Recip Presentation BKV

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