By: Cims  09-12-2011
Keywords: Valve, Compressor

The Purpose

The purpose is to get the maximum throughput or output for the minimum dollar.  This is accomplished through (1) full utilization horsepower, (2) reduction of downtime and lost production, (3) lower maintenance costs (reduction of parts and labor), and (4) lower fuel consumption (Energy Cost).

How can we achieve the best profitability from engines and compressors?

Select a maintenance concept most suitable for each unit.

  1. Breakdown
  2. Scheduled (preventative time based)
  3. Predictive (condition and performance based)

Where and how does the recip analysis fit in with the different maintenance concepts?

  1. Breakdown Maintenance - A recip. analyzer can be used as a troubleshooting tool.
  2. Scheduled Maintenance - This is determined by manufacturer’s recommendation, past experience and records of maintenance and operations.  A. Recip. analyzer can be used to evaluate the performance and condition of the unit using the indicators it provides,between the scheduled intervals.   B. I f 100% online reliability to required and scheduled (preventative) maintenance is most suitable, a recip. analyzer can be used to determine the scheduled intervals.
  3. Predictive Maintenance - A set of performance and condition indicators, that point to specific needs for maintenance are monitored and trended.  The maintenance or repair is scheduled to correct the failing parts or components.

The Reciprocating Analysis

Recip. analyzers gather and display five different inputs, relative to crank shaft position.
These inputs provide indicators and actual data about the machines condition and performance.
The inputs to the analyzer are:

  • pressure
  • vibration
  • ultrasonic
  • electrical
  • temperature

Listed below are the indicators and data obtained from the analyzer.

1.  Pressure

  •   Horse power developed or consumed per cylinder
  • Throughput of each compressor cylinder
  •   Horse power loss due to compressor valves, cylinders, bottles and piping.
  •   Actual gas rod load and can use collected data to calculate net rod load.
  • Can use real data to produce/calculate curves.
  • Compression pressure, peak firing pressure and deviation proper ignition timing.
  • Rate and timing of combustion
  • Exhaust and intake operation.
  • Power balance engines by horse power.
  • Significant leaks such as compressor valves, intake and exhaust valves, compressor and power piston rings and main pressure packing.

**The limitations of the pressure sample are affected by how well it represents the actual pressure cycles inside the cylinder.

Indicator passage resonance and thermal shift of the pressure transducer are the most common causes of slight inaccuracies.

2.   Vibration

The following information can be revealed from the vibration crank angle pattern of a power cylinder:
valve action

  • ring action
  • exhaust blow by
  • piston slap
  • cylinder condition
  • bearing pin and brushing failure (excessive clearance that causes high amplitude vibration and or knocks)
  • cam and lifter action
  • detonation
  • pre-ignition
  • compression leaks

All vibration caused by malfunction or failed parts and components

Compressor Cylinder

  • valve action
  • ring action
  • bearing, pin bushing failure (excessive clearance that causes a knock)
  • crosshead action
  • cylinder condition

all vibration caused by malfunctioning or failed parts and components

3.   Ultra Sonic

Ultrasonic converts high frequency (35 KHz to 45 KHz) airborne acoustics and mechanical energy that is undetectable to the human ear to an electrical signal. It compliments both the pressure and vibration trace as second indictor in diagnosing of components.

This can also be use for internal or external leak detection on Recycle valves, dump valve and PSVs.

4.    Electrical

This signal is used to trouble shoot and monitor ignition systems.

Both primary and secondary can be checked for proper operations and failed components can be identified.

Note :  The shielded plug wires need to be changed with normal plug wires to be able to analyze the secondary ignition.
The pressure vibration ultrasonic and electrical events occur at a given time and duration relative to crank shaft rotation, any deviation indicates a potential problem.

5.     Temperature

  • Pressure drops causing gas temperature change
  • Hotter or cooler than normal process temperatures
  • Valve temperatures indicate leaking valves
  • Temperatures indicating plugged or inefficient exchangers

The recip analysis program is an integral part of a good maintenance program for reciprocating equipment.  It establishes a set of valid indicators to determine performance and condition of engines and compressors and often pin points to wearing, failing, and incorrectly used parts and components.

Other indicators are pressure, temperature, flow, energy consumption, oil/wear trap analysis, past experience, history, inspection and those indicators not yet thought of.

A good efficient and effective Analysis. Program can deliver:

  •   increased throughput and productivity
  • reduced energy consumption
  •   reduce maintenance and operational cost
  • extend overhaul intervals

Compressor Analysis

Full Performance and Mechanical Analysis

Pressure readings from compressor cylinder head end, crank end, suction and discharge bottles.

*It provides a full set of performance data.

  • unit capacity
  • horse power, horse power losses and capacity per horse power
  • pressure drops in the system
  • pulsation levels
  • volume clearance
  • valve performance
  • indications of components causing performance losses. Valves, rings, and packing

Complete Vibration Survey of the Unit  

*It provides a full set of mechanical condition data for analysis and trending.  

  • valve vibration and ultrasonic signatures
  • valve cap temperatures
  • crosshead and main bearing vibration signatures
  • compressor frame, cylinder, pulsation bottle and piping vibration signatures
  • auxiliary equipment vibration signatures

Note:    Suction and discharge bottle pressure readings are only required for the initial analysis and if operating condition change significantly.  However, this information is very important to evaluate pressure drops in the system.  High pressure drop are inefficiencies that consume/waste horse power and therefore reduce the potential capacity of the compressor.

Engine Analysis

2 stroke engine where pressure points are available.

Full performance and mechanical condition analysis collects pressure data from power cylinders.  *It provides:

  • horsepower developed by each power cylinder
  • peak firing pressure and crank angle of occurrences
  • rate and quality of combustion
  • running compression pressure
  • 4 stroke engines
  • collects vibration trace timed to crankshaft position

*It provides:

  • signatures of the events that take place during the four strokes, valve and ring action, check for compression leaks and any unusual vibration such as knocks.
  • cam and lifter operation
  • check reciprocating components for excessive clearance that causes high vibration and/or knocks (note: it can’t detect a normal worn sleeve bearing or bushing in the engine or compressor that doesn’t generate high vibration).
  • main bearing vibration; internal component looseness
  • Primary ignition data is collected to check and compare for proper operation and ignition timing where accessible.
  • Special vibration data is collected on the auxiliaries for analysis and trending.
  • Water Pump, Oil Pump, Fan, Bearings if accessible.
  • Visual inspection of the unit by an experienced technician is also performed; any issues found will be mentioned in the report so these potential problems can be addressed at the next scheduled down time.
  • The base line analysis report consists of the pressure curves and vibration traces.  Computer generated performance reports, ignition primary plots, and ignition timing.  Auxiliary’s vibration alarm report, plus written significant observations a recommendation for improvement and/or corrections.

Same for the compressor report.

This tool is very useful when preformed prior to scheduled services to see what is wearing out on the compressor of what components may fail between service intervals.  These parts can be changed out and the service to prevent unscheduled down time between the service intervals.

Also a good indication of what units need to be overhauled prior to a turn around. This will allow you to focus on the units which need attention and save money on the units which are in good running condition.

Is also recommended to perform a full analysis on new or recently overhauled equipment to insurer that the equipment is performing as expected, and in a safe manner.

A savings estimate when performing a full engine/compressor analysis on a regular basis (2 analyses per year) increased run time by 1% on a unit that produces 5 mmscfd with gas priced at $5.00

$5.00 x 5,000 = $25,000/day total revenue
$250/day or $91,250. /year + extended overhauls

The information in this article was current at 06 Dec 2011

Keywords: Compressor, Valve

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