Equipment Failure Modeling

This document describes how to model equipment failures in NeqSim, including failure types, capacity factors, and reliability data.

Failure Types

FailureType Enum

public enum FailureType {
    TRIP,           // Complete stop, requires restart
    DEGRADED,       // Reduced capacity operation
    PARTIAL_FAILURE,// Some functions lost
    FULL_FAILURE,   // Equipment non-functional
    MAINTENANCE,    // Planned shutdown
    BYPASSED        // Flow routed around
}

Failure Type Characteristics

Type Capacity Recovery Typical Duration
TRIP 0% Manual restart 1-4 hours
DEGRADED 10-90% Continues operating Until repair
PARTIAL_FAILURE 20-80% May continue Until repair
FULL_FAILURE 0% Major repair Days to weeks
MAINTENANCE 0% Planned Hours to days
BYPASSED 0% Reconfiguration Until restored

Creating Failure Modes

Using Static Factory Methods

// Quick creation for common failure types
EquipmentFailureMode trip = EquipmentFailureMode.trip("Compressor A");
EquipmentFailureMode trip2 = EquipmentFailureMode.trip("Compressor A", "High vibration");

EquipmentFailureMode degraded = EquipmentFailureMode.degraded("Pump B", 0.5);  // 50% capacity

EquipmentFailureMode maintenance = EquipmentFailureMode.maintenance("Heat Exchanger", 8.0);  // 8 hours

Using Builder Pattern

EquipmentFailureMode failure = EquipmentFailureMode.builder()
    .name("Compressor surge")
    .description("Compressor enters surge condition")
    .type(FailureType.TRIP)
    .capacityFactor(0.0)        // Complete loss
    .efficiencyFactor(1.0)      // N/A when tripped
    .mttr(24.0)                 // 24 hours to repair
    .failureFrequency(0.5)      // 0.5 per year
    .requiresImmediateAction(true)
    .autoRecoverable(false)
    .build();

Capacity Factor

The capacity factor defines the fraction of normal output during failure:

\[C_f = \frac{\text{Output during failure}}{\text{Normal output}}\]
Value Meaning
0.0 Complete loss (TRIP, FULL_FAILURE)
0.5 50% capacity (DEGRADED)
0.8 80% capacity (minor degradation)
1.0 No effect on capacity

Example: Degraded Compressor

// Compressor running at 70% capacity due to fouling
EquipmentFailureMode fouling = EquipmentFailureMode.builder()
    .name("Compressor fouling")
    .type(FailureType.DEGRADED)
    .capacityFactor(0.7)         // 70% capacity
    .efficiencyFactor(0.85)      // 85% efficiency
    .build();

double normalFlow = 100.0;  // kg/s
double degradedFlow = normalFlow * fouling.getCapacityFactor();  // 70 kg/s

Efficiency Factor

For degraded operation, efficiency may also be reduced:

\[\eta_{\text{degraded}} = \eta_{\text{normal}} \times E_f\]

Where $E_f$ is the efficiency factor (0.0 to 1.0).

Example: Reduced Efficiency

// Compressor with fouled internals
EquipmentFailureMode fouling = EquipmentFailureMode.builder()
    .name("Fouling")
    .type(FailureType.DEGRADED)
    .capacityFactor(0.9)        // 90% capacity
    .efficiencyFactor(0.8)      // 80% of normal efficiency
    .build();

double normalEfficiency = 0.75;
double degradedEfficiency = normalEfficiency * fouling.getEfficiencyFactor();  // 0.6

Reliability Data Source

OREDA-Based Data

The ReliabilityDataSource provides reliability data from OREDA (Offshore Reliability Data):

ReliabilityDataSource source = ReliabilityDataSource.getInstance();

// Get reliability data for equipment type
double mttf = source.getMTTF("Compressor");        // Mean Time To Failure (hours)
double mttr = source.getMTTR("Compressor");        // Mean Time To Repair (hours)
double failureRate = source.getFailureRate("Compressor");  // Failures per year

Equipment Types with Reliability Data

Equipment Type MTTF (hours) MTTR (hours) Availability
Compressor 8,760 24 99.7%
Pump 17,520 8 99.95%
Separator 43,800 4 99.99%
Heat Exchanger 43,800 12 99.97%
Valve (Control) 26,280 4 99.98%
Turbine 8,760 48 99.5%

CSV Data Format

Reliability data is stored in CSV files under src/main/resources/reliabilitydata/:

equipment_reliability.csv:

EquipmentType,MTTF_hours,MTTR_hours,Source
Compressor,8760,24,OREDA-2015
Pump,17520,8,OREDA-2015
Separator,43800,4,OREDA-2015
HeatExchanger,43800,12,OREDA-2015
Valve,26280,4,OREDA-2015

failure_modes.csv:

EquipmentType,FailureMode,Probability,CapacityFactor,TypicalMTTR
Compressor,Trip,0.6,0.0,24
Compressor,Degraded,0.3,0.7,48
Compressor,Partial,0.1,0.5,72

Mathematical Background

Failure Rate

Failure rate $\lambda$ is the expected number of failures per unit time:

\[\lambda = \frac{1}{\text{MTTF}}\]

For a Poisson process, the probability of $k$ failures in time $t$:

\[P(k) = \frac{(\lambda t)^k e^{-\lambda t}}{k!}\]

Availability

Inherent availability:

\[A = \frac{\text{MTTF}}{\text{MTTF} + \text{MTTR}} = \frac{\text{Uptime}}{\text{Total Time}}\]

For multiple independent equipment in series:

\[A_{\text{system}} = \prod_{i=1}^{n} A_i\]

For redundant equipment in parallel:

\[A_{\text{parallel}} = 1 - \prod_{i=1}^{n} (1 - A_i)\]

Reliability Function

Exponential reliability function (constant failure rate):

\[R(t) = e^{-\lambda t}\]

Probability of failure before time $t$:

\[F(t) = 1 - R(t) = 1 - e^{-\lambda t}\]

Common Failure Scenarios

1. Compressor Trip

EquipmentFailureMode compressorTrip = EquipmentFailureMode.builder()
    .name("Compressor trip - high vibration")
    .description("Trip due to vibration exceeding 25mm/s")
    .type(FailureType.TRIP)
    .capacityFactor(0.0)
    .mttr(24.0)
    .failureFrequency(0.5)  // Once every 2 years
    .requiresImmediateAction(true)
    .build();

2. Pump Degradation

EquipmentFailureMode pumpWear = EquipmentFailureMode.builder()
    .name("Pump impeller wear")
    .description("Gradual performance degradation")
    .type(FailureType.DEGRADED)
    .capacityFactor(0.8)    // 80% of design flow
    .efficiencyFactor(0.75) // Reduced efficiency
    .mttr(72.0)             // Impeller replacement
    .failureFrequency(0.2)
    .build();

3. Separator Level Control Failure

EquipmentFailureMode levelFailure = EquipmentFailureMode.builder()
    .name("Level control failure")
    .description("Level transmitter malfunction")
    .type(FailureType.PARTIAL_FAILURE)
    .capacityFactor(0.7)  // Manual level control possible
    .mttr(4.0)
    .requiresImmediateAction(false)
    .autoRecoverable(false)
    .build();

4. Planned Maintenance

EquipmentFailureMode turnaround = EquipmentFailureMode.builder()
    .name("Planned turnaround")
    .description("Annual maintenance shutdown")
    .type(FailureType.MAINTENANCE)
    .capacityFactor(0.0)
    .mttr(168.0)  // 7 days
    .failureFrequency(1.0)  // Annual
    .requiresImmediateAction(false)
    .build();

Integration with Process Simulation

Applying Failure to Equipment

// Get compressor from process
Compressor compressor = (Compressor) process.getUnit("HP Compressor");

// Create failure mode
EquipmentFailureMode failure = EquipmentFailureMode.trip("HP Compressor");

// Analyze impact
ProductionImpactAnalyzer analyzer = new ProductionImpactAnalyzer(process);
ProductionImpactResult result = analyzer.analyzeFailureImpact(failure);

System.out.println("Production loss: " + result.getPercentLoss() + "%");
System.out.println("Affected equipment: " + result.getAffectedEquipment());

Best Practices

  1. Use OREDA data when available for realistic reliability values
  2. Define multiple failure modes for critical equipment
  3. Include degraded modes - not all failures are complete trips
  4. Consider auto-recovery for transient failures
  5. Document failure causes in descriptions for maintenance planning
  6. Validate with historical data when possible

See Also