How to Perform a Stroke Test

A stroke test verifies that an actuated valve moves from its normal position to its fail-safe position and back within the required time. Stroke testing is required for emergency shutdown valves (ESDVs), blowdown valves, and control valves in safety instrumented systems (SIS).

Full Stroke Test Procedure

Step	Action	Details
1	Review valve data sheet	Confirm the valve tag, fail-safe action (fail-close or fail-open), required stroke time, and actuator type.
2	Notify operations	Coordinate with the control room. A full stroke test will interrupt the process flow or isolate equipment. Use a bypass if available.
3	Verify initial position	Confirm the valve is in its normal operating position. Record the position feedback (open/close limit switch status) on the DCS/SIS.
4	Initiate the stroke	Send the trip command from the SIS or use the solenoid valve manual override. For pneumatic actuators, vent the air supply to simulate a fail-safe trip.
5	Measure stroke time	Using a stopwatch or the SIS time-stamped diagnostics, measure the time from trip command to full travel (confirmed by the end-of-travel limit switch).
6	Verify end position	Confirm the valve reaches the full fail-safe position (fully closed or fully open). Check the position indicator and limit switches.
7	Return to normal	Reset the trip command and verify the valve returns to its normal operating position. Measure the return stroke time.
8	Record and evaluate	Document stroke times, limit switch operation, and any anomalies (hesitation, sticking, slow response). Compare against acceptance criteria.

Partial Stroke Test (PST)

A partial stroke test moves the valve 10-20% from its normal position without fully closing or opening, allowing proof testing without process interruption.

Parameter	Full Stroke Test (FST)	Partial Stroke Test (PST)
Valve travel	100% (full open to full close or vice versa)	10-20% of full travel
Process interruption	Yes (requires bypass or shutdown)	No (valve remains in service)
Detectable failures	All (stuck valve, slow response, broken spring, failed solenoid)	Most (stuck valve, slow initial response), but not end-of-travel issues
SIL credit	Full proof test coverage	Partial proof test coverage (typically 60-80% diagnostic coverage)
Frequency	Annually (or per SIL assessment)	Monthly to quarterly
Automation	Manual or automated	Typically automated via smart positioner or SIS

Acceptance Criteria

Parameter	Typical Requirement
Full stroke time (close)	Depends on valve size; typically 2-10 seconds for ESDVs (per API 6D and project spec)
Full stroke time (open)	Typically equal to or longer than close time
Stroke time tolerance	+/- 10% of the specified time (or per project specification)
Limit switch operation	Both open and close limit switches must activate within 2% of end position
Valve seat tightness	Class V or Class VI per API 598 / FCI 70-2 (for tight shutoff valves)
No sticking or hesitation	Valve must move smoothly without stops, jerks, or excessive delay

Pro Tip

For SIL-rated emergency shutdown valves, the proof test interval directly affects the achieved safety integrity level. IEC 61511 requires that the proof test interval (and the test coverage factor) be documented in the SIL verification report. Partial stroke testing can extend the interval between full stroke tests while maintaining the required SIL level.

Key Points

• Stroke testing of safety-critical valves is governed by IEC 61508/61511 for SIL-rated systems.
• For valve actuator and trim components, refer to the manufacturer’s maintenance manual for specific settings.
• Smart positioners with built-in diagnostics can automate partial stroke testing and provide valve signature analysis.
• Document all stroke test results in the plant’s SIS maintenance database.

Read the full guide to piping inspections