Emerson Exchange 365

This is Part 3 of white paper by Tom Jeansonne who is technical product manager at Emerson Process Management Valve Automation, Waller, TX.  He has more than 30 years of experience in the valve and valve automation industry with both distributors and manufacturers.  He can be reached at tom.jeansonne@emersonprocess.com

What Should The Integrated FCE Include?

Based on the joint work of Emerson and the owner/operator the recommended FCE should be designed with the following summary of typical components and concerns in mind:

• The valve used as part of the FCE should be a minimum 300 ANSI rated, full ported, quarter-turn ball valve, either trunnion-mounted or floating.  It would need to be fire rated   per API-607 or ASME B16.34.
• Existing valves, sensors and other equipment shall not be used. Only new equipment purchased and validated for the FCE shall be used.
• The supplier of the actuator component of the FCE should offer as standard, published guaranteed minimum torque outputs which are critical to operate the valve to “a safe state” for the SIF.
• The actuator shall be sized with a minimum torque output of 125% against the torque recommended by the valve manufacture at all positions and both directions of travel. The actuator maximum torque output shall not exceed the maximum allowable valve input torque (MAVIT). 
• The valve actuator should be of a symmetric, scotch-yoke design and  control system shall contain a fusible plug with a maximum 250° F melting point in the event of a fire not necessarily related to tank overfill.  Rack and pinion configurations were deemed unacceptable for this application.  The FCE should normally remain in the open position. The actuator should be pneumatically powered with air, nitrogen or a special self-contained local hydraulic system. 
• The actuator must   be totally enclosed and weatherproof with Xylan™ cylinder coating or a minimum of 25 micron, electroless nickel plating.   No manual overrides or lock-out devices are permitted.
• Hydraulic actuators should only be used when ambient temperatures are extremely low and could drop below -50° F.  Hydraulic FCE’S are not recommended because of    potential flammability issues.  If necessary, hydraulic pressurized components shall  be designed to ASME   Section VIII. 
• Electric actuators (part turn or multi turn) shall not be used in this application.   
• A digital valve controller (DVC) should be included in the FCE for valve position determination, partial stroke and diagnostic capabilities and alerts. Additional design concern requirements include:
  • DVC should be designed to typically accept a 24 VDC signal and have  self-diagnostics using HART communication protocol.
  • SIS or FCE may be based on relay logic when appropriate.
  • System  may utilize limit switches  for redundancy only and shall not be included in SIL calculations
  • DVC will abort any test, before the actuator supply pressure can drop to a level to cause a false trip if the valve is physically immobile. The DVC shall alert the operator that the valve is immobile (Fail Dangerous Detected)
  • FCE shall have the capability of performing a partial stroke test without  significantly disturbing the process while in receipt service. 
  • DVC shall be able to configure and automatically initiate and record partial stroke travel and retain records of such events
  • FCE shall also restrict stroking speed as required to avoid hydraulic shock to the pumping system.