CHEVRON Compressors - Maintenance and Trouble Shooting

800 Maintenance and Troubleshooting

AbstractThis section reviews reciprocating compressor/engine predictive maintenance, reciprocating piston rod reconditioning, and contains troubleshooting checklists for centrifugal and reciprocating compressors. Maintenance checklists referred to in this section are included in the Appendix. For information on predictive maintenance of centrifugal compressors and vibration troubleshooting, see the CUSA, IMI Candi-date Manual.

Contents Page

810 Performance Analysis of Reciprocating Compressors and Engines 800-3

811 Introduction

812 Principles of Compression Analysis

813 Principles of Combustion Analysis

814 Characteristics of Ignition Problems

815 Vibration vs Crankangle

816 Hardware

817 Example of a Typical Predictive Maintenance Program

818 Examples of Program Benefits

820 Maintenance Checklists 800-28

830 Reciprocating Compressor Piston-Rod Reconditioning 800-30

831 Introduction

832 Rod Leakage/Surface Finish

833 Rod Deviations

834 Rod Reconditioning

835 Rod Coating Processes

836 Experience

Chevron Corporation 800-1 December 1998

800 Maintenance and Troubleshooting Compressor Manual

837 Recommendations

838 Inspection and Specifications

840 Troubleshooting 800-52

841 Introduction

842 Troubleshooting Guidelines

843 Problem Solving Guides

December 1998 800-2 Chevron Corporation

Compressor Manual 800 Maintenance and Troubleshooting

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810 Performance Analysis of Reciprocating Compressors and Engines

811 IntroductionPerformance analysis is employed in several Company locations as one of several available methods of predictive maintenance.

Performance analysis is a program involving several elements, which can include:

• Analysis of power-cylinder pressure versus time,• Analysis of compressor-cylinder pressure versus time, or volume,• Analysis of vibration caused by mechanical events,• Analysis of computed values, such as horsepower, and/or• Analysis of power-cylinder ignition.

The concept of predictive maintenance is being successfully used throughout thindustry to reduce maintenance expense. The essential philosophy behind a prtive maintenance program is a concentrated effort to gather pertinent data on aodic basis. Data acquisition is covered later on in this section.

The advantages of a predictive maintenance program include:

• Elimination of catastrophic damage, thereby avoiding very high expense.

• Avoiding equipment (and plant) downtime.

• Performing only necessary maintenance.

• Avoiding disassembly of healthy machinery (periodic “overhauls,” for example) and exposing it to risks of maintenance errors.

• Allowing reliable machinery to continue operation.

• Optimizing fuel consumption.

The following is information summarized from two programs: one at a producinfacility, the other at a large refinery.

812 Principles of Compression Analysis

Pressure-Volume AnalysisThe purpose of this analysis is to:

• Detect mechanical problems before they become serious enough to causesignificant damage to the machine,

• Evaluate compressor/engine performance in conjunction with P-T (PressurTime) and vibration analysis, and

• Automatically compute indicated horsepower, volumetric efficiency, compressor horsepower loading, and power loss.



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Compressor CylindersFigure 800-1 is a simplified summary of a typical Pressure-Volume display and how it correlates to piston/valve actions. It gives the basic pattern and events relative to piston travel.

Figure 800-2 represents one format to display the compression cycle. Note that it is similar to Figure 800-1, except for being reversed. Figure 800-2 also shows typical problems that can be detected (with interpretation).

Figures 800-3 and 800-4 further illustrate methods for detecting impending compressor valve problems.

813 Principles of Combustion AnalysisMuch of the material in Sections 813, 814, 815 and 816 has been extracted from materials provided by Rotating and Reciprocating Specialists.

The purpose of this analysis is to:

• Optimize fuel consumption, and

• Detect mechanical problems before they become serious enough to causesignificant damage to the machine.

Typical combustion patterns are depicted on Figure 800-5 and may be defined follows:

1. Normal Combustion—Ignition timed correctly, proper air/fuel mixture, no malfunctions.

2. No Combustion (Dead miss)—Cause: ignition or mixture, also water in cylinder.

3. Early Combustion—Cause: ignition timing, mixture, or temperature.

4. Late Combustion—Cause: late ignition, mixture (rich or lean) or water in cylinder.

– Terminal pressure high—rich mixture– Terminal pressure low—lean mixture

5. Detonation (too rapid combustion rate—uncontrolled)—Cause: mixture, excess load. Rich mixture tends to detonate.

6. Pre-ignition (auto-ignition)—Cause: hot spot, carbon or foreign matter in thcombustion chamber, excess cylinder temperature, presence of heavy hydrocarbons.



Fig. 800-1 Typical Pressure Volume Display (Courtesy of the American Gas Association)



Fig. 800-2 Typical Compressor Cylinder Problems Identified with P-V Displays (1 of 5) (Courtesy of the American Gas Association)















Fig. 800-3 Detection Patterns for Valve Problems

Fig. 800-4 Detection Patterns for Valve Problems



Fig. 800-5 Typical Combustion Patterns (Courtesy of the American Gas Association)NOTE: Frames 1-6 are all cylinder pressure vs. crankangle displays.



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2-Stroke Cycle versus 4-Stroke CycleBoth types of engines have advantages and disadvantages. The individual applica-tion governs the selection of a 2-stroke cycle or 4-stroke cycle unit.

The primary difference between the engines is cylinder design, and:

• The 2-stroke cycle requires the piston to make only two strokes through thecylinder (one revolution of the crankshaft) for each complete combustion cy

• The 4-stroke cycle requires the piston to make four strokes through the cyli(two revolutions of the crankshaft) for each complete combustion cycle.

• The 2-stroke cycle engine is the less complicated of the two, since it has noCAM-actuated intake valves and most have no CAM-actuated exhaust valvSome 2-stroke cycle units do, however, have CAM-actuated exhaust valve

• The 2-stroke cycle engine requires a positive scavenging air pressure (recicating scavenging air cylinder, mechanically-driven blower or turbocharger)The 4-stroke cycle engine can be naturally aspirated. More horsepower caderived from the 4-stroke cycle engine by utilizing a mechanically-driven blower (supercharger or turbocharger).

• The 4-stroke cycle engine has a longer functional stroke than the 2-stroke cengine, since the 4-stroke cycle maintains a positive pressure (due to combtion) on the piston for more degrees of crankshaft rotation and opens the exhaust valve near the bottom dead center. Therefore, if a 2-stroke cycle a4-stroke cycle cylinder had the same displaced volume and were operatingthe same crankshaft speed with the same average cylinder pressures, the 2-stroke cycle would be developing 65 to 75% more horsepower.

• The 2-stroke cycle engine develops more power per cubic inch of displacedvolume.

• The 2-stroke cycle performs efficiently 100 to 110% of its rated load. The eciency drops rapidly as the load is reduced. Modern 2-stroke cycle enginesoperate more efficiently at lighter loads than the earlier generations did.

• The 4-stroke cycle engine is more efficient over a wider load range and responds faster to drastic load changes, since the flow of gases is better controlled by the intake and exhaust valves.

814 Characteristics of Ignition ProblemsIgnition can be analyzed similar to compression and vibration. The following describes such an analysis:

(Also, refer to Figures 800-6 and 800-7.)

Point A—Breaker points close/transistor turns on. If there is any abnormal voltachange at this point, or if this point varies horizontally, a problem is expected wthe points or the switching mechanism.



Fig. 800-6 Details of Combustion Pattern (Primary) (Courtesy of the American Gas Association)

Fig. 800-7 Details of a Combustion Pattern (Inductive Secondary) (Courtesy of the American Gas Association)



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Point B—Breaker points open/transistor turns off. This occurs at the same degreach cycle if normal, and varies if the drive is worn or if the points stick or arc.

Point C—(line I) Peak ionization voltage. Voltage required to ionize the plug gapAs this increases, the duration (line III) will decrease.

High voltage indicates:• Wide plug gap of bad plug. Arc voltage (II) will be high also

• High resistance in the secondary lead (arcing broken strands or corroded connectors)

• Heavy cylinder load (rich, dense mixture)

• Misfires—Excessive ionization voltage with no arc (III)—plug or secondary lead bad

Low voltage indicates:• Narrow plug gap• Shorted plug—No or very little voltage rise• Shorted secondary—Low voltage with no arc (III)• Transformer—No arc (III)• Light cylinder load—Arc voltage (II) also low and duration (III) long

No voltage rise—Shorted primary or primary distributer problem

Point D—Arc voltage (II) and arc duration (III)

High arc voltage indicates:• Bad plug or wide gap• High resistance in the secondary lead• Heavy cylinder load

Low voltage indicates:• Narrow plug gap• Light cylinder load

Things to Remember:• Be sure to analyze the whole pattern.

• Watch for multiple fires. Voltage rises at wrong crankangles.

• Approach the ignition analysis systematically.

• Be sure all cylinders are firing at the correct crankangle. Variation is often found between the cylinders.

• Know the characteristics of your ignition system.



815 Vibration vs CrankangleThe purpose of vibration analysis is to display the vibration amplitude vs cran-kangle and to analyze the pattern. The vibration is composed of many different components as they vibrate at various frequencies, amplitudes, and degrees of crankshaft rotation.

If you know the exact degree at which each event occurs, its amplitude of vibration, and its shape, you can determine if this event is normal for this type cylinder, the condition of the various components, and even predict failures or schedule the exact repairs as needed before the unit fails.

Refer to Figure 800-8 for typical vibration patterns and problems associated with power cylinders. Although not discussed, similar patterns are evident on compres-sion cylinders. Figure 800-9 shows typical compression-analysis signals.

Point A

Peak Pressure Vibration. The flame front is moving at maximum velocity at this point and usually causes this normal vibration. If detonation occurs, this vibration becomes a high-amplitude sharp spike. Piston slap also occurs at or near this point, since the piston will rock in a worn cylinder under the maximum pressure.

Excessive wear in the wristpin or bushing is often seen at this point.

Fig. 800-8 Typical Vibration Patterns with a 2 Stroke Power Cylinder. (Courtesy of the American Gas Association)



A badly worn rod bearing will knock at this point or slightly later, normally detected at BDC long before it appears at this point. The same is true of a worn wristpin. We normally look for the rod bearing, wristpin, or a piston loose on the hanger at 10 degrees before and after BDC when it is in the early stages of wear.

Point B

Top Ring Enters the Exhaust Port. If the top ring is doing its job, the pressure will be released when this event occurs. If this ring becomes worn, stuck, broken, or the piston or cylinder port area wear, this vibration becomes a high-amplitude, sharp spike. If something happens to the top ring, the second ring will hold most of the pressure, resulting in a vibration spike when it enters the port. (This spike will occur earlier, since the second ring enters the port at an earlier degree of crank rotation.)

Evaluate the ring condition by watching this area. Also watch for carbon buildup in the ports, which will cause the rings to clip. This can occur in the intake port as well as the exhaust. Normally, a ring is not picked up as it enters the intake port unless there is a problem. The same is true of the rings going back up through the ports on the compression stroke. Since there is no pressure to hold the rings against the cylinder walls, they do not clip in the ports on the compression stroke unless there is a problem with the rings or the cylinder port.

If one of the lower rings is broken, it will cause a sharp spike in the exhaust port on the power stroke, indicated by the degree at which it occurs.

Fig. 800-9 Typical Vibration Patterns with Compression Cylinders (Courtesy of the American Gas Association)



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Watch these ring vibrations, and they will increase in amplitude as the condition gets worse. A new set of rings will clip in the ports until they wear in. Then the vibration will drop down to a normal level until they begin to deteriorate.

Point CExhaust Blowdown—This is vibration of the gas as it leaves the cylinder. This vibration will be present when the cylinder fires on a normal cycle and will disappear when the cylinder has no combustion within the cycle. Use the exhaust blodown as a standard to compare all other vibrations within the pattern. If the mounting or transducer changes, it will affect the whole pattern amplitude, whicthe operator will note if he compares to a standard within the pattern.

The exhaust will elongate if the ports are restricted by carbon.

The operator may also note that on V-type units with a common exhaust manifobetween the V, the exhaust blowdown from the cylinder on the other bank may over in the vibration trace. This blowdown (or ghost vibration) will always be there and in the same place or crankangle. The operator can disregard it once identifies it.

Point DInjection Valve Opens—This vibration is caused by the slack taken out when thevalve train activates the injection valve. The operator can get a fix on the CAM timing and lobe condition from this vibration and the closure vibration. Some unwith hydraulic lifters will not have this vibration unless there is a problem with thCAM or lifter. To pick up this vibration on such a unit, put the pick-up directly onthe rocker arm pin.

This vibration will be excessive if there is any wear in the valve actuation assemPressure applied to the rocker arm sometimes will eliminate much of the vibratiand allow the operator to make a true analysis of the rest to the pattern, possibdistorted by this vibration.

Point EInjection Valve Closes—The front (flat) side of this vibration is the degree at which the valve hits the seat. The higher the amplitude, the harder the valve hitseat. The wider the vibration spike, the wider the mating surfaces. This is a gooindication of valve lash, CAM timing, injection valve, and seat condition.

If the vibration fades into the baseline, it is a good indication that the valve has sealed. If it balloons out or continues to vibrate for too long, the valve is leakingNote the pattern in Figure 800-10.:

816 HardwareA variety of electronic equipment is used to make the program analysis. This eqment is continually being improved and perfected to obtain additional or more precise information. The system components are as follows:



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Analyzer—This unit is the control center for the analyst. Various signals are selected, calibrated, and controlled for accuracy of display, and if applicable computing the horsepower. There are two available types

• Type I—Maintenance Analyzers—These devices display ignition, vibra-tion/ultrasonic and pressure waveforms on an oscilloscope versus crankantime for condition analysis.

• Type II—Performance Analyzers—These devices have all the capabilities othe maintenance analyzers plus RPM, and accurate pressure versus volumdisplay, and digital readouts of horsepower developed or consumed by a cylinder. These are the most expensive.

Oscilloscope—The oscilloscope displays electrical signals. It only understands voltage. The signals it receives can be amplified and changed, but it primarily displays the signals it receives as voltage wave forms. Scopes have one or movertical inputs and at least one horizontal input. The scope then provides a dynX-Y plot of the wave form. These wave forms are observed or photographed foanalysis or evaluation.

Transducers—A transducer is a device that takes a mechanical or nonelectricalsignal and converts it into an electrical signal that can be displayed on the oscilscope. The program analyzer uses various types of transducers. These transduare:

• Ignition—Since ignition is an electrical signal, it requires no transducer, onlan ignition pickup. The ignition pickup carries the voltage from any point onthe ignition system (excluding direct secondary ignition voltage) to the osciscope form display. A 10:1 ignition attenuator is provided for voltage reduct

Fig. 800-10 Vibration Patterns (Courtesy of the American Gas Association)



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• Vibration—The accelerometer uses a piezoelectric crystal device to convethe physical or mechanical movement (1 Hz to 6 Hz) of the transducer intoelectrical signal proportional in amplitude to the actual movement or vibrati

• Pressure—Pressure transducers convert the instantaneous pressure into eltronic signals that can be displayed or processed by the programming unit.pressure transducers can be used to sample the pressure inside any cylindat any accessible point on the engine/compressor system. The transducerscurrent state-of-the-art strain gage pressure transducers that can be automcally calibrated by the program analyzer.

• Crankshaft Position—The encoder converts the physical crankshaft positioninto electronic pulses. The crankangle may be determined by key-phasors measuring each revolution, or by an encoder which produces one pulse fordegree of crankshaft rotation.

• Ultrasonic—The ultrasonic probe converts the high-frequency vibrations (36 Hz to 44 Hz) to lower frequency electronic signals that can be displayedthe oscilloscope or evaluated audibly through headphones.

X-Y Plotter—This is a multi-pen X-Y plotter for large-scale, hard-copy records opressure traces and alphanumeric data.

Commercial Hardware AvailableListed in Appendix M are the established analyzer systems on the market today(December 1988). These analyzers will be upgraded as electronic and digital tenologies are expanded. Long-term digital storage of the various parameters is currently being incorporated into these analyzers.

817 Example of a Typical Predictive Maintenance ProgramThe philosophy of predictive maintenance is to predict when, and what mainte-nance will be necessary. It is best implemented as an element of an integrated ability program, as outlined below:

Record Keeping. Records of maintenance history, cost, performance and vibratidata are essential.

Machinery Surveillance and Diagnostics. Routine surveillance to monitor online conditions: vibration diagnostics, performance testing, oil analysis are utilized.

Design Review. Excessive maintenance and down time usually indicates a desigfault or misapplication.

Quality Control. Provide detailed maintenance checklists, inspection by qualifiepersonnel, and on-the-job technical advisors.

Machinery Protection. Shut the unit down before catastrophic failure, utilizing appropriate shutdown protection, such as vibration, low-lube-oil pressure, high-discharge temperatures, etc.



The above are the standard elements developed by the CUSA Manufacturing IMI (Integrated Machinery Inspection) Program.

The essential philosophy behind a predictive maintenance program is a concen-trated effort to gather pertinent data on a periodic basis. Data acquisition includes the recording of visual inspections, temperature and pressure readings, along with photographs of pressure, vibrations, and ultrasonic patterns. The conditions listed in Figure 800-11 should be checked on a periodic basis: typically every 30 days on critical machinery and 60 to 90 days on basic units.

Fig. 800-11 Summary of Typical Records Maintained: Reciprocating Compressor/Engine Predictive Maintenance Program

Power Cylinders Compressor CylindersGeneral Operating Conditions Scavenger Cylinders

Original specifications, or baseline data, plus recent trends as appropriate:

Horsepower per cylinder Horsepower per head-end and crank-end

Power loss per cylinder, suction and discharge

Oil temperature

Jacket water temperature

Compression per cylinder RPM during test Oil pressure

RPM during test Suction and discharge pressure and temperature

Oil filter differential

RPM surge Effective horsepower Crankcase pressure

Ignition timing Brake horsepower Scavenging air pressure

Exterior examination of fuel valves, rocker arms, push rods, coils, plug wiring, starting air valves, etc.

Percent of rated load

Operation of unloaders and clearance pockets

Valve cover and cylinder temperatures

Visual inspection of cylinder parameters, jack stands, piping, etc.

Exhaust pressure

Motor amperage, power factor, field current, etc.

System parameters, knock-outs, pot liquid level, spill-back opera-tion, flow rates, specific gravity, etc.

Photographic/X-Y Plot Records:

Pressure versus crank angle degree


Vibration verses crank angle degree

Vibration versus crank angle degree

Vibration versus crank angle degree

Pressure versus volume

Ultrasonic versus crank angle degree

Ultrasonic versus crank angle degree




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Followup SurveillanceDuring the time between periodic compression analysis, plant personnel may perform followup surveillance of equipment highlighted by the analysis team. This followup surveillance consists of the following:

• Visually inspect the compressor/engine;

• Record gage pressures and temperatures per individual equipment “road m

• Monitor and record valve cover temperatures;

• Note oil levels; i.e., crankcase, McCord, Trabon, etc.;

• Use ultrasonic translator to help locate leaking and broken valves, valve corod packing, and auxiliary equipment leaks; and

• Monitor temperatures on fuel injection valves and starting air check valves.

Plant personnel should also review the surveillance schedule to determine whiccompressors are due for analysis the next period. Notification should be given responsible parties to make sure the equipment is online and available.

A periodic surveillance report should be prepared for each piece of equipment order to inform operations of any problems in their plant. Care should be taken ensure that all interested parties understand this information.

Machinery Surveillance and DiagnosticsAn engine/compressor surveillance program's main objective is to keep machinrunning reliably as long as possible, thereby reducing maintenance expense ansupporting production. Scheduled maintenance is recommended only when it isthat the machine will not “last” until the next surveillance period. The term “last”can mean: (1) if equipment continues to operate, a failure could cause machinebecome unsafe, or (2) a catastrophic failure could occur resulting in extended dtime and more expensive repairs.

The following parameters may be established to classify machinery conditions:

Phase I. Potential problem. Symptom of a potential problem is present, but of lomagnitude. If, however, the unit is shutdown for another reason, before the nexanalysis, it would be advantageous to make the repair.

Phase II. Predictable failure stage. Schedule maintenance within a few days. Cotions call for scheduled maintenance. Experience indicates that machinery in thcondition can deteriorate rapidly.

Phase III. Failure imminent. Recommended immediate shutdown. Analysis indicates probable catastrophic failure. The shutdown surveillance team will gatherneeded data and then immediately contact the operator to shut down the unit. Tsurveillance team will then notify proper personnel and present them with supporting data.



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Through coordinated efforts between the surveillance team, operations, and mainte-nance, the recommended repairs are scheduled, and when complete, are recorded for review by interested personnel.

Design ReviewRepetitive failures are almost always caused by design deficiencies. A design review consists of first identifying repetitive problems, then reviewing and rede-signing the system to eliminate them.

The following case history is one example of a persistent problem solved by an analysis program, combined with a design review. The problem was excessive fail-ures of inboard suction valves on a high-stage hydrogen-booster compressor in a large refinery.

Compression analysis showed several instances of cylinder-pressure variations. Normal compressor valves required an average differential pressure of 20 psig to open suction valves. Prior to valve failure, however, the differential pressure increased to as high as 220 psig. With this information, the surveillance crew began to gather data on a twice-per-month basis to study valve life in relation to the pres-sure differential. They concluded that after the differential exceeded 75 psig, less than two weeks valve life could be expected.

A criterion was established for these valves to be considered in a “Phase II” condi-tion when the pressure differential exceeded 50 psig. After this criterion for repawas established, the breakage of inboard suction valves ceased.

Investigation also showed that the only time failures occurred were during, or athe outboard end of the cylinder had been operated in the unloaded position.

Subsequent investigation of the valve repairs found that the plates and seats wbeing honed to a mirror-like surface. With oil between the seat and plate, it wasimpossible to lift the plate off the seat. This phenomenon was labeled “stiction.”

Valves were subsequently rebuilt with machined surfaces which alleviated a larpercentage of this “stiction”. Inboard valves were breaking because all the oil supplied to the cylinder was dissipated during each stroke, except when the outboard end was unloaded. This allowed oil to travel back through the outboarsuction valve and coat the inboard valve with excess oil. The following steps wetaken to eliminate the excessive failures of inboard suction valves:

• Valve surfaces were closely monitored to ensure proper finish.

• Lubrication rate to the cylinder was modified to the minimum required.

• Operations alternated outboard loads when notified of Phase I conditions by the surveillance team.



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Machinery ProtectionInstrumentation for shutdowns and alarms are monitored, repaired, and upgraded as necessary to prevent catastrophic failures of reciprocating equipment. The following parameters are commonly considered critical for constant monitoring:

• Oil pressure,• Discharge temperature,• Jacket water temperature,• Liquid knockout level,• Vibration,• Lubrication rate, and• Amperage.

An important element of machinery protection is periodic testing of alarms and shutdowns. In locations where there are regular, documented testing programsare conducted as often as weekly, but more commonly monthly. Longer intervalalso used. One thing is clear: You cannot rely on shutdown protective devices if they are not being tested and documented regularly.

Analysis worksheets used in the Warren Petroleum program are included in Appendix M. They may be ordered from Warren or used as models to develop checklists.

818 Examples of Program BenefitsThe justification of an analyzer program depends on many factors which must banalyzed for each individual location. Several locations have adopted programsseveral others use less-sophisticated, less-costly methods such as periodic motoring of valve temperatures.

Some factors worth considering include the cost of the program itself, the level attention the equipment gets from operators and/or other predictive maintenancremoteness, number and sizes of machines, criticality of service (production vaand past maintenance costs.

Warren Petroleum and the El Segundo Refinery currently (1988) have active programs in place. The following text illustrates some typical savings noted by Warren, who have primarily integral-engine compressors. The cost-justification worksheet (Figure 800-12) at the end of this sub-section was developed at El Segundo, where most machines are slow-speed, motor driven.

In summary, the following discusses:

• Background,• Fuel savings,• Problems and cost,• Power cylinders,• Compressor cylinders, and• Cost justification worksheet.



Fig. 800-12 Cost Justification Worksheet (1 of 2)

Engine/Compressor Analyzer

Part I. Operating and Maintenance Data:

1. Horsepower

2. Cost per installed horsepower:

3. Fuel cost, per year:

4. Value of production per year:

5. Repair material cost, per year:

6. Load factor:

II. Cost Justification—Calculations

1. Reduced fuel consumption (per BHP Hr.) resulting from the following:

a. Correct Engine Balancing, using horsepower measurements of the Engine/Compressor Analyzer:

5.0% of I (3)

b. Elimination of Defects in Ignition System using ignition analysis:

1.0% of I (3)

SUBTOTAL, Reduced Fuel Consumption

2. Added Production, or throughput:

a. Elimination of restriction on horsepower utilization, through the following:

1. Measurement of indicated horsepower to help accomplish:

a. Correct loading, to utilize 100% of installed H.P.:3% of I (4)

b. Proper balancing of power cylinders using H.P. measurements:

1.0% of I (4)

2. Elimination of defects in ignition system using ignition analysis:

0.25% of I (4)

3. Elimination of improper firing conditions through pressure-time analysis:

0.25% of I (4)

b. Elimination of excessive compressor power or valve loss through measurement of HP.

2% of I (4)

c. Improved volumetric efficiency through measurement of V.E. on P-V card display:

1.0% of I (4)



BackgroundTypical maintenance programs consist of repairs only after failures, or doing peri-odic overhauls. Needlessly, all power pistons and cylinders would be pulled and inspected for damage, when only one or two pistons or cylinders on each engine might need repair or replacement. A complete power cylinder overhaul of a Clark RA-8 can cost a conservative $40,000 in parts, not including labor.

With a routine analyzer program, power piston rings that are worn, broken, or stuck can usually be spotted and pulled for repair before the cylinder is damaged. A costly overhaul, or worse, catastrophic damage, is thereby avoided.

Fuel SavingsWhen an engine is not balanced, some of the power cylinders carry more than their share of the load. Consequently, the unbalanced engine will use more fuel to carry the same load. This extra fuel varies depending on the severity of unbalance and the type of engine. Besides the extra fuel, maintenance problems will arise from the overloaded cylinders.

d. Elimination of excessive downtime which may result from:

1. Catastrophic failure.

2. Shutdown for visual inspection.

0.5% of I (4)

SUBTOTAL, ADDED PRODUCTION

3. Reduction in cost of repair parts through reduction of:

a. Catastrophic failure.

b. Periodic inspection.

5% of I (5)

4. Reduction in manpower costs resulting from reduced maintenance requirements:

TOTAL ESTIMATED VALUE, operation and maintenance savings, and added production:

Per Year

Multiplied by: Additional conservative factor: .05

Estimated Value of operation and maintenance savings and added protection

Per Year

Fig. 800-12 Cost Justification Worksheet (2 of 2)



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Balancing the horsepower between the power cylinders evenly distributes the load, and wear is not excessive on any one cylinder. This is a basic preventive mainte-nance procedure.

Ignition problems and poor ignition timing will cause the engine to use more fuel than required. If there is no combustion in a power cylinder due to ignition difficul-ties, then the fuel will be swept out the exhaust. If the spark is early or late by as little as four degrees, it will cause the engine to consume more fuel than necessary.

Other problems that will cause excessive fuel consumption are improper fuel and air quality, improper air/fuel ratios, engine load, and engine RPM. The result of these problems can cause the engine to consume as much as 15 to 25% more fuel than necessary.

Example: A Cooper Bessemer GMVA-8, rated at 1350 HP, consumes 250 MCFD at an estimated price of $1.50/MCF. If it consumes 20% extra fuel, or 50 MCFD, the annual cost of the extra fuel would exceed $27,000.

Problems and Costs SummaryAn analyzer program can discover many compressor engines running at less than a full load. It can determine if the cylinder is moving the assumed amount of gas. It checks the indicated horsepower consumed for each compressor cylinder.

Typical problems are listed below that are frequently found from an analysis program. In all cases, simple, inexpensive problems are caught and corrected before they lead to serious, very costly repairs. The approximated costs are typical for the West Texas region. The costs do not reflect any labor cost to install or replace the various components. Labor typically runs 100 to 150% of parts costs.

A Clark RA is a medium-sized, slow-speed integral engine. A Clark BA is a slightly larger, slow-speed integral engine.

Problems and Costs: Power CylindersPiston Slap—This creates a major wear pattern in the cylinder and piston whichwill have to be completely changed out. If the cylinder and piston have to be replaced, the costs are approximately $2500 to $4500 for a Clark RA and Clarkrespectively.

Ring Blow-by—This leads to oil contamination and also leads to piston slap if leundetected and allowed to progress. If the repair is limited to piston ring changethe cost is approximately $250 to $450 for a Clark RA and a Clark BA, respec-tively. If the cylinder and piston require repair, the cost is about 10 times higher

Detonation—This can be a very serious problem if allowed to continue for very long. It breaks rings, cracks pistons, cracks heads, and wears piston bearings overy quickly. The costs for replacing broken rings are noted under Ring Blow-by. The reworking of the piston dome and cylinder costs approximately $700 each,the piston bearings cost $400 for a Clark RA. If the crankshaft is cracked or ruina used RA-8 crankshaft costs $25,000, and a new one costs $65,000, with an extended delivery time.



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Cracked Head—This leads to detonation and visa versa. The costs for this are detailed under Detonation.

Carbon in Ports—This only takes labor and gaskets to fix, but leads to a loss inhorsepower, which causes the other cylinders to overload, and high cylinder tematures. This eventually leads to a major wear pattern detailed in Piston Slap. If the carbon begins to get hot and cause premature ignition or detonation problems,more maintenance costs are incurred as a result of this relatively simple probleNote that excess carbon can also be caused by improper lubricating oils.

Knock in Wristpin/Bushing—This can be replaced for approximately $400. If thcondition is allowed to deteriorate, it creates excessive wear in the piston, cylinand rings. These costs are noted in Piston Slap.

Bad Valves—If the intake and exhaust valves on a 4-stroke engine are leaking, worn, or need adjustment, the cylinder loses horsepower, causing the other cylders to overload and have high cylinder temperatures. This can also lead to hearepair, which costs $600 to $1000, depending on the type of head.

Worn Rocker Arms Bushing—This is relatively simple to repair for $10 to $20. If it is not repaired, it can cause a fuel valve, pushrod, and rocker arm to fail, costing $200.

Problems and Cost: Compressor Cylinders

Leaking Valves—Repair this valve before it completely fails. Minor repair can coabout $20; a new 7¼-inch valve costs $400. Replacing a cylinder destroyed bybroken valve can easily exceed $10,000.

Ring Wear—One cause may be hot valves not changed before the rings were damaged. If the rings fail, the compressor cylinder might be damaged. Reliningcompressor cylinder costs approximately $100 per diameter inch. Compressor cost approximately $25 per diameter inch.

820 Maintenance ChecklistsExperience has invariably shown that complex machinery cannot be reliably repaired without using detailed checklists and without documenting the details disassembly and reassembly.

Maintenance checklists which are employed in the Manufacturing OrganizationCUSA are included in Appendix N. They may be helpful in other locations. Theare as follows:

Centrifugal Compressors• IMI Guidelines for Completing the Overhaul Checklist for Centrifugal

Compressors

• Centrifugal Compressor Overhaul Checklist

• IMI Guideline for Inspection and Repair of Centrifugal Compressor Rotors



Reciprocating Compressors• Compressor Lubricating Systems• Compressor Piston and Piston Rod• Compressor Packing Box and Packing• Compressor Cylinder and Crosshead• Compressor Valves and Unloaders• Compressor Valve Gaskets and Cages• Compressor Crankshaft and Bearings• Repair Sheet for Clark Engines• Compressor Cylinder Repair Report• Compressor Crankcase Repair Report• Engine Repair Sheet for Ingersoll-Rand XVG• Ingersoll-Rand HHE Packer Rebuilding Procedure• Ingersoll-Rand HHE Packer Rebuilding Check Sheet• Ingersoll-Rand Packing Box and Packing Worklist• Engine Driven Reciprocating Compressor Regrout• Four and Eight Month Maintenance Checklist Prior Shutdown Information• Ingersoll-Rand HHE Connecting Rod Rebuilding• Aluminum Bronze Pin Bushing HHE Cylinder Connecting Rod• Splitting HRA Engine CAM Lobes• Clark HRA—Engine Power Cylinder Reconditioning• Clark HRA—Power Cylinder Repair Flow Chart• Clark HRA Main Crosshead Rebuilding• Clark HRA Power Cylinder Head Rebuilding• Clark HRA Gas Injection Valve Rebuilding• Clark HRA Wesco Valve Lifters• Clark HRA Power Piston and Connecting Rod Rebuilding• Clark HRA Packer Rebuilding• HRA Packer Rebuilding Check Sheet• Clark Compressor Air Starting Check Valves• Crankshaft Inspection and Reconditioning• Crosshead Rebuilding• Connecting Rod Reconditioning• Connecting Rod Check Sheet• Piston Reconditioning• Piston/Rider Ring Clearance Tables



830 Reciprocating Compressor Piston-Rod Reconditioning

831 IntroductionThis section summarizes field experience and provides guidance on reconditioning reciprocating compressor piston rods. Sections 832 through 836 contain back-ground information; Section 837 contains recommendations. (It may save you time to refer directly to the Recommendations Section, 837.)

When equipment is not spared, any improvement in component service life can have a significant effect on plant availability. Properly selected and applied hard facings can improve reciprocating compressor reliability.

In many cases, worn or scored piston rods may be reconditioned at a fraction of the cost of new rods.

This section is also applicable to reconditioning positive displacement pump plungers. (In addition, certain processes used for rod and plunger reconditioning are also applicable to reconditioning centrifugal compressor and turbine journals and seal areas.)

832 Rod Leakage/Surface Finish

Factors Affecting Rod Packer LeakageAny packing will weep or bleed a certain amount of gas. Minor amounts of weeping will occur due to gas forced into rod pores or into the lubrication film. This gas is released when the rod comes out of the high pressure portion of its stroke. In some cases, dissolved gases reduce the effectiveness of the lubricant, possibly resulting in increased friction. More commonly, leakage occurs due to incorrect fit of packing rings to rod and disturbances along the sealing surfaces.

Excessive leakage, if permitted over long periods of time, will cause deterioration to the point that it will become difficult to correct. Even new packing cannot be expected to seal adequately if the surface condition of the piston rod is poor or rod runout is excessive. For any given service, factors such as rod undersize or over-size, surface finish, taper and runout significantly influence the degree of leakage.

Surface Hardness and FinishRod wear rates are greatly influenced by whether a packer is lubricated or not, and the operating pressure and corrosivity of the gas. API 618 provides design stan-dards for hardness and surface finish for various services. Without proper hardness, rod wear rates can be excessive. Surface hardness and finish become increasingly important as the amount of lubrication is reduced. In general, most rod and packing materials will perform well against each other if the surface finish and fitup are correct.

Manufacturers’ standard piston rods are normally made of case hardened, highly polished steels. Two common rod surface hardening techniques are induction and



flame hardening. Both processes involve heating the surface of rods above the upper critical temperature followed by rapid quenching using water or other suitable cool-ants. Typical case thicknesses range from 1/16 to 1/8 inch, with surface hardnesses in the range of Rockwell C50 to 60.

In certain cases, the hardness must be limited due to potential embrittlement prob-lems. Sour hydrocracking services are one such service. For these applications, rods are often fabricated from softer steels, then hardfaced for wear resistance in the packing and oil wiper ring areas.

Figure 800-13 provides general guidance on appropriate hardness and surface finishes for various applications. These hardnesses and finishes have normally resulted in acceptable packer sealing and life.

As metal is removed from the surface of case hardened rods, hardness decreases. Wear rates accelerate and susceptibility to galling and abrasion increases. The acceptable degree of packer leakage depends to a large extent on the nature and severity of the process application. In less severe applications such as lubricated, low-pressure service, it is possible to accept much greater wear before replacing or reconditioning a rod. In high-pressure hydrogen applications, however, leakage of hydrogen results in further heating of packing, lubricant and the rod (due to Joule-Thompson effect). An unacceptable operating condition quickly results.

Fig. 800-13 Hardness and Surface Finish Recommendations

ServiceOperating Pressure (psi)

Lube or Non-Lube Rod Material

Minimum Rod Hardness(1) (Rockwell C)

Surf. Finish(1) (Micro-inches RMS)

Noncorrosive Through 6000 L,NL Low-Alloy Steel, Through Hard-ened or Surface Hardened

50 10-20

Above 6000 L 55 10-20

Above 6000 NL Hardened or Coated

60 6-8

Corrosive Through 1000 L, NL 17-4 PH(2) 50(3) 10-20

Above 1000 L 55(3) 10-20

Above 1000 NL Plated or Coated

60(3) 6-8

(1) Hardness and surface finish recommendations apply to the packing area of the rod.(2) Commonly used material for corrosive applications. Review each material selection specifically for service intended.(3) These are general guidelines. Determine appropriate hardness and hardening procedures for each specific service.



833 Rod Deviations

Undersized RodsUsing standard size packing rings with an undersized rod can still result in an effec-tive seal as long as the rod is truly circular and is without taper. However, this generally results in an extended break-in period, with leakage greater during break-in. In lubricated applications, there is an additional possibility that lubricant may be blown away at gas pressures in the packing. Contact surfaces become dry and subsequently overheat. Some packing materials, such as Teflon, will degrade rapidly if they become dry after once having been lubricated. Under this condition, an abra-sive paste or small, hard beads are formed in the packing area. Beads and abrasive paste can quickly cause deterioration in rod and packing contact surfaces.

For normal applications, standard size packing rings can be used successfully on rods which are not undersized by more than approximately 0.002 inch per inch of rod diameter. For high-pressure applications (1000 psi), experience indicates that standard size packing should be used only if rods are no more than 0.003 inch undersize. When rod undersize exceeds the above guidelines, specially bored packing can be purchased. The major problem with the use of special bore packing is the chance that the wrong size may be installed. Additionally, the use of various bore packings creates stocking problems.

Oversized RodsWhen packing rings have a slightly smaller bore than the piston rod diameter, the segments contact only at one end. The center portion of each ring segment provides a direct gas passage along the rod surface. This condition is permissible if it is not too severe. During the break-in process, packing will gradually wear to the point of conformation with the general rod surface curvature.

The potential for overheating due to lack of proper lubrication exists for oversized rods for the same reasons stated for undersized rods.

Tapered RodsIn lubricated services, a certain degree of rod taper can be tolerated. Lubricating films tend to block small passages through which gas can escape. A tapered rod combines both the effects of oversized and undersized rods in that packing rings constantly try to adjust to the variations in surface profile. Excessive amounts of taper, however, will rapidly destroy the packers’ ability to seal.

Generally, the worst taper condition occurs at one end of the stroke. Reasonable leakage rates and packer life can be expected if the degree of taper does not exceed approximately 0.0005 inch per inch of stroke. For non-lubricated and high-pressure, low molecular weight gas services, acceptable taper will be less than this value.

MisalignmentMisalignment of piston rod and packer rings cause another leak path. Rod-to-ring surface contact area is reduced. In addition, edges of rings at the bore become worn.



This permits gas flow from one radial cut in the ring to another. In API 618, the maximum allowable rod runout at operating temperature is 0.00015 inch per inch of stroke. Alignment of cylinder, distance piece and crosshead guides should be adjusted in order to meet this guideline. Runout should always be checked following installation of piston rods, crossheads, wrist pins, etc. Noncontacting probes can be used very effectively to measure and monitor rod runout.

WearWear mechanisms include abrasion, adhesion, corrosion, fretting, erosion, surface fatigue, etc. Adhesive and abrasive wear are the principal kinds encountered in the sliding sites of a gas compressor or positive displacement pump packer.

Adhesive-type wear occurs when two parts make metal-to-metal contact and adhere. Fragments are detached from one surface and welded to the other surface. To mini-mize this type of wear, one surface must have films and coatings to minimize the initial adhesion.

Abrasive wear is a cutting-type action where hard fragments embedded in the softer component (packing) or trapped between relatively hard packing and rod material act as a cutting tool.

834 Rod Reconditioning

When Is Reconditioning AdvisableLeaking rod packing is not a problem unless it is excessive. Depending upon the particular service, excessive leakage can result in reduction of cylinder discharge pressure, release of toxic or noxious gases, and in some cases, contamination of crankcase lubricants. Excessive leakage eventually results in the need for a mainte-nance shutdown. In many cases, it also results in some loss in plant throughput since compressors may not be fully spared.

In many instances, rod condition is partially or totally responsible for this excessive leakage. A rod should be reconditioned before wear is so excessive that required coating thicknesses (to build it back to original dimension) exceed 20-30 mils. In many cases, coating processes are less successful when more than a 30-mil buildup is required. Peeling, spalling and fragmentation problems are commonly encountered.

Rods are most successfully reconditioned if required coating thickness can be held to less than 10 mils.

Other factors which affect the sealing ability of a packer include:

• Gas pressure,• Gas properties (molecular weight, corrosivity, wetness),• Supply of proper quantity and type of lubricant,• Break-in procedure (refer to Section 700), and• Type of packing material and packer design.



to

n con-

of

etal ona-sses ends rty econ-ly

ing:

Reconditioning ProcessesIn selecting a wear-resistant coating for rods, the following factors are important:

• Coating roughness and surface texture (smoothness, porosity),• Coating hardness,• Combination of sliding materials (rod coating and packer material),• Corrosion resistance,• Adhesion of coating to base metal (bond strength), and• Previous coating/heat-treating history.

Numerous reconditioning processes are available today for restoring worn rodstheir original size and surface conditions. These processes may also be used toprovide extended life of rods in new equipment, especially in difficult services. Igeneral, only rods in sound condition should be considered as candidates for reditioning. Base metal surface condition must be carefully inspected prior to useany type of coating (discussed later).

Major hardfacing processes include the general categories of flame spraying (mspray and plasma spray), electroplating (chrome plating) and flame plating (dettion gun). Figure 800-14 summarizes the relative characteristics of these proceand the resultant coatings they produce. The acceptability of each process depon the service conditions, i.e., lubricated or non-lubricated, sour, corrosive or digas, etc. Only certain coatings applied by each major process are suitable for rditioning rods to resist adhesive and abrasive sliding-type wear. For the relativelow-service temperatures of interest here (up to 400°F), changes in physical proper-ties and strength of various coatings are of minimal concern.

835 Rod Coating ProcessesIn selecting appropriate coating processes and compositions consider the follow

• Bonding

Bond strength between the coating and base metal is of paramount importance.

• Residual Stresses

Residual stresses are a primary concern for spray coatings. Residual stresses have a significant effect on coating bond strength. Generally, the outer portion of the spray coating is in tension. This reduces the stress required to cause frac-ture. Thick electroplated chrome coatings, on the other hand, may develop compressive residual stresses, increasing their resistance to cracking.

• Density

The density of spray coatings depends on individual particle size and density, degree of oxidation during deposition, and kinetic energy of the impinging particles. Density of electroplating processes depends primarily on plating bath temperature and current density.


Compressor M

anual800 M

aintenance and Troubleshooting

Chevron Corporation800-35

December 1998

F

s

Surface Finishing

Characteristics Comments

Fair

Good Not permitted on hard-enabled (SAE 4041, etc.) rods. Must consider effect of fusion process on base metal physical properties.

Good

Good

Post-plating heat treatment at approxi-mately 350-375°F required to liberate hydrogen.

Depends largely on base metal surface finish

Ditto

ig. 800-14 Comparative Characteristics of Major Coating Processes

Process Porosity HardnessCorrosion

Resistance Bond Strength

Maximum Coating

Thickness (Approx.)

Effect of Application

Procedure on Rod Base Metal

Lubrication Holding

Characteristic

1. Metal Spray High Low-Moderate Poor-Sealer Required

Poor-Fair 0.040 inch None Good

2. Metal Spray with fusion (Wall Colmonoy Spraywelding)

Low Mod-High Excellent Excellent 0.065 inch Significant Good

3. Plasma Spray Moderate Moderate Fair-Sealer Required

Fair 0.006 inch None-Slight Good

4. Flame Plate (Linde D-Gun)

Low Very High Fair-Good Sealers occa-sionally used

Good-Excellent 0.010 inch None Good

5. Electroplate (Hard Chro-mium)

a. Porous Mod-High High Good-Excellent Good-Excellent 0.015 inch Causes H2 occlusion

Good

b. Non-Porous Low High Excellent Good 0.015 inch Causes H2 occlusion

Poor-Fair


n . The orm. ate-d. rs

• Corrosion Resistance and Porosity

The corrosion resistance of all coatings is determined by chemical composi-tion. In addition, coating porosity and cracking may allow corrosion of the base metal. For lower temperature applications, various epoxy, silicone wax, and vinyl materials may be used to seal coatings. For high-temperature applica-tions, sintering (a heat-treating process) may be needed to seal spray coatings.

• Thermal Properties

Thermal conductivity and coefficient of thermal expansion must be considered when selecting coatings for a particular application. High-pressure, high-temperature applications require coatings which effectively remove heat from the contacting surfaces and are resistant to thermal shock.

• Lubricant Retention

Surface porosity and cracks provide storage voids for lubricant.

• Friction

Friction depends on the materials, surface roughness, and the lubricant.

Flame Spray—The Metal Spray ProcessMetal spray is the process of applying molten metal to the surface of the rod to form a hard, wear-resistant coating. The coating material is melted in a flame and its minute particles are sprayed at relative low velocities onto a prepared surface by a stream of air. The molten particles impinging on the rod are flattened and inter-locked to provide a mechanical bond. Alloying with the base metal does not occur.

A subsequent diffusion or sintering heat treatment may be required to obtain accept-able bonding conditions. The metal spray process requires roughing of the base metal (sandblasting, rough turning, etc.) prior to coating. Both pure metal and alloy materials in powder and wire form can be applied. The term “metallizing” is ofteused to describe the type of metal spray process which uses metal in wire formterm “thermospray” is used to describe the process of using metals in powder fOxyacetylene torches or electrodes are common methods of melting coating mrials. To seal the resulting porous coating, several types of sealers are employePhenolic sealers and silicone-alloyed resins are two common examples. Powdeand application equipment are available from suppliers such as Metco, Wall Colmonoy, Stellite Division (Cabot), and others.

Advantages include:

• Low base material temperatures are maintained during application.• Minimal distortion or warping (if diffusion heat treatment is not required).• Applicable to a wide variety of rod base materials.• Good lubricant retention characteristics.• Relatively low cost.• Can be applied to thicknesses up to approximately 40 mils.



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a aled in r-f

e. the art thin

Disadvantages include:

• Bond strength is low. Coatings are mechanically bonded to the base metal.

• Fracture/peeling will occur unless the coating is continuously bonded to itse

• Coatings are very porous. Must be impregnated with suitable sealers to minmize porosity (and avoid base metal corrosion).

• Coatings have relatively low hardness (Rc 30-40).

• Surface preparation prior to coating is critical to adequacy of bond.

• Coating quality is likely to vary widely from shop to shop.

• Relatively slow powder/wire heating results in greater oxidation and some change in coating chemical composition.

• Fair surface finishing characteristics.

• Finish machining is required.

An extension of the basic metal spray process is the post-application fusing of ings. Coatings are applied in the manner described above. Then one additionais taken. The deposited metal spray coating is fused with the base metal by useoxyacetylene torch or controlled furnace atmosphere. The resulting bond is moular in nature and is claimed to be much stronger. Coatings up to 0.065 inch caapplied. Hardness ranges from approximately Rc 55 to 63. Corrosion resistancexcellent.

In order to utilize the metal spray and fusion process, the base metal must havemelting point higher than 1950°F. High temperatures required to achieve fusing ofthe coating may result in rod distortion. In addition, when the carbon content ofsteel rods exceeds 0.25%, special precautions must be taken to avoid an annemetal. Any previous heat treatment applied to the rod to achieve improvement physical properties is lost. Annealed rods must be derated to maintain safe opeating stress levels. Fusing followed by air cooling could result in the formation obrittle martensite, depending on the hardenability of the base metal alloy.

Flame Spray—The Plasma Spray ProcessPlasma spray coatings are produced by passing powdered material through a specially designed gun which ionizes an inert gas to form a plasma. Flame tempera-tures of 10,000 to 30,000°F are reached. Powder is then injected into the plasma flame. This rapidly heated powder is propelled at speeds of 400 to 1000 feet per second onto the part being reconditioned. The resultant coating microstructure consists of thin lenticular particles, or “splats.”

The principal value of the high temperatures of the plasma process is that the melting point of the material being sprayed is reached very quickly. Unlike the oxyacetylene flame (6000°F), powder remains in the hot zone a much shorter timThere is little oxidation and little change in powder chemical composition. Also,powder can be propelled through the plasma at higher speeds and reach the pbeing coated with greater impact. In addition, spraying may be done entirely wi



eve

s are

s

n.

datory

Upon secure

a protective atmosphere chamber in order to further protect the sprayed material. Minimizing oxides produces a more cohesive coating capable of being finished to a better surface condition. Numerous powder formulations are available to suit the particular application. Powders are available from suppliers such as Metco, Wall Colmonoy, Stellite Division (Cabot) and others.

Advantages include:

• Low base material temperatures of 400 to 500°F (205 to 261°C) are main-tained during application. No head affected zone is created.

• Minimal distortion or warping.

• No subsequent stress relief or heat treatment required.

• As applied, coatings are relatively smooth and require little grinding to achifinished dimensions.

• Applicable to a wide variety of base materials.

• Good lubricant retention characteristics.

• Reasonably dense coating structure.

• Low oxide content.

• Low-moderate cost.


• Fair bond strength. Coatings are susceptible to spalling.

• Coatings are porous. Base metal corrosion protection is poor unless sealerused.

• Thickness of coating is very limited (.006 inch). Excessive coating thicknesincreases susceptibility to chipping and spalling.

• Coatings may reduce base material fatigue life.

• High dependence on proper base material cleaning and surface preparatio

• Powder quality and application process parameters must be carefully adhered to.

• Coating quality can vary from shop to shop.

• Finish machining is required.

Piston rods usually require a grit blasting, grooving, or knurling operation to achieve an adequate bond between base metal and plasma coatings. It is manthat all parts in the process be clean and dry. Frequent in-process and product quality control checks are also necessary.

Because a plasma spray coating is relatively porous, it allows gas to penetrate.release of the gas pressure, the coating may separate from the base metal if a



lur- by

rol.

bond has not been achieved. Peeling can result in considerable damage to packing and perhaps cylinder components.

To obtain a reasonable degree of corrosion protection, plasma coatings must be impregnated with suitable sealers to minimize porosity.

Flame Plating—Linde Detonation Gun Process (D-Gun)Flame plating procedures such as Linde’s Detonation Gun provide a bond which is both mechanical and metallurgical in nature. The Detonation Gun procedure is a process patented by Union Carbide (Linde Division). Coatings are produced by passing measured quantities of powder, oxygen and acetylene into a firing chamber. A timed spark then detonates the mixture, creating a hot (6000°F) high-speed gas stream which in turn instantly heats the powder particles. Powders are composed principally of tungsten carbine particles. Nearly molten particles leave the firing chamber at approximately 2500 fps, impinging on the surface of the piston rod and produce a microscopic welding-type bond. Because of the intense noise generated, the operation is carried out in a soundproof room, remotely controlled by an oper-ator. Rapid-fire detonations, as the firing chamber moves along the rod, build up the coating to the specified thickness. Linde provides several D-Gun powder composi-tions to suit a variety of process conditions.

Advantages include:

• Low base material temperature [less than 300°F (149°C)] are maintained during application. No metallurgical changes to the base material occur.

• No distortions or warping.

• No subsequent stress relief or heat treatment required.

• Bond strength is very good (10-25 ksi). Bond is both mechanical and metalgical in nature. (For some coatings, bond strength can be further improvedpost-application heat treatment.)

• Can be applied to a wide variety of base materials.

• Low porosity (sealers can be used to further reduce porosity).

• Good oil retention characteristics.

• Good corrosion protection.

• Very hard coating (Rc 67-76).

• Proprietary process closely controlled by Union Carbide. Good quality cont


• Relatively high cost.

• Limited coating thickness (generally <0.010 inch).

• Finish grinding required.



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treat-

Electroplating—Porous and Non-porous Hard Chrome PlatingElectroplating procedures, such as chromium plating, have been widely used for many years. The combination of high hardness, corrosion resistance, and low coeffi-cient of friction have made chrome plating a commonly used reconditioning proce-dure. Basically, the chrome plating process involves depositing chromium on the rod surface by setting up the part (rod) as the cathode in an electrolytic bath. The bath consists of a solution of chromic acid, water, and one more acid radicals (usually sulfate and fluoride). The gap between anode and cathode is controlled to ensure that chrome is deposited evenly along and around the circumference of the rod. Time, current density, bath temperature, and proprietary chemical additives are critical parameters which must be carefully regulated. To achieve more rapid plating rates, bath temperature is normally increased.

Cleanliness and integrity of the base material is critical in assuring good bonding. Extremely good adhesion to the base metal is required for hard chrome deposits to perform acceptably in service.

In general, two types of chrome plating are available, non-porous and porous. Non-porous platings are used not only in restoring piston rods but also to restore such components as crankshaft journals, crosshead pins, bearing journals, etc. In lubri-cated service, non-porous chrome platings provide minimal lubricant retention capa-bility. This in turn causes additional friction and the need for increased lubrication. For non-lubricated services, non-porous chrome is a poor choice, because packing material does not adequately deposit on the rod surface. Again, this causes increased friction, heating, and packing wear.

The difficulty of assuring adequate wettability led to the development of porous chrome having a high degree of porosity. Porous chrome platings are etched after the plating has attained a predetermined thickness. For a short time, chromium is removed selectively from the plated rod surface through an electroetching process. Small pores or channels are thus produced. These act as lubricant reservoirs. Pores do not extend entirely through the chrome plating. This process is a patented devel-opment of the Van der Horst Corporation under the trade name of “VanderkromAlthough the patent has since expired, few chroming shops have demonstratedcapability to duplicate the electroetching process.

A detrimental effect of chrome plating is hydrogen occlusion. During plating, hydrogen penetrates the base metal, causing a reduction in mechanical propermost importantly, poor resistance to crack propagation. Many chrome plating control procedures incorporate a final baking to remove this hydrogen. Commobaking temperatures employed are in the range of 350 to 370°F (177 to 191°C). Approximately 50 to 60% of the total hydrogen present is removed at these tematures with minimal effect on plating hardness. Higher temperatures result in removal of a greater amount of hydrogen at the expense of decreasing plating ness and corrosion resistance.

Advantages include:

• Low base metal temperatures are maintained during plating. Original heat ment of the rod is unaffected.



).

).

base

al

ff.

lied lied to he

most es.

• Good lubricant retention and wettability (porous chrome plating only).

• Good bonding strength. Molecular type bond.

• Minimal distortion or warping.

• Corrosion resistant (reduces pitting susceptibility of rods in standby service

• High thermal conductivity. Aids in maintaining low surface temperatures.

• Moderately thick coatings can be applied (up to 0.015 inch).

• Moderately hard coating.

• Can be applied to a wide variety of base materials (ferrous and nonferrous

• Moderate cost.

• Ease of application and control.

• Low coefficient of friction.


• Quality of workmanship varies widely from shop to shop.

• Bond is highly dependent on proper cleaning and surface preparation.

• Surface finish of chrome plating is highly dependent on smoothness of the metal before plating (should be 20 micro-inches RMS or better).

• Fair to poor lubricant retention and wettability (non-porous platings).

• Hydrogen penetrates base metal during coating process causing base methydrogen embrittlement and reduction of fatigue strength. Final baking is required.

• In services badly corrosive to base metal, chromium plating tends to flake o

UndercoatingIn some instances, a metallic undercoat such as nickel or nickel alumide is appbetween the base metal and the hardface coating. Metallic undercoats are appincrease the coating system's resistance to thermal shock and to improve bondstrength. Bonding of the metallic undercoat to the base metal is stronger than tbond between coating and base metal. In addition, the as-sprayed undercoat provides a good surface for the coating to mechanically bond. Undercoating is frequently used with the weaker bond strength metal and plasma spray process

Coating Composition and Compatible PackingFigure 800-15 summarizes composition of the various types of commonly usedcoatings plus compatible packing materials.



Fig. 800-15 Common Coating Compositions and Compatible Packing Materials

Process VendorCoating Designation

Coating Composition

Vendor Recommended Packing Materials

1. Flame Plating (Detonation-Gun)

UCAR - Linde Divi-sion

LW-1(AMS 2435A)

91% W9% Co

Reinforced Teflon, Carbon, Bronze, Cast Iron

LW-15 86% W10% Co4% Cr

Reinforced Teflon, Leaded Bronze

LW-1N30 87% W13% Co


LW-1N40(PWA-46)

85 % W15% Co


2. Electroplating (Hard Chrome)

Van der Horst Vanderkrome 100% Cr Cast Iron, Rein-forced Teflon (limited applica-tions only), Bronze

3. Plasma Spray Metco #2 High Cr. Stainless Steel

Bronze, Reinforced Teflon

#439 50% W50% Co

Bronze, Reinforced Teflon

#451 Hi Ni w/Ni-Al Bronze, Reinforced Teflon

4. Metal Spray Wall Colmonoy Wallex 55 45% Co19% Cr18% Ni10% W Balance Fe, B, C, Si

Reinforced Teflon

Walcoloy #2 420 Stainless Steel Bronze

Colmonoy #6 74% Ni14% Cr5% Fe Balance Si, B, C

Reinforced Teflon, Cast Iron

Notes: 1. Recommended packing materials depend on the nature of the gas handled (corrosiveness, wetness, type of gas, pressure, etc.). For specific applications, consult compressor vendor, packing suppliers and Company experience.



836 Experience

Company ExperienceFigures 800-16 and 800-17 summarize the results of a May, 1978 Company-wide survey of experience with various hardface reconditioning processes. These summa-ries reflect both refinery and producing field experience. Refinery experience covers gas compressor applications in plants such as Catalytic Reformers, Isomax, Isomer-ization, Ammonia, FCC, Naphtha Hydrotreater and Crude Units. Producing experi-ence generally covers the handling of sweet (wet and dry) natural gas in low- and high-pressure separation and gas lift services.

Fig. 800-16 Rod Reconditioning Survey Summary (Sweet, Non-Corrosive Gas Services) (1 of 2)

Maximum Operating Pressure

Lubricated or Non-lubricated Process Unit Experience

Below 500 psig Lubricated Ammonia 4+ yrs service life w/chromed rods. Tinized C.I. packing. Low-pressure (165 psi), medium piston speed (700 ft/min) compressor. Total of 12 D-Gun coated rods in service w/carbon-filled Teflon packing. 1-2 yr service without signs of wear.

Below 500 psig Lubricated Producing 10 yrs average life w/metal spray (Metco SS # 2) 4140 rods. Bronze packing. Low-pressure (vacuum to 150 psi) services. Wide range (low to high) piston speed compressors.

Below 500 psig Non-lubricated Air 2-3 yrs service life w/chromed rods. Carbon-filled Teflon w/bronze backup packing. Low-pressure, high-temperature (320°F) air compressor.

500-1000 psig Lubricated HGO 2-1/2 yrs life w/plasma-coated (Metco # 450/451) on X20CR13 rods. Carbon-filled Teflon packing higher wear rate and cracking of coating noted. Bare X20CR13 rods lasted 4-1/2 yrs.

500-1000 psig Lubricated Cat Ref New 4140 rods coated w/D-Gun (LW-1) installed 10/77. Teflon w/C.I. backup packing. Good service experi-ence. No problems reported to date.

500-1000 psig Lubricated Cat Ref 1-2 yrs life w/D-Gun coatings. One month life w/chrome plating.

500-1000 psig Lubricated Cat Ref Varied experience w/chromed (non-porous) rods. Teflon and tinized C.I. packing. Chromed rod lasted 4-7 months.

500-1000 psig Lubricated Naphtha

HDTR

Good (5-6 yrs) service on chromed 4140 rods. Glass-filled Teflon packing. Low pressure ratio per stage, 760 ft/min piston speed.

500-1000 psig Lubricated Producing Good service experience metal spray (420SS) on 4140 rods. Bronze packing. 3-5 years life for gas lift service (500-1000 psig).



Results show that for lubricated, low-pressure (less than approximately 1000 psi) services, good service lift has been afforded by chroming, plasma spray, metal spray and D-Gun coating processes. Average service life of reconditioned rods when used with various grades of Teflon packing has been approximately four years in sweet, noncorrosive gas services and approximately two years in sour, corrosive gas environments.

For difficult, high-pressure (above 1000 psi) services, Linde D-Gun coatings have proven superior. D-Gun coatings have performed consistently well (two to three years and longer) in high-pressure (up to 5000 psi) lubricated, low- and high-molec-ular weight gas services. Producing reports acceptable service from metal sprayed and fused coatings at elevated pressures.

No Company experience was reported for coated rods in high-pressure, non-lubricated service.

Other petrochemical company users report mixed success with metal spray and plasma spray restoration of compressor rods. One user stated that Linde D-Gun flame-plated rods were found to perform much better than new (bare) rods.

500-1000 psig Non-lubricated Isomerization Chrome plating wears and peels within 6 months. 1+ year service w/spray-welded (Wall-Colmonoy Wallex 55) 4140 rods. Carbon packing. Low (490 ft/min) piston speed.

1000-1500 psig Lubricated FCC Feed Hydrofiner

3-4 yrs service life w/chromed 4140 rods. Carbon-filled Teflon w/C.I. backup ring packing. 1200 psi maximum discharge pressure, 700 ft/min piston speed.

1000-1500 psig Lubricated Isomax 3+ yrs service life w/plasma spray (Metco #439) on 4140 rods. Teflon packing. 760 ft/min piston speed.

Above 1500 psig Lubricated Isomax 2 yrs life w/D-Gun (LW-1 w/nickel undercoat) over 4140 rods. Teflon with C.I. backup ring packing. High (2870 psi) discharge pressure, moderately high (810 ft/min) piston speed.

Above 1500 psig Lubricated Ammonia 1+ year life w/D-Gun (LW-15) 4140 rods. Bronze packing. 4780 psi discharge pressure. High (850 fit/min) piston speed. No wear after 1 yr.

Above 1500 psig Lubricated Producing Acceptable service life reported w/sprayed and fused (Tuftin 500 Twin Arc Process) coating on 4140 rods. Bronze packing. Bond reportedly good up to 6000 psig. Metal or plasma sprayed steel rods failed after 1 month at Swanson River.

Fig. 800-16 Rod Reconditioning Survey Summary (Sweet, Non-Corrosive Gas Services) (2 of 2)


Lubricated or Non-lubricated Process Unit Experience



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of

Compressor Vendor ExperienceGeneral experience and recommendations from reciprocating compressor vendors on various reconditioning processes are summarized in Figure 800-18. Flame Plating (Linde D-Gun) and porous hard chroming (Vanderkrome) processes are reported to be the most reliable reconditioning techniques. Specific comments offered by compressor equipment vendors are summarized below.

Electroplating (Chroming)Two major compressor vendors indicate generally poor experience restoring piston rods with various chroming processes. Vendor “A” recommends against recondtioning by any electroplating procedure because of the high number of oilers reported. In addition, there is also a concern that the electroplating process intrduces the risk of fatigue failure from hydrogen penetration into the rod. Vendor recommends against chrome plating due to the wide variation in the quality of tplating operation from shop to shop.

If rods are reconditioned by the electroplating process, Vendor “B” strongly recomends that: (1) plating be of the “porous” type; (2) plating thickness not exceed0.005 to 0.006 inch; (3) rod surface finish prior to plating be 20 micro-inches RMor better; (4) rods be ground undersize along their full length, plate only on top

Fig. 800-17 Rod Reconditioning Survey Summary (Sour, Corrosive Gas Services)


Lubricated or non-lubricated

Process Unit Experience

Below 500 psig Lubricated HDS Less than 1 yr service w/plasma spray (Comp. Products #3) on steel rods. Steel/babbitt packing. 800 ft/min piston speed.

Below 500 psig Lubricated Isomax Good (6 yrs) service life w/chromed rods. Teflon w/tinized C.I. backup ring packing. Low-pressure (195 psi) service. Moderate (750 ft/min) piston speed. Total of 18 D-Gun coated rods in service, carbon-filled Teflon packing life exceeds 2–3 yrs.

Below 500 psig Lubricated Crude 2–3 yrs service w/plasma spray (Metco #2) on 18-8 SS rods. Teflon packing. 150 psi max. discharge pressure, low (520 ft/min) piston speed.

Below 500 psig Lubricated Flare Gas Recovery

2+ yrs. service with D-Gun (LW-1N30) rods. Teflon packing.

Below 500 psig Lubricated FCC 1–1/2 yr service w/chromed steel rods. Micarta packing. Low (165 psi) discharge pressure, 660 ft/min piston speed.

500-1000 psig Lubricated HDS 10–18 months service w/plasma spray (Comp. Products #3) on steel rods. Steel/babbitt packing. 800 ft/min piston speed.

500-1000 psig Lubricated Rhen. 1–2 yrs. service for plasma spray (Metco #2) on 4140 rods. Carbon-filled Teflon packing. 750 ft/min piston speed.

Above 1000 psig Lubricated HDN 3+ yrs. service w/D-Gun (LW-1N30) 4140 rods. Carbon-filled Teflon packing. High (1650 psi) discharge pressure, high (890 ft/min) piston speed.



hard-

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e

the undersize area, allowing the plate to fade to the undersize diameter outside the packing travel area; and (5) inspect the rod surface carefully prior to and after plating.

Vendor “C” recommends only porous type chrome platings. These platings are normally provided as original manufacture on such service as high-pressure hydrogen and sour gas (up to 2% H2S). These environments require moderateness base materials with high hardness wear-resistant coatings.

Flame Plating (Linde D-Gun)Vendor “A” highly recommends the Linde D-Gun process due to its “wide adaptability to a variety of operating conditions.” Field reports indicate long wear life services where cylinder discharge pressures are both above and below 1000 pVendor “A” recommends that: (1) final coating thickness be in the range of 0.000.003 inch, and (2) rods be in their final heat-treated condition before coating. Vendor “D” recommends reconditioning of 4140 rods in noncorrosive gas servicby use of Linde D-Gun type LW-1 coatings. Good field experience is cited.

Fig. 800-18 Reciprocating Compressor Vendor Experience Summary (Reconditioning Process)

Vendor Chroming Flame Plating Plasma Spray Metal Spray

A Not recommended. Not considered a reliable procedure.

Linde D-Gun highly recommended. Excel-lent field experience.

No comment. Not considered good technique. Possible rod distortion prob-lems with metal spray and fusing process

B Not generally recom-mended due to enor-mous quality variations between platers. Only porous-type chroming considered acceptable

No experience Not considered acceptable

Not considered acceptable

C Recommends only porous chrome coating. Good experi-ence in H2 and H2S (up to 2%) services

No experience No comment Mixed experience. Problem with changing base metal strength/hardness

D Not recommended. Peeling problems. Teflon packing (lube and non-lube) not recommended

Linde D-Gun Coating LW-1 highly recom-mended on 4140 rods, noncorrosive gas service. Outlasts noncoated rods by at least a factor of 2

Not recommended. Peeling problems

Not recommended. Metal spray plus fusing is recommended in corrosive gas services. Consider effect of fusing on base metal

E Fairly good experi-ence. Chroming quality varies widely from shop to shop

No experience Experience varies: some good, some bad

Many peeling failures reported.



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Metal SprayIn general, metal spray coatings were not recommended by compressor vendors. Vendor “A” does not consider the metal spray and fusing process to be a good reconditioning procedure. Main problems reported are (1) distortion of rod's finished surface, and (2) overlay of steel rod whose carbon content exceeds 0.2without special proper precaution. Vendor “B” similarly recommends against thirestoration method.

Vendor “C” cites mixed experience with this technique. In one case a 5-inch diaeter rod in hydrogen service was hardfaced to a 50-mil thickness by SprayweldShortly after startup, the rod cracked in half, causing significant damage to the compressor. Later investigation showed base metal hardness in the range of 500 BHN (originally 240 BHN). Hydrogen embrittlement was thought to be the cause of this failure.

Plasma SprayVendor “B” indicated that their experience shows “no acceptable or successful process exists to restore rods reliably by plasma spray.” Vendor “D” cited peelinproblems with this reconditioning technique.

Experience SummaryOverall, consistently best service experience in low-pressure and even high-pressure, difficult services has been afforded by the use of the Linde D-Gun coings. In addition to favorable Company and compressor vendor experience, UnCarbide cites numerous applications throughout the domestic petrochemical industry where D-Gun coatings have performed well. These coatings have beeused in both lubricated and non-lubricated services up to 6000 psi.

Experience with chrome plating and flame spray (metal and plasma) coatings vthroughout the industry. Most diversity is noted in the chroming process. Qualitycontrol varies enormously from shop to shop. Many chroming problems are likethe result of changes in chrome shop personnel and the use of new shops seemoffering comparable quality at lower cost. Because commonly used non-porouschrome has poor lubricant retention quality, special precaution must be taken toinsure adequate lubrication. Many times, these steps are not taken, resulting inpacker and rod life.

Metal and plasma spray coating processes are generally less successful (espeat higher pressures) due to low bonding strength and the need for strict quality control during the preparation and coating processes. Where reliable shops habeen established, metal spray has proven an economical, reliable reconditionintechnique in lubricated low-pressure services. Metal spray and fused coatings agood choices in very corrosive services as long as proper attention is given to tmetallurgical effects of the fusing operation. Little experience is available supporting the general use of plasma spray.



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837 RecommendationsBased on service experience available to date, the following procedure is recom-mended when considering reconditioning used rods or coating new ones.

1. Confirm the technical adequacy and quality control procedures for every coating shop to be used. Do this periodically for shops used repeatedly for years.

2. Avoid reconditioning rods which are scored, galled or worn to a depth of more than 20 to 30 mils; 5 to 10 mils is preferred.

3. Consider hardfacing new rods before putting in service.

4. Complete Figure 800-19 for each individual rod sent to a coating shop. Require the vendor to complete and return Part II of this figure after all coating and machining operations are complete. Retain this as a permanent record in the file for that compressor.

5. For difficult and critical services, consider in-shop inspection prior to, during, and following coating application.

6. Unless otherwise dictated by local service experience, the following restoration processes are recommended in order of preference:

a. Union Carbide Linde D-Gun flame plating (most lubricated and non-lubricated, high- and low-pressure services), and

b. Metal spray and fuse (extremely corrosive services only).

c. Porous chrome, Van der Horst Corp. “Vanderkrome” (lubricated serviceup to moderate pressures)

d. Plasma spray (limited to low-moderate pressure, lubricated services)

e. Metal spray without fusing (limited to low-pressure, lubricated services

f. Non-porous chrome (limited to low-pressure noncritical, lubricated services)

7. Maintain a record of the service life of the coated rod (Part III of Figure 800-18).

838 Inspection and Specifications

Inspection and Quality ControlReconditioned rods must be closely inspected for proper bonding, surface finistaper at ends of coating, hardness, thickness and finish dimensions. Of these itverification of proper bonding between coating and base material is of primary importance. Careful inspection is mandatory when machining or working the finished coating. Any spalling during machining indicates an inadequate coatingjob. Coatings should be completely removed and reapplied. Lack of adequate b



Fig. 800-19 Specification Worksheet for Reconditioned Reciprocating Compressor Rods (1 of 2)

Compressor No. K-_______________________

Stage No.______________________________

Cylinder No.____________________________

Rod Designation No. (if any) ______________

Part I. Information to be completed by Purchaser

A. Service Conditions1. Gas Composition Yes No Composition(Mol. Pct.)

H2

HC

CO2

O2

N2

H2S

NH3

Air

Chlorine

Other Describe _________

2. Nature of Gas

Wet Dry

Clean Dirty

If wet, liquid is

If dirty, foreign matter is

3. Operating Conditions

Cylinder Discharge Pressure: ______ (psia) ( )

Cylinder Discharge Temperature: ______ (F) (C)

Piston Speed: _______ (ft/min) ( )

B. Packing and Lubrication1. Packing Material Used:____________________________________________

2. Lubrication: Non-Lube _____ Mini-Lube _____ Lubricated _______________

3. Type Lube-Oil Used:_______________________________

4. Is Packer Cooling Provided: Yes _____ No _____

C. Piston Rod Metallurgy1. Base Material Specification:

2. Rod Prev. Plated/Coated? Yes _____ No _____ Not Known ___________________________

If yes, describe type coating and approximate thickness:_________________________________________________________________________________________________________

D. Piston Rod Dimensions/Finish1. Surface Finish in Packing Area ____ (Micro-inches RMS) ( )



can result in peeling and spalling with consequential rapid deterioration of packing. Disbonding can also result in cylinder bore and piston ring damage.

Following initial grinding of a used rod, but prior to plating or coating, the rod must be carefully inspected for cracks and grinding heat checks by magnaflux or equal inspection techniques. In addition, base metal surfaces must be properly cleaned.

Certain coating processes demand much closer attention to surface cleanliness than others. The importance of clean base metal is underscored by a recent two-year survey by a major chrome plating company. Results showed 80% of the premature plating failures were attributable to lack of cleanliness. Contamination can arise

2. Description of Area of Rod to be Plated/Coated:

(Attach Sketch) _____________________________________________________________

3. Finish Tolerances (Attach Sketch):

Diameter: _____ (in)(mm) Length: _____ (in)(mm)

Part II. Information to be completed by Vendor after finishingA. Date:________________________________________________________________

B. Location of Coating Shop:________________________________________________

C. Vendor Coating Designation:______________________________________________

D. How Applied:__________________________________________________________

E. Finish Thickness (in)(mm): Min____, Max____

F. Undercoat used? Yes _____ No _____

G. Surface Hardness: _____ (Rc)( )

H. Sealer Used? Yes ____ No ____

If yes, describe_________________________________________________________

I. Max. Base Metal Temp. During Coating: ____ (F)(C)

J. Heat Treatment After Coating? Yes _____ No _____

If yes, describe:______________________________________________________________

K. Was Previous Coating, if Any, Removed Prior to Recoating?

Yes _____ No _____

L. Rod Diameter After Grinding/Blasting, but Prior to Coating (in)(mm):

Min_____, Max____

M. Description of Pre- and Post-Coating Inspection Techniques Used:

Part III. Maintenance Service RecordA. Service Life of Original Bare Rod:_____ (yrs)(mos)(wks)

B. New Coated Rod Placed in Service, Date: __________________________________________

C. Measured Rod Runout (in)(mm): Horiz____, Vert_____

D. Rod Removed from Service for Regrinding, Date:____________________________________

Remaining Coating Thickness (in)(mm):______________________________________________

Fig. 800-19 Specification Worksheet for Reconditioned Reciprocating Compressor Rods (2 of 2)



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from (1) nonmetallic, abrasive particles embedded in the surface or adhering elec-trostatically from grinding, sandblasting, polishing, and honing operations, (2) residual traces of metal working fluids, coolants, lubricants used during machining operations, (3) dusty, moisture-laden coating environment, (4) insuffi-cient interim protection during various stages of coating, and (5) lack of caution by people handling parts (dirty or perspiring bare hands).

Close review of a coating shop’s quality control standards is essential. Microscopic examination of rods before and after coating, intermittent inspection between coating phases and strict adherence to proper handling procedures are mandatory requirements for every coating process.

When a particular coating has not been previously applied by a coating shop, it is recommended that the vendor be required to demonstrate the adequacy of his proposal. One method is to require coating of a short rod of identical material and similar heat treatment to the proposed rod. After coating, this specimen should be bent repeatedly on a diameter equal to the diameter equal to the diameter of the rod, until it fractures.

Acceptable coating adhesion will show no separation from the base metal.

In general, it should be noted that the quality of work by coating shops varies widely, except for such proprietary processes as Linde D-Gun, which is closely controlled by Union Carbide.

Specification for Reconditioning RodsObtaining proper coatings to achieve acceptable rod life depends largely on (1) good communications between user and coating vendor, (2) selection of quali-fied coating facilities, and (3) adherence to appropriate quality control standards. Potential areas which may lead to unacceptable rod repair include:

• Rod base metal metallurgy not known. Previous coating history unknown.• Improperly selected coating for actual operating conditions.• Inadequate quality control prior to and/or during coating application.• Poor compatibility of coating with packing material.• Incorrect or incomplete specification of rod area to be coated.• Finished rod dimensions and tolerances not specified.• Improper taper at ends of coating.• Desired surface finish not stated.• Excessive coating thickness required to build up badly worn or gouged rod• Poor bond strength between undercoat, if any, and base metal.

Figure 800-18 (Part I) includes basic operating, design, dimensional, and metalgical information essential to the coating vendor. This section should be carefulcompleted by the Purchaser and included with each piston rod sent to a recondtioning shop. Purchase orders for coating work should require that Part II of Figure 800-18 be completed by the coating vendor after coating work is compleThe completed figure, specifying the as-finished coating condition, should thenreturned with the reconditioned rod and become part of the compressor



p e

ling,

ll -re

sid-

maintenance records. Any refinishing performed after the rod has been in service should be noted in Part III of Figure 800-18. This information will assist in evalu-ating the extension of service life afforded by the coating process.

840 Troubleshooting

841 IntroductionMachinery problems can be exceptionally complex; however, practical solutions can, in many cases, be simple.

No machine operates perfectly, nor in a perfect environment. Numerous deviations exist in every machine, yet do not normally surface as operational or maintenance problems. For example, every machine operates with some imbalance, some misalignment, some imperfections in installation, etc.

Therefore, when called upon to solve a problem that has surfaced, expect to find several “deviations” during the investigation. The job is not to find a deviation (or even several), but to find the deviation, or combination of deviations which are causing the problem that needs to be corrected.

As in any problem-solving effort, one of the most important steps is to define the problem. A problem given as “lube-oil pump will not put out—repair as neces-sary” can result in considerable time and expense spent on overhauling the pumwhen replacing a faulty pressure gage or adjusting a turbine governor may havbeen all that was required. Look for the simple cause/solution first!

Many problems with compressors fall into one of the following categories:

1. Improper component assembly.

2. Component wear or failure.

3. Deposit-buildup imbalance or flow restriction.

4. Controls/instrumentation out of calibration or faulty.

5. Auxiliary system/driver malfunction.

6. Support system (seals, lubrication, alignment, piping strain, foundation settbaseplate warped or poorly grouted).

7. Off-design operating conditions.

By considering the above categories when attempting to define a problem, it wioften be discovered that there is no real problem with the compressor at all. Recalibrating instrumentation, adjusting piping supports, etc., are all solutions which afar less expensive than compressor overhaul. Be sure simple solutions are conered and eliminated before going to more costly solutions.



842 Troubleshooting Guidelines

Step 1Define the desired performance. Define the deviation from that performance. This is the real problem.

Step 2Analyze the cause of the deviation, based on a combination of practical and tech-nical knowledge.

Use all available resources. Do not attempt to solve the problem single-handedly. Input from both technical and non-technical personnel operators, maintenance mechanics, process engineers, etc., can be invaluable. Obtain the manufacturer’s input as appropriate.

Accurate and current performance and maintenance records should be maintained on all equipment. Use these records as a valuable source of data to identify changes since the unit was last operating properly.

Keep an open mind. Avoid jumping to conclusions. Make every attempt to obtain and analyze all relevant facts. Do not resist changing conclusions if warranted by discovery of new information.

Step 3Take corrective action to eliminate the cause.

Step 4Monitor performance following corrective action.

Step 5Document the important points and communicate to those who will benefit from the knowledge gained.

843 Problem Solving GuidesAlthough the troubleshooting checklists that follow are generally aimed at helping in Step 2, it is important to remember Steps 1 through 5. Repetitive problems are usually caused by failing to complete one of the steps listed previously. The check-lists which follow are:

• Reciprocating Compressor Troubleshooting Checklist• Centrifugal Compressor and Lube System Troubleshooting Checklist

Both checklists reproduced from Reciprocating Compressors, by Bloch and Hoefner. Copyright 1986 by Gulf Publishing Company. Used with permission. All rights reserved.



Reciprocating Compressor Troubleshooting ChecklistSymptoms Possible CausesNoise Vibration

Knocking 7-8-9-10-11-12-14-15-17-18-25Vibration 3-11-14-18-19-25-32

PressureDischarge Pressure High 3-25Discharge Pressure Low 1-3-5-23-24-32Inter-Cooler Pressure High 2-4-6-27Inter-Cooler Pressure Low 1-3-5-21-22Discharge Temperature High 1-3-13-14-17-25-27-30

TemperatureOutlet Cooling Water Temperature High 1-3-13-25-27-30Overheating Valves 1-3-25-31Overheating Cylinder 1-3-13-14-17-25-30-32Overheating Frames 15-25-32

FlowLow Capacity 1-3-5-21-22-23-32

Inspection FindingsAbnormal Carbon Deposits 1-3-5-16-17-21-25-26-27-30-32-33Excessive Piston Ring/Cylinder Wear 5-14-17-21-28-29Valve Wear/Breakage 1-3-14-16-17-20-21-28-29

Possible Causes1. L.P. Valves Wear Breakage

2. H.P. Valves Wear Breakage

3. L.P. Unloading System Defective

4. H.P. Unloading System Defective

5. L.P. Piston Rings Worn

6. H.P. Piston Rings Worn

7. Piston Rod Nut Loose

8. Piston Loose

9. Head Clearance Too Small

10. Bearing Clearance Too High

11. Flywheel or Pulley Loose

12. Crosshead Clearance Too High

13. Cooling Water Quantity Too Low

14. Cylinder Lubrication Inadequate

15. Frame Lubrication Inadequate

16. Cylinder Lubrication Excessive

17. Lubricating Oil Incorrect Spec.

18. Foundation/Grouting Inadequate

19. Piping Support Inadequate

20. Resonant Pulsations (Suction or Discharge)

21. Suction Filter Dirty/Defective

22. Suction Line Restricted

23. System Leakage Excessive

24. System Demand Exceeds Compressor Capacity

25. Discharge Pressure Too High

26. Discharge Temperature Too High

27. Intercooler Fouled

28. Liquid Carry-Over

29. Dirty/Corrosive Products Into Cylinder

30. Cylinder Cooling Jackets Fouled

31. Running Unloaded Too Long

32. Speed Incorrect

33. Suction Pressure Too Low



Centrifugal Compressor and Lube System Troubleshooting Checklist

Symptoms Possible Causes

Excessive Vibration 1-4-5-6-8-9-10-11-12-13-14-15-22-23-24-25

Compressor Surges 6-7-16-17

Loss of Discharge Pressure 18-19-20

Low Lube-Oil Pressure 27-29-30-31-32-36-37-38-39-40-41

Excessive Bearing Oil Drain Temperature 2-3-21-28-33-34-35-42-43-44

Units Do Not Stay in Alignment 25-26

Water in Lube-Oil 45-46

Possible Causes Possible Solutions

1. Excessive Bearing Clearance Replace bearings

2. Wiped Bearings Replace bearings

Determine and correct cause

3. Rough Rotor Shaft Journal Surface Stone or restore journals Replace shaft

4. Bent Rotor (caused by uneven heating or cooling) Turn rotor at low speed until vibration stops, then gradually increase speed to operating speed.

If vibration continues, shut down, determine and correct the cause

5. Operating in Critical Speed Range Operate at other than critical speed

6. Build-up of Deposits on Rotor Clean deposits from rotor

Check balance

7. Build-up of Deposits in Diffuser Mechanically clean diffusers

8. Unbalanced Rotor Inspect rotor for signs of rubbing

Check rotor for concentricity, cleanliness, loose parts

Rebalance

9. Damaged Rotor Replace or repair rotor

Rebalance rotor

10. Loose Rotor Parts Repair or replace loose parts

11. Shaft Misalignment Check shaft alignment at operating temperatures

Correct any misalignment

12. Dry Gear Coupling Lubricate coupling

13. Worn or Damaged Coupling Replace coupling

Perform failure analysis

14. Liquid “Slugging” Locate and remove the source of liquid

Drain compressor casing of any accumulated liquids

15. Operating in Surge Region Change operating point

16. Insufficient Flow Increase recycle flow through machine

17. Change in System Resistance due to Obstructions or Improper Inlet or Discharge Valve Positions

Check position of inlet/discharge valves

Remove obstructions

18. Compressor not up to Speed Increase to required operating speed

19. Excessive Inlet Temperature Correct cause of high inlet temperature



20. Leak in Discharge Piping Repair leak

21. Vibration Probably imbalance or coupling.

Refer to IMI Candidate Manual, or other references.

22. Sympathetic Vibration Adjacent machinery can cause vibration even when the unit is shut down, or at certain speeds due to foundation or piping resonance.

A detailed investigation is required in order to take corrective measures.

23. Improperly Assembled Parts Shut down, dismantle, inspect, correct

24. Loose or Broken Bolting Check bolting at support assemblies

Check bed plate bolting Tighten or replaceAnalyze

25. Piping Strain Inspect piping arrangements and proper installation of pipe hangers, springs, or expansion joints.

26. Warped Foundation or Bed plate Check for possible settling of the foundation support

Correct footing as required

Check for uneven temperatures surrounding the foundation casing

27. Faulty Lube-Oil Pressure Gage or Switch Calibrate or replace

28. Faulty Temperature Gage or Switch Calibrate or replace

29. Oil Reservoir Low Level Add oil

30. Clogged Oil Strainer/Filter Clean or replace oil strainer or filter cartridges

31. Relief Valve Improperly Set or Stuck Open Adjust relief valve

Recondition or replace

32. Incorrect Pressure Control Valve Setting on Operation Check control valve for correct setting and operation

33. Poor Oil Condition/Gummy Deposits on Bearings Change oilInspect and clean lube-oil strainer or filter

Check and inspect bearings

Check with oil supplier to ascertain correct oil species being used

34. Inadequate Cooling Water Supply Increase cooling water supply to lube-oil cooler

Check for above design cooling water inlet temperature

35. Fouled Lube-Oil Cooler Clean or replace lube-oil cooler

36. Operation at a very Low speed without the auxiliary oil Pump Running (if main L.O. pump is shaft driven)

Increase speed or operate auxiliary lube-oil pump to increase oil pressure

37. Bearing Lube-Oil Orifices Missing or Plugged Check to see that lube-oil orifices are installed and are not obstructed

Refer to lube-oil system schematic diagram for orifice locations

38. Oil Pump Suction Plugged Clear pump suction

39. Leak In Oil Pump Suction Piping Tighten leaking connections

Replace gaskets

40. Failure of Both Main and Auxiliary Oil Pumps Repair or replace pumps

41. Oil Leakage Tighten flanged or threaded connections

Replace defective gaskets or parts

42. Clogged or Restricted Oil Cooler Oil Side Clean or replace cooler




43. Inadequate Flow of Lube-Oil If pressure is satisfactory, check for restricted flow of lube-oil to the affected bearings

44. Water in Lube-Oil Probably a steam leak condensing in bearings or lube-oil cooler leak.

45. Leak in Lube-Oil Cooler Tube(s) or Tube Sheet Hydrostatically test the tubes and repair as required

Replace zinc protector rods (if installed) more frequently if leaks are due to electrolytic action of cooling water

46. Condensation in Oil Reservoir During operation maintain a minimum lube-oil reservoir temperature of 120°F to permit separation of entrained water

When shutting down, stop cooling water flow to oil cooler

Commission lube-oil conditioning unit

Refer to lube-oil management guide

NOTE: Vibration may be transmitted from the coupled machine. To localize vibration, disconnect coupling and operate driver alone. This should help to indicate whether driver or driven machine is causing vibration.



CHEVRON Compressors - Maintenance and Trouble Shooting

Documents

american gas

subsequent

gather pertinent

heat treatment

actuated exhaust

inboard suction

stroke cycle

speed integral