Vibration Measurement and Analysis on a Helium Cycling Compressor

[1] Condition Monitoring 2015, GfM Gesellschaft für Maschinendiagnose mbH [2] Seminarunterlagen, GfM Gesellschaft für Maschinendiagnose mbH

Dirk Pflueckhahn dirk.pflueckhahn@helmholtz-berlin.de Fon +49-30-80 62-1 46 54

Dirk Pflueckhahn, Wolfgang Anders, Axel Hellwig, Jens Knobloch, Stefan Rotterdam Helmholtz-Zentrum Berlin Albert-Einstein-Str.15, 12489 Berlin, Germany

INTRODUCTION Availability and reliability belong to the most important demands towards a cryogenic plant. The condition of rolling bearings in cycling helium compressors is a critical point for a possible system failure. Monitoring of rolling bearings condition leads to a cost-effective and predictive maintenance. Vibration analysis with multichannel data acquisition enables to detect damages not only on rolling bearings but also misalignments between shafts, imbalances, gearing damages, mechanical slackness and loose parts. Diagnostic vibration measurements on a KAESER ESD 441 SFC helium cycling com-pressor for a LINDE TCF50 liquefier after 80.000 hours of operation indicated a pitting damage on the outer ring of one of the main rotor bearings pressure side (7320B). The general overhaul of the compressor block after this operation time was substantiat-ed by this indication.

MEASURING SETUP ON KAESER ESD441SFC HELIUM CYCLING COMPRESSOR

Calculated kinematics of rolling bearings

color remark Nos. of roll-ing elements (RE)

Cage [Hz]

RE-spin [Hz]

RE-cycl. freq. [Hz]

Outer ring [Hz]

Inner ring [Hz]

Motor

SKF 6317 both-sides 8 9.620 51.882 103.764 76.959 122.320

Main rotor

SKF NU320E Suction/pressure side 13 9.956 59.582 119.164 129.429 194.399

SKF 7320B Pressure side 12 10.163 49.944 99.888 121.809 177.109

SKF 7310B Pressure side 11 10.113 48.699 97.397 111.098 162.910

Female Rotor

SKF NU2215E Suction side 18 8.885 70.163 140.325 159.838 213.809

SKF 7316B Pressure side 12 8.552 44.007 88.015 102.753 146.345

SKF NU316E Pressure side 13 8.320 50.251 100.503 108.156 161.700

An 8-channel PeakStore410 data acquisition system was used for the diagnostic meas-urement. Sensors with permanent magnet mounting were attached on motor and com-pressor block to measure the casing vibrations. The compressor was in normal opera-tion during installation of the equipment and data acquisition which only took 26.2 s.

Eight accelerometers are magnetically mounted at the compressor block and motor housing near the rolling bearings to pick up vibrations in horizontal and vertical direction. The acquired measurement data is saved in the PeakStore410 for later analysis.

Damages on bearings, gear mesh, shafts, imbalance or misalignments, loose parts lead to significant patterns in the vibration analysis diagrams that have to be calculated from recorded raw data. The understanding of relationship between mechanical processes of single compo-nents of a machine and the relationship to a specific vibration signal enables to identify vari-ous kinds of damage symptoms. The knowledge of process parameters, rotation frequency, gear ratio and used bearing types including its manufacturer is essential for a successful ma-chine condition analysis and has to be provided by the manufacturer of the equipment [2].

RESULTS OF VIBRATION ANALYSIS The vibration analysis report of GfM shows conspicuous and significant values in the envelop curve spectrum on the main rotor, pressure side in horizontal orientation. The ball pass frequency of outer ring (BPFO) of bearing 7320B (121.809 Hz) as well as its harmonics are found as a considerable high peak in the envelop curve spec-trum. A damage on the outer ring of this bearing is indicated.

CONCLUSIONS

• Vibration measurement and analysis was successfully used to assess the condition of a KAESER ESD 441 SFC helium compressor after 80.000 h of operation. A damage on the outer ring of an rolling bearing in the compressor block was ob-tained and lead to a service.

• High expertise and experience is necessary to provide the required kinematic de-tails and to analyse the measurement data. This expertise can be supplied by ex-ternal providers as a service.

• An offline measurement system like PeakStore410 can be used for periodic diag-nostic purpose on various types of rotating machines. For large scale helium plants a permanent online condition monitoring system with an integrated analysis and critical threshold notification might be valuable.

www.helmholtz-berlin.de

MULTICHANNEL VIBRATION MEASUREMENT AND ANALYSIS

Technical Data PeakStore410 [1] Signal Input 8 channels Sensors Accelerometers (ICP) or sensors +/- 50 V output voltage Sampling rate 50 kHz Bandwidth 0.1 Hz .. 21.3 kHz (-3 dB) Amplitude resolution 16 bit (adjustable preamplifier) Additional rotational speed input 1 kHz sample rate, 32 MHz count frequency

Recording All channels simultaneously Measurement duration 26.2 s, 52.4 s, 188.7 s and up to 1 h Data Storage CF-Card 2 .. 8 GB (40 .. 160 measurements with 52.4 s) Data Exchange PeakStore - Software over Ethernet connection Dimensions Height: 80 mm, width: 265 mm, depth: 300 mm, weight: 3 kg, total weight: typical 9.5 kg

Software PeakStore (included), optional for signal analysis: PeakStoreCalc, FAMOS (© imc Messsysteme GmbH)

1 mm pitting on the outer ring of bearing 7320B Main rotor pressure side

Kinematics of KAESER ESD441 SFC compressor Main rotor Female rotor Number of teeth 5 6 Rotation speed [rpm] 1494.590 1245.492 Rotational frequency [Hz] 24.9098 20.7582 Gear mesh frequency [Hz] 124.549

The required kinematic details and measured raw data were handed over to GfM (Gesellschaft für Maschinendiagnose mbH) for an analysis by diagnostic specialists. A detailed report with commented spectra of vibration acceleration and envelope spectra as well as statistical failure probability was obtained.

After disassembling of the compressor block and rolling bearings the damage can be recognized by visual inspection. A 1 mm pitting on outer ring surface represents a sign of wear and would have been caused a failure of the bearing in the next future.

Diagnosis report with spectra, results and recommendations

envelop curve spectrum on the main rotor, pressure side, horizontal

PeakStore410 8-channel data acquisition system, IMI industrial accelerometer with permanent magnet mounting

Courtesy of GfM

Sensor setup for 8-channel vibration measurement with PeakStore410

1

2

6

3

5

4

8 7

Main rotor

Female rotor

Motor

Suction side

Pressure side