Monitoring solutions for reciprocating compressors Specialized Techniques (Performance Monitoring) Speaker: Michael Hastings
Dec 29, 2015
Monitoring solutions for reciprocating compressorsSpecialized Techniques (Performance Monitoring)
Speaker: Michael Hastings
Contents
• Recip maintenance requirements• Recip monitoring requirements• Monitoring strategies• Specialized monitoring techniques (performance)• Process conditions• Diagnostics – Array, scalars• Summary
Recip Maintenance Requirements – Challenge
• Critical role in petrochemical processes (like centrifugal and axial compressors)
• Cyclic and reciprocating movement with several moving parts• More prone to failure• Requires more maintenance
Recip Maintenance Requirements – Fault summary
Recip Monitoring Requirements – Challenge
• Subject to special kinematics and dynamic forces• Complex vibration signatures• Sensitive to operating conditions• Difficult to detect and diagnose developing faults early and trend
these using overall vibration measurements
Recip Monitoring Requirements – Summary
Component Failure Mode Fault DetectionValves Wear, breakage Vibr., Temp, PV, Pres.Piston rings Wear, breakage Vibr., PV, Pres.Wear rings Wear, breakage Vibr., Rod positionPacking Wear, breakdown Vibr., PVCrosshead Wear, rubbing, lack of lubricant,
overheatingVibr., Temp. Rod load, Rod reversal
Piston, cylinder, piston rod
Water ingestion impact, breakage, bending, overloading
Vibr., Rod load, Rod position
Main bearings Wear, lack of lubricant, overheating Vibr., Temp.Frame Wear, bending, looseness Vibr.Cooling water, lube oil system
Faulty function Vibr., Temp., Pres.
Monitoring Strategies
Basic monitoring solution – Minimum safety and basic condition monitoring requirements
Specialized monitoring solution (performance) -Early fault detection and diagnosis concept
Specialized Monitoring Solution - Performance
More maintenance lead-time, accuracy, reliability for:• Valves, reciprocating component defects• Cylinder leaks• Rod, cross head pin defects
Valves, Reciprocating Components
Cylinder head, rod position and crosshead vibration vs. crank angle monitoring
Cyl. Head and Crosshead Vibration vs. Crank Angle
Technique• Vibration is monitored at different crank angles for each sensor• Diagnostic spectrum plots• Each segment trended and monitored to alarm limits
Faults detected• Head-end sensor can detect impacts due to liquid ingestion,
faulty valves, damaged piston rings (or rider rings)• Crosshead sensor can detect loose/worn crosshead pins,
crosshead shoes, damaged piston rod
Crosshead – Monitoring Vibration vs. Crank Angle
Simultaneous display of crosshead vibration at different crank angles
Crosshead – Vibration vs. Crank Angle Trend
Crosshead vibration trendof 4 segments Displayed:0-1920-39 40-59 60-79
Cyl. Head & Crosshead – Vibration Time Signal
Crosshead and cylinder headvibration
Rod Position (Rod Drop) vs. Crank Angle
Technique• Rod displacement/vibration is monitored at different crank
angles• Displacement and vibration is compensated by a geometric
factor at the wear rings for the different positions of the rod• Diagnostic time waveform plot• Each segment trended and monitored to alarm limits
Faults detected• Worn wear rings, worn crosshead pin/shoe, damaged or
overloaded piston rod
Rod Position (Rod Drop) – Geometric Factor
L2Fixed
L1Variable
GF = L2/L1
RDmeasRRmeas
RRmeas = (RDmeas – Offset) x GF + Shift
Cylinder Leaks
PV plot, monitoring
PV Analysis – Purpose
Technique• Pressure is plotted against the corresponding swept volume at
different crank angles• Shape of plot is influenced by process conditions, capacity
control and leaks • Diagnostic display with theoretical PV• Automatic diagnostic monitoring (polytropic exponent)
Faults detected:• Leaking valves, piston rings and seals
PV Plot
• Actual PV• Theoretical PV
Pressure vs. Crank Angle Plot
Differential Polytropic Exponent
Differential Polytropic Exponent
AP1, V1
B
P2, V2
P1, V1
P2, V2
nA
nB
C
Differential Polytropic Exponent
A
B
C
D
1,221,211,221,20
A
B
D
1,312,732,571,30
A
B
C
D
1,221,191,221,20
A
B
C
D
1,201,211,191,22
C
Cylinder 1 CE Discharge valve leak
Rod, Cross Head Pin
Rod load, rod reversal monitoring
Rod load, Rod Reversal
Technique• Rod load is calculated from gas load and inertia of piston/rod
components, and plotted at different crank angles• Affected by capacity control, speed, gas composition, PS and
PD, compression ratio, leaking valves, rings and seals• Diagnostic plot display• Automatic trending and monitoring of peak load and rod reversal
Faults detected• Rod overloading• Load balance• Rod reversal
Monitoring – Rod Load – Concept
Monitoring – Rod Load – Finertia Calculation
rω cos ωtrl cos 2ωt
Where:
mrecip = mass of reciprocatingcomponents (piston/piston rod, crosshead shoe/pin)r = crank radius (stroke/2)ω = angular velocity, l = connecting rod length
θ
Crank Angle (◦)Com
pressionTension
Inertia LoadLoad(N)
Com
pressionTension
Monitoring – Rod Load Plot Display
Load(N)
Crank Angle (◦)Com
pressionTension
Gas Load
Load(N)
Crank Angle (◦)Com
pressionTension
Rod Load
Gas Load
Inertia LoadLoad(N)
Crank Angle (◦)Com
pressionTension
Rod Load
Cross-over
Peak Load: Compression
Peak Load: Tension
Cross-over
Rod Load Plot
• Inertia force• Gas force• Combined rod load
Monitoring – Rod Load – Rod Reversal
Affected by:• Change in speed (Finertia)• Change in compression ratio• Capacity control
Monitoring – Rod Load – Rod Reversal
Monitoring – Rod Load – Standards
API 618• Compressive and tensile peak load difference – 3%• Minimum rod reversal – 15%• Max. rod load < less than 80% of design load
Process Classes
Recips can operate under variable conditions:• Input process conditions• Capacity control (step-less, clearance volume, unloaders,
variable speed, recycle/bypass, etc.)• Gas composition (for theoretical PV or discharge temperature
calculations)
Under such conditions it is difficult to diagnose gradual changes in PV shape, identify trends of a developing fault or monitor to alarm limits. To facilitate this B&K Vibro offers:
• Machine states• Gas composition classes
Diagnostics – Specialized Monitoring Array Plots
Measurement Technique vs. Time
vs. Swept volume(Calculated)
vs. Crank Angle (Calculated)
Cyl. head and crosshead vibration
Rod position (rod drop)
HE/CE pressure
Suction/discharge pressure
Valve temp. spread
Rod load
Gas discharge temp.
Diagnostics – Scalar Values Converted from Arrays
Measurement Technique Scalar Trend Alert, Danger Alarm Limits
Differential polytropicexponent
Rod position (rod drop)
Crosshead vibration
Cylinder head vibration
Rod reversal
Peak load
Differential peak load.
Diagnostics – Summary: Array vs. Scalar Value
Diagnostic plots• Specialist needed to look at
plots at intervals• No monitoring
Diagnostic monitoring• Array converted to scalar data• Easier to diagnose • Easier to trend• Monitored to process classes• Specialist needed only when
alarm occurs
Summary
• Condition monitoring strategy important for recips• Specialized monitoring techniques give early detection of faults,
greater lead-time to maintenance, more reliability• Automatic monitoring and diagnostics of PV, rod load, rod
reversal, etc. (array parameters)
Summary – Performance: PV, Rod LoadMon. Tech. Faults
Pressure vs. crank angle
Over-pressure, under-pressure
Pressure vs. Swept volume
Leaking valves, piston rings, seals
Suction and discharge pressure
Used for calculating theoretical PV, valve losses, etc.
Flow balance, volumetric eff.
Leaking valves
Rod load vs.crank angle
Overload, insufficient rod reversal
Discharge Temperature
Capacity control and suction valve problems
Note: A number of other parameters available
Flow
Gas Comp.
Pressure
Pressure
Temperature
Tacho
Summary – Condition & Safety Monitoring Strategy
References
Borealis, Germany• Cylinder Head and Crosshead Vibration vs. Crank Angle• Rod Position (Rod Drop) vs. Crank Angle
Linde, Germany• Cylinder Head and Crosshead Vibration vs. Crank Angle
Shell Pohokura, New Zealand• PV plot• Differential polytropic exponent