Loop Checking and Field Instrument Testing Procedure

Everybody knows that loop checking and field instrument testing is the last piece of the puzzle in each project before commencing the commissioning of any system. It is time-consuming and depends upon the completion of other systems like piping, electrical equipment, control valves etc.

Each contractor or company has its own procedure and common practices for instrument loop checking and functional testing. I found this forum is good place to discuss this topic in more detail, for example:

  1. Can we have a common or guide line procedure for loop checking?
  2. Can we illustrate all the required drawings, specification and forms required for loop checking?
  3. Can we build a flow chart for loop checking which illustrates the rule of operation, maintenance, engineering and inspection for example?


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  • <p>I fully agree with all 3 points. A guide is really needed. I takes much time to get agreed such procedure in every new project and a unified approach would be very effective here. To the second point I may add that a list of such documents would be very useful as well to avoid creating of a huge dossier and got all needed papers in place. Templates for certificates would be fine. As to the third point I'd a recommended list of personal of performing and witnessing parties. Mikhail Aravin, Senoir Instrument Commissioning Engineer. </p>


  • <p>The loop testing procedure can vary depending on the instrumentation and I/O infrastructure. A foundation fieldbus or Profibus PA based system would be different from a system using conventional or HART instrumentation on a system with HART I/O cards.</p> <p>While one can perform a loop test with a handheld communicator when HART I/O is not present on the automation system that process would require multiple people similar to performing loop tests with conventional instruments. One benefit HART instrumentation has over conventional is the non intrusive nature of the testing. One does not need to break the loop to insert a mA simulator. HART instruments have a Loop Test method that allows the tester to drive the mA output of the instrument from a hand held communicator or an Asset Management Software application, When using Asset Management software, testing can be done more efficiently because a single person can be commanding devices from one window and observing results on another. An additional benefit when using Asset Management software is that multiple instruments can be put into loop test simutaneously which allows one to incorporate interlock logic checks along with the loop tests which further streamlines the comissioning process.</p> <p>Since loop tests are often the final step before start-up, and projects schedules often slip, there is always pressure on the loop testing team to gain efficiencies to pull in the plant startup milestone.</p>


  • <p>Unfortunately, even today's large manufacturers have lost qualified process control specialists and engineers, leaving sometimes, unqualified personnel to decide how a "system" should be validated. A systematic approach is necessary and a legitimate step towards ensuring the "completeness" of even the smallest of project, upgrade or change to or within a BPCS or SIS on the plant floor. Of course regulations apply to safeties, but many times the even the fundamentals of instrumentation go unchecked and now become a liability. Standardization is needed - especially within chemical and petro-chemical applications. T.Dotts, Contract EI&amp;C Technician / Project manager.</p>


  • <p>I would like to share some perspectives : Loop testing and plant commissioning done in-house is one aspect. Naturally the requirement for policies and procedures is mandatory ( as in both cases) Things change slightly when this work is been done under contract by a 3rd party. Once again the policies and procedures are required. FAT and SAT procedures should be issued to the supplier/contractor within 30 days of contract signature. As a Consultant, I have witnessed so many poor FAT and SAT company procedures in many different countries ( Cultures if you like). This has compounded poor FAT testing into total SAT failures as the fault could not be isolated to Panel or Field . Many hours could have been saved if the bookwork had been done up front.</p>


  • <p>I would like to summarize the requirement prior to start the loop check activity as follows:</p> <p>1. SAT of DCS/ESD/F&amp;G and IAMS system shall be completed and ready with all pre-requisites completed. 2. Total IO's shall be divided into loops &amp; Loop Folder shall be prepared and approved from PMC/Client. 3. Loop folder shall contain the following documents as a minimum : a) Loop test record format (To enter the details of the Instrument subjected to loop check and the master instrument used). b) Instrument Data sheet(s) related with the loop. c) P&amp;ID sheet related to the Instrument(s) d) Instrument(s) loop drawing (derived from Intools which shall contain termination details from Field through JB's to Rack Room) e) C&amp;E sheet (For logic checks) f) IO Point Database (To refer : Ranges, Alarm Points, Controller action etc) g) Calibration sheet of Instruments in loop. h) Observation sheet (To note down any observations during loop check/logic check activity for necessary corrective action). 4. Prerequisites like HVAC, Utilities shall be ensured 5. Loop check shall be carried with Handheld communicator / Calibrators or from IAMS system (For both FF &amp; HART devices). 6. The checks shall be witnessed &amp; loop folder documents shall be signed by DCS contractor, EPC contractor, PMC &amp; Client.</p> <p>The preparation of above said document is time consuming but these will ease the loop / logic checks as all data's will be available in a single folder.</p> <p>This is the procedure we are following in our Greenfield Petrochemical Project.</p>


  • <p>The details of 4-20 mA loop checking is slightly different for each device but the general principle is the same. The basics of the loop testing procedure is explained in the loop checking tutorial found here: <a href="http://www.eddl.org/DeviceManagement/">http://www.eddl.org/DeviceManagement/</a></p>


  • How to work loop cheeck job instrutation.


  • Instrument loop testing is going to be a tough thing to standardize. As an instrument engineer at an EPC company for many years I have run into many clients who often make unreasonable demands of us. Additionally it depends on things as varied as what kind of FAT was preformed, and do you have documentation on it. Were the field devices bench checked before installation and again can documentation be provided to verify it. It can also depend on the state of the construction. I have seen units declared "mechanically complete" in order to satisfy a schedule (so managers could get a bonus) which were far from complete. In these cases all bets are off and the loop testing can take months. The goal is clearly to have a safe and efficient start up. It is not to redo everything that has already been done. I do agree it is often a matter of personalities and experience of the parties involved. If everyone can agree then it typically goes pretty well (depending on the quality of construction).


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