Compresor reciprocante.pdf

8/18/2019 Compresor reciprocante.pdf

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2000 Bently Nevada Corporation Reciprocating Compressor Best Practices Data Subject to Change (September 2001)

Protecting and Managing

Reciprocating Compressors

Best Practices


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Table of Contents

I NTRODUCTION.................................................................................... 3

PROTECTION

/ MANAGEMENT

................................................................... 3

TRANSDUCER SELECTION .........................................................................4

DRIVERS................................................................................................... 4 Electric Motors ...................................................................................................... 4

Gas Engines ........................................................................................................... 6

Integral Engine ...................................................................................................... 7

CRANKSHAFT / CRANKCASE .....................................................................7Main Journal Bearing........................................................................................... 7Frame ..................................................................................................................... 9

Vibration................................................................................................................ 9

CROSSHEAD............................................................................................11 Shoe Temperature ............................................................................................... 13

PRESSURE PACKING ...............................................................................14 Case Temperature ............................................................................................... 14

Vent Line Temperature ...................................................................................... 14Purge Flow........................................................................................................... 15

Purge Pressure..................................................................................................... 16

PISTON AND R OD....................................................................................17 Rod Position......................................................................................................... 17

CYLINDER ..............................................................................................19 Cylinder Pressure................................................................................................ 19

Valve Temperature ............................................................................................. 20Discharge Temperature ...................................................................................... 22

HYPER R ECIPROCATING COMPRESSORS .................................................23 Plunger Position.................................................................................................. 24


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Protecting and Managing Reciprocating Compressor


3

Introduction

This best practices document contains recommendations for the selection and installationof Bently Nevada transducers, monitoring systems, and trending systems on reciprocatingcompressors. These recommendations apply to both new and existing machines targeted

for retrofit installations.

Continuous collection and trending of the vibration, rod position, cylinder pressure, andtemperature data using a machinery management system such as Bently Nevada's System1™ is highly recommended. Bently Nevada’s reciprocating compressor monitoring

systems are also compatible with Bently Performance. Use of these tools willmaximize the ability to diagnose problems and analyze the performance of reciprocating

compressors.

Protection / Management

Minimal Protection System – The minimal recommended protection system for

reciprocating compressors include crankcase Velomitor and main bearing temperature probes. See Crankshaft in the Transducer Selection Section.

Minimal Management Solution – The minimal recommended management system forreciprocating compressors include the minimal protection system with the addition of

crosshead accelerometers. See Crosshead and Crankshaft in the Transducer SelectionSection.

Recommended Management Solution – The recommended management system forreciprocating compressors includes the minimal management solution with the addition

of piston rod position, cylinder pressure, and temperature monitoring on compressor

valves, pressure packing, and crosshead shoes (slippers). Figure 1 shows the placementof each transducer on a reciprocating compressor. Each item is discussed in detail in the

Transducer Selection section of the document.

Fully Instrumented Reciprocating Compressor


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Transducer Selection

The following table summarizes the transducer selection for reciprocating compressors.

Component Monitoring Point Transducer

Stator Temperature RTD or Thermocouple

Bearing Temperature RTD or Thermocouple

Driver

Crankcase Bearing Temperature RTD or Thermocouple

Crankshaft Position Reference Keyphasor / Multi-event Keyphasor

Frame Vibration Velomitor

Crosshead Machine Vibration Accelerometer

Shoe Temperature RTD or Thermocouple

Pressure Packing Case Temperature RTD or ThermocoupleVent Line Temperature RTD or Thermocouple

Purge Flow Flow Transmitter

Purge Pressure Pressure Transmitter

Piston and Rod Rod Position Horizontal and Vertical Proximity Probes

Cylinder Internal Cylinder Pressure Pressure Transducer

Valve Temperature RTD or Thermocouple

Discharge Temperature RTD or Thermocouple

Drivers

Electr ic Moto rs

Stator Temperature

System Monitor Transducer3500 3500/60 (No recorder output) RTD / Thermocouple

3500/61 RTD / Thermocouple

Benefits - Electric motor stator winding temperature can indicate problems

related to the stator, including unloaded balances between phases, low /

improper line voltage, short circuit in windings, and ground in winding.

System Description – Six channel continuous temperature monitoring on3500 systems.

Applications – Can be used on both induction and synchronous motors.


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Installation – installation includes imbedding either a RTD or thermocouple

into each winding lead. Typically the OEM does this during manufacturing, but motors can be retrofitted.

Filtering – N/A

Alarm / Danger – In the absence of actual engineering data the

recommended* initial alarm and danger set points are:Alarm: 180 oFDanger: 200 oF

*These should be adjusted based on actual operating conditions

Stator winding temperature is typically not a shutdown parameter.

Bearing Temperature



Benefits -Electric motor main bearing temperature can indicate problems

related to fluid-filmed bearings, including overload, bearing fatigue orinsufficient lubrication. Measuring temperatures at the main bearingtemperature and correlating them with other process variables can assist in

determining the overall condition of reciprocating compressors.


Applications – No known restrictions

Installation - Bently Nevada offers six channel monitors for temperaturemonitoring using either thermocouples or resistance temperature detectors(RTD).

Main bearing caps may be drilled and tapped to accept temperature probes

during the manufacturing process. If not, the bearing caps can always beremoved and drilled to accept the temperature probes.

Filtering – N/A

Alarm / Shutdown – In the absence of actual engineering data therecommended* initial alarm and danger set points are:

Alarm: 180 oF

Danger: 200 oF*These should be adjusted based on actual operating conditions

Bently Nevada highly recommends that customers use bearingtemperature as a shutdown parameter.


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Dynamic Power

This Section Intentionally Left Blank

Gas Engines

Beari ng Temperature



Benefits - crankshaft main bearing temperature on gas engines can indicate problems related to fluid-filmed bearings, including overload, bearing fatigue

or insufficient lubrication.


Applications – No known restrictions.

Installation - Bently Nevada offers six channel monitors for temperaturemonitoring using either thermocouples or resistance temperature detectors(RTD). Measuring temperatures at the main bearing temperature and

correlating them with other process variables can assist in determining theoverall condition of reciprocating compressors.

Main bearing caps may be drilled and tapped to accept temperature probeduring the manufacturing process. The bearing caps can be removed and

drilled to accept the temperature probes after machine installation.

Filtering – N/A


recommended* initial alarm and danger set points are:Alarm: 180 oF


Bently Nevada highly recommends that customers use bearing

temperature as a shutdown parameter.

Turbocharger

See Turbocharger Best Practices


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Integral Engine

See Gas Engine and Crankshaft / Crankcase Sections

Cranksh aft / Crankcase

Main Journal Bearing

Temperature



Benefits - High crankshaft main bearing temperature can indicate problemsrelated to fluid-filmed bearings, including overload, bearing fatigue or

insufficient lubrication. Measuring temperatures at the main bearingtemperature and correlating them with other process variables can assist in

determining the overall condition of the engine.

System Description – Six channel continuous temperature monitoring on

3500 systems.

Applications – No known restrictions.

Installation - Bently Nevada’s six channel monitors for temperature

monitoring using either thermocouples or resistance temperature detectors(RTD).

Main bearing caps may be drilled and tapped to accept temperature probeduring the manufacturing process. The bearing caps can be removed and

drilled to accept the temperature probes after machine installation.

Filtering – N/A


recommended* initial alarm and danger set points are:


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Alarm: 180 oF


Bently Nevada highly recommends that customers use bearingtemperature as a shutdown parameter.

Keyphasor Transducer

System Monitor Transducer3500 3500/25 Proximity probe

A Keyphasor® transducer produces a voltage pulse for each turn of the

crankshaft. This voltage signal is used to measure crankshaft rotative speedand serves as a reference for measuring vibration phase lag angle. TheKeyphasor® transducer is typically a proximity probe (recommended for

permanent installations in which the probe observes a physical gap).

Benefits – Provides a reference signal based on crankshaft position.

System Description – The 3500/25 provides two channels of Keyphasor

signal conditioning for proximity probe input from either a single notch or projection on the crankshaft or from a multi-event wheel (see Multi EventKeyphasor System section).

Applications – A Keyphasor® is mandatory for use with the cylinder

pressure monitor and is highly recommended for use with rod positionmeasurements (see rod position). A Keyphasor® is also essential fordiagnostic purposes since it provides the necessary reference signal, usually

based on the position of the #1 piston.

Installation – The Keyphasor® transducer is typically mounted on thefoundation at a 45 degree angle from true vertical. A notch is made on theflywheel with reference to the #1 piston at Top Dead Center (TDC) of the

cylinder stroke.

Note: The #1 piston is normally the first from the oil pump end of themachine, which is the non-drive end of the machine.

Filtering – N/A

Alarm/Shutdown – N/A

Mult i Event Keyph asor System

System Monitor Transducer3500 3500/25 Proximity probe

The multi-event Keyphasor® system is a special variation of the standardKeyphasor® transducer system that produces a voltage pulse for every 30


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degrees of shaft rotation. The signal produced is used by the 3500 compressor

monitoring systems as an accurate reference of crankshaft position. The MultiEvent Keyphasor® transducer is typically a proximity probe (recommended

for permanent installations in which the probe observes a physical gap).

Benefits – Provides a reference signal based on every 30 degrees of

crankshaft rotation in addition to a once per turn event to establish a once per

turn reference.

System Description – The multi-event Keyphasor® system is a specialconfiguration of the standard 3500/25 monitors.

Applications – The multi-event Keyphasor® system is required for the

cylinder pressure monitor, 3500/77M. The multi-event wheel is highlyrecommended to attain the highest accuracy on the cylinder pressuremeasurements and provide the most accurate pressure-volume (PV) curves

Installation – The multi-event wheel is mounted to the shaft on the outboard

end of the driver. Drilling and tapping of the driver shaft is normally required.The once per turn reference is normally aligned with the top-dead-center position of the #1 cylinder.

Filtering – N/A

Alarm/Shutdown – N/A

Frame

Vibration

System Monitor Transducer3500 3500/42 Velomitor XA

The cylinders on balanced-opposed compressors are physically offset, causing

moments to be generated on the crankshaft. The pressure forces across themachine can become unbalanced due to process changes, valve unloading, ordamaged valve assemblies. These forces are transmitted through the bearing to

the frame, resulting in crankcase vibration at one or two times machine runningspeed. Frequencies on the order of ½x to 2x the machine speed and their

harmonics can also occur on reciprocating compressors due to their layout.Excessive amplitudes at these frequencies may indicate mechanical or operational problems. Velomitor® Piezo-velocity Sensors are ideal for detecting machinery

problems on reciprocating compressors where rotation-related vibration istransmitted to the compressor frame. Velomitor® Sensors eliminate the cross-


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axis sensitivity problems inherent to moving coil velocity sensors. At the same

time, they have a better signal-to-noise ratio at the low running speed (frequency)of reciprocating machines when compared to standard accelerometers.

Benefits -Typical operational problems that the Velomitor® sensor and monitorcan detect include:

• Imbalance due to an unusual pressure differential or inertial imbalance.

• Looseness in the foundation attachment (such as deteriorating grout orshims).

• High moments caused by excessive rod load.

System Description - Frame vibration detection system consists of two

components: the Velomitor® XA Piezo-Velocity Sensor and the 3300 or 3500Velocity Monitor. The Velomitor® Sensor employs an accelerometer with a piezoelectric crystal at its core along with a low noise amplifier /integrator that

provides an output in velocity units. The result is a small sensor with no moving parts, integrated electronics, and a virtually unlimited lifespan. The transducer

provides a vibration signal in velocity units.

Applications - The Velomitor® XA transducer is ideally suited for measuring

casing vibration on reciprocating compressors with a running speed above 270rpm.

Installation - The best locations to mount Velomitor® XA Sensors are on thecrankshaft frame in the horizontal axis between each pair of cylinders. Mounting

Velomitor® XA transducers level with the bearing split line is preferred, as it places the transducers in the direct path of the forces acting on the machine.

Filtering – When used with accelerometers mounted above the crosshead, the

high and low bands filters should be set 4X and 1/2X, respectively. When usedwithout accelerometers mounted above the crosshead, no band bass filteringshould be used.

Alarm / Shutdown – In the absence of actual engineering data therecommended* initial alarm and danger set points are:

Alarm: 0.25 in/s pkDanger: 0.5 in/s pk*These should be adjusted based on actual operating conditions

Bently Nevada highly recommends that customers use frame vibration as a

shutdown parameter. It is a recommended shutdown parameter in API 618.

Limitations - When applying velocity measurements on reciprocating machinery,

it is important to understand the effect that the Timed OK/Channel Defeat andlatching have on the behavior of the alarms. This is particularly true when a

catastrophic failure occurs from an impact-type event. Impact-type events canresult in vibration many orders of magnitude greater than the typically rated 50in/s pk for a Velomitor® Sensor. This condition can force the transducer to


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operate well outside its linear range and will indicate to the monitoring system

that the transducer is in a fault condition (Not OK).

To prevent a false alarm due to an intermittent wire connection, Bently Nevadamonitors are shipped with Timed OK/Channel Defeat enabled. This means that ifthere is a not OK fault condition, the channel is disabled and the alarms are

bypassed for 3 to 6 seconds. If the Timed OK/Channel Defeat is enabled and an

impact event occurs, the transducer may be driven outside its linear (OK) range.The monitoring system will indicate a transducer failure, bypassing the alarms.Therefore, you will not get the alarm annunciation you are expecting.Furthermore, if the alarm relays are wired to shutdown the machine, the impact

event could prevent automatic shutdown of the machine from the velocitymonitor.

The above scenario may be an acceptable situation if accelerometers are installedto complement the velocity measurement or if multiple velocity transducers are

installed. Even so, a large impact could cause all velocity transducers andaccelerometers to go “Not OK”. If you are using a stand alone velocity monitor

and a single input, this is certainly not a favorable situation.

To ensure machinery protection, the possibility of missed trips should be virtually

eliminated. To do this, disable the Timed /OK Channel Defeat feature simply bychanging the monitor configuration. With this feature disabled, an impact eventmay still cause the transducer to operate outside its linear range, and the monitor

will still indicate a transducer failure. However, the monitor will also go intoalarm and the alarm relays will shut down the machine if they are wired for

shutdown.

Crosshead

Vibration

System Monitor Transducer3500 3500/42M 330400 Accelerometerand 37439-01 Mounting

Base

Placing accelerometers over each crosshead provides the best method to detectmachinery problems due to impact-type events. Impact-related events

characteristically cause free vibrations and are typically due to liquid ingestioninto the cylinder or mechanical problems such as looseness in the crosshead

and piston assembly.


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Acceleration can detect impact-type machinery problems better than a velocitymeasurement due to the high frequency vibrations created by impact events.

Under normal conditions, the vibration level should be very small. As impactsoccur, the vibration level increases and the waveform will resemble the classicimpact ring-down response over each stroke, as shown in the figure below.

The large increase in amplitude should be readily apparent from looking at an

acceleration waveform generated by an impact.

Benefits - The benefits of monitoring free vibration using accelerometersinclude the ability to detect the following machinery faults:

• Liquid ingestion into the cylinder.

• Excessive crosshead clearance.

• Loose or cracked nuts or bolts.

• Excessive clearance in the wrist pin bushing.

• Detonation on power cylinders for integral engine compressors.

System Description - The 3500/42M Proximitor®/Seismic Monitor is a 4-channel monitor that accepts input from proximity and seismic transducers,

conditions the signal to make various vibration and position measurements,and compares the conditioned signals with user-programmable alarms. Eachchannel of the 3500/42M should be programmed for acceleration.

Applications - The 330400 Accelerometer transducer is ideally suited for

measuring free vibration events on reciprocating compressors.

Installation - To detect impact-type events, mount an accelerometer on each

cylinder over the crosshead, distance piece or cylinder. For best results with asingle accelerometer per throw, mount the accelerometer directly above the

crosshead in the vertical plane.

Filtering – When used in conjunction with a case mounted Velomitor the

filtering should be set between 2k and 20k hertz. If the accelerometer is theonly monitoring or protection system then no filtering is recommended.


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recommended* initial alarm and danger set points are:Alarm: 2.0 g’s

Danger: 5.0 g’s*These should be adjusted based on actual operating conditions

Bently Nevada recommends that customers use crosshead vibration as a

shutdown parameter.

Shoe Temp erature



Benefits – Crosshead shoe (slipper) temperature can indicate problemsincluding overload, fatigue, or insufficient lubrication.

System Description – Six channel continuous temperature monitoring on

3500 system.

Applications – On reciprocating compressors there is an up running and adown running crosshead. The up running side is on the left side of the

machine when viewing from driver to driven equipment with the machineturning in the clockwise direction. If the machine were turning in the counter

clockwise direction then the up running side would be on the right side of themachine. If only one temperature probe is requested it should be placed onthe active side (e.g. top on up running side and bottom on down running side).

Installation – An RTD or thermocouple may be mounted either on the bottom

or top of the crosshead guide. Precise machining of the crosshead is requiredto make the necessary provisions for the temperature probes.

Filtering – N/A

Alarm / Danger – In the absence of actual engineering data therecommended* initial alarm and danger set points are:

Alarm: 180 oF


Crosshead shoe temperature is typically not a shutdown parameter.


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Pressure Packing

Case Temperature



Benefits – Pressure packing temperature can indicate problems related to the

packing, including excessive wear, insufficient cooling or insufficientlubrication.

System Description – Two and six channel continuous temperaturemonitoring on 3300 systems. Six channel continuous temperature monitoring

on 3500 systems.

Applications – Applies to both high and intermediate pressure packing

glands.

Installation – The RTD or thermocouple should be installed as close as possible to the packing. Typically, provisions are made on the packing caseflange to insert a temperature probe into the case. API 618 requires

temperature monitoring on the high pressure packing case when discharge

pressures exceed 500 psi.

Filtering – N/A


Alarm: 140 oFDanger: 160 oF


Packing case temperature is not typically a shutdown parameter.

Vent Line Temperature



Pressurized packing was originally designed to prevent corrosive gases from

leaving the cylinder and entering the distance piece and crankcase. With the


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increase in concern for the release of volatile organic compounds, pressurized

packing glands have grown in popularity. (See purge pressure and flowsections)

Benefits – As the purge packing begins to leak from the atmospheric side, theleaking gas exits through the packing vent line to flare. With the increase in

process gas flow, the vent line becomes hotter. For years, operators have used

the subjective method of touching the line to see if gas is leaking.

System Description– Two and six channel continuous temperaturemonitoring on 3300 system. Six channel continuous temperature monitoring

on 3500 system.

Applications – The application of vent line temperature monitoring is well

suited for all reciprocating compressor applications.

Installation – A RTD or thermocouple may be embedded or affixed on the packing case vent line. It is important to have only one packing case vent line

at each monitoring point. The placement of the temperature probe should beas close to the packing vent discharge as practical.

Filtering – N/A


recommended* initial alarm and danger set points are:Alarm: 140 oF


Vent line temperature is not typically a shutdown parameter.

Purge Flow

System Monitor Transducer3500 3500/62 Flow Transducer

Pressurized packing was originally designed to prevent corrosive gases fromleaving the cylinder and entering the distance piece and crankcase. With theincrease in concern for the release of volatile organic compounds, pressurized

packing glands have grown in popularity.

Purge F low should be used with Purge Pressure Monitor ing

Benefits – As the pressure packing begins to wear, leakage can occur at eitherthe atmospheric or the process sides. If the purge pressure decreases and the purge flow increases then the atmospheric side packing needs replacement. If

the purge pressure increases and the purge flow decreases then the processside packing needs replacement.


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System Description – The 3500/62 Process Variable Monitors are well suited

for this application.

Applications – The application of purge flow is applicable to anyreciprocating compressor packing gland which incorporates nitrogen purged packing.

Installation – The installation of the packing case purge flow requires a signalfrom a flow transducer.

Filtering – N/A


recommended* initial alarm and danger set point are:Alarm: N/ADanger: N/A


Purge flow is not typically a shutdown parameter.

Purge Pressure

System Monitor Transducer3500 3500/62 Pressure Transmitter

Pressurized packing was originally designed to prevent corrosive gases from

leaving the cylinder and entering the distance piece and crankcase. With theincrease in concern for the release of volatile organic compounds, pressurized

packing glands have grown in popularity. (See purge temperature and flow

sections).

Purge Pressure should be used with Pur ge Flow Monitoring

Benefits - As the pressure packing begins to wear leakage can occur at eitherthe atmospheric or the process sides. If the purge pressure decreases and the purge flow increases then the atmospheric side packing needs replacement. If

the purge pressure increases and the purge flow decreases then the processside packing needs replacement.

System Description - The 3500/62 Process Variable Monitors are well suitedfor this application.

Applications - The application of purge flow is applicable to any

reciprocating compressor packing gland which incorporates nitrogen purged packing.

Installation - The installation of the packing case purge pressure requires asignal from a pressure transducer.


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Filtering – N/A


recommended* initial alarm and danger set point are:Alarm: N/ADanger: N/A


Purge pressure is not typically a shutdown parameter.

Piston and Rod

Rod Posi t ion

System Monitor Transducer3500 3500/72M X &Y Proximity Probes

Reciprocating compressors typically have rider bands to minimize wear of the

cylinder liner and damage due to contact between piston and cylinder. The primary problem with rider bands is determining how much wear has occurredwhile the machine is operating so the machine can be shut down prior to

contact between the piston and cylinder.

The 3500/72M monitor is designed to monitor the rod position from the idealcenter of the cylinder bore. Based on configuration data, a circular acceptanceregion is defined. When the piston moves too close to the cylinder wall in any

direction, as defined by leaving the acceptance region, an alarm or danger

signal is generated.

The 3500/72M monitor also accommodates the special case of the hypercompressor plunger position somewhat differently than the normal rod

position (see hyper compressor section).

Although not recommended as a Best Practice, the 3500/72M Rod PositionMonitor may also be configured with a single probe to provide rod position orrod drop.

Benefits - The Bently Nevada Rod Position Monitoring System continuously

monitors the crosshead looseness, rod bow and rider band condition of eachcylinder in a reciprocating compressor. The monitor has the followingfeatures:

• Continuous online indication of maximum magnitude and direction of rodmovement along with the crank angle at which the maximum occurs. This

information points to the source of movement enabling you to schedulemaintenance to replace rider bands or repair the crosshead only whenrequired, maximizing the lifespan.


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• Alert and Danger alarm level indications warn of potential cylinder

damage.

System Description - The 3500/72M monitor is a four-channel monitor providing rod position measurements for two piston rods using an X-Y probe pair on each rod. The monitor provides alarms on rod position and rod

position angle using data from the orthogonal probe pairs and position crank

angle, peak to peak amplitude, gap, 1X amplitude, 2X amplitude, and Not 1Xamplitude measurements for each of the horizontal and vertical probes.

Applications – The 3500/72M monitor can be applied to any horizontal,

vertical, V-shaped, or hyper (see hyper compressor section) reciprocatingcompressor.

Installation - X and Y proximity probes must be mounted in an orthogonalarrangement. The probes should be mounted directly on the high pressure

packing gland. A Keyphasor sensor is required which is typically mounted toread a notch in the flywheel.

Monitor configuration requires the following user supplied parameters:

• Proximity probe pair calibration data, physical mounting location and

mounting angles

• Cylinder and piston diameter

• Cylinder to bottom of piston clearance (rider band effective thickness)

• Cylinder to top of piston clearance (piston to cylinder effective

clearance)

• Piston Material

• Piston rod length and diameter

• Operating temperatures

Filtering – N/A

Alarm / Danger - In the absence of actual engineering data the

recommended* initial alarm and danger set points are:Alarm: 70% of hot radial clearance.Danger: 85% of hot radial clearance.Alarm Time Delay should be set for its maximum value of 3 seconds.


Bently Nevada does not recommend that customers use rod position as a

shut down parameter. It is primarily a machinery management tool tohelp customers determine when to replace rider bands.


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Cylinder

Cylinder Pressure

System Monitor Transducer3500 3500/77 Cylinder Pressure

Transducer

.

The 3500/77M Cylinder Pressure Monitor is a four channel monitor with provisions for inputs from up to four pressure transducers.

Benefits - The most effective method to determine the overall health of areciprocating gas compressor is through examination of the cylinder pressure

profile. The cylinder pressure monitor provides online access to the internal pressure for each cylinder on the compressor. This enables continuous

monitoring of cylinder pressures, compression ratios, peak rod loads, and rodreversal. This provides valuable information on the condition of suctionvalves, discharge valves, piston rings, packing glands, and crosshead pin.

System Description – Cylinder pressures are monitored through the use of

permanently mounted pressure transducers located on each chamber of thecylinder. The cylinder chamber pressure along with crankshaft position isused for both continuous monitoring data and also performance data. Separate

alarm and danger set points can be set for each continuous monitored point.

Continuous monitoring data includes the following

• Discharge pressure

• Suction pressure

• Maximum pressure for each crankshaft revolution

• Minimum pressure for each crankshaft revolution

• Compression ratio

• Peak rod load for both compression and tension

• Number of degrees of rod reversal

With an interface to System 1tm , the following performance data is generated

from the cylinder pressure monitor data output:

• Indicated horsepower

• Capacity at suction conditions

• Capacity at discharge conditions

• Suction horsepower losses

• Discharge horsepower losses

• Theoretical clearance

• Flow balance of suction to discharge


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• Median capacity between suction and discharge capacity

• Theoretical flow balance between theoretical discharge and suctionflow

• Power to median capacity

• Displaced volume

• Adiabatic discharge temperature

With an interface to System 1tm , the following software plots are generatedfrom the cylinder pressure monitor data output:

• Pressure verses displaced volume (P-V Diagram)

• Log pressure versus log volume (Log P – Log V Diagram)

• Force (rod load) versus crank angle

• Force (rod load) versus displaced volume

• Pressure versus crank angle

• Pressure versus time

Applications – The 3500/77M monitor is applicable to all reciprocating gas

compressors with either single or double acting cylinders in either single ortandem arrangements. Due to the high pressures involved, the 3500/77M

cannot be used on hyper compressors or reciprocating compressors withcylinder pressures greater than 5000 psig.

Installation – Pressure ports are required on each chamber of the cylinder.Per API 618, 4th Edition, Section 2.6.4.6, all compressor cylinders are to be

supplied with pressure ports. When retrofitting an existing cylinder,machining of the cylinder and liner may be required. Special pressuretransducers are mounted on the cylinder pressure ports, which are connected

to the cylinder pressure monitor. A multi-event Keyphasor is required (seemulti-event Keyphasor).

Filtering – N/A


Rod Reversal (per API option)Alarm: Less than 25 degrees of rod reversalDanger: Less than 15 degrees of rod reversal


Bently Nevada highly recommends that customers use rod reversal as ashut down parameter. Rod reversal is a recommended shut down

parameter per API 618.

Valve Temperature

System Monitor Transducer3500 3500/60 (no recorder output) RTD / Thermocouple



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Suction and discharge valves are the highest maintenance items on areciprocating compressor. Faulty valves can significantly reduce the

efficiency of the compressor. The six channel valve temperature monitordisplays the temperatures of the compressor valves and can help you tomanage your valuable reciprocating equipment.

Benefits - The benefits of using a valve temperature monitor include thefollowing:

• Detect bad or damaged valves at an early stage. Bad valves can result inreduced capacity, reduced efficiency, and damage to the cylinder liner due

to valve parts falling into the cylinder.

• Determine if gas leakage is occurring between the head and crank ends of

the piston due to damaged or worn piston rings.

System Description- During normal process conditions, an increase in the gastemperature near a valve is a primary indication of a failing valve. The Bently Nevada 3500/62 Temperature Monitor provides early warning of valve

temperature changes and allows the operator to identify the bad valve(s).

Applications - By recompressing the same gas, a leaky valve becomes hotterthan normal, causing the valve cover plate temperature to increase. Since thenormal operating temperature of each valve varies with changes in load, gas

stream and ambient temperature, it is necessary to compare the temperaturesof similar valves in the same process conditions. Measuring the differential

temperature between these valves provides an early and reliable indication ofa degrading valve. If a valve is unloaded, however, it may affect thetemperature of that individual valve and can cause a wide variation in

temperature. In these instances, bypass that channel before unloading the

valve in order to minimize these effects on the group.

Leaking piston rings will cause the temperature of the entire cylinder toincrease through the reworking of gas between each side of the piston.

Therefore, detecting changes in absolute valve temperature is also important.If a temperature increase for all valves in the same cylinder is not due to a

process change or lubrication problem, it is most likely due to piston ringleakage. Both intake and discharge valves at the head end and crank end willshow an increase in temperature due to piston ring leakage. Similarly, a

temperature increase for all valves on only the crank end of a cylinder is anindication of leakage in the cylinder packing.

Installation – The thermocouple or RTD should be placed as close to thevalve as possible. With the older style cage type valve hold-downs, the

temperature probe will need to be mounted on the valve cover.

With the new o-ring type valve cover, installation of the probe into the gas passage is possible. This is accomplished by mounting a thermowell directlyto the valve cover that enters the gas passage. The thermowell should extend

into the gas passage as far as possible allowing placement close to the valve.


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Under no circumstance should the valve jackbolt be altered in anyway

without review and specific recommendations from the OEM.

Filtering – N/A

Absolute Alarm / Danger – In the absence of actual engineering data the

recommended* initial alarm and danger set points are:Alarm: 20 oF above suction or discharge temperatureDanger: 30 oF above suction or discharge temperature


Relative Alarm / Danger – In the absence of actual engineering data the

recommended* initial alarm and danger set point are:Alarm: 20 oF above other valves in same group

Danger: 30 oF above other valves in same group


Valve temperature is not typically a shutdown parameter.

Discharg e Temperature



Discharge temperature is one of the first parameters used to monitor the conditionof reciprocating compressors. Discharge temperature gives a good indication of

overall cylinder health.

Benefits - Monitoring of discharge temperature can give an indication of worn

valves, unloaders, piston rings, inadequate lubrication, excessive compressionratio, or insufficient cooling water.

System Description – Two and six channel continuous temperature monitoringon 3300 system. Six channel continuous temperature monitoring on 3500 system.

Applications – Should be standard on all reciprocating compressors.

Installation – The temperature sensor should be mounted in the discharge line asclose as possible to the cylinder. This is typically in the neck of the discharge

nozzle.

Filtering – N/A

Alarm / Danger – In the absence of actual engineering data the recommended*

initial alarm and danger set points are:Alarm: 20 oF above normal maximum


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Shutdown: 30 oF above normal maximum*These should be adjusted based on actual operating conditions

Bently Nevada highly recommends that customers use discharge temperature

as a shutdown parameter.

Hyper Reciprocating Compressors

The polyethylene and polypropylene polymerization processes require process pressures

in the range of 30,000 to 50,000 PSI. (Structural grade steel yields at 36,000 psi.) Forthe majority of these applications, process plants choose a specially designed

reciprocating compressor to deliver these pressures. The industry refers to thesecompressors as hyper compressors. Hyper reciprocating compressors typically have verystrong rigid running gear (connecting rod, crosshead and piston) designs to handle the

large loads generated by the high pressure gases. Hyper compressors also have a veryhigh strength piston, usually made from tungsten carbide. The piston has no compression

or rider rings. To differentiate this design from the more common piston design, thesehyper pistons are referred to as plungers. To reduce bending stress in the brittle plunger,the overall length of the plunger is usually shorter than a typical reciprocating compressor

piston and piston rod assembly.

There are two major types of hyper-compressors as shown in the figures 1 and 2 below.The first type was designed and constructed for hyper-compressor applications. Thesecond incorporates a standard reciprocating compressor frame with special cylinders

attached.

Figure 1 – specifically design for hyper compressor service

Figure 2 – Standard reciprocating compressor frame with special cylinders for hyper compressor service


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Except for the difference in monitoring a plunger as contrasted to a piston rod,

monitoring of hyper compressors is identical to that for lower pressure reciprocatingcompressors.

Plunger Posi t ion

System Monitor Transducer3500 3500/72M X &Y Proximity Probes

In a hyper reciprocating compressor the piston rod, piston, and piston rings are

replaced by a solid tungsten carbide plunger. These plungers are capable of handlinglarge compressive fo rces but are much weaker when exposed to tensile or bendingforces.

The plunger in each cylinder uses numerous rows of bronze packing rings to seal the

gas from atmosphere. Typically, the packing is monitored for leakage to determinetheir condition.

Benefits – Monitoring of both plunger position and vibration give a good indicationof the bending forces on the plunger, packing condition, and crosshead shoe wear.

System Description - The 3500/72M monitor has been designed for monitoring the plungers on hyper compressors. The monitor provides alarms on gap and vibration

measurements for the horizontal and vertical probe. Since the plungers are generally brittle, can shatter, and may destroy probe tips in the process, the monitor sets timed-

ok/channel defeat as disabled. This configuration will cause a danger signal to beissued if both probes enter the not OK condition.

Applications - The monitors provide a convenient place for gathering the dynamicdata from both the horizontal and vertical probe simultaneously. This will assist in

analysis of dynamic plunger motion. The access to these signals is also importantduring commissioning.

Installation – The X and Y probes must be mounted in the true vertical andhorizontal direction, respectively. The probes must be mounted on the pressure

packing gland. (Note typical proximity probe scale factor for the tungsten carbide plunger is 290 mV/mil.) Custom calibrated proximitors can be specified to output thestandard 200 mV/mil for various plunger materials.

Filtering – N/A.

Vibration Alarm / Danger – In the absence of actual engineering data therecommended* initial alarm and danger set points are:

Alarm: 6 milsDanger: 8 milsAlarm Time Delay should be set for its minimum value of 100 ms for danger.



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Gap Alarm / Danger – In the absence of actual engineering data the recommended*

initial alarm and danger set points are:Alarm: +/- 6 mils

Danger: +/- 8 milsAlarm Time Delay should be set for its minimum value of 100 ms for danger.


Bently Nevada highly recommends that customers use both plunger vibration and

position as a shutdown parameter

Compresor reciprocante.pdf

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