ISO 20816-3: Mechanical vibration – Measurement and evaluation of machine vibration – Part 3: Industrial machines

Summary

ISO 20816-3 is the current, modern standard that provides specific numerical values for acceptable vibration of common industrial machines. It is the direct, practical application of the general framework established in ISO 20816-1 and serves as the official replacement for the widely used ISO 10816-3. This standard is a critical, day-to-day document for reliability engineers and maintenance technicians for assessing machine condition based on vibration measurements taken on non-rotating parts (e.g., bearing housings).

Table of Contents (Conceptual Structure)

The standard follows the structure of its predecessor but with updated criteria, providing a clear guide for practical application:

1. 1. Scope:

   This initial chapter clearly defines the boundaries of the standard’s application. It specifies that these guidelines are intended for industrial machines with power ratings above 15 kW and operating speeds between 120 RPM and 15,000 RPM. The scope is focused on common industrial machinery such as pumps, electric motors, compressors, and fans. Crucially, it clarifies that the evaluation criteria provided are for in-situ broadband measurements taken on the non-rotating parts of the machine (e.g., bearing housings) under normal, steady-state operating conditions. This section sets the stage by ensuring the user knows precisely which machines and under what conditions this standard’s valuable numerical limits can be reliably applied.

2. 2. Machine Classification (Groups):

   This chapter is the most critical for the correct application of the standard, as the vibration limits are entirely dependent on the machine’s classification. The standard groups machines based on their size (power rating), the type of driver (motor, turbine, etc.), and the flexibility of their support foundation. The primary groups are:

   • Group 1: Large machines, typically with power ratings above 300 kW, mounted on heavy, rigid foundations (e.g., large concrete blocks). Examples include large power generation turbines and major process pumps.
   • Group 2: Medium-sized machines, with power ratings between 15 kW and 300 kW, also mounted on rigid foundations. This is the most common category, covering a majority of standard industrial pumps, fans, and electric motors.
   • Group 3 & 4: These groups cover large (Group 3) and medium-sized (Group 4) machines that are mounted on lightweight, flexible support structures (e.g., steel skids or vibration isolators). The standard provides a technical definition for a flexible foundation based on whether the machine’s first natural frequency is above or below its main operating speed.

   Correctly identifying which group a machine belongs to is the essential first step before the vibration severity charts can be used.

3. 3. Vibration Severity Zone Values (The Chart):

   This is the practical core of the standard, providing the definitive numerical values for vibration assessment. The section contains tables that clearly list the specific RMS Velocity levels (in mm/s and inches/s) which form the boundaries between the four evaluation zones (A/B, B/C, and C/D). These values are provided for each of the machine groups defined in the previous chapter. For instance, a user can look up “Group 2” for medium-sized machines on rigid foundations and find the exact velocity values. The table might specify that for this group, the boundary between Zone B (unrestricted long-term operation) and Zone C (unsuitable for long-term operation) is 4.5 mm/s. This allows a technician to take a measurement, compare it directly to the table, and make an immediate, standards-based judgment on the machine’s health.

4. Guidance on Alarm Settings:

   This final section provides practical advice on how to translate the evaluation zone boundaries into effective operational alarms for continuous or periodic monitoring. It reinforces the two-level alarm strategy recommended in ISO 20816-1. The first level, the Alert alarm, is typically set at a level that indicates the machine’s vibration has significantly increased from its normal baseline or has entered Zone C. This serves as an early warning that warrants investigation and analysis. The second, higher level, the Trip or Danger alarm, is an absolute limit that should not be exceeded. This is often set at the boundary between Zone C and Zone D. Breaching this limit indicates a high probability of severe damage, and it should trigger immediate action, potentially including an automatic shutdown of the machine to prevent a catastrophic failure. This guidance allows operators to move from simple assessment to proactive, automated machine protection.

Key Concepts and Updates

• Direct Replacement for ISO 10816-3: This standard is the official successor to ISO 10816-3. While the fundamental approach is the same, the numerical limits and some classifications have been reviewed and updated based on new industry data and experience.
• Practical and Actionable Limits: The main purpose of this document is to provide clear, actionable numbers. A technician can measure the vibration on a pump, classify it into the correct group (e.g., Group 2, rigid foundation), and compare the reading to the table to make an immediate assessment of its condition.
• Foundation Type is Critical: The standard continues to emphasize the crucial difference between rigid and flexible foundations. A machine on a flexible support structure is allowed a higher level of vibration than the same machine on a solid, rigid base.
• Focus on Non-Rotating Parts: It’s important to remember this standard (like its predecessor) applies to measurements taken on the machine’s stationary structure, such as its bearing housings. It is used in conjunction with other parts of the ISO 20816 series for shaft vibration measurements where applicable.

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