Global Services Pte Ltd. Confidential 2
  3. 3. Abstract Carrying out safety analysis is important to prevent accidents and helpCarrying out safety analysis is important to prevent accidents and help in the design of control and protective systems for process plants. Control and sensor devices and their related control actions can be presented in a Cause & Effect chart to help with the analysis process.p p y p The "Cause & Effect" chart is the preliminary document used for the development of Interlock. It is applicable to Emergency shutdowns / Process shutdowns. It lists the manual and automatic actions (Cause) and the equipment such as control valves, pumps etc. (Effect) to be put into a safe state. ©2012 QuEST Global Services Pte Ltd. Confidential 3
  4. 4. Safety actions Classification "ESD" (Emergency Shut Down) This causes aESD (Emergency Shut Down). This causes a complete or partial shutdown of a process unit. An ESD can also isolate a process equipment item asESD can also isolate a process equipment item as well as a "package" equipment. "PSD" (Process Shut Down). This is an automatic action initiated by one or several i t t i t ll d i th i d tinstruments installed in the process in order to protect the equipment. ©2012 QuEST Global Services Pte Ltd. Confidential 4
  5. 5. Logic identification All causes and effects associated with a specificAll causes and effects associated with a specific unit of a process must be shown on the C & E Matrix.Matrix. Several Process units may also be grouped on the same C & E Matrix. I t l k b h ll b i di t d i C & EInterlock numbers shall be indicated in C & E matrix as per PID as a base for logic identification ©2012 QuEST Global Services Pte Ltd. Confidential 5
  6. 6. Cause The causes are defined by the "TAG Number" and by the "SERVICE DESCRIPTION“and by the SERVICE DESCRIPTION "SERVICE DESCRIPTION": "Low pressure, High level etc". need not be shown in the C & E matrix. "NOTES" shall be used to explain special"NOTES" shall be used to explain special requirements and to be indicated on the matrix. The section reserved for notes may be modifiedThe section reserved for notes may be modified according to the volume of information to be detailed. ©2012 QuEST Global Services Pte Ltd. Confidential 6
  7. 7. Other Logic representation When the “Cause” of a shutdown comes from another logic system it will be indicated in thisanother logic system it will be indicated in this column: C&E When several causes generate an action in different process units only the reference of thisdifferent process units, only the reference of this logic will be shown in the logic systems concernedconcerned. ©2012 QuEST Global Services Pte Ltd. Confidential 7
  8. 8. Override Only "Operational" bypasses will be shown on the C&E.C&E. The by-pass has a direct action on the cause: ©2012 QuEST Global Services Pte Ltd. Confidential 8
  9. 9. Effects The effects are defined by the "TAG Number” byThe effects are defined by the TAG Number”, by the "SERVICE DESCRIPTION" and by the type of action detailed on the "MATRIX"action detailed on the MATRIX It may be necessary to double the effects when due to the causes a command can have an open or close or stop or start action. ©2012 QuEST Global Services Pte Ltd. Confidential 9
  10. 10. Service description It will not normally be necessary to indicate in theIt will not normally be necessary to indicate in the description information shown on the matrix such as "Open", "Start".as Open , Start . When the cause of a shutdown is used on different pages of a C&E for the same logic function, the continuation is indicated on the line SERVICE DESCRIPTIONSERVICE DESCRIPTION. ©2012 QuEST Global Services Pte Ltd. Confidential 10
  11. 11. Actions Description Remarks A Activate Indicates an action on another logic system (another C&E) C Close Closes the valve O Open Opens the valve St Start Starting a pump or Unit or sequence Sp Stop Stopping a pump or UnitSp Stop Stopping a pump or Unit T Trip Trip a motor or Unit I Inhibit Forbids the action when the cause is present P Permissive Authorises the action when the cause is present. For example authorises the opening of a valve if other valves are closed. The action will be initiated by the operator or the system. R Reset Authorises a re-start, a re-opening after an ESD and return to normal conditions.p g This action is generally carried out by the operator. V OVerride This is a special case of inhibition. ©2012 QuEST Global Services Pte Ltd. Confidential 11
  12. 12. Procedure 1 Identify the various interlock section unit and1. Identify the various interlock section, unit and plant based on the Process description and PID’s. 2. Identify the “Causes” based on Section / Unit / Plant. Provide Tag numbers, if required. 3. Identify the “Effects” and relate the same to i b d th d i tivarious causes based on the process description & PID’s. ©2012 QuEST Global Services Pte Ltd. Confidential 12
  13. 13. Procedure ……. 4 “Effects” due to the presence of all causes4. Effects due to the presence of all causes (Single Cause should not lead to the effect) shall be adequately defined through notes.be adequately defined through notes. 5. “Causes” which are to be effectuated on running equipment, the same shall be adequately defined through notes. For eg. In a Cooling water t Wh fi t i i dsystem, When first pump is running and maintaining the pressure, a sudden fall in cooling water pressure should start the second pump in ©2012 QuEST Global Services Pte Ltd. Confidential 13 water pressure should start the second pump in order to maintain the header pressure.
  14. 14. Special Case – Operational bypass This function is indicated in the column OVERRIDE TAG number in the section CAUSE of the diagram.g Its function is to temporarily inhibit a cause: At unit start up (start up override) i e an FSLL or PSHHAt unit start-up (start-up override), i.e. an FSLL or PSHH which closes a valve on the same circuit on which it is installed. It may be: • Automatic, i.e. the bypass is activated by a "Start" or "Reset" command.Reset command. • Manually activated by the operator i.e. HS. FSLL - Flow Switch Low Low ©2012 QuEST Global Services Pte Ltd. Confidential 14 FSLL - Flow Switch Low Low PSHH - Pressure Switch High High
  15. 15. Special Case – Operational bypass…. Automatic cancellation of the bypass is mandatory after a time delay and if the operating conditionsafter a time delay and if the operating conditions have returned to normal. This will be defined in a "typical" drawing and will not be shown on the C&E. This is applicable during startup. The bypass of a cause is either applicable to allThe bypass of a cause is either applicable to all effects or to a limited number of effects. An operational bypass may be necessary to allow certain unit operational cases. When this is the ©2012 QuEST Global Services Pte Ltd. Confidential 15 case it will be detailed in a note.
  16. 16. Voting Only the result of a vote is indicated as a cause. A note will indicate the type of vote: 1 out of 2 2 out of 2 2 out of 3 The tag numbers of the instruments are listed in the instrument index and the data base. ©2012 QuEST Global Services Pte Ltd. Confidential 16
  17. 17. Information external to Cause & effect chart Certain information found in the project job specifications need not be shown on the C&E suchspecifications need not be shown on the C&E such as: Maintenance bypasses (Maintenance Override) ©2012 QuEST Global Services Pte Ltd. Confidential 17
  18. 18. Sample Cause & effect chart ©2012 QuEST Global Services Pte Ltd. Confidential 18
  19. 19. Reference Instrument Engineers' Handbook Volume 2 by Bella G LiptakInstrument Engineers' Handbook – Volume 2 by Bella G Liptak http://www.aidic.it http://instrumentationportal.com ©2012 QuEST Global Services Pte Ltd. Confidential 19
  20. 20. Thank You Sreejesh.S ©2012 QuEST Global Services Pte Ltd. The information in this document is the property of QuEST Global Services Pte Ltd. and may not be copied or communicated to a third party or used for any purpose other than that for which it is supplied without the written consent of QuEST Global Services Pte Ltd. j sreejesh.s@quest-global.com

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