MACHINE VIBRATIONS AND DIAGNOSTICS

THE WORLD OF ISO

Copyright Material IEEE Paper No. PCIC-2013-44

Dr. Horst Kuemmlee Thomas Gross Prof. Dr. Josef Kolerus Member, IEEE DIN – Deutsches Institut National Instruments Germany Siemens Large Drives Division fuer Normung Consultant Nonnendammallee 72 Burggrafenstrasse 6 Eichenstrasse 49 13629 Berlin 10787 Berlin 81375 München Germany Germany Germany horst.kuemmlee@siemens.com thomas.gross@din.de dr.josef@kolerus.de

Abstract – The paper gives an overview of the organization, standardization philosophy and existing standards within ISO, especially ISO/TC 108 “Mechanical vibration, shock and condition monitoring" concerning machine vibrations and vibration diagnostics. It gives a brief summary of the most important standards, i.e.

the ISO 7919 and ISO 10816 series, and includes guidelines for usage. The paper highlights the actual status of major projects of ISO/TC 108/SC 2 "Measurement and evaluation of mechanical vibration and shock as applied to machines, vehicles and structures" and ISO/TC 108/SC 5 "Condition monitoring and diagnostics of machine systems”. The collaboration of ISO with other international

standardization authorities (e.g. IEC of which the IEC series 60034 is well known) and national committees in the US and Europe are discussed.

I. INTRODUCTION

A. The Aim of Standardization The aim of standardization is an agreement between all

parties involved in a subject in order that they can rely on the specifications given in a standard. Therefore the principle of standardization work is the involvement of all those who are concerned with a certain subject, e.g. manufacturers, users, occupational safety institutes and authorities in the case of machinery standards. To this end, standards are developed in a "democratic" way, i.e. they are drafted in round table meetings, are made available to the public as drafts for comments and vote, and finally are published as soon as the technical content has reached approval by the members of the dedicated standardization organization. Standards, by their definition as an agreement, are not

mandatory in their usage. However, everyone is well advised to base his contracts and decisions on standards which do reflect the state of the art in a certain technical area. To keep standards up to date they should be revised regularly. That keeps standardization work going on. There are many organizations elaborating standards, on a

national level (e.g. ANSI, BSI, DIN), on a regional level (e.g. CEN within the European Union), and on the international level (e.g. IEC, ISO).

B. The Organization of ISO

ISO, the International Organization for Standardization, is the world’s largest developer of voluntary International Standards. It was founded in 1947, and since then has published more than 19 000 International Standards covering almost all aspects of technology and business. Actually 164 countries are members of ISO. The technical work is performed by some 220 Technical Committees (ISO/TC) which may be subdivided into Sub-Committees (SC) consisting of several Working Groups (WG). ISO closely collaborates with other standardization

institutes. Collaboration with the International Electrotechnical Commission IEC is documented by a double logo on the ISO/IEC publications. Figure 1 shows the logos of ISO and IEC.

Fig. 1 – Logos of ISO and IEC

C. Collaboration between Standardization Organizations Collaboration with other institutes does exist even if not

marked on the standards cover sheets. ISO/TC 67 "Materials, equipment and offshore structures for petroleum, petrochemical and natural gas industries" or ISO/TC 118 "Compressors and pneumatic tools, machines and equipment" adapt publications of the American Petroleum Institute API and convert them into ISO standards, e.g. ISO 10441 "Petroleum, petrochemical and natural gas industries — Flexible couplings for mechanical power transmission — Special-purpose applications" is based on API 671 "Special-purpose couplings for petroleum, chemical, and gas industry services" or ISO 10440-1 "Petroleum, petrochemical and natural gas industries — Rotary-type positive displacement compressors — Part 1:

Process compressors" bases on API 619 "Rotary-type positive-displacement compressors for petroleum, petro-chemical and natural gas industries". On the other hand, International Standards of ISO or IEC

can be converted into regional or national standards to encourage their use which is additionally supported by translations into languages other than the official ones — English and French. For instance, if an ISO standard has been taken over in the European Union as EN ISO standard it is published in Germany, after translation into German, as DIN EN ISO standard.

II. ISO/TC 108

The standardization for machine vibration and diagnostics

is carried out in the Technical Committee ISO/TC 108 "Mechanical vibration, shock and condition monitoring". The Technical Committee ISO/TC 108 consists of five

subcommittees: SC 2: "Measurement and evaluation of mechanical vibration

and shock as applied to machines, vehicles and structures"

SC 3: “Use and calibration of vibration and shock measuring instruments”

SC 4 “Human exposure to mechanical vibration and shock" SC 5: "Condition monitoring and diagnostics of machine

systems" SC 6: “Vibration and shock generating systems” In the following the work of two of its sub-committees (SC 2

and SC 5) are discussed more in detail.

III. ISO/TC 108/SC 2

Sub-committee SC 2 "Measurement and evaluation of

mechanical vibration and shock as applied to machines, vehicles and structures" is mainly concerned with drafting International Standards covering the measurement and evaluation of mechanical vibration of machinery. SC 2 consists of the following working groups:

JWG 1 "Joint TC 108/SC 2-IEC/TC 4 WG; Vibration of hydraulic machine sets"

WG 1 "Rotodynamics and vibration of machines" WG 2 "Vibration of ships" WG 7 "Vibration of machines with active magnetic bearings" WG 8 "Ground-borne noise and vibration from rail systems" WG 10 "Basic techniques for vibration diagnostics" WG 11 "Joint between ISO/TC 108/SC 2, ISO/TC 118/SC 1

and ISO/TC 118/SC 6; Vibration in reciprocating compressor systems"

WG 31 "Balancing" WG 1 deals with vibration behaviour of industrial machines.

There are two main standards series:

ISO 10816 "Evaluation of machine vibration by measurements on non-rotating parts"

like bearing pedestals or bearing caps, and

ISO 7919 "Evaluation of machine vibration by measurements on rotating shafts"

considering both shaft absolute and relative vibration. Part 1 of both series gives a general description of the

principles that are generally applicable for the measurement and evaluation of vibration. The subsequent parts deal with the individual applications. Both standards series define the appropriate measurement

quantities, suitable measurement locations and directions on a machine, give advice to perform a vibration measurement within a given frequency range, and — very helpful — provide limit values for the measured vibration in terms of zone boundary values. These boundary values reflect wordwide experience with this kind of machinery and guarantee that the machine runs satisfactorily. Especially for electric machinery, the ISO 7919 and ISO

10816 series focus on vibration behaviour at site. The acceptance criteria under test field conditions, however, are standardized in the IEC 60034 series, for vibration especially in IEC 60034-14. There is no comparable standard for test field criteria within ISO and on the other hand no comparable standard for in-situ conditions within IEC. To classify the vibration at normal operating speed under

steady-state operating conditions in situ, the following four evaluation zones are defined: Zone A: The vibration of newly commissioned machines

normally falls within this zone. Zone B: Machines with vibration within this zone are

normally considered acceptable for unrestricted long-term operation. Zone C: Machines with vibration within this zone are

normally considered unsatisfactory for long-term continuous operation. Generally, the machine may be operated for a limited period in this condition until a suitable opportunity arises for remedial action. Zone D: Vibration values within this zone are normally

considered to be of sufficient severity to cause damage to the machine. The vibration level associated with a particular classification

range depends on the size and mass of the vibrating body, the characteristics of the mounting system, and the power and use of the machine. It is therefore necessary to take into account the various purposes and circumstances concerned when specifying different ranges of vibration level for a specific class of machinery. Where appropriate, reference should be made to the product specification. Two criteria are provided for assessing the machine

vibration. One criterion considers the magnitude of the observed vibration; the second considers the changes in the magnitude. It must be recognized, however, that these criteria do not form the only basis for judging the severity of vibration.

For long-term steady-state operation, it is common practice to establish operational vibration limits. These limits take the form of ALARMS and TRIPS for which rules are given to set the appropriate levels. Additionally, these standards present guidelines to judge the machine vibration also under transient operating conditions, such as run-up or run-down. The standards series ISO 10816 and ISO 7919 actually

cover the following machinery (Figure 2):

Fig. 2 – ISO 7919 and 10816 series For a decision which standard should be used for a given

machine, the Technical Report ISO/TR 19201 "Methodology for selecting appropriate machinery vibration standards" can be consulted giving an overview over the most important machinery vibration standards which shortly are described and summarized. Machinery can be subdivided into four categories for the

purposes of vibration measurement and evaluation:

a) Reciprocating machinery having both rotating and reciprocation components, such as diesel engines and certain types of compressors and pumps. The vibration is usually measured on the main structure of the machine at low frequencies, typically in the range 2 Hz to 1 000 Hz.

b) Rotating machinery having rotors with rigid behaviour,

such as certain types of electric motors, single-stage pumps and low-speed pumps. The vibration is usually measured on the main structure (such as on the bearing caps or pedestals) where the vibration magnitudes are indicative of the excitation forces generated by the rotor due to unbalance, thermal bows, rubs and other sources of excitation.

c) Rotating machinery having rotors with flexible behaviour, such as large gas or steam turbine generator sets, multi-stage pumps and compressors. The machine may be set into different modes of vibration as it accelerates through one or more resonance speeds to reach its service speed. On such a machine, the vibration magnitude measured on a structural member may not be totally indicative of the vibration of the rotor. For example, a flexible rotor may experience very large displacements resulting in failure of the machine, even though the vibration magnitude measured on the bearing cap is low. Therefore, it is essential to measure also the vibration of the shaft directly.

d) Rotating machinery having rotors with quasi-rigid

behaviour, such as some steam turbine rotors, axial-flow compressors, and fans. Such machinery contains a special class of flexible rotor where vibration magnitudes measured on the bearing cap are indicative of the shaft vibration.

A. ISO 10816 – Measurements made on non-rotating parts

ISO 10816-1 provides general guidelines that describe

procedures for the measurement and evaluation of vibration based on measurements made on non-rotating parts of the machine. This is the first part of a series of International Standards that provide individual criteria for each general class of machine covered, which are unique to those machines. These criteria, which are presented in terms of both vibration magnitude and change of vibration, relate to operational monitoring and acceptance testing. ISO 10816 accomplishes the following: ─ to cover the broadband frequency range of both low- and high-speed machines

─ to set the vibration criteria to include various operational zones

─ to incorporate vibration criteria through a worldwide survey ─ to include unique criteria and measurement procedures for specific types of machines.

Figure 3 shows a typical zone definition of vibration velocity versus frequency. ISO 10816-2 covers large steam turbine generator sets with

power greater than 50 MW. ISO 10816-3 covers coupled industrial machines when

measured in situ, like ─ steam turbines up to 50 MW ─ steam turbine sets with power greater than 50 MW and

speeds below 1 500 r/min or above 3 600 r/min (which are not covered by ISO 10816-2)

─ compressors, industrial gas turbines with power up to 3 MW

─ generators, electric motors of any type, all blowers, fans with power greater than 300 kW and other fans that are not too flexibly mounted

─ pumps which are not dealt with by ISO 10816-7.

Figure 3 – Typical zone definition according to ISO 10816

Significant differences in design, type of bearings and type

of support structures require a division in ISO 10816-3 into two machinery groups, namely: Group 1: large machines with rated power above 300 kW or

electrical machines with shaft heights above 315 mm Group 2: medium-sized machines with a rated power above

15 kW up to and including 300 kW or electrical machines with shaft heights from 160 mm to 315 mm.

ISO 10816-4 covers gas turbine sets with fluid-film

bearings. It applies to heavy-duty gas turbines used in electrical and mechanical drive applications covering the power range above 3 MW and a speed range under load between 3 000 r/min and 30 000 r/min. Generally, the criteria apply to both the gas turbine and the driven equipment; however, for generators above 50 MW, the criteria of ISO 10816-2 are used for assessing the vibration severity, and for generators up to 50 MW, those of ISO 10816-3. ISO 10816-5 covers hydraulic machines when measured in

situ. It applies to machine sets in hydraulic power generation and pumping plants where the hydraulic machines have speeds from 120 r/min to 1 800 r/min, shell or shoe type sleeve bearings and main engine power of 1 MW or more. The position of the line shaft may be vertical, horizontal or at an arbitrary angle between these two directions. ISO 10816-6 covers reciprocating machines. In general, it

refers to vibration measurements made on the main structure of the machine and the limit values are defined primarily to secure a reliable and safe operation of the machine, and to avoid problems with the auxiliary equipment mounted on the machine structure. In the case of reciprocating machines, the vibration measured on the machine main structure, and qualified according to this International Standard, may only give a rough idea of the stresses and vibratory states of the components within the machine itself. E.g. torsional vibration of rotating parts cannot generally be determined by measurements on the structural parts of the machine. ISO 10816-7 covers pumps for industrial applications with

nominal power above 1 kW. It describes the requirements for evaluation of vibration measurements on non-rotating parts.

It also provides guidance for assessing the severity of vibration measured on the bearings, both in situ or at the manufacturer’s test facility, or in the plant. Zones and limits are provided for acceptance tests at the manufacturer’s test facility, if specified and special criteria are given. The included zone limits are for the vibration of horizontal and vertical pumps, irrespective of their support flexibility. For long-term operation, two additional criteria are provided. One criterion considers the magnitude of the observed vibration and the second considers changes in magnitude. The criteria are applicable for the vibration produced by the machine itself, and not for vibration transmitted to the machine from external sources. ISO 10816-8 covers reciprocating compressor systems. The

vibration values are defined primarily to classify the vibration of the compressor system and to avoid fatigue problems with parts in the reciprocating compressor system, i.e. foundation, compressor, dampers, piping and auxiliary equipment mounted on the compressor system. The guidelines are not intended for condition monitoring purposes. This part of ISO 10816 applies to reciprocating

compressors mounted rigidly with typical speed ratings greater than 120 r/min and up to and including 1 800 r/min. Guidance values for acceptable overall vibration displacement, velocity and acceleration for horizontal and vertical compressor systems are given. The general evaluation criteria relate to operational measurements. The criteria are also used to ensure that machine vibration does not adversely affect the equipment directly mounted on the machine, e.g. pulsation dampers and the pipe system.

B. ISO 7919 – Measurements made on rotating parts

ISO 7919-1 provides specific guidelines for vibration

measurements on the rotating shafts of machines. Such machines generally contain flexible rotor-shaft systems and changes in the vibration condition can be detected more decisively and more sensitively by measurements on these rotating elements. Also, machines having relatively stiff and/or heavy casings, in comparison to the rotor mass, are typical of those classes of machines for which shaft vibration measurements are frequently preferred. Machines such as industrial steam turbines, gas turbines

and turbo-compressors, all of which have several modes of vibration in their service speed range and their responses due to unbalance, misalignments, thermal bows, rubs and the unloading of bearings can be better observed by measurements on the shafts. There are three principle factors by which the vibration

magnitude of a machine is judged, namely:

─ bearing kinetic load

─ absolute motion of the rotor

─ rotor clearance relative to the bearing. If the bearing kinetic load is of concern to ensure against

bearing damage, the vibration of the shaft relative to the bearing structure should be monitored as the over-riding criteria. If the absolute motion of the shaft (a measure of rotor

bending stress) or rotor-bearing clearance are of concern, the type of measurement used depends on the vibration magnitude of the structure which supports the relative-motion transducer. Hence, if the vibration magnitude of this support structure is significant, the absolute shaft vibration will be the more valid measurement. The rotor clearance to the bearing needs to be monitored to ensure against rotor seal and blading rubs which can cause rotor or blading failures. The shaft vibration of machines, measured close to the

bearings, is evaluated on the basis of two criteria:

Criterion I: The reliable and safe running of a machine under normal operating conditions requires that the shaft vibration displacement remains below certain limits consistent with e.g. acceptable kinetic loads and adequate margins on the radial clearance envelope for the machine. The maximum shaft vibration is assessed against evaluation zones.

Criterion II: Changes in shaft vibration displacement, even

though the limits of Criterion I are not exceeded, can point to incipient damage or some other irregularity. Consequently, such changes relative to a reference value should not be allowed to exceed certain limits. If this reference value changes by a significant amount, steps should be taken to ascertain the reasons for the change and, if necessary, appropriate action taken. In this context, a decision on what action to take, if any, should be made after consideration of the maximum magnitude of the vibration, and whether the machine has stabilized at a new condition.

General guidelines for establishing evaluation zones under

steady-state operating conditions are described which provide the basis for the machine-specific evaluation criteria in the subsequent parts of ISO 7919. The definition and application of the different zones are the same as those adopted for ISO 10816 (Figure 4). ISO 7919-2 provides the special features required for

measuring shaft vibration on the coupled rotor systems of steam turbine generator sets for power stations, having rated speeds in the range of 1 500 r/min to 3 600 r/min, and power outputs greater than 50 MW. Evaluation criteria, based on experience, are presented which can be used as guidelines for assessing the vibratory conditions of such machines. The vibration magnitudes specified are for both relative and

absolute shaft vibration measured at, or close to, the main load carrying bearings, at rated speed and under steady-state conditions. Higher magnitudes of vibration can be permitted at other measuring positions and under transient conditions, such as start-up and run-down (including passing through resonance speed ranges). The recommended shaft vibration values for large steam

turbine generator sets measured relative to the bearings are included for relative shaft-to-bearing vibration and for absolute

shaft vibration. These limit values are graphically shown as severity zones. The definition of these zones is the same as that in ISO 7919-1. Also included are the bearing clearance effects on the zone boundaries.

Figure 4 – Typical zone definition according to ISO 7919 ISO 7919-3 gives guidelines for application of evaluation

criteria for shaft vibration measured close to the bearings under normal operating conditions. These guidelines are presented in terms of both steady-state conditions and any changes that can occur in these steady values. This International Standard applies to coupled industrial machines with fluid-film bearings, comprising: turbo compressors,

turbines, turbine generators and electric drives, all having maximum rated speeds in the range of 1 000 r/min to 30 000 r/min, and power between 30 kW and 50 MW. The numerical values specified are not intended to serve as

the only basis for acceptance specifications. In general, the vibratory condition of these machines is usually assessed by consideration of both the shaft vibration and the associated casing vibration. As a result, this International Standard should be used in conjunction with ISO 10816-3. ISO 7919-4 applies to industrial gas turbine sets (including

those with gears) with fluid-film bearings, power outputs greater than 3 MW and shaft rotational speeds from 3 000 r/min to 30 000 r/min. Aircraft type gas turbines are excluded, since they differ fundamentally from industrial gas turbines, both in the type of bearings (rolling element) and in the stiffness and mass ratios of the rotors and support structures. Depending on the construction and mode of operation,

there are three types of industrial gas turbines:

─ single-shaft constant-speed

─ single-shaft variable-speed

─ gas turbines having separate shafts for hot-gas

generation and power delivery. Guidelines are given for the application of criteria for shaft

vibration measured close to the bearings of industrial gas turbines under normal operating conditions.

ISO 7919-5 lists the special features required for

measuring shaft vibration on coupled hydraulic machine sets. This International Standard applies to all types of hydraulic machines having nominal speeds between 60 r/min and 3 600 r/min, with fluid-film bearings and rated power of 1 MW or more. These machines may consist of turbines, pumps, pump turbines, generators, motors and motor generators, including couplings, gears or auxiliary equipment in the shaft line. The position of the shaft may be vertical, horizontal or at an arbitrary angle between these two directions. The guidelines are given for the application of criteria for

shaft vibration measured close to the bearings of coupled hydraulic machine sets, under normal operating and steady-state conditions, and any changes that can occur in these steady values. The numerical values specified present rotor displacements relative to the bearings as a function of shaft rotational speed. Figure 5 shows the decision tree for selecting the

appropriate standard within the ISO 7919 and ISO 10816 series. It is planned within ISO/TC 108/SC 2 to combine and align the ISO 7919 and ISO 10816 series under the new unique number ISO 20816, but this project is not yet officially approved at this time.

C. Additional standards ISO 10817-1 gives details of how to obtain reproducible

measurement results in order to enable the monitoring and evaluation of shaft vibration according to the ISO 7919 series. As such, it is of importance primarily for the measurement of

shaft vibration of large machines (e.g. steam turbine generator sets, gas turbines, industrial turbo sets, and hydraulic machines). This part of ISO 10817 is applicable to radial vibration

measuring systems on shafts, both for absolute and relative measurements. It covers the sensing device (i.e. transducer), signal conditioning, attachment methods and calibration procedures.

Fig. 5 – Selection diagram for ISO 7919 and ISO 10816 series The standards series ISO 13373 "Vibration condition

monitoring" was also prepared by ISO/TC 108/SC 2. Part 1 of this series includes general guidelines for the measurement and data collection functions necessary for the assessment of machinery vibration for condition monitoring and diagnostics purposes. It is applicable to all kinds of rotating machinery and also describes the narrowband analysis procedures and techniques to perform discrete frequency analyses of the vibration signals, which are beyond the scope of the ISO 10816 and ISO 7919 series. Part 2 of the series ISO 13373 deals with processing, analysis and presentation of vibration data. Further parts of this standards series are currently under development (see IV. ISO/TC 108/SC 5).

D. ISO 14839 – Vibration of rotating machinery equipped with active magnetic bearings (AMB)

The ISO 14839 series deals with machines equipped with

active magnetic bearings. Part 1 gives the vocabulary. Part 2 addresses steady-state values of rotor vibration and the AMB coil current and voltage measured during nominal steady-state operation, but not the transient condition while passing through resonance speeds. The guidelines for transient vibration at resonance speeds are established in ISO 21940-31 (formerly ISO 10814) in which the modal sensitivity, the so-called amplification factor (Q-factor), is then evaluated. Because of the stiff support of oil-film bearings with small

clearances, shaft vibration should be regulated within low levels to avoid oil-film rupture of the lubricant and metal contact inside the bearing. In contrast, the relatively soft support of AMBs and correspondingly large clearances, a larger vibration level is often observed in AMB rotors, but is quite normal and acceptable. The lower stiffness introduces no major problems in the transmission force to the machine foundation. Compared to the oil-film bearing rotor standards (ISO 7919 series), ISO 14839-2 provides greater values of zone limits for vibration assessment and acceptance. ISO 14839-3 describes the evaluation of stability margin.

While passive bearings, e.g. ball bearings or oil-film bearings are essentially stable systems, magnetic bearings are inherently unstable due to the negative stiffness resulting from static magnetic forces. Therefore, a feedback control is required to provide positive stiffness and positive damping so that the active magnetic bearing operates in a stable equilibrium to maintain the rotor at a centred position. A combination of electromagnets and feedback control system is required to constitute an operable AMB system. In addition to ISO 14839-2 on evaluation of vibration of AMB

rotor systems, evaluation of the stability and its margin is necessary for safe and reliable operation of the AMB rotor system; this evaluation is specified in ISO 14839-3, the objectives of which are as follows: a) to provide information on the stability margin for mutual

understanding between vendors and users, mechanical engineers and electrical engineers, etc.

b) to provide an evaluation method for the stability margin that can be useful in simplifying contract concerns, commission and maintenance

c) to serve and collect industry consensus on the requirements of system stability as a design and operating guide for AMB equipped rotors. For evaluation of the stability margin, zone limits are given in

ISO 14839-3. The definition of each stability zone is determined by adapting the guidelines of ISO 7919-1. E. Balancing Currently, ISO/TC 108/SC 2 revises all rotor balancing

standards. Since confusion could arise because of the large quantity of appropriate standards with unsystematic numeration, re-numbering and revision was started to collect all balancing standards under the unique number ISO 21940.

The gaps in numbering allow for further parts in a systematic order. The current state is shown in Table 1.

ISO 21940 "Mechanical vibration — Rotor balancing"

New number Old number Status

ISO 21940-1

Introduction: Guidelines on the use and application of balancing standards

ISO 19499:2007 R

ISO 21940-2 Vocabulary

ISO 1925:1990 R

ISO 21940-11

Procedures and tolerances for rotors with rigid behaviour: Specification and verification of balance tolerances and balance quality

requirements

ISO 1940-1:2003 R

ISO 21940-12 Procedures and tolerances for rotors with flexible behaviour

ISO 11342:1998 R

ISO 21940-13:2012 Criteria and safeguards for the in-situ

balancing of medium and large rotors

ISO 20806:2009 I

ISO 21940-14:2012 Procedures for assessing balance errors

ISO 1940-2:1997 I

ISO 21940-21:2012 Description and evaluation of

balancing machines

ISO 2953:1999 I

ISO 21940-23:2012

Enclosures and other protective measures for the measuring station of balancing machines

ISO 7475:2001 I

ISO 21940-31

Susceptibility and sensitivity of machines to unbalance

ISO 10814:1996 R

(Draft)

ISO 21940-32:2012 Shaft and fitment key convention

ISO 8821:1989 I

Symbols for balancing machines and associated instrumentation

ISO 3719:1994 W

Status code:

I = Issued as ISO standard R = Currently under revision W = Withdrawn

Table 1 – Renumbering of ISO standards for rotor balancing

IV. ISO/TC 108/SC 5

The other sub-committee of ISO/TC 108 which is relevant to

the in-situ running condition of machinery is SC 5 "Condition monitoring and diagnostics of machine systems". The International Standards prepared by SC 5 are concerned with methods of monitoring the physical state of a machine when running in situ by monitoring vibration, temperature, acoustic emission, electric current, etc.

SC 5 consists of the following working groups:

AG A "Vibration condition monitoring procedures and instrumentation used for the purposes of diagnostics"

AG E "Strategic planning" WG 1 "Terminology" WG 2 "Data interpretation and diagnostics techniques" WG 3 "Performance monitoring and diagnostics" WG 4 "Tribology-based monitoring and diagnostics" WG 5 "Prognostics" WG 6 "Formats and methods for communicating, presenting

and displaying relevant information and data" WG 7 "Training and accreditation in the field of condition

monitoring and diagnostics" WG 8 "Condition monitoring and diagnostics of machines" WG 10 "Condition monitoring and diagnostics of electrical

equipment" WG 11 "Thermal imaging" WG 14 "Acoustic techniques" WG 15 "Ultrasound" WG 16 "Condition monitoring and diagnostics of wind

turbines" WG 8 also deals with the vibration behaviour of industrial

machines. The introductory document is ISO 17359 "Condition monitoring and diagnostics of machines – General guidelines". It is the parent document of a group of standards which cover the field of condition monitoring and diagnostics, outlining general procedures to be considered when setting up a condition monitoring program. This standard also includes references to other International Standards and other documents which are required or useful in this process. Recently, the project ISO 17359-2 "Condition monitoring and diagnostics of machines – Part 2: Parameter selection and set-up" was established in SC 5. Figure 6 gives an overview about the most important ISO

standards for condition monitoring.

Fig. 6 – Most important ISO condition monitoring standards

ISO 13373 is the standards series for vibration condition

monitoring which is a central topic in most condition monitoring

systems. This ISO series is edited by SC 2 as already mentioned but since it is crucial to vibration condition monitoring it is discussed here in detail. ISO 13373-1 provides general guidelines for the

measurement and data collection functions of machinery vibration for the purposes of condition monitoring. It is intended to promote consistency of measurement procedures and practices which usually concentrate on rotating machines. In this International Standard, the principles of vibration

condition monitoring programs are outlined, see Figure 7. Furthermore it covers all basic principles for ─ Measurement methods ─ Measurement parameters ─ Transducer selection ─ Transducer location ─ Transducer attachment ─ Data collection ─ Machine operating conditions ─ Vibration monitoring systems ─ Signal conditioning systems ─ Interfaces with data-processing systems ─ Continuous monitoring and periodic monitoring. A table of the most common causes of machinery vibration

is given in Annex C of ISO 13373-1. ISO 13373-2 describes procedures for processing and

presenting vibration data and analyzing vibration signatures for the purposes of monitoring the vibration condition of rotating machinery, and performing diagnostics as appropriate. ISO 13373-3 is still under development. It is intended to

provide general guidelines for vibration condition monitoring for a range of machinery. Guidance for specific machines will be provided in other parts of this standards series as planned:

Part 4 – Diagnosis of steam turbines Part 5 – Diagnosis of fans and blowers Part 6 – Diagnosis of gas turbines Part 7 – Diagnosis of hydraulic power generation and pumping plants Part 8 – Diagnosis of industrial pumps Part 9 – Diagnosis of electric motors Part 10 – Diagnosis of generators Part 11 – Diagnosis of gearboxes. Diagnostics is a collective designation for procedures and

methods to identify a failure mode in case of a fault indicated by a monitoring system. For vibration based condition monitoring, the most common vibration causes useful for diagnosis are described in ISO 13373-1, Annex C, see also Table 2. However, this method will handle different vibration parameters separately, independent from each other. General procedures that can be used to determine the condition of a machine relative to a set of baseline parameters are described in the standard series ISO 13379. However, although this standard exceeds vibration-based methods and includes also other condition monitoring methods in a multivariate system it is mentioned here since vibration will be the most important feature in most cases.

Fig. 7 – Vibration condition monitoring flowchart according to ISO 13373-1

Cause Characteristic vibration frequencies

Remarks

(Phase measurements can give additional information for many causes)

Unbalance 1x (i.e. once per revolution)

Changes in balance will give changes in 1x vector. Vibration will be highest when running speed coincides with a rotor system critical speed. Significant vibration phase change will occur when passing through critical speeds. At a fixed speed vibration magnitudes are constant.

Bearing misalign-ment

1x or higher harmonics

Parallel or angular bearing misalignment is generally caused by foundation movements. Bearing misalignment is not a direct cause of vibration excitation but changes the dynamic characteristics of the support system.

Shaft misalign-ment

1x, 2x or higher harmonics

Angular/parallel misalignment due to coupling geometric inaccuracies. It introduces vibration excitation due to shaft bending. In some cases, the axial vibration component may be of similar magnitude to the radial components.

Journal bearing operating condition/ geometry

Subsynchronous or 1x, 2x, 3x

Changes in the bearing operating conditions or geometry can cause changes in the steady-state vibration at 1x and higher harmonics, or cause subsynchronous instability (oil or steam whirl). In the latter case the vibration is usually unsteady and can increase with time, often rapidly.

Rolling element bearing wear

Wideband acceleration at high frequency

Detection requires transducers with high-frequency response. Vibration tends to be localized to the region of the defective bearing. Vibration readings are usually unsteady and increase with time. Other techniques may be necessary to characterize the type of fault.

Stiffness dissym-metry (e.g. axial winding slots in generator/motor rotors)

2x Vibration peaks when a 2x stimulus is coincident with a rotor critical speed. At a fixed rotor speed vibration magnitudes are constant. Compensation grooves are used on large machines to minimize the stimulus.

Bent rotor

(see also thermal dissym-metry)

1x, 2x or higher harmonics

Change of 1x is most common. If the rotor is bent near the coupling, a high 2x axial vibration is frequently observed. At a fixed speed the rotor vibration values are constant.

Cracked rotor

1x, 2x or higher harmonics

A growth in the 2x vector is an indication that the growth of a transverse crack is getting critical. Changes in the 1x or higher harmonic vectors can also occur.

Compo-nent looseness in rotor

1x and harmonics of running speed frequency

Vibration values may be erratic and inconsistent between successive start-stop cycles. Sometimes subharmonic frequencies are also observed.

Eccentric or non-circular journals

1x and for non-circular journals at harmonics of running speed frequency

Vibration values can be abnormal or excessive at low rotor speeds as well as at rotor critical speeds. At a fixed rotor speed the vibration values are constant.

Thermal dissym-metry

1x Can be caused by non-uniform rotor ventilation or shorted electrical windings or non-uniform tightness of parts. Causes rotor to bow with the same vibration characteristics as for unbalance.

Gear defects

High frequencies corresponding to harmonics of gear mesh/rotational frequency and associated sidebands

Detection requires transducers with high-frequency responses.

For defect in one tooth: 1x and multiples.

For worn teeth: Gear mesh frequencies with sidebands and multiples.

Resonan-ce

At the excitation frequencies such as when rotor speed equals a natural frequency of the rotor/support system

Vibration magnification occurs at each machine resonant speed and large phase angle changes are evident in the 1x response as the rotor passes through critical speeds. Rotor unbalance is also the most common stimulus which can produce resonant responses of the machine in its non-rotating systems. On electric machines, the other major stimulus is at 2x which results from electromagnetic forces that the rotor induces on the stator.

Rubs Most commonly 1x, but also multiples of 1x, subsynchronous frequencies and natural frequencies

Slight rubs that are initiated at low speed may clear themselves. However, rubs that are initiated at high speed may result in an abrupt change in vibration that rises rapidly to a magnitude that requires machine shut-down. Sometimes rubs occur due to machines being loaded too rapidly or as a result of sudden changes in the thermal condition within the machine. In other cases rubs may result from clearances being set too small between rotating and stationary parts, or a result of parts shifting during service.

Table 2 – Most common causes of machinery lateral

vibration and resulting vibration characteristics (ISO 13373-1)

ISO 13379 is the ISO series on data interpretation and

diagnostic techniques. Part 1 "General guidelines" gives guidance for the data interpretation and diagnostics of machines. Further parts are currently under development in SC 5: Part 2 – Data-driven applications Part 3 – Knowledge based applications. Figure 8 shows the subdivision of the central condition

monitoring standards in several parts. ISO 13373 is specialized on vibration condition monitoring, whereas ISO 13379 exceeds the field of vibration, outlining the principles of multivariate condition monitoring systems.

Fig. 8 – Details of central ISO condition monitoring standards

Nowadays, certification is an important topic in condition monitoring. The ISO 18436 series (see Figure 9) maintains the basis documents for qualification and assessment of personnel in the field of condition monitoring. Part 2 defines the requirements for vibration condition monitoring and diagnosis personnel.

Fig. 9 – ISO 18436 standards for qualification and certification of personnel

Furthermore, there is a couple of standards dedicated to

special machine types as shown in Figure 10. ISO 19860 for gas turbines already exists. ISO 16079 is a new project for wind turbines, based on today’s knowledge that is recorded in VDI 3834 and the German Lloyd Guideline for the Certification of Condition Monitoring Systems for Wind Turbines. This standard will be updated later by further parts as the knowledge increases. In addition, a liaison to IEC/TC 88 Wind turbines is maintained.

Fig. 10 – ISO standards dedicated to special machine types

Besides the common standards as mentioned before, there are further International Standards dealing with data processing, communication and presentation (ISO 13374) or signal processing (ISO 18431). An overview is given in ISO/TR 19201 "Methodology for selecting appropriate machinery vibration standards". ISO 2041 gives the vocabulary for mechanical vibration,

shock and condition monitoring while ISO 13372 defines the vocabulary for condition monitoring and diagnostics of machines. However, although vibration measurement and analysis will

in most cases be the central part of a monitoring system, a strict limitation to vibration topics will not be useful any more. This is clearly reflected in the development of the standards of ISO/TC 108/SC 5.

There are a couple of standards of interest from other TCs. Two of them should be mentioned here: ISO 19859 "Gas turbine applications — Requirement for power generation" (currently draft) established by ISO/TC 192 "Gas turbines". Normative references include the relevant ISO 10816 and ISO 7919 vibration standards. ISO 19860 "Gas turbines — Data acquisition and trend monitoring system requirements for gas turbine installations" also established by ISO/TC 192. This standard applies to data acquisition and trend monitoring systems for gas turbine installations and associated systems. It classifies and defines monitoring systems and their technical terms. For these very complex systems with extremely important safety aspects (e.g. for aircraft engines), performance monitoring concepts covering multiple operational and other parameters (not only restricted to unique quantities such as vibrations) are very important to prevent failures and to keep the safety on a high level. The following future project is in progress in SC 5:

ISO 18129 "Condition monitoring and diagnostics of machines — Approaches for performance diagnosis".

V. REFERENCES

The following reference list gives an overview of publicly

available International Standard concerning machine vibration and condition monitoring. Some of the references are not mentioned in the text body but listed for completeness. [1] ISO 1925, Mechanical vibration — Balancing —

Vocabulary

[2] ISO 1940-1, Mechanical vibration — Balance quality requirements for rotors in a constant (rigid) state — Part 1: Specification and verification of balance tolerances

[3] ISO 2041, Mechanical vibration, shock and condition

monitoring — Vocabulary

[4] ISO 2954, Mechanical vibration of rotating and reciprocating machinery — Requirements for instruments for measuring vibration severity

[5] ISO 3719, Symbols for balancing machines and associated instrumentation (withdrawn)

[6] ISO 4866, Mechanical vibration and shock — Vibration of fixed structures — Guidelines for the measurement of vibrations and evaluation of their effects on structures

[7] ISO 5348, Mechanical vibration and shock — Mechanical mounting of accelerometers

[8] ISO 7919-1, Mechanical vibration of non-reciprocating machines — Measurements on rotating shafts and evaluation criteria — Part 1: General guidelines

[9] ISO 7919-2, Mechanical vibration — Evaluation of machine vibration by measurements on rotating shafts — Part 2: Land-based steam turbines and generators in excess of 50 MW with normal operating speeds of 1500 r/min, 1800 r/min, 3000 r/min and 3600 r/min

[10] ISO 7919-3, Mechanical vibration — Evaluation of machine vibration by measurements on rotating shafts — Part 3: Coupled industrial machines

[11] ISO 7919-4, Mechanical vibration — Evaluation of machine vibration by measurements on rotating shafts — Part 4: Gas turbine sets with fluid-film bearings

[12] ISO 7919-5, Mechanical vibration — Evaluation of machine vibration by measurements on rotating shafts — Part 5: Machine sets in hydraulic power generating and pumping plants

[13] ISO 8528-9, Reciprocating internal combustion engine driven alternating current generating sets — Part 9: Measurement and evaluation of mechanical vibrations

[14] ISO 8579-2, Acceptance code for gears — Part 2: Determination of mechanical vibrations of gear units during acceptance testing

[15] ISO 10814, Mechanical vibration — Susceptibility and sensitivity of machines to unbalance

[16] ISO 10816-1, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 1: General guidelines (plus Amendment 1)

[17] ISO 10816-2, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 2: Land-based steam turbines and generators in excess of 50 MW with normal operating speeds of 1500 r/min, 1800 r/min, 3000 r/min and 3600 r/min

[18] ISO 10816-3, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 3: Industrial machines with nominal power above 15 kW and nominal speeds between 120 r/min and 15000 r/min when measured in situ

[19] ISO 10816-4, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 4: Gas turbine sets with fluid-film bearings

[20] ISO 10816-5, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 5: Machine sets in hydraulic power generating and pumping plants

[21] ISO 10816-6, Mechanical vibration — Evaluation of machine vibration by measurements on non-rotating parts — Part 6: Reciprocating machines with power ratings above 100 kW

[22] ISO 10816-7, Mechanical vibration — Evaluation of

machine vibration by measurements on non-rotating parts — Part 7: Rotodynamic pumps for industrial applications, including measurements on rotating shafts

[23] ISO 10816-8, Mechanical vibration — Evaluation of

machine vibration by measurements on non-rotating parts — Part 8: Reciprocating compressor systems (draft)

[24] ISO 10817-1, Rotating shaft vibration measuring

systems — Part 1: Relative and absolute sensing of radial vibration

[25] ISO 11342, Mechanical vibration — Methods and criteria

for the mechanical balancing of flexible rotors

[26] ISO 13372, Condition monitoring and diagnostics of machines — Vocabulary

[27] ISO 13373-1, Condition monitoring and diagnostics of machines — Vibration condition monitoring — Part 1: General procedures

[28] ISO 13373-2, Condition monitoring and diagnostics of

machines — Vibration condition monitoring — Part 2: Processing, analysis and presentation of vibration data

[29] ISO 13374-1, Condition monitoring and diagnostics of

machines — Data processing, communication and presentation — Part 1: General guidelines

[30] ISO 13374-2, Condition monitoring and diagnostics of machines — Data processing, communication and presentation — Part 2: Data processing

[31] ISO 13374-3, Condition monitoring and diagnostics of machines — Data processing, communication and presentation — Part 3: Communication

[32] ISO 13379-1, Condition monitoring and diagnostics of machines — Data interpretation and diagnostics techniques — Part 1: General guidelines

[33] ISO 13381-1, Condition monitoring and diagnostics of

machines — Prognostics — Part 1: General guidelines

[34] ISO 14694, Industrial fans — Specifications for balance quality and vibration levels

[35] ISO 14695, Industrial fans — Method of measurement of fan vibration

[36] ISO 14839-1, Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 1: Vocabulary (plus Amendment 1)

[37] ISO 14839-2, Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 2: Evaluation of vibration

[38] ISO 14839-3, Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 3: Evaluation of stability margin

[39] ISO 14839-4, Mechanical vibration — Vibration of rotating machinery equipped with active magnetic bearings — Part 4: Technical guidelines

[40] ISO 15242 (all parts), Rolling bearings — Measuring methods for vibration

[41] ISO 17359, Condition monitoring and diagnostics of machines — General guidelines

[42] ISO 18431 (all parts), Mechanical vibration and shock — Signal processing

[43] ISO 18436 (all parts), Condition monitoring and diagnostics of machines — Requirements for qualification and assessment of personnel

[44] ISO/TR 19201, Mechanical vibration — Methodology for selecting appropriate machinery vibration standards

[45] ISO 19499, Mechanical vibration — Balancing — Guidance on the use and application of balancing standards

[46] ISO 19859, Gas turbine applications — Requirement for power generation (draft)

[47] ISO 19860, Gas turbines — Data acquisition and trend monitoring system requirements for gas turbine installations

[48] ISO 20283-4, Mechanical vibration — Measurement of vibration on ships — Part 4: Measurement and evaluation of vibration of the ship propulsion machinery

[49] ISO 21940-13, Mechanical vibration — Rotor balancing — Part 13: Criteria and safeguards for the in-situ balancing of medium and large rotors

[50] ISO 21940-14, Mechanical vibration — Rotor balancing — Part 14: Procedures for assessing balance errors

[51] ISO 21940-21, Mechanical vibration — Rotor balancing — Part 21: Description and evaluation of balancing machines

[52] ISO 21940-23, Mechanical vibration — Rotor balancing — Part 23: Enclosures and other protective measures for the measuring station of balancing machines

[53] ISO 21940-31, Mechanical vibration — Rotor balancing — Part 31: Susceptibility and sensitivity of machines to unbalance (draft)

[54] ISO 21940-32, Mechanical vibration — Rotor balancing — Part 32: Shaft and fitment key convention

[55] ISO 22266-1, Mechanical vibration — Torsional vibration of rotating machinery — Part 1: Land-based steam and gas turbine generator sets in excess of 50 MW

[56] IEC 60034-14, Rotating electrical machines — Part 14: Mechanical vibration of certain machines with shaft heights 56 mm and higher — Measurement, evaluation and limits of vibration severity

[57] IEC 60994, Guide for field measurement of vibrations and pulsations in hydraulic machines (turbines, storage pumps and pump-turbines)

[58] API 541, Form-wound squirrel-cage induction motors — 500 horsepower and larger

[59] API 546, Brushless synchronous machines — 500 kVA

and larger

[60] API 547, General purpose form-wound squirrel cage induction motors — 250 horsepower and larger

[61] API 617, Axial and centrifugal compressors and expander-compressors for petroleum, chemical and gas industry services

[62] API RP 684, Paragraphs rotodynamic tutorial: lateral

critical speeds, unbalance response, stability, train torsionals and rotor balancing

VI. VITA

Dr. Horst Kuemmlee is the head of the Research and Developement Department for large electrical machines in the Large Drives Division of the Siemens Industrial Sector in the Siemens Dynamowerk in Berlin, Germany. He is responsible for the basic mechanical and electrical design, rotor dynamics, simulation of electro-mechanical systems, measurement procedures and systems and standardization. He worked at Siemens Dynamowerk since 1985 as research engineer, head of the Special Machines Order Processing and Design Department and in his current position. He is member or chair of several working groups within ISO, IEC, DIN, VDI and API. Dr. Kuemmlee graduated from Technical University of Berlin

with a Dipl.-Ing. degree in Mechanical Engineering (1980). He has received the degree Dr.-Ing. for his work on Hyperelastic Coupling Elements and Dampers (1985).

Thomas Gross is member of staff of DIN Deutsches Institut fuer Normung in Berlin since 1991. He is associated with the department Acoustics, Noise control and Vibration. Since mid 2013 he is Secretary of ISO/TC 108/SC 2 and since many years already Secretary of some ISO and a couple of DIN working groups. Thomas Gross graduated from Technical University of Berlin

with a Dipl.-Ing. degree in Mechanical Engineering (1982). From 1984 to 1989 he was scientific fellow for acoustics at the same university. Prof. Dr. Josef Kolerus was graduated from Technical

University of Vienna with a Dip.-Ing. degree in Physics (1965) and has received the degree of Dr. of technical sciences at the department of mechanical engineering for his work self-excited vibrations (1971). After some years with Bruel & Kjaer he was employed at Mueller-BBM, a consulting company for acoustics and vibration in Munich until 2004. Nowadays he still working as a consultant for vibration

analysis and condition monitoring. Additionally he gives lectures at the Technical University of Vienna for machinery monitoring and acoustics. He is member and chair of several working groups within ISO, DIN and VDI.