IS 14773-4: Mechanical Vibration of Non-reciprocating Machines - Measurements on Rotating Shafts and Evaluation Criteria, Part 4: Gas Turbine Sets

11 Pages·2000·1.2 MB·English

by  Bureau of Indian Standards

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IS 14773-4 (2000): Mechanical Vibration of
Non-reciprocating Machines - Measurements on Rotating
Shafts and Evaluation Criteria, Part 4: Gas Turbine Sets
[MED 28: Mechanical Vibration and Shock]
“!ान $ एक न’ भारत का +नम-ण”
Satyanarayan Gangaram Pitroda
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“!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता हहहहै””ै”
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IS 14773 (Part 4):2000
ISO 7919-4:1996
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Indian Standard
MECHANICAL VIBRATION OF
NON-RECIPROCATING MACHINES —
MEASUREMENTS ON ROTATING SHAFTS
AND EVALUATION CRITERIA
PART 4 GAS TURBINE SETS
ICS 17.160; 27.040

0 BIS 2000
BUREAU OF IN DIANSTAN DAR DS
MANAK BHAVAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
Ju/y 2000 Price Group 3
—
Mechanical Vibration and Shock Sectional Committee, ME 28
NATIONAL FOREWORD
This Indian Standard which is identical with ISO 7919-4:1996 ‘Mechanical vibration of non-
reciprocating machines — Measurements on rotating shafts and evaluation criteria — Part 4: Gas
turbine sets’ issued by the International Organization for Standardization (ISO) was adopted by the
Bureau of Indian Standards on the recommendation ofthe Mechanical Vibration and Shock Sectional
Committee and approval of the Mechanical Engineering Division Council.
The text of ISO standard has been approved as suitable for publication as Indian Standard without *
deviations. In the adopted standard certain conventions are not identical to those used in Indian
Standards. Attention is especially drawn to the following:
a) Wherever the words ‘International Standard’ appear referring to this standard, they should be .%.
read as ‘Indian Standard’.
b) Comma (,) has been used as a decimal marker while in Indian Standards, the current practice
is to use a full point (.) as the decimal marker.
In this adopted standard, reference appears to certain ‘International Standards for which Indian
Starrdards also exist. The corresponding Indian Standards which are to be substituted in their place
are listed below along with their degree of equivalence for the editions indicated:
International Corresponding Indian Degree of
Standard Standard Equivalence
ISO 7919-1:1996 1S14773 (Part 1) : 2000/1S0 7919-1 :1996 Identical
Mechanical vibration of non-reciprocating
machines — Measurements on rotating shafts
and evaluation criteria : Part 1 General
guidelines (first revision)
ISO1O816-1 :1995 IS 11724 (Part 1) :2000/1S0 40816-1:1995 do

Mechanical vibration — Evaluation ofmachine

vibration by measurements on non-rotating
parts: Part 1General guidelines
For the purpose of deciding whether a particular requirement of this standard is complied with, the
final value, observed or calculated, expressing the result of test or analysis, shall be Founded off in
accordance with IS 2 : 1960 ‘Rules for rounding off numerical values (revise@’. The number of
significant places retained in the rounded off value should be the same as that of the specified value
in this standard.
IS 14773( Part 4 ): 2000
ISO 7919-4:1996
/ndian Standard
MECHANICAL VIBRATION OF
NON-RECIPROCATING MACHINES —
MEASUREMENTS ON ROTATING SHAFTS
AND EVALUATION CRITERIA
PART 4 GAS TURBINE SETS
1 Scope NOTEII Initially these three groups will be assessed in a
uniform manner. It is possible, however, that individual
cases will have to be assessed differently.
This part of !S0 7919 gives guidelines for applying 2 Normative references
evaluation criteria for shaft vibration under normal op-
erating conditions, measured at or close to the The following standards contain provisions which,
bearings of gas turbine sets. These guidelines are through reference in this text, constitute provisions
presented in terms of both steady running vibration of this part of ISO 7919. At the time of publication, the
and any magnitude changes which may.occur in these editions indicated were valid. All standards are subject
steady values. The numerical values specified are not to revision, and parties to agreements based on this
intended to serve as the only basis for vibration eval- part of ISO 791”9 are encouraged to investigate the
uation since, in general, the vibratory condition of a possibility of applying the most recent editions of the
machine is assessed by consideration of both the standards indicated below. Members of IEC and ISO
shaft vibration and the associated structural vibration maintain registers of currently valid International
(see the introduction to ISO 7919-1). Standards.
ISO 7919-1:1996, Mechanica/ vibration of non-
This part of ISO 7919 applies to all gas turbine sets
reciprocating machines — Measurements on rotating
(including those with gears) with fluid-film bearings,
shafts and evaluation criteria — Part 1: General
outputs greater than 3 MW and shaft rotational fre-
guidelines.
quencies from 3000 r/rein to 30000 r/rein. Aircraft
derivative engines are excluded, since they differ
IS(3 10816-1:1995, Mechanica/ vibration — Evacuation
fundamentally from industrial gas turbine sets, both in
of machine vibration by measurements on non-
the type of bearings (rolling element bearings) and in
rotating parts — Part 7: General guidelines,
the stiffness and mass ratios of the rotor and support
structure. Depending on the construction and mode
of operation, there are three principle groupings of gas 3 Measurement procedures
turbine sets:
The measurement procedures to be followed and the
— single-shaft constant-speed gas turbine sets; instrumentation used shall be as described in
Iso
7919-1.
— single-shaft variable-speed gas turbine sets;
In gas turbine sets, shaft vibration relative to the
— gas turbine sets with separate shafts for hot gas bearing is normally measured. Therefore, unless
generation and power delivery. stated otherwise, the vibration displacements referred

1
IS 14773( Pan 4 ): 2000
1s0 7919-4:1996
to in this part of ISO 7919 conform to this convention. orthogonal measurement directions. The values pre-
In view of the relatively high rotational frequencies sented are the result of experience with machinery
involved with gas turbine sets, measuring methods of this type and, if due regard is paid to them, ac-
using non-contacting transducers are most common ceptable operation may be expected. If only one
and are generally preferred on rotor elements with measuring direction is used, care should be taken to
operating frequencies of 3 000 r/rein and above. For ensure that it provides adequate information (see
monitoring purposes, the measuring system shall be 1s0 7919-1).
capable of covering overall vibration up to a frequency
equivalent to 2,5 times the maximum service speed. The criteria are presented for the specified steady-
state operating conditions at the rated speed and load
However, it should be noted that for diagnostic pur-
ranges. They apply for normal slow changes in load
poses it may be desirable to cover a wider frequency
range. but do not apply when different conditions exist or
during transient changes, for example during start-up
and shut-down and when passing through resonance
4 Evaluation criteria
ranges. In these cases alternative criteria are
necessary.
Criteria for vibration magnitude, changes in vibration
magnitude and operational limits are presented in an-
It should be noted that an overall judgement of the
nex A.
vibratory state of a machine is often made on the ba-
sis of both relative shaft vibration as defined above
The vibration magnitude is the higher value of the
and of measurements made on non-rotating parts
peak-to-peak displacement measured in two selected
(seeISO 10816-1).
IS 14773(Part4) :2000
1s0
7919-4:1996
Annex A
(normative)
Evaluation criteriafor relativeshaft vibration of gasturbine sets under
specifiedoperating conditions
A.1 General Zone D: Vibration values within this zone are normally ‘—
considered to be of sufficient severity to cause dam-
Two evaluation criteria are used to assess the relative age to the machine.
shaft vibration of gas turbine sets, measured at or
close to the bearings. One criterion considers the A.2.2 Evaluation zone limits
magnitude of the observed broad-band relative shaft
vibration; the second considers changes in magni- In accordance with present accumulated -experience
tude, irrespective of whether they are increases or of shaft vibration measurements in this field, the rec-
decreases. ommended values for the zone boundaries are in-
versely proportional to the square root of the shaft -
A.2 Criterion 1:Vibration magnitude at rotational frequency n (in revolutions per minute). The
recommended values presented in fgure A.1 dre d-
rated speed under steady operating
rived from the expressions below
conditions
Zone boundary A/B
This criterion is concerned with defining limits for
-shaft vibration magnitude consistent with acceptable
dynamic loads on the bearing, adequate margins on
Zone boundary B/C
the radial clearance envelope of the machine, and ac-
ceptable vibration transmission into the support
S(WJ=9000/fi pm
structure and foundation. The maximum shaft vi-
bration magnitude observed at each bearing is as-
Zone boundary C/D
sessed against four evaluation zone s established from
international experience. SIH)=13 200/J ~m
A.2.1 Evaluation zones NOTE2 ForadefinitionofS(m),see ISO 7919-1.
The following typical evaluation zones are defined to These values are not intended to serve as acceptance
permit a qualitative assessment of the shaft vibration specifications, which shall be subject to agreement
on agiven machine and provide guidelines on possible between the machine manufacturer and customer.
actions. However, they provide guidelines for ensuring that
gross deficiencies or unrealistic requirements are
Zone A The vibration of newly commissioned ma- avoided.
chines would normally fall within this zone.
In certain cases, there may be specific features as-
Zone B: Machines with vibration within this zone are sociated with a particular machine which would re-
normally considered acceptable for unrestricted long- quire different zone bounda~ values (higher or lower)
term operation. to be used. For example, wilh a tilting pad bearing it
may be necessary to specify alternative vibration val-
Zone C: Machines with vibration within this zone are
ues, whilst inthe case of an elliptical bearing, different
normally considered unsatisfactory for long-term con-
vibration criteria may apply for the directions of maxi-
tinuous operation. Generally, the machine may be
mum and minimum bearing clearances. In particular,
operated for a limited period in this condition until a
it should be recognised that the allowable vibration
suitable opportunity arises for remedial action.
may be related to the journal diameter since, gener-
ally; running clearances will be greater for larger di-
ameter bearings. Consequently different values may

3
IS 14773 ( Part 4) :2000
1S0 7919-4:1996
apply for measurements taken at different bearings effects of the crack propagation by looking at the
on the same rotor line. In such cases, it is normally change in the broad-band vibration only. Therefore,
necessary to explain the reasons for this and, in par- although monitoring the change in broad-band vi-
ticular, to confirm that the machine will not be en- bration will give some indication of potential prob-
dangered by operating with higher vibration values. lems, it may be necessa~ in certain applications to
use measuring and analysis equipment which is ca-
Higher values of vibration can be permitted at other “pable of determining the trends of the vector changes
measuring positions and under transient conditions,
that occur in individual frequency components of the
such as start-up and run-down (including passage vibration signal. This equipment may be more sophis-
through critical speed ranges). ticated than that used for normal supervisory moni-
-—
toring and its use and application requires specialist
A.3 Criterion 11C: hange in vibration knowledge. Hence, the specification of detail criteria
magnitude for measurements of this type is -beyond the scope
of this part of ISO 7919.
This criterion provides an assessment of a change in
vibration magnitude from a previously established A.4 Operational limits
reference or baseline value. A significant increase or
decrease in shaft vibration magnitude may occur For long-term operation it is common practice to es-
which requires some action even though zone C of tablish operational vibration limits. These limits take
Criterion I has not been reached. Such changes can the form of ALARMS and TRIPS.
be instantaneous or progressive with time and may
indicale that damage has occurred or be a warning of ALARMS: To provide a warning that a defined value
an impending failure or some other irregularity. Cri- of vibration has been reached or a significant -change
terion II is specified on the basis of the change in has occurred, at which remedial action may be
shaft vibration magnitude occurring under steady- necessa~. In general, if an ALARM situation occurs,
state operating conditions. operation can continue for a period whilst investi-
gations are carried out to identify the reason for the
The reference value for this criterion is the typical, change in vibration and define any remedial action.
reproducible normal vibration, known from previous
measurements for the specific operating conditions. TRIPS: To specify the magnitude of vibration beyond
If this reference value changes by a significant which further operation of the machine may cause
amount, and certainly if it exceeds 25 of the upper damage. If the TRIP value is exceeded, immediate
YO
limiting value for zone B, regardless of whether this action should be taken to reduce the vibration or the
increases or decreases the magnitude of vibration, machine should be shut down.

steps should be taken to ascertain the rea sons for the
Different operational limits, reflecting differences in
change. A decision on what action to take, if any,
dynamic loading and support stiffness, may be speci-
should then be made after consideration of the maxi-
fied for different measurement positions and di-
mum value of vibration and whether the machine has
rections.
stabilized at a new condition.
When Criterion II is applied, the vibration me~sure- A.4.1 Setting ofALARMS
ments being compared shall be taken at the same
transducer location and orientation, and under ap- The ALARM values may vary considerably, up or
proximately the same machine operating conditions. down, for different machines. The values chosen will
normally be set relative to a baseline value deter-
It is necessary to appreciate that a criterion based on mined from experience for the measurement position
change of vibration has limited application, since sig- or direction for that particular machine.
nificant changes of varying magnitude and rates can
and do occur in individual frequency components, but It is recommended that the ALARM value should be
the importance of these is not necessarily reflected in set higher than the baseline by an amount equal to
the broad-band shaft vibration signal (see ISO 7919-1). 25 YO of the upper limit of zone B. If the baseline is
For example, the propagation of a crack in a rotor may low, the ALARM may be below zone C.
introduce a progressive change in vibration compo-
Where there is no established baseline, for example
nents at multiples of rotational frequency, but their
with a new machine, the initial ALARM setting should
magnitude may be small relative to the amplitude of
be based either on experience with other similar ma-
the once-per-revolution rotational frequency compo-
chines or relative to agreed acceptance values. After
nent. Consequently, it may be difficult to identify the
a period of time, the steady-state baseline value will
4
IS 14773(Part 4): 2000
ISO 7919-4:1996
be established and the ALARM setting should be ad- specific design features which have been introduced
justed accordingly. to enabh$ the machine to withstand abnormal dynamic
forces. The values used’ will, therefore, generally be
If the steady-state baseline changes (for example after
the same for all machines of similar design and Would
a machine overhaul), the ALARM setting should be
not normally be related to the steady-state bas~tine
revised accordingly. Different operational ALARM
value used for setting ALARMS.
settings may then exist for different bearings on the
machine, reflecting differences in dynamic loading There may, however, be differences for machines of
and bearing support stiff nesses. different design and it is not possible to give more
precise guidelines for absolute TRIP values. In gen-
A.4.2 Setting ofTRIPS eral, the TRIPvalue will be within zone C or D. .....—
The TRIP values will generally relate to the mechanical
integrity of the machine and be dependent on any

10
346 8 10 20 30
Shaftrotationalfrequencyx1000 (r/rein)
figure A.1 — Recommended valuesfor maximum relativedisplacement of the shaft asafunction of the
maximum servicespeedfor gasturbine sets