Disclaimer: The author is not trying to present himself as an authority on all available CM standards. This blog post is simply an attempt to help those who may be unaware that such guidance exists or of the extent of such standards.

Are you looking for some guidance on a well-designed approach to condition monitoring and/or acceptance criteria for some types or categories of equipment? The International Standards Organization (ISO) has brought together standards groups from around the world and compiled excellent general guidelines for the condition monitoring (and in some cases acceptance testing) of many major groups of machine types.

The U.S. participant in the development of the standards is the American National Standards Institute (ANSI). ANSI itself has hundreds if not thousands of member societies that are well represented on the sub-committees such as the sub-committee “ISO/TC 108/SC 2” which is responsible for the development of the ISO 20816-1 standard. Many of the members of ANSI are quite recognizable to those of us who have been around the industry for some time including ASHRAE, ASME, SAE, ABMA, AGMA, ASNT, AWEA, HI, and API.

If you are interested in standardized guidance to condition monitoring on your equipment, then consider beginning with the standard “ISO 20816-1” which is the compilation of the general vibration monitoring guidelines for numerous other standards, each of which applies to a specific group of equipment types. The current standard was completed in 2016 and is titled:

ISO 20816-1: 2016

Mechanical vibration – Measurement and evaluation of machine vibration

Part 1: General guidelines

The scope of this standard is quoted below from the ISO.org preview page (quotation in bold listed below):

Scope:

This document establishes general conditions and procedures for the measurement and evaluation of vibration using measurements made on rotating, non-rotating and non-reciprocating parts of complete machines. It applies to both absolute and relative radial shaft vibration measurements concerning the monitoring of radial clearances but excludes axial shaft vibration. The general evaluation criteria, presented in terms of both vibration magnitude and change of vibration, relate to both operational monitoring and acceptance testing. They have been provided primarily concerning securing the reliable, safe, long-term operation of the machine while minimizing adverse effects on associated equipment. Guidelines are also presented for setting operational limits.

NOTE 1 The evaluation criteria for different classes of machinery will be included in other parts of ISO 20816 when they become available. In the meantime, guidelines are given in Clause 6.

NOTE 2 The term “shaft vibration” is used throughout ISO 20816 because, in most cases, measurements are made on machine shafts. However, the ISO 20816 series is also applicable to measurements made on other rotating elements if such elements are found to be more suitable, provided that the guidelines are respected.

For the purposes of ISO 20816, operational monitoring is considered to be those vibration measurements made during the normal operation of a machine. The ISO 20816 series permits the use of different measurement quantities and methods, provided that they are well-defined and their limitations are set out so that the interpretation of the measurements is well-understood.

The evaluation criteria relate only to the vibration produced by the machine itself and not the vibration transmitted to it from the outside.

This document does not include consideration of torsional vibration.

To read the ISO’s preview of this standard, click here.

Stay tuned as we will be introducing other standards in this xx816 track in the coming weeks, beginning today with the current part 2, which was completed in 2017:

ISO 20816-2: 2017

Mechanical vibration – Measurement and evaluation of machine vibration

Part 2: Land-based gas turbines, steam turbines, and generators over 40 MW, with fluid-film bearings and rated speeds of 1 500 r/min, 1 800 r/min, 3 000 r/min, and 3 600 r/min

The scope of this standard is quoted below from the ISO.org preview page (quotation in bold listed below):

Scope:

This document applies to land-based gas turbines, steam turbines, and generators (whether coupled with gas and/or steam turbines) with power outputs greater than 40 MW, fluid-film bearings, and rated speeds of 1 500 r/min, 1 800 r/min, 3 000 r/min or 3 600 r/min. The criteria provided in this document can be applied to the vibration of the gas turbine, steam turbine, and generator (including synchronizing clutches). This document establishes provisions for evaluating the severity of the following in-situ, broad-band vibration:

1. structural vibration at all main bearing housings or pedestals measured radial (i.e. transverse) to the shaft axis;
2. structural vibration at thrust bearing housings measured in the axial direction;
3. vibration of rotating shafts radial (i.e. transverse) to the shaft axis at, or close to, the main bearings.

These are in terms of the following:

• vibration under normal steady-state operating conditions;
• vibration during other (non-steady-state) conditions when transient changes are taking place, including run up or run down, initial loading and load changes;
• changes in vibration which can occur during normal steady-state operation.

This document does not apply to the following:

1. electromagnetic excited vibration with twice line frequency at the generator stator windings, core, and housing;
2. aero-derivative gas turbines (including gas turbines with dynamic properties similar to those of aero-derivatives) 
   • NOTE ISO 3977-3 defines aero-derivatives as aircraft propulsion gas generators adapted to drive mechanical, electrical, or marine propulsion equipment. Large differences exist between heavy-duty and aero-derivative gas turbines, for example, in casing flexibility, bearing design, rotor-to-stator mass ratio, and mounting structure. Different criteria, therefore, apply for these two turbine types.
3. steam turbines and/or generators with outputs less than or equal to 40 MW or with rated speeds other than 1 500 r/min, 1 800 r/min, 3 000 r/min, or 3 600 r/min (although generators seldom fall into this latter category) (see ISO 7919-3 and ISO 10816-3);
4. gas turbines with outputs less than or equal to 40 MW or with rated speeds other than 1 500 r/min, 1 800 r/min, 3 000 r/min or 3 600 r/min (see ISO 7919-3or ISO 7919-4and ISO 10816-3 or ISO 10816-4);
5. the evaluation of combustion vibration but does not preclude monitoring of combustion vibration.

To read the ISO’s preview of this standard, click here. Check out the standards. If they sound like they may be helpful to you, they can be purchased at numerous places on the web including the ANSI website, ISO store, and/or the one I use, Techstreet store.

An analyst or organization using these standards should be aware that RMS overall velocity from 600cpm to 60kcpm (or 10Hz to 1kHz – the primary quantity used in the standard) does a fairly good job generally gauging the effect of things like unbalance, misalignment, mechanical looseness, resonance involvement, and even some electrical problems characterized by single-digit multiples of the line frequency, but may not give an acceptably early warning for several failure modes and certainly not for bearing defects in many cases. The overall or “unfiltered” measurement is not intended in any way to identify the source or cause of the vibration.

There is an ISO standard that is targeted to provide guidance on diagnosing specific faults (ISO 13373) which will likely be the subject of a future blog post after finishing the series on the xx816 family of standards.