Case Study
Successful Early Detection of a Crosshead Fracture

A PROGNOST Systems customer in Germany operates four 4-cylinder reciprocating compressors at a natural gas production facility in Northern Germany. Different parameters such as crosshead slide vibration and piston rod position are monitored for the detection of the failure and shutdown of the compressor. On this January at 12:59 the monitoring system detected a catastrophic crosshead failure and it triggered an automatic shutdown of the machine

First warnings

The first early warnings were registered around 12:38. Around 21 hours prior to the shutdown, PROGNOST was delivering first messages of the early failure recognition.  

Fractured crosshead

On this January at 12:59 the monitoring system detected a catastrophic crosshead failure and it triggered an automatic shutdown of the machine.  The first early warnings were registered around 12:38. Around 21 hours prior to the shutdown, PROGNOST® was delivering first messages of the Early Failure Detection. The safety limit (RMS/40 m/s²) for segment 8 (70 - 80° CA)  was exceeded at 12:38 the first time.  The shutdown took place 11 minutes later.

Editorial

Thank you for taking the time to read this first edition of the Compressor Diagnostics Bulletin. This E-Newsletter will be issued every other month and inform you about the latest developments in the field of Asset Performance Management for reciprocating compressors and pumps. 

Our next edition is scheduled for Aug/Sep and will focus on critical rotating equipment in LDPE service.

Your
PROGNOST Systems-Team

Internationally, PROGNOST Systems GmbH is the No.1 partner for companies who want to ensure safe, reliable, and economic operation of their reciprocating piston compressors.

PROGNOST Systems offers Asset Performance Systems and services based on over 15 years of engineering experience in recording, analyzing and interpreting high-frequency status data for reciprocating piston machines.

PROGNOST Systems offers the only system in the industry that records and analyzes status data in real time and compares them using "pattern recognition" based on actual experience. It provides machine operators with a timely analysis of the causes in the form of plain text information. This means that any reciprocating piston machine monitored by this system can be shut down fast an reliably with virtually no risk of false trips.

The diagram shows the safety relevant signals of cylinder 2 over one revolution. The purple signals are at the moment of shutdown, the red signals are 3 hours before and the blue one represents a known good condition. For a better representation the signals (purple, red, and blue) are shown with an offset.  This high speed data was stored in the PROGNOST®-NT ring buffer.

The increased vibration is clearly visible between 40° and 100° CA. Within this time period a machine normally experiences the moment of rod load reversal. Exact determination of the force points of reversal can take place only by indicated pressure signals, which are not installed here. The piston rod position signal shows likewise an increased movement, which lies however below the safety limit of 600 µm. The data evaluations are showing no indication for liquid impacts or foreign particles in the compression chamber. Such an event becomes manifested as increased vibrations and strong piston rod movements are found approximately around the dead centers.  In fact the crank angle position of the increased vibrations and the relatively small deflection of the piston rod position pointed to a problem with the crosshead and/or the crosshead connections.  

This is where a modern CM systems with diagnostic capabilities does add real value to daily operational challenges.

Events
PROGNOST Systems User Forum at the South Shore Harbour, Texas

Skip Morrison conducted the meeting

More than 30 users joined in

Diagnostics
Hazardous or Harmless - A Marketing Phrase ?

Case Study
Condition Monitoring of a Compressor in an Oil Shale Plant

With the increase of energy prices the use of oil shale to produce liquid fuels and hydrocarbon gases is getting more popular. Oil shale, a fine-grained sedimentary rock with significant amounts of kerogen, are located around the world. This material can be burned directly as a low-grade fuel for power generation and heating purposes or can be used as a raw material in the chemical and construction industries.

As of 2008, industry uses oil shale in Brazil, China, Estonia and to some extent in Germany, Israel and Russia. Several additional countries started assessing their reserves or had built experimental production plants, while others had phased out their oil shale industry.  

This article was previously published in the CompressorTech2 magazine. Read full article

  ...detect Valve Malfunctions

Malfunctions of the suction and discharge valves are are the Number 1 reasons for unscheduled downtimes of reciprocating compressors. The three most important indicators for the failure detection are: 
• Valve temperatures 
• deviations in the pV-diagram 
• Increase of vibration levels 
Condition information on the valves is provided by the vibrations measured at the cylinders. The characteristic changes of the signals in the case of a discharge valve damage  is shown by the following example: 

Vibrations measured at cylinder 1 as well as the cylinder pressure curve of the crank-end compression chamber with normally functioning valves.

Over nearly the entire crank rotation, increased vibrations occur at the cylinder. Only the zone of the output (70 - 180 degree CA) of the crank-end compression phase indicates lesser vibrations. The compression now progresses steeper and the re-expansion is significantly flatter than previously. The re-expansion begins about 10 degrees later. If we observe the pV-diagrams of the 1st and 2nd stage, the changes are even clearer.

The monitoring system reports at the cylinder of the 1st stage a violation of the vibration limits and the pV-characteristic values of the crank-end compression chamber. The pV-diagram of the 1st stage is visibly distorted and no longer reaches the intermediate pressure of 20.3 bar. The pressure ratio of the 2nd stage, and therefore the loading of the piston rod, increases as a result of the decreased discharge pressure of the 1st stage. The inserted intermediate pressure is determined by the sister machine.

The analysis leads to the following conclusions: The compression line progresses steeper, the re-expansion line is flatter however, meaning, in these areas there is a gas carryover into the cylinder chamber. This can only occur from the high pressure level of the discharge side. This is normally prevented by the sealing effect of the outlet valves. Therefore, the cause can be attributed to a damage of the discharge valves. Another cause, such as a leakage along the piston rings can be ruled out because, in this case and during a crank rotation, the direction of the gas carryover changes between crank-end and head-end cylinder chamber. In such a case, compression and re- expansion would progress more steeply.

Project News

Indian state owned Numaligarh Refinery Limited based in Assam awarded a contract for a turn key installation of a PROGNOST®-NT Asset Performance Management system. The project was based on a public tender and will be commissioned in the 3rd quarter 2010.

Innospec opted  for a permanent installation after a 17 months PROGNOST®-NT Swift operation period.

Long-time customer E.ON Hanse operates two underground storages for natural gas in Germany. A new compressor at the Kraak site will be equipped with a full PROGNOST®-NT. 

The strong US demand of previous months continuous and new orders have been received for retrofitting three fully equipped compressors of a LDPE line. At the same time more and more users are upgrading their existing traditional PROGNOST®-NT systems with new PROGNOST®-SILver 19" SIL-certified hardware.

Read all Project News online

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