Safeguards of non-functioning compressor anti-surge valve
Safeguards of non-functioning compressor anti-surge valve
What are the safeguards if an anti-surge valve for compressor does not function as intended?
Re: Safeguards of non-functioning compressor anti-surge valve
Many modern compressor control systems include dedicated surge detection based on:
Rapid flow reversals
Pressure oscillations
High-frequency vibration
Characteristic changes in differential pressure
If surge is detected repeatedly or for a defined duration, protective action is initiated, typically an automatic trip.
Rapid flow reversals
Pressure oscillations
High-frequency vibration
Characteristic changes in differential pressure
If surge is detected repeatedly or for a defined duration, protective action is initiated, typically an automatic trip.
Re: Safeguards of non-functioning compressor anti-surge valve
I am providing you some inputs related to performing a risk assessment in this case.
Anti-surge control failure is one of the more dangerous upset scenarios on centrifugal compressors, since surge cycles can destroy the rotor (thrust bearing failure, seal damage, blade fatigue) within seconds to minutes.
The safeguards are layered, following a typical independent protection layer (IPL) philosophy. Here's how they usually stack up:
1. Basic Process Control Layer
- **Anti-surge controller (ASC)** — dedicated, fast-scan controller (often <100 ms cycle time) separate from the general DCS, running a surge control line (SCL) with a safety margin offset from the actual surge limit line (SLL), derived from compressor performance curves.
- **Recycle/blowoff valve** — sized and positioned close to the compressor, with an actuator fast enough (typically full-stroke in 1–3 seconds) to dump flow before the operating point crosses the surge line.
- **Redundant flow/pressure/temperature transmitters** feeding the algorithm, often voted (2oo3) for critical machines.
2. Valve-specific safeguards
- **Fail-open (FO) on loss of signal/air/power** — the recycle valve is almost always specified fail-open so any instrument air failure or ESD trip automatically opens the anti-surge path.
- **Volume booster / quick-exhaust on the actuator** to guarantee stroke speed independent of controller output rate.
- **Partial stroke testing (PST)** on the valve during operation to catch a stuck or sluggish valve before it's needed — this is a key mechanical integrity check you'd verify during inspection/turnaround, along with actuator diaphragm/piston condition and positioner calibration.
- **Local/hardwired trip logic** that can force the valve open independent of the ASC software, sometimes hardwired from vibration or high discharge temperature switches.
3. Safety Instrumented System (SIS) Layer — independent of BPC
- **Surge detection via redundant, independent transmitters** (not shared with the ASC) triggering an SIS logic solver.
- **High-high discharge pressure / low-low suction flow trips** that shut down the compressor (trip the driver — steam turbine trip valve, motor breaker, or gas turbine fuel shutoff) if surge is detected or persists.
- **Vibration monitoring (API 670 systems)** — radial and axial (thrust) probes with alarm/shutdown setpoints; repeated surge cycling shows up first as axial (thrust) displacement and destabilized radial vibration, which can independently trip the machine even if the ASC and its own surge logic both fail.
- **Rate-of-change and reverse-flow detection** on suction/discharge as an additional trip parameter.
4. Mechanical/Passive Protection
- **Non-return (check) valves** on discharge to prevent reverse flow from downstream volume during a trip or surge event.
- **Thrust bearing and thrust collar design margins**, monitored via axial position probes — this is your last line of defense against catastrophic mechanical damage if surge cycling does occur.
- **Relief valves** sized for blocked discharge / other overpressure scenarios (not for surge itself, but part of the overall protection envelope).
5. Organizational/Procedural layers
- **Compressor performance map validation** after any process change (different gas composition, MW, suction conditions) since the SLL and SCL are only as good as the curve they're based on — this is a common root cause of "the anti-surge valve didn't respond in time" events (control line was stale, not that hardware failed).
- **Functional testing / valve stroke testing** at defined intervals per RBI/SIS proof-test schedules, especially where the recycle valve is a SIL-rated final element.
- **MOC review** whenever ASC tuning, valve trim, or actuator sizing changes.
Anti-surge control failure is one of the more dangerous upset scenarios on centrifugal compressors, since surge cycles can destroy the rotor (thrust bearing failure, seal damage, blade fatigue) within seconds to minutes.
The safeguards are layered, following a typical independent protection layer (IPL) philosophy. Here's how they usually stack up:
1. Basic Process Control Layer
- **Anti-surge controller (ASC)** — dedicated, fast-scan controller (often <100 ms cycle time) separate from the general DCS, running a surge control line (SCL) with a safety margin offset from the actual surge limit line (SLL), derived from compressor performance curves.
- **Recycle/blowoff valve** — sized and positioned close to the compressor, with an actuator fast enough (typically full-stroke in 1–3 seconds) to dump flow before the operating point crosses the surge line.
- **Redundant flow/pressure/temperature transmitters** feeding the algorithm, often voted (2oo3) for critical machines.
2. Valve-specific safeguards
- **Fail-open (FO) on loss of signal/air/power** — the recycle valve is almost always specified fail-open so any instrument air failure or ESD trip automatically opens the anti-surge path.
- **Volume booster / quick-exhaust on the actuator** to guarantee stroke speed independent of controller output rate.
- **Partial stroke testing (PST)** on the valve during operation to catch a stuck or sluggish valve before it's needed — this is a key mechanical integrity check you'd verify during inspection/turnaround, along with actuator diaphragm/piston condition and positioner calibration.
- **Local/hardwired trip logic** that can force the valve open independent of the ASC software, sometimes hardwired from vibration or high discharge temperature switches.
3. Safety Instrumented System (SIS) Layer — independent of BPC
- **Surge detection via redundant, independent transmitters** (not shared with the ASC) triggering an SIS logic solver.
- **High-high discharge pressure / low-low suction flow trips** that shut down the compressor (trip the driver — steam turbine trip valve, motor breaker, or gas turbine fuel shutoff) if surge is detected or persists.
- **Vibration monitoring (API 670 systems)** — radial and axial (thrust) probes with alarm/shutdown setpoints; repeated surge cycling shows up first as axial (thrust) displacement and destabilized radial vibration, which can independently trip the machine even if the ASC and its own surge logic both fail.
- **Rate-of-change and reverse-flow detection** on suction/discharge as an additional trip parameter.
4. Mechanical/Passive Protection
- **Non-return (check) valves** on discharge to prevent reverse flow from downstream volume during a trip or surge event.
- **Thrust bearing and thrust collar design margins**, monitored via axial position probes — this is your last line of defense against catastrophic mechanical damage if surge cycling does occur.
- **Relief valves** sized for blocked discharge / other overpressure scenarios (not for surge itself, but part of the overall protection envelope).
5. Organizational/Procedural layers
- **Compressor performance map validation** after any process change (different gas composition, MW, suction conditions) since the SLL and SCL are only as good as the curve they're based on — this is a common root cause of "the anti-surge valve didn't respond in time" events (control line was stale, not that hardware failed).
- **Functional testing / valve stroke testing** at defined intervals per RBI/SIS proof-test schedules, especially where the recycle valve is a SIL-rated final element.
- **MOC review** whenever ASC tuning, valve trim, or actuator sizing changes.
Re: Safeguards of non-functioning compressor anti-surge valve
What kind of documented preventive checks were already made on ASV?
Re: Safeguards of non-functioning compressor anti-surge valve
In high-integrity applications, the compressor may have a dedicated Safety Instrumented Function that trips the compressor based on conditions such as:
High vibration
High axial displacement
High bearing temperature
Confirmed surge events
This SIF is typically implemented in a Safety Instrumented System (SIS) and is independent of the basic process control system.
High vibration
High axial displacement
High bearing temperature
Confirmed surge events
This SIF is typically implemented in a Safety Instrumented System (SIS) and is independent of the basic process control system.