Reference Standards for Vibration Monitoring and Analysis

Standards are documented agreements containing technical specifications or other precise criteria to be used consistently as rules, guidelines, or definitions of characteristics, to ensure that materials, products, processes and services are fit for their purpose. A good standard represents consensus of opinion, is easy to use, and contains no ambiguities or loopholes.

In the field of machinery vibration monitoring and analysis, a variety of relevant standards are developed and published by ISO (International Organization for Standardization). ISO is a worldwide federation of national standards bodies from 145 countries, and considers itself a bridge between the public and private sectors.

In addition to ISO, various trade organizations such as National Electrical Manufacturers  Association (NEMA) and American Petroleum Institute (API) have developed and published vibration standards, which are widely accepted and applied (and therefore relevant). In most cases, these standards have been developed by consensus of consumers and manufacturers, and their use is considered voluntary.

Most of the ISO standards for machinery vibration monitoring and analysis are guided by technical committee TC108, Mechanical vibration and shock. TC108 is comprised of 22 Participating (P-member) countries and 25 Observer countries. As of May 2003, there are a total of 98 published ISO standards related to TC108 and its SCs (subcommittees). Noteworthy subcommittees include; SC1, Balancing, including balancing machines, SC2, Measurement and evaluation of mechanical vibration and shock as applied to machines, vehicles and structures, and SC5, Condition monitoring and diagnostics of machines .

Standards for evaluation of vibration severity are considered one of the most important activities of ISO/TC108. Unfortunately, due to the range of machinery categories and classifications, itmay also be the most confusing. A wide variety of published standards describe acceptablevibration limits, including the ISO/7919 series (5 parts) “Mechanical vibration of nonreciprocating machines – Measurements on rotating shafts and evaluation criteria” and the ISO/10816 series (6 parts) “Mechanical vibration – Evaluation of machine vibration by measurements on non-rotating parts”.

As detailed in Table 1, ISO 7919-1 is the basic document describing the general requirements for
measurement and evaluation of machinery vibration using shaft measurements. Similarly, ISO 10816-1 is the basic document describing the general requirements for evaluating machinery vibration using casing and/or foundation measurements. Subsequent parts of each series of documents apply to different classes and types of machinery, and include specific evaluation criteria used to assess vibration severity .

The evaluation procedures in the ISO/7919 and ISO/10816 series of standards are limited to broadband measurements, without reference to frequency components or phase. Measurement procedures are detailed in Part 1: General Guidelines of each series, including shaft relative, shaft absolute, and pedestal vibration measurements

At the May 13 – 16, 2003 meeting of ISO/TC108/SC2, Professor Hiroshi Kanki of Japan proposed “Guidelines for selecting vibration evaluation methods by measurement on the rotating shaft and/or on non-rotating parts”, referred to as the “umbrella document”. The scope of the umbrella document is to provide general guidelines for selecting the appropriate vibration standards for a specific machinery classification. The proposed method includes 2 key evaluation criteria; 1) shaft displacement from the journal centerline, and 2) stiffness ratio of pedestal to bearing (which determines the ratio of the shaft relative vibration to the pedestal vibration) .

In general, machines equipped with rolling element bearings will tend to have high bearing stiffness, a stiffness ratio less than 1, and are better suited to vibration measurements at the pedestal and/or casing. Conversely, machines using fluid film bearings and supported on relatively soft pedestals, will have a much higher stiffness ratio, and are better suited to shaft vibration measurements.

Vibration Magnitude is defined within this group of standards as the maximum value of the broadband rms velocity in the specified frequency range (typically from 10 to 1,000 Hz), as evaluated on the structure at prescribed points. Note that other quantities such as displacement or acceleration and peak values instead of rms values are permitted, but may not easily correlate to criteria based on rms values. Evaluation criteria to assess vibration severity include both vibration magnitude and changes in vibration magnitude.

ISO Standards For Vibration Measurements
ISO 13373-1:2001 Condition monitoring and diagnostics of machines — Vibration condition monitoring — Part1: General procedures provides general guidelines for the measurement of machinery vibration for condition monitoring. Recommendations are provided for the following;

• measurement methods and parameters .
• transducer selection, location, and attachment
• data collection
• machine operating conditions
• vibration monitoring systems
• signal conditioning systems
• interfaces with data processing systems
• continuous and periodic monitoring

Due to the wide variety of approaches to condition monitoring, specific topics will be addressed in more detail in additional parts of 13373. At the time of writing this article, Part 2: Processing, analysis and diagnostics is at the committee draft stage.

ISO 17359:2003 Condition monitoring and diagnostics of machines — General guidelines sets out guidelines for the general procedures to be considered when setting up a condition monitoring program.

ISO Standards For Training and Certification
ISO standards for personnel training and certification are a relatively new and significant initiative for ISO/TC108. In August, 2003, ISO 18436-2:2003 Condition monitoring and diagnostics of machines — Requirements for training and certification of personnel — Part 2: Vibration condition monitoring and diagnostics received an affirmative vote at the FDIS stage, and was affirmed as an international standard. 18436-2 describes a 4-category scheme for certification of vibration analysis personnel who perform condition monitoring and diagnostics.

Certification candidates are required to meet prerequisite education, training, and experience, and successfully pass a qualification examination.

Future parts of the 18436 series will include;
1. Part 1: Requirements for certifying bodies and the certification process
2. Part 3: Requirements for training bodies
3. Part 4: Lubrication management and analysis
4. Part 5: Thermography
5. Part 6: Diagnostics and prognostics
6. Part 7: Condition monitoring specialists
7. Part 8: Balancing

American Petroleum Institute (API) Standard
API produces a wide range of documents, including reference standards which are well suited for shop testing of new and rebuilt machinery. Note that these standards generally apply to equipment for use in the petrochemical industries, below, shows a selection of API standards.