analysis/knowledge/failure_modes.yaml

# CSH2 Cryogenic Pump — Failure Mode Knowledge Base
# Derived from maintenance_log.xlsx (Jul 2025) and Technical PDF (Phase 1B results)
# 8 failure modes ordered by frequency and system priority

failure_modes:
  - id: FM-001
    name: "ICV Reverse Flow"
    category: "check_valve"
    symptoms:
      primary: "Low pressure build — PT130 plateaus well below target"
      secondary:
        - "Degrades more at higher motor speeds"
        - "DCV leak test normal (rules out DCV)"
        - "Volumetric efficiency significantly below expected"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "Plateaus at 40-60% of expected peak pressure"
        - tag: TT110
          tagindex: 24
          behavior: "Gradual warming from high-pressure leakback through ICV"
        - tag: FT140
          tagindex: 7
          behavior: "Flow rate reduced proportionally to leak severity"
    physical_mechanism: >
      ICV does not fully seat against head block during compression stroke.
      Creates reverse flow path from high-pressure chamber back to inlet.
      Volumetric efficiency drops proportionally with gap area and pressure
      differential. Higher motor speeds worsen the leak because the pressure
      differential per stroke increases while the seating time decreases.
    candidate_causes:
      - cause: "ICV installation orientation error"
        prior: 0.45
        evidence: "Jul 22 — fixed orientation restored 700 bar"
        refs: ["2025-07-22"]
      - cause: "ICV/head block tolerance mismatch"
        prior: 0.30
        evidence: "Jul 14 — manually polished ICV not flat"
        refs: ["2025-07-14"]
      - cause: "ICV sealing surface wear"
        prior: 0.15
        evidence: "Jul 1 — new valve helped but some leakage remained"
        refs: ["2025-07-01"]
      - cause: "Thermal distortion from cryo cycling"
        prior: 0.10
        evidence: "Theoretical — differential CTE at ICV/head block interface"
    discriminating_tests:
      - test: "DCV leak test (PT130 decay, pump stopped)"
        rules_out: "DCV leak if decay < 0.5 bar/min"
      - test: "Compare pressure build at 10% vs 50% motor speed"
        interpretation: "ICV leak worsens disproportionately at higher speeds"
      - test: "Visual inspect ICV seating — flashlight gap check"
        confirms: "Installation tolerance issue"
    recommended_actions:
      immediate: "Check ICV seating orientation and gap against head block"
      long_term: "Implement ICV installation jig or go/no-go gauge"
    system_priority: "HIGH"
    occurrence_count: 3
    notes: "Most frequently recurring failure mode (3x July 2025)"

  - id: FM-002
    name: "DCV Leakage"
    category: "check_valve"
    symptoms:
      primary: "PT130 decays during static hold test"
      secondary:
        - "Pressure build OK but cannot maintain pressure after pump stops"
        - "Rate of PT130 decay proportional to leak severity"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "Exponential decay during hold period (pump stopped)"
        - tag: TT130
          tagindex: 27
          behavior: "May show slight cooling as high-pressure fluid expands backward"
    physical_mechanism: >
      DCV sealing surface does not fully seat, allowing high-pressure fluid
      to leak backward through the discharge check valve. The leak rate is
      proportional to the pressure differential and the effective orifice area
      of the gap. This is a static leak — it occurs even when the pump is stopped.
    candidate_causes:
      - cause: "DCV sealing surface damage/scoring"
        prior: 0.50
        evidence: "Jul 1 — DCV sealing surface polished to restore seal"
        refs: ["2025-07-01"]
      - cause: "DCV spring fatigue"
        prior: 0.25
        evidence: "Theoretical — spring force decreases with cycling"
      - cause: "Particulate contamination on seat"
        prior: 0.25
        evidence: "Theoretical — cryo system should be clean but possible"
    discriminating_tests:
      - test: "Pressurize to 500 bar, stop pump, log PT130 for 5 minutes"
        interpretation: "Decay rate > 5 bar/min = actionable leak"
      - test: "Compare decay rates before and after DCV polishing"
        interpretation: "Improvement confirms surface damage as cause"
    recommended_actions:
      immediate: "Run PT130 decay test and compute leak rate"
      long_term: "Establish DCV inspection/polishing interval based on cycling data"
    system_priority: "MEDIUM"
    occurrence_count: 1

  - id: FM-003
    name: "HP Seal Blowby / Energizer Degradation"
    category: "seal"
    symptoms:
      primary: "Increased blowby leakage — reduced volumetric efficiency"
      secondary:
        - "Seal friction initially high after replacement (7-9 kgf)"
        - "Friction breaks in to 4-5 kgf after ~1000 cycles"
        - "Degradation rate very slow (8.2M cycle lower bound on seal life)"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "Gradual pressure build degradation over thousands of cycles"
        - tag: MC130_VFD_Speed
          tagindex: 13
          behavior: "Higher motor current at same speed = increased friction"
    physical_mechanism: >
      The HP seal energizer may degrade from repeated thermal cycling to 116K.
      This reduces the radial sealing force against the cylinder bore, allowing
      high-pressure fluid to leak past the piston (blowby). The seal life lower
      bound from reliability testing is 8.2M cycles, equivalent to 3+ months
      at 20 fills/day.
    candidate_causes:
      - cause: "Seal energizer thermal fatigue"
        prior: 0.40
        evidence: "Jul 18 — seal energizer possibly degraded from cryo cycling"
        refs: ["2025-07-18"]
      - cause: "Bore surface roughening"
        prior: 0.30
        evidence: "Theoretical — scoring increases blowby"
      - cause: "Piston ring wear"
        prior: 0.30
        evidence: "Theoretical — progressive wear"
    discriminating_tests:
      - test: "Static blowby rate measurement at multiple pressures"
        interpretation: "Higher blowby at higher P = seal gap increasing"
      - test: "Track motor current at fixed speed over time"
        interpretation: "Decreasing friction = seal wearing in (expected). Increasing = bore damage"
    recommended_actions:
      immediate: "Monitor blowby rate and motor current trends"
      long_term: "Schedule seal inspection at cumulative stroke threshold"
    system_priority: "LOW"
    occurrence_count: 1
    notes: "Seal life is very long — this is a slow degradation mode"

  - id: FM-004
    name: "Pressure Safety Loop Oscillation"
    category: "controls"
    symptoms:
      primary: "Rapid pressure oscillations near setpoint"
      secondary:
        - "AOV141 opening/closing rapidly"
        - "VFD speed oscillating"
        - "Pressure overshoots followed by undershoots"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "High-frequency oscillation (>0.5 Hz) near setpoint"
        - tag: AOV140
          tagindex: 1
          behavior: "Rapid cycling between open and closed"
    physical_mechanism: >
      The pressure safety control loop has insufficient damping or incorrect
      PID tuning. When pressure approaches the setpoint, the relief valve
      (AOV141) opens and closes rapidly, causing pressure oscillation.
      This stresses the valve mechanism and can cause premature wear.
    candidate_causes:
      - cause: "PID tuning too aggressive (insufficient damping)"
        prior: 0.60
        evidence: "Jul 22 — AOV141 rapid cycling observed at high pressure"
        refs: ["2025-07-22"]
      - cause: "Relief valve setpoint too close to operating pressure"
        prior: 0.30
        evidence: "Theoretical — narrow margin causes hunting"
      - cause: "Valve actuator response delay"
        prior: 0.10
        evidence: "Theoretical"
    discriminating_tests:
      - test: "Ramp pressure slowly to setpoint and monitor AOV141 position"
        interpretation: "Oscillation onset pressure identifies the trigger"
    recommended_actions:
      immediate: "Review safety loop PID parameters and increase damping"
      long_term: "Tune safety loop with proper step-response testing"
    system_priority: "MEDIUM"
    occurrence_count: 1

  - id: FM-005
    name: "Dry Running"
    category: "operational"
    symptoms:
      primary: "PT130/PT110 ratio drops below expected AND TT130 rises abnormally"
      secondary:
        - "Pump compressing gas instead of liquid"
        - "Very damaging to seals and valves"
        - "Mass flow drops to near zero"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "Cannot reach target — pressure builds very slowly"
        - tag: TT130
          tagindex: 27
          behavior: "Abnormal temperature rise (adiabatic gas compression)"
        - tag: FT140
          tagindex: 7
          behavior: "Near zero flow"
    physical_mechanism: >
      When the inlet has insufficient liquid (boil-off, empty tank, blocked line),
      the pump compresses gas instead of liquid. Gas has very low bulk modulus
      compared to liquid, so pressure builds much slower. Adiabatic compression
      of gas produces much higher discharge temperatures than liquid compression.
      This is the most damaging operating condition — stop pump immediately.
    candidate_causes:
      - cause: "Insufficient cooldown (two-phase inlet)"
        prior: 0.40
        evidence: "D1 diagnostic signature"
      - cause: "Cryotank empty/low liquid level"
        prior: 0.30
        evidence: "Check LT200"
      - cause: "Inlet line blockage (ice formation)"
        prior: 0.20
        evidence: "Check TT110 for sudden changes"
      - cause: "Valve stuck closed in inlet path"
        prior: 0.10
        evidence: "Check valve positions"
    discriminating_tests:
      - test: "Check TT110 — must be below saturation temperature at PT110"
        interpretation: "TT110 > T_sat = two-phase or gas inlet"
    recommended_actions:
      immediate: "STOP PUMP. Verify inlet conditions before restart."
      long_term: "Implement automatic dry-running protection based on D1"
    system_priority: "CRITICAL"
    occurrence_count: 0
    notes: "Diagnostic D1 monitors for this continuously"

  - id: FM-006
    name: "ICV Thermal Backflow"
    category: "check_valve"
    symptoms:
      primary: "TT110 rises while PT130 is high"
      secondary:
        - "Hot compressed fluid flowing backward through ICV"
        - "Can cause inlet boiling — cascading failure"
      sensor_signatures:
        - tag: TT110
          tagindex: 24
          behavior: "Rising temperature correlated with high PT130"
        - tag: PT130
          tagindex: 18
          behavior: "High pressure (normal operation)"
    physical_mechanism: >
      High-pressure, heated fluid leaks backward through the ICV during the
      compression stroke. This hot fluid heats the inlet line, potentially
      causing the subcooled inlet liquid to boil. Once boiling starts at the
      inlet, the pump transitions to gas compression (FM-005 cascade).
    candidate_causes:
      - cause: "ICV not seating properly (same root cause as FM-001)"
        prior: 0.70
        evidence: "D3 diagnostic signature"
      - cause: "ICV spring force insufficient at high pressure"
        prior: 0.30
        evidence: "Theoretical"
    discriminating_tests:
      - test: "Monitor TT110 rate of change during high-pressure operation"
        interpretation: ">2 K/min rise = significant backflow"
    recommended_actions:
      immediate: "Check ICV seating. Same remediation as FM-001."
      long_term: "Implement TT110 rate-of-rise protection"
    system_priority: "HIGH"
    occurrence_count: 0
    notes: "Diagnostic D3 monitors this. Shares root cause with FM-001."

  - id: FM-007
    name: "Gas Entrainment / Insufficient Subcooling"
    category: "thermal"
    symptoms:
      primary: "Reduced pump efficiency with two-phase inlet conditions"
      secondary:
        - "Inlet quality > 0 (not fully subcooled liquid)"
        - "Volumetric efficiency reduced by gas fraction"
        - "Less severe than full dry running (FM-005)"
      sensor_signatures:
        - tag: TT110
          tagindex: 24
          behavior: "Near or above saturation temperature at inlet pressure"
        - tag: PT110
          tagindex: 17
          behavior: "May be low (insufficient supply pressure)"
    physical_mechanism: >
      When inlet liquid is not sufficiently subcooled (temperature close to
      boiling point at inlet pressure), flash gas forms in the cylinder during
      the suction stroke. This gas takes up volume that should be liquid,
      reducing the effective displacement. The pump is 169x more efficient
      with fully subcooled liquid than with gas (Technical PDF p.17).
    candidate_causes:
      - cause: "Cooldown incomplete"
        prior: 0.40
        evidence: "Check TT110 vs saturation temperature"
      - cause: "Cryotank pressure too low (reduced subcooling margin)"
        prior: 0.30
        evidence: "Check PT110"
      - cause: "Heat leak into inlet piping"
        prior: 0.20
        evidence: "Check insulation"
      - cause: "Rapid pressure transients causing flash gas"
        prior: 0.10
        evidence: "Theoretical"
    discriminating_tests:
      - test: "Calculate subcooling margin: T_sat(PT110) - TT110"
        interpretation: "< 2K margin = risk of flash gas"
    recommended_actions:
      immediate: "Verify adequate subcooling margin before fill"
      long_term: "Add subcooling verification to pre-fill checklist"
    system_priority: "MEDIUM"
    occurrence_count: 0

  - id: FM-008
    name: "Cryotank Pressure Decay"
    category: "system"
    symptoms:
      primary: "Pressure response drifts downward during extended fills"
      secondary:
        - "PT130 and flow rate decline over the fill duration"
        - "Due to decreasing cryotank pressure (small tank)"
        - "Not a pump fault — operational characteristic"
      sensor_signatures:
        - tag: PT130
          tagindex: 18
          behavior: "Gradual downward drift during extended fills"
        - tag: PT110
          tagindex: 17
          behavior: "Decreasing during fill (cryotank depleting)"
        - tag: LT200
          tagindex: 12
          behavior: "Decreasing (if available)"
    physical_mechanism: >
      The pump operates with a fixed pressure ratio. As cryotank pressure
      drops (small tank being depleted), the inlet pressure drops, and since
      the pump's pressure ratio is approximately constant, the discharge
      pressure also decreases. This is documented in the Technical PDF p.22
      and is an expected operational characteristic, not a fault.
    candidate_causes:
      - cause: "Normal tank depletion (small tank)"
        prior: 0.80
        evidence: "Technical PDF p.22 — documented behavior"
      - cause: "Boil-off reducing tank pressure faster than expected"
        prior: 0.15
        evidence: "Check boil-off rate"
      - cause: "Tank regulator malfunction"
        prior: 0.05
        evidence: "Theoretical"
    discriminating_tests:
      - test: "Plot PT110 and PT130 together over the fill"
        interpretation: "Parallel decline = tank depletion. PT130 drops faster = pump issue"
    recommended_actions:
      immediate: "Expected behavior — no action unless decline rate is abnormal"
      long_term: "Size production tank to maintain pressure over target fill profile"
    system_priority: "LOW"
    occurrence_count: 0
    notes: "Not a fault — operational characteristic of small test tank"