Embed Size (px)
Citation preview
CLASSIFICATION NOTES
No.10.2
GUIDANCE FOR CONDITION MONITORING
JANUARY 2003
DET N ORS KE VERITAS AS BIBLIOTEKET
DET NORSKE VERITAS
Veritasveien 1, N-1 322 mivik, Norway Tel.: +47 67 57 99 OOFax: +47 67 57 99 11
FOREWORD
DET NORSKE VER IT AS is an autonomous and independent Foundation with the objective of safeguarding life, property and the environment at sea and ashore.
DET NORS KE V ERIT AS AS is a fully owned subsidiary Society of the Foundation. lt undertakes classification and certification of ships, mobile offshore units, fixed offshore structures, facilities and systems for shipping and other industries. The Society also carries out research and development associated with these functions.
DET NORSK£ VERITAS operates a worldwide network of survey stations and is authorised by more than 130 national administrations to carry out surveys and, in most ca.-:es, issue certificates on their behalf.
Classification Notes Classification Notes are publications that give practical information on classification of ships and other objects. Examples of design solutions, calculation methods, specifications of test procedures, as well as acceptable repair methods for some components are given as interpretations of the more general rule requirements.
A list of Classitication Notes is found in the latest edition of Pt.O Ch. l of the "Rules for Classification of Ships", and the "Rules for Classification of High Speed, Light Craft and Naval Surface Crnft".
The list of Classification Notes is also included in the current "Classification Services - Publications" issued by the Society, which is available on request. All publications may be ordered from the Society's Web site http://exchange.dnv.com.
It is assumed that the execution of the provisions of this Classification Note is entrusted to appropriately qualified and experienced people, for whose use it has been prepared.
Comments may be sent by e-mail lo [email protected] For subscription orders or infonnation about subscription terms, please use [email protected] Comprehensive information about DNV and the Society's services is found at the Wch site http://www.<lnv.com
© Dct Norske Veritas Computer Typesetting (FM+SGML) by Det Norske Veritas Printed in Norway by Gan Grafisk
If any p8<$0n suffers IO&S or damage which is proved to have been caused by any negllgenl actor omission or Del Norske Veritas, ttien Dot Norske V&rltes shall pay ce>mpensalion to such person lor his proved direct loss or damage. However, the oomp&nsation shall not exceed an amount equal to ten times the fee charged for the service In Question. provided that the maximum compen· satie>n shall never excood USO 2 million. In this provision "Del Noreke Veritas" shall mean the Foundation Det Norske Verltlls as well as all its subsidiaries, directors. t>fflcers. employees. 11gents ancl any other acrlng on behalf of Del Norske Verltas.
Classification Notes • No. 10.2
January 2003
3
CONTENTS
l. GENERAL ........... ,,, ................................................... 4 APPENDIXB 1.1 Introduction .......................... ....................................... .4 ESTABLISHING OF MEASURING POINTS ................. 8 1.2 Machinery systems and equipment covered by the
arrangement ................................................................. 4 APPENDIXC 1.3 Approval process machinery CM programme ............ .4 2. DOCUMENTATION TO BE SUBMITTED FOR
BASELINE MEASUREMENTS ........................................ 9
APPROVAL .............................................................. 4 APPENDIXD 2. 1 General .. ... .. ... .. .............. ........ .. .............. ..... ....... ...... ..... 4 2.2 The maintenance strategy .... ... .......... ........................... 4 2.3 Monitoring methods for components including
PERFORMANCE AND EVALUATION OF VIBRATION MEASUR EMENTS ................................... 11
baseline ............................... .... .... .... .. ........................... 4 2.4 Condition monitoring equipment... ............. ................ .4 2.5 Implementation of condition monitoring in the
APPENDIXE DIESEL ENGINE PERFORMANCE ANALYSIS ........ 13
planned maintenance system .............. .... ................ ..... 4 2.6 Training programme and plan .................................... 4 2.7 Programme for fuel oil bunker analysis ....................... 5
APPENDIXF REQUIREMENTS TO OIL ANALYSIS ........................ 14
2.8 Programme for lubricating and hydraulic oils analysis ........................................................................ 5
3. SPECIAL CONSIDERATIONS .............................. 5
APPENDIXG CONDITION MONITORING FOR WATER JETS ..... 15
3.1 Renewal survey for main steam turbines ..................... 5 APPENDIXH
APPENDIX A CONDITION MONITORING FOR PROPULSION CONDITION MONITORING EQUIPMENT .................. 6 AND POSITION THRUSTERS ....................................... 16
DET NORSKE V ERITAS
4
1. General
l .1 Introduction Thi.s Classification Note is a supplement to DNV Rules for Classification of Ships Pt.7 Ch.8 Sec. I E Machinery CM (Condition Monitoring). The information in this Classification Note is to he considered mandatory unless otherwise stated when preparing and maintaining the Machinery CM survey arrangement.
Guidelines for replacement of separate surveys by condition monitoring for waterjets, propulsion- and position thrusters (including podded propulsors), are found in Appendix G and H.
It is emphasised that operating on Machinery CM described in the following paragraphs, do not replace either the nomml daily surveillance or the chief engineer's responsibility for Laking decisions in accordance with his judgement.
1.2 Machiner y systems and equipment covered by the arrangement In Pt.7 Ch.8 Sec. I Table A 1 su. vey methods for the d ifferent machinery systems and equipment related to this survey arrangement is stated.
Explanation of the different configurations used in Table Al :
4: lt is mandatory to perform c:<.mdition monitoring on this component. The component wi 11 he credited based on the condition monitoring results
4*: As above, in ad<litiou, the condition moni toring should include spectrum analysis (FPT analysis)
3: Credited based on rewrds in the planned maintenance sy.~lt:m
3 and 4: Credited based on both recnrds in the planned maintenance system and condition monitoring records
3 or 4: Credited hased on either records in the planned maintenance system or condition monitoring records. The manager can adopt the most suitt:d method according to their operation
1.3 Approval process machinery CM programme
1) It is required that the ship/manager is operating according to a condition monitoring strategy before applying for Machinery CM.
2) The Manager submits doc;umentation as described in Pt.7 Ch.8 Sec.1 £201 to DNV.
3) The documentation is reviewed.
4) If documentation is found satisfactory, an implementation survey onboard will be carried out by a DNV surveyor.
5) When the implementation survey is carried out with satisfactory result, Machinery CM will be granted.
2. Documentation to be Submitted for Approval
2.1 General A Condition Monitoring (CM) programme shall be submitted to DNV for approval. The submitlcd CM programme shall contain information as described in this chapter (ref. Pt.7 Ch.8 Sec. 1 £203).
Classification Notes - No. 10.2
January 2003
2.2 The maintenance strategy
1) Description of the condition monitoring objective in the company (Why condition monitoring is considered beneficia l).
2) Description of the desired condition monitoring goals.
j) vocumentatiou describing qualificalion of the crew and shore based personnel involved with CM in the daily opera~on of the ship with regards to condition monitoring equipment, measurements and analyses.
4) Responsi bi I ity chart for the organisation showing dedicated personnel for condition monitoring.
5) W orkflow diagram/description of condition monitoring activities.
2.3 Monitoring methods fo r components including baseline For each component included in Machinery CM, the following info1mation shall be submitted for approval:
1) Derailed description of condition monitoring technique used.
2) Component information that will contribute to forcing freq uencies for high capital cost items and items where FFT analysis arc required according lo Tahle A I. (such as r.p.m., bearing specification, couplings, number of fan or propeller blades, motor bars, gear teeth, aerodynamic or hydraulic frequencies, etc.).
3) Schematic sketch of each component with clearly marked measuring point(s) , see Appendix B.
4) Measured frequency range(s)(scc Appendix A).
5) Baseline data (see Appendix C).
6) Predefined alann limits (see Appendix D).
7) Measurement interval (see Appendix D).
8) Relevant pre-defined actions based on condition monitor-ing results.
2.4 Condition monitoring equipment The following shall be submitted for approval related to the equipment used onboard:
1) Equipment data sheet for sensors and collectors.
2) Dncumentation describing requirements in Appendix I.
2.5 Implementation of condition monitoring in the planned maintenance system The following shall be submitted for approval:
1) Examples describing condition monitoring jobs in the planned maintenance system.
2) Procedures describing how the condition monitoring results are handled.
3) Procedures for handling of results close to or above predefined alarm limits.
4) The PMS shall be able to handle t1exiblc maintenance in-tervals for CM based jobs.
2.6 Training programme and plan It should be ensured that the vessel at all times is manned with personnel with adequate training in CM techniques. Plans, records and training for the responsible persons are to be established.
The following shall be s uhmitted for approval:
DET NORSKR VRRTTAS
Classification Notes • No. 10.2
January 2003
1) A plan for qualification and training of future crewmembers.
2) A short description of the elements in the training programme.
3) A plan describing the crew rotation with regal'ds to main-taining qualified personnel on board at all times.
2.7 Programme for fuel oil bunker analysis The following shall be submitted for approval:
- Description of programme for fuel oil bunker analyses.
For requirements see Appendix F.
2.8 Programme for lubricating and hydraulic oils analysis The fo llowing shall be submitted for approval:
Description of programme for lubricating and hydraulic oils analyses. Details on equipment and kit used for onboard water content testing.
5
For requiremcnLc; see Appendix F.
3. SPECIAL CONSIDERATIONS In addition to the Machinery CM arrangement, there are some special considerations for selected components. These arc described in this chapter.
3. t Renewal survey for main steam turbines A limited survey shall consist of the following:
inspection of the low pressure (LP) turbine from the condenser lifting of the covers of the flexib le couplings to permit visual inspection opening up of the axial bearing of the HP and LP turbine to permit visual inspection. inspection and control of the gear through the inspection openings.
DF.T NORSKE Vr!RITAS
6
Appendix A
Classification Notes - No. 10.2
January 2003
CONDITION MONITORING EQUIPMENT
A.1 Basic requirements The requirements to the condition monitoring equipment are as follows:
1) Recordings, measurements and trends shall be presented in~ ~imp!t:> ei.nd t:>?.si!y r~~dat-k !1'!!'.!1!1er.
2) Historical data storage and trend presentation facilities shall be available so as to al low the surveyor acce.11s to al.I measurements since last survey.
3) The equipment and hardware shall be fit for operation in a marine environment and the intended use (Ref. Rule Pt. 4 Ch. 9 Sec. 5).
A.2 Vibration meter The minimum instrumentation requirements for vibration measurements (suitable for e.g. centrifugal and screw pumps, separators and ventilation equipment) is a vibration meter that complies with (ISO 2372) and the following requirement'\:
1) A vibralion meter with an accelerometer with provisions for measuring the vibration level as velocity and preferably also acceleration or shock pulse.
2) Minimum measuring requiremem shall be overall r.m.s. (Root Mean Square) values in two frequency ranges 10 -1000 LHzJ and 10 - 10000 [H7.J and [rnm/s]. Alternatively, l 0 - 10000 LHz] velocity levels, a high frequency range as acceleration lgJ or shock pulse readings is acceptable.
3) Sufficient memory to slorc at least one complete route.
In use, the overall level to be read on the instnunent and then compared against the severity crileria, ref. Appendix IV, for an assessment of mechanical condition .
It is of importance to realise that a vibr.ation meter only displays the overall vibration level, including both internal and external vibration (Internal vibration is defined as the vibration excited by the actual component itself. External vibration is defined as the vibration excited by other equipment) . This type of insu-ument is therefore not suitable for detecting and identifying specific problems in rotating machinery, except the general condition of roller and ball bearings (when shock pulse measurements or equivalent is utilised).
A.3 Data collector, (Frequency spectrum analyser) For turbine.-;, gears, piston pumps, piston compressors, water jets and thrusters, a spectrum analyser (Fa.~t Fourier transform, FFT analyser), is required.
The measured results may be presented as either a PEAK or r.m.s. (Root Mean Square) level in respectively acceleration lgJ or velocity [mm/s].
This kind of equipment is a powc1ful analysis tool for extracting information to determine the origin of a problem as well its severity. A spectrum analyser with a compatible computerised analysis program is an appropriate tool for both condition monitoring and troubleshooting on rotating machinery.
Not.e: Several FFT-based monitoring systems offer expert systems. guiding the operators in lhe analysis and evaluation of the vibration monitoring. Normally, expert systems use the severity guidance from recognised international standards (e.g. ISO & VDI -Verein Deutscher Ingenieure) and the baseline measurements as basis.
---e-n-<l--·of· ·-N·o·t·c---
A.4 Accelerometer The pie:w-clectric acceleromeler is by far the most common in
machinery applications. A typical piezo-electric accelerometer contains one or more piezo-clei:;tric crystal elements and u mass. When the piezo-electric crystal is stressed it produces an electrical output proportional to acceleration. The crystal is stressed by mass when the mass is vibrated by the component tn whic'h th~v nrP. ::itt::irhPrl ArrP1Pr"mPIPr-.: .:lrP no ""P..l rlPuirP~ . ., . . ....... --- - . - -· - - -- - - - --- -- - . . -- - - ·-oc- - -- . ·- - ... that operate in a very wide frequency range; this is the accelerometer's major strength. However, be aware of that excc.~.~ive heat and careless handling could damage the accelerometer.
A.5 Diesel engine performance analyser Not considered as a standard equipment and therefore subject to sepaialc approval. The following documentation is to be submitted:
I) Equipment data sheet or spci:;ification for sensor, data acquisition and analysis equipment.
2) Data sheet or specificati<m for the software including which parameters that are calculated and how the curves are displayed.
The following technical requirements applies:
1) The measuring equipment is to have a dynamic response suflicicnt to accurately measure the true maximum cylinder pressure.
360 samples/rev. for medium and high speed 4-slroke engines 720 samples/rev. for slow speed 2-stroke engines
2) Pressure resolution shall be equal to or better than 0.2 bar.
3) The analysis system is as a minimum to have facilities so as to provide the following performance related parameters: Pcomp, Pmax, aPmax, aTDC, MIP/cylinder power. engine speed.
4) The system shall utilise a physical reference point as a basis for detennining TDC.
5) Software is to be utilised so that it allows the entire cylinder pressure curve to be measured, analysed and presented at a resolution of at least one degree crank angle.
6) Sot'lware should be capable of presenting the work diagram.
7) Software should preferably be capable of presenting information on all cylinders simultaneously in the diagrams.
8) Facilities to allow easy comparison between measurements should be available.
Note: The length of the distance piece for indicator cocks must he so as to avoid pulsation in the reading~.
··-e·n-d···Of---N-o-L-e---
A.6 Calibration procedure For all equipment used for condition monitoring measurements, the calibration intervals shall be according to makers' specifications or recognised standards. If no such intervals are specified, the equipment should be calibrated at least every second year. A job shall be i:;reated in the PMS for calibration of the measuring equipment.
Test equipment shall be furnished by a suitable indicator (for example a tag or a label) to show calibration status.
A. 7 Overall measurements vs. spectrum analysis The major benefit of selecting certain individual frequencies for each measuring point is that thi~ will provide information,
DET NORSKE VF.RIT AS
Classification Notes - No. 10.2
January 2003
which helps identifying the type of fault causing a vibration problem.
As a consequence of a particular fault condition, the vibralion velocily al a given frequency is beginning co increase. Ref. example 2 below. This may be undetected by overall r.m.s. for a long lime, since the influence of chis velocity component on an overall r.m.s.- value will be quite small until it becomes the dominant peak value in the frequency spectrum.
In order to illustrate the difference in the two measuring methods, overall r.m.s. (vibration meter) and spectrum-based (FFI' analyser) the response is measured on a steam turbine. The same measurement, in the range 10-1000 Hz is carried out in one position and one direction. The comparison of the two methods clearly shows that only measuring the overall level, is more inaccurate than the spectrum method.
Example 1: Overall r.m.s. (vibration meter) velocity level:
The results are given as a numerical value on a dL~play.
Baseline measurement: Overall r.m.s.-Level = 5,1 mm/s.
7
Current measurement:Overall r.m.s.-level = 5,8 mm/s.
Example 2: Spectrum analyser velocity level:
Vibration measurement producing for instance a frequency spectrum with only two significant peaks V 1 and V2, at the frequencies f 1 and f2 respectively.
Baseline measurement:V 1 = 5 mm/s (1 ~ L order of turbine rotor)
V 2 = 1 mm/s (2°d order of turbine ro~
Calculation ofoverallr.m.s.-level = ,J(52 + 12
) = 5, lmm/s
Current measurements: V 1 = 5 mm/s
V2 = 3 mm/s
Calculation ofoverall r.m.s.-level = J ( 5 2 + 3
2) = 5, 8 mm/s
The example iJJust:rates the fact that although the increase of V 2 in example 2 (from I to 3 mm/s) is quite significant, the increase in overall r.m.s. is quite small and no suspicion would be aroused of a possible development of a fault condition if only overall r.m.s.- values were read.
DETNORSKE VERlTAS
8
AppendixB
Classification Notes - No. 10.2
January 2003
ESTABLISHING OF MEASURING POINTS Tt is recommended that a professional engineering company carries out the installation. Provided the crew has necessary knowledge and sufficient iostalla1ion instructions from the equipment's supplier, they may carry out the preparation of the measuring points and installation of the equipment (sensors).
For a total view of the mechanical condition. the vibration si2"nal from an operating component should be measured at each bearing. The measurements should be taken on the bearing support housing or other structural parts, wh ich is in close contact with the beari.ngs.
Note: Avoid bearing housing and electrical motor caps, which are of thin metal and are thus poor conductors of vibration energy.
---e-n-d---or---N-0-1-e---
To define the vibration behaviour at each measuring point, measurements should preferably be taken in three directions: horizontal, vertical and axial. For single direction measuring
equipment, the requirement for condition monitoring is usually met by performing the measuremenL<i in the horizontal or the vertical direction. lf possible, these can be supplemented by measurement of axial vibration. The latter is nonnally of significance on Lhrust bearing location~ where direct axial dynamic forces are transmitted.
The position .should be clearly marked and uniquely identified so that all periodic readings are taken in the exact same position every time.
For velocity measurements (up to approximately 2 kHz) the sensor can be attached by magnetic mounting to the machines bearing/casing if the position make a good contact between the sensor and the surface. However, for acceleration measurement (above 2 kHz) sensors are required to be either glued with epoxy to the bearing/casing or threaded into the casing.
A hand-held sensor (accelerometer) is not accepted for any type of measurements.
DET NORSKE V£RITJ\..S
Classification Notes - No. 10.2
January 2003
Appendix C BASELINE MEASUREMENTS
C.1 GENERAL The following general requirements apply to establishment of all baseline measurements:
1) The vessel's crew may carry out the baseline measurements if they are familiar with the set-up of the instmmentation and the analysis program.
2) The measurements shall be obtained at a clearly defined operating condition represe ntative for future in-service operation.
3) Make sure there are steady state conditions before the measurements are carried out. Of particular importance is similarity in shaft rotational speed. Differences i.n power load, suclion condilions, exhaust conditions, and fluid medium, can have a significant influence of the vibration levels recorded.
4) Make a proper evaluation of the measurements in order to detect any fault conditions. The faults should be corrected before the baseline is settled.
5) Baseline measurement with a vibration meter (overall r.m.s. value) will include both types of excitation in one single value. If the measured level for a componenl exceed an acceptable level, the vibralion environment should be checked in accordance with ISO 3954. That implies, for alJ measuring positions the overall r.m.s. level from 10 to l 000 H7. has to be measured for two conditions:
1) r.m.s.r -is the overall level with the actual machinery item running
2) r.m.s.nr - is the overall level with the actual machinery Slopped
According to ISO 3954, a non-active vibration environment is said to exist when: r.m.s.;r.m.s.nr ~ 3. If the ratio 53 actions should be taken to correct the situation. Probably most of the excitation is coming fro m the main engine. Therefore the baseline and future vibration measurements have to be carried out with the propulsion machinery stopped.
C.2 BASELINE MEASUREMENT REQUIREMENTS Thi:-i chapter gives the requirements to establishment of baseline data for the different types of components. All the parameters listed shall be a part of the documentation submitted for approval of baseline data.
C.2.1 Main steam turbines Baseline measurements for main turbines shall contain the fol lowing parameters:
1) Vibration measurements (spectmm) from all relevant bearings.
2) Axial displacements of HP and LP turbine rotor shaft.
3) Axial displacement of main gear shaft, if applicable.
4) Vibration levels of the HP and LP turbine monitored by the two fixed, continuously monitoring and remotely reud vibration sensors installed by the turbine manufacturer.
5) Steam pressure and temperatures at the inlet and the bleeder sections together wilh the gland seal pressure.
6) Condenser vacuum, atmospheric pressure and sea water temperature.
7) Governor oil pressure.
8) Bearing lubricating oil pressure.
9) Propeller shaft torque and r.p.m.
10) Maneuver valve (ahead) position.
C.2.2 Auxiliaryskam turbines
9
Baseline measurements for auxiliary turbines shall contain the following parameters:
l ) Vibration measurements (spectrum) from all relevant bearings.
2) Vibration measurement from fixed monitoring equipment, if applicable.
3) Axial displacements of the rotor, if applicable.
4) Steam pressure between the in lei and exit sections and gland seal of Lhe turbine.
5) Lubricating- and governor oil pressure.
6) Output (speed and power).
C.2.3 Reduction gears Baseline measurements for reduction gear shall contain the following parameters:
1) Vibration measurements (spectrum) from all relevant bearings with a max frequency of at least 2 times the gear mesh frequency.
2) Axial displacements of shaft, if applicable (by means inte-grated equipment).
3) Bca1ing lub. oil pressure.
4) r.p .m. and power.
C.2.4Pumps Baseline measurements for pumps shall contain the following parameters, as far as applicable:
l) Vibration measurements from all relevant bearings.
2) Power consumption of centrifugal pump's electrical motor (to be recorded when the pump is running under normal operating conditions) and speed (r.p.m.).
3) Corresponding suclion and discharge pressure.
4) The axial displacement of the rotor, if applicable.
For systems with speed regulation of pumps, all baseline data shall be recorded at maximum pump speed. In regard to vibration, ba<ieline data are also to be recorded at the normal runni.ng speed.
C.2.5 Compressors Baseline measurements for compressors shall contain the following parameters, as far as applicable:
Vibration measurements (spectrum) from all relevant bearings. Power consumption of compressor's electrical motor {to be measured at a discharge pressure of 2 bars below maker's design pressure or recommended tripping pressure which ever is lower) and r.p.m. The steam pressure belween the inlet and exit sections and gland seal of the turbine. The lubricating and governor oil pressure.
Later measurements shall be taken at the same discharge pressure.
DET NORSKE VERlTAS
10
C.2.6 Generators Baseline measurements for generators shall contain the following parameters:
I) Vibration measurements (spectrum) from all relevant bearings.
2) Corresponding load for the prime mover (not less than 80 % ofrnaximwn continuous rating) and speed (r.p.m.).
C.2.7 Turbochargers Baseline measurements for turbochargers shall contain the following parameters
I ) Vibration measurements from all relevant bearings
2) Corresponding discharge pressure.
3) Turbocharger r.p.m.
4) Engine power and r.p.m.
5) Lubricating oil temperature.
C.2.8 Water jets
Classification Notes - No. 10.2
January 2003
Baseline measurements for water jets shall contain the following parameters:
1) Vibration measurements (spectrum) from aJ\ relevant bearings.
2) Vibration measurements (spectrum) from shafting and impeller.
3) Corresponding load for the prime mover and speed (r.p.m.).
C.2.9 Propulsion thrusters Baseline measurements for thrusters shall contain the following parameters:
1) Vibration measurements (spectrum) from all relevant bearings.
2) Vibration measurements (spectrum) from shafting, gear and propeller.
3) Corresponding load for the prime mover and speed (r.p.m.).
DET NORSKE VERITAS
Classification Notes - No. 10.2
January 2003
AppendixD
11
PERFORMANCE AND EVALUATION OF VIBRATION MEASUREMENTS
D.1 OPERATION CONDITIONS DURING CONDITION MONITORING The periodic measurements to be carried out by the ship's crew or a professional engineering company.
The general rule is that machinery operating continuously when the ship is at sea shall be controlled minimum once a month. Machinery used only periodically (i.e. standby or backup machinery) ro be controlled with 1 to 3 months interval.
It is extremely important that the periodic mea.surement.f are carried out under load conditions as near as possible to the baseline measurement obtained for the same machinery component.
Of punicular importance is similarity in shaft rotational speed. Differences in power load, suction conditions, exhaust conditions, and fluid medium, can have a significant influence of the vibration levels recorded.
Measurement.<i should not be started until stable running conditions have been obtained.
D.2 EVALUATION OF OVERALL MEASUREMENTS These guidelines are applicable only for the vibration produced by the component itself and not for vibration which is transmitted to the component from external sources.
The componenl condition can be evaluated according to ISO 108 I 6-3 standard (10 - I 000 Hz) for acceptable vibration level
Table D.1 Vibration cause Frequency
Unbalance I xr.p.m.
Misalignment of couplings or l x r.p.m. usually bearings and bent shaft 2 or 3 x r.p.m. some times Mechanical looseness 2 x r.p.m.
Defective ball or roller bearings Erratic, many times r.p.m., Shocks and transients
Defective plain bearings Erratic, Shocks and transients Oil whirl. oil whip 0 5 x r.p.m. critical r.p.m. of rotor Defective or damaged gears Number of gear teeth x r.p.m. = gear
mesh frequency and harmonics (2, 3, etc. times) and in any frequency from r.p.m. to mesh frequency. E.g. single tooth damage "" l x r.p.m.
Drive belt problems 1, 2 and higher x r.p.m.
Elecrric Motor 2 x slip x No. of Poles problems Reciprncating forces I, 2 and higher x r.p.m. Combustion forces 0 5 x. N x r.p.m.
Ix Nx r.p.m. N -number of cylinder units
Aerodynamic or hydraulic Number of blades x r.p.m. and high-forces (cavitation) er orders. Forced vibration Depends on vibration source
D.3.1 Reduction gears Gears typically generate a dominant vibration peak at the gear mesh frequency (gear rotating speed x number of teeth) and its hannonics (harmonics series are peaks of a spectrum which are integral multiples of the fundamental frequency).
of rigidly and resiliently mounted machinery.
The following guidance apply lo the velocity overall vibration measurement of machinery with, for instance, steam turbine or other rotating machinery driven by separate electrical motor with power above 15 kW:
Grade A: Grade 8: Grade C:
Grade D:
Good Acceplable Still acceptable, but improvements de· sirable to necessary Risk of breakdown
< 1.8 mm/s r.m.s. 1.8 mm/s to 4.5 mm/s r.m.s. 4.5 mm/s to 11.2 mrnli;r.m.s.
> l l .2 rnm/s r.m.s.
D.3 EVALUATION OF SPECTRUM MEASUREMENTS Evaluation of spectrum measurements is dependent of type of component. The following includes both general and specific guidelines.
Table 4.1 summaries the relationship between different sources of vibration (mostly fault condition) and the corresponding frequencies at which significant vibration velocity peaks arc likely to sh ow up. The frequencies are specified in terms of the fundamental frequency referred to in the table as r.p.m., i.e. the unit used for frequency is r.p.m . rather than Hz (Hertz).
Please be infonned that Table D.1 is for information only.
Remarks
Vihration proportional to rotor unbalance. Position and size ofbalanc-in_g holes or weights may be determined hy vibration measurement Usually severe axial vihratioo Realign until minimum vibration Usually accompanied by unbalance or misalignment. Higher harmon-ics peak:; can he expected. Vibration signature is significantly different from similar bearing Po.s-itive detection by SPM shock pulse meter Vibration signature is significanUy different from similar bearings Resonance of oil film in journal bearings Constant gear ''whine" may be ignored Change of pitch or erratic sig-nal indicates defects. These signal may occur at gear mesh frequency (all teeth damaged) or by l...Z x r.p.m. (Z is number of teeth)
Ea~ily confused with unbalance. Belt resonance with no relationship to rotational r.p.m. Can increase bearing wear Sometimes cause.~ 2 x slip sideband.I\ around 120 Hz
Inherent in reciprocating machinery 4 cycle 2 cycle
Also higher order~ Load dependent
Variable, depends on throttle position, suction, pressure, etc
Vibrations caused by other macb propeller, hull Vibration source may be identified by narrow band spectrum analysis. Critical in cases of resonance. May also cause damage co machinery out of use especially roller bearings.
The mesh frequency may be a s ingle vibration peak, or it may be surrounded by sidebands spaced on either side of the mesh frequency ar intervals of the shaft running frequencies. If sidebands occur around a tooth mesh, it is easy to determine which gear is defective by the sideband spacing.
Typical values of the amplitude at mesh frequency will gener-
DET NORSK.l:l VER IT AS
12
ally be within the range from 0.5 -6.0 [g) acceleration. However, it is not uncommon and may not be abnormal to observe gears with amplitude at mesh frequc11cy well above this value.
D.3.2 Ball and Roller bearings The first stages of ball or roller bearing defects will produce non-synchronous vibration frequencies called becu-ing tones and their harmonics (non-synchronous vibration peaks are not exact multiples of I x the fundamental frequency). Depending on the instrumentation. the first indication will most lik.elv be high frequency bearing tones with lst order sidebands. ·
The existence of non-synchronous vibration peaks in a spectrum is a red flag to the analyst that bearing problems rnay ex-
ist.
Classification Notes - No. 10.2
January 2003
Bearing tones at 0.15 mm/s r.m.s. (0.0025 g r.m.s.) or higher are considered significant.
An example of simple calculations of (approximate) the bearing tone frequencies for most common bearings are as follows:
Outer race fault= No. ofrollers x r.p.m. x 0.4. Inner race fault= No. ofrollers x r.p.m. x 0.6. Fundamental Train Frequency (FTF) = 0.4 x r.p.m.
DET NORSKE VERITAS
Classification Notes - No. 10.2
January 2003
Appendix E
13
DIESEL ENGINE PERFORMANCE ANALYSIS
E.1 GENERAL It is required to perlorm diesel engine perlormance analyses on main engines onboard. For diesel generators, sec below. Documentation of such analyses shall be made available to the attending surveyor, covering the period .since last survey.
Since there are still fault conditions that are rather difficult to detect, as cracked cylinder liners, developing ovality, pitted surfaces etc, the only bullet-proof method of discovering faulty conditions is opening up.
Therefore DNY will not credit any items based on diesel engine performance analysis. Crediting of items will be based on the history in the planned maintenance system. The surveyor will, however, review the documentation and conduct a third party verification of the analyses.
Performing diesel engine perfonnance analyses on a regular basis is important to maintain a close follow-up of the engine condition. These analyses can provide important information regarding different fault conditions on the engine. Examples are:
delayed or advanced ignition worn and/or defective piston rings burnt piston crown worn liner leaking fuel injection nozzle retarded or advanced fuel pump timing leaking fuel pump suction valve worn fuel pump unbalanced engine (can cause uneven main bearing wear).
The most evident advantages will be detection of faults or irregularities early in the developing stage. This will again contribute to reduction of down time, repair costs and indirect costs, as loss of contracts etc. Minor efficiency improvements can ~ive substantial fuel savings, and thereby increased economtc profit. A combination of performance analyses and experience can become a powerful tool in terms of extending or prolonging maintenance intervals for the d iffercnt engine components.
E.2 PERFORMING MEASUREMENTS lt is recommended to follow requirements to steady state conditions (sec Appendix Ill Ch. l ltem 3), when performing diesel engine pcrfonnance measurements.
For best results, measurements should be performed al minimum 80 % of maximum continuous rating.
In addition the following is of great importance:
- good air flow, i.e. clean air filters and air coolers - cmTect fuel viscosity
The cylinder balance for each cylinder, should be checked by measurement and evaluation of the following recommended criteria:
the maximum combustion pressure should not vary more than 3% of the certified value from the average at any cylinder the mean indicated pressure should not vary more than ± I bar from the average at any cylinder.
It is important to analyse the results from the measurements in form of a systematic examination of the pressure diagrams. Focus should be on the following parameters:
compression pressure time of ignition time of max pressure max pressure expansion pressure mean indicated pressure.
In addition, the following is important parameters:
fuel pump index exhaust gas temperature indicated effect spread between cylinders.
E.3 DIESEL GENERATORS For diesel generators with indicator cocks, a maximum pressure test should be performed at lea.st once a month, or every 500 running hours. The test should be performed with the engine running at minimum 80% of maximum continuous rating. The pressure should be recorded on each cylinder with the following corresponding parameters:
exhaust gas temperature for each cylinder fuel rack setting on each fuel pump main fuel rack position FO pressure air inlet temp sea water temp cooling water temperature LO temperature nozzle cooling oil/water temp scavenge air pressure scavenge air temperature.
DE'f NORSKF. VERITAS
14
Appendix F REQUIREMENTS TO OIL ANALYSIS
F.1 Fuel oil bunker analysis The bai;ic requirements to the fuel oil bunker sample are as fol lows:
Sample shall be obtained from each bunkering, alternatively each fuel oil, for analysis. The oil sampling point should be located at the manifold of the receiving vessel where the supplier's hose is connected. Jn order to obtain representative oil samples, the samples should he taken as continuos drip .~amples throughout the entire bunkering period by the use of proper line sampler. Designated sample bottles or containers should be used.
Marine Fuel Oil analysis shall as a minimum include the fol lowing parameters:
density viscosity water ash micro carbon reside (MCR) Sulphur total sediment potential {TSP) tlash point pour point Aluminium and Silicon Vanadium and Sodium Calculated Carbon Aromaticity index (Cetanc Number).
(Refer to: ISO 8217, Petroleum product - fuels - specification of marine fuels).
F.2 Lubricating and hydraulic oil analysis The basic requirements to the lubricating/hydraulic oi I samples arc as follows:
A complete round of oil samples shall at a minimum be submitted for analysis twice a year. Last laboratory analysis report and documentation of follow-up of recommended actions shall be made available to the attending surveyor. The oil sampling point should be clearly identified and positioned to ensure that the sample is taken at the same position each time. 1f possible samples should be acquired
Classification Notes - No. 10.2
January 2003
from the return flow, usually this will mean immediately downstream from the component in question. For diesel engines, the lubricating oil sample shall preferably be acquired after the filters, before the engine. Oil samples are always to be acquired while the equipment is operating and the oil is circulating. Before sampling, a sufficient draining is required lo ensure representative oil samples. Wherever samples intended for particle counting arc acquired, special ultra-clean particle free equipment and bottles are to be used. Both the sampling point and the procedure are to be designed so as to minimise the risk of contamination.
Lubricating and hydraulic oil samples shall be submitted to the delivering oil company or an independent oil analysis laboratory. When submitted to an independent laboratory, one should ensure that the analyses of lub1icating oil for combustion engines are performed in accordance with guidelines put down by Cimac (the International Counsil on Combustion engines). For other samples, recommended values from the manufacturer of the system or the oi 1 supplier should be followed.
For lubricating oils the scope of work should, as a minimum, be:
water content sodium content (salt) flash point wear particles viscosity base number insoluble material.
For hydraulic oils the scope of work should, as a minimum, be:
water content viscosity wear particles acid number.
For hydraulic systems with high cleanliness demands specified by manufacturer particle counting should be performed.
DET NORS.KE VERlTAS
Classification Notes· No. 10.2
January 2003
Appendix G
15
CONDITION MONITORING FOR WATER JETS
G.1 GENERAL The condition monitoring arrangement described in this Appendix is an alternative to the traditional survey method for water jets.
The condition monitoring concept is based on the following guidelines and requirements listed in Part 1.3: Approval process machinery CM program.
All items except item 5, instead of Machinery CM, a Condition Monitoring Certificate for the water jets will be issued.
Part 2: Documentation to be submitted for approval.
Complete documentation except item 2.7 and 3.
G.2 PARAMETERS TO BE MEASURED OR MONITORED. Carry out performance- and vibration measurements at, once a month, see Appendix C and D.
The impeller r.p.m., load and other performance conditions must be as close as possible to the baseline condition (see Appendix III)
G.3 IMPLEMENTATION SURVEY The surveyor will carry out, or monitor vibration mea.~urements and other condition monitoring measurements similar to those carried out when the baseline measurement data were established. This is to confirm that the baseline data and the equipment are operated as intended and in accordance with the CM programme.
The following will generally be reviewed and may also be tested if found necessary:
The functionality of insb·umcntation and analysis program for condition monitoring. The installation of condition monitoring equipmenL
Verify program for lubricating and hydraulic oils analysis, see Appendix F. Verify the crew's ability to operate the condition monitoring arrangement.
G.4 ANNUAL SURVEY
The extent of annual survey, reference is made to the HSLC in operation Rules: Pt.7, Ch.2, Sec.2, Table El and E2. Review of planned maintenance system, together with a historic and trend analysis of the condition monitoring da· ta, including lubricating and hydraulic oil analysis, recorded since the last annual survey have to be presented to a DNV Surveyor. Verify the crew's ability to operate the condition monitoring arrangement. Verify calibration status of the measuring equipment Other special tests may be required if deemed necessary by the attending DNV surveyor.
G.S RENEWAL SURVEY (EVERY 2,5 YEARS) Preferably carried out concurrent with the nearest bottom survey in dry-dock.
In addition to the annual survey the following have to be included:
A visual inspection (without dismantling) of:
impeller housing, NDT if found necessary stator housing and guide vanes, NDT if found necessary steering pins and bushes impeller shaft in way of seal box.
Finally a re-evaluation of the baseline data, see Appendix C.
Other special tests may be required if deemed necessary by the attending DNV surveyor.
DET NORSKE VERlTAS
16
Appendix H
Classification Notes - No. 10.2
January 2003
CONDITION MONITORING FOR PROPULSION AND POSITION THRUSTERS
H.1 GENERAL This condition monitoring program is intended to replace visual internal inspection of the thrusters and is thus intended to monitor condition of the mechanical power transmission train (i.e. bearings and gears). This program may also be implemented for nodded tvoe thrusters. i.e. thrusters eou inned with integrated eieclric dri~e motor, instead of gear trans~ission, to monitor shaft bearings and sealing condition.
The condition-monitoring concept is based on the fo llowing guidelines and requirement~ I isted in Part 1.3: Approval process machinery cm program
All items except item 5, instead of Machinery CM, a Condition Monitoring Cettificate for the thruster will be issued.
Part 2: Documentation to be submitted for approval.
Complete documentation except item 2.7 and 3.
H.2 PARAMETERS TO BE MEASURED OR MONITORED. Carry out oil analysis and vibration measurements al, once a month for propulsion thruster~· and minimum quarterly for position thrusters, sec Appendix C, D and F.
The propeller r.p.m. and pitch , the load on the drive motor, and other perfonnancc conditions must be as close as possible to the baseline condition (see Appendix C). For thrusters it is advisable to establish baseline data at part load, e.g. at 50% of nominal rating.
B.3 IMPLEMENTATION SURVEY The surveyor will carry out, or monitor vibration measurements and oil analysis similar to those carried out when the baseline measurement data were established . This is to confinn that the baseline data and the equipment are operated as intended and in at:cordance with the CM programme.
The fo llo wing will generally be reviewed and may also be tested if found necessary:
the functionality of instrumentation, analysis program for oil analysis and v.ibration measurements equipment for oi l sampling and handling the installation of vibration measurement equipment verify the crew's ability to operate the condition monitoring arrangement.
verify planned maintenance system and/or documentation for maintenance in accordance with maker's instructio ns.
H.4 ANNUAL SURVEY
review of planned maintenance system and maintenance documentation review historic and trend analysis of the vibration measurement data and lube nil analysis, recorded since the last annual survey verity the crew's ability to operate the condition monitoring arrangement verify equipment calibration status other special tests may be required if deemed necessary by the attending DNV Surveyor.
H.S INTERMEDIATE SURVEY In addition to the annual survey the following have to be ver.ified:
Sealing arrangement of propeller blades, propeller shaft and steering column, preferably carried out concurrent with bottom survey. Other special tests may be required if deemed necessary by the attending DNV Surveyor.
H.6 RENEWAL SURVEY Tn addition to the annual and intcnnediate survey the following have to be carried out:
test run at normal load to prove operating ability, as far as applicable according to the ship 's present operating condition testing of controllable pitch mechanism testing of alarm and safety functions re-evaluation of the baseline data, see Appendix C other speci al tests may be required if deemed necessary by the attending DNV surveyor.
DET NORSKE VRRT'fAS
