What machines does ISO 20816-2 cover?

ISO 20816-2 applies to steam turbines and generators with power output greater than 40 MW and operating speeds between 1500 and 3600 RPM. This includes large power station turbine-generator sets, industrial steam turbines, and combined-cycle plant generators.

What is the difference between bearing housing and shaft relative measurement?

Bearing housing vibration is measured with accelerometers or velocity sensors mounted on the bearing cap, expressed in mm/s RMS. Shaft relative vibration is measured with proximity probes installed inside the bearing, measuring shaft displacement relative to the bearing, expressed in μm peak-to-peak. Both should be monitored for a complete picture.

Why are shaft vibration limits important for steam turbines?

Steam turbines use fluid-film (journal) bearings where the bearing housing may not vibrate significantly even when the shaft has high vibration. Shaft relative measurement captures the actual rotor dynamic behavior, detecting issues like unbalance, misalignment, oil whirl, and rotor cracks that bearing housing sensors might miss.

What should I do if vibration reaches Zone C?

For Zone C on steam turbines: investigate the root cause immediately, increase monitoring frequency, plan corrective action during the next scheduled outage, inform plant management. The turbine may continue operating for a limited period but should not remain in Zone C indefinitely. Common causes include unbalance, misalignment, bearing wear, and thermal bowing.

How does ISO 20816-2 relate to ISO 7919-2?

ISO 20816-2 consolidates the content of the former ISO 10816-2 (bearing housing vibration) and ISO 7919-2 (shaft vibration) into a single standard. It covers both measurement types with updated guidance and zone boundaries for steam turbines and generators.

Free Engineering Tool #020

Vibration Limits — Steam Turbines & Generators >40 MW

Evaluate vibration severity for steam turbines and generators per ISO 20816-2. Supports bearing housing velocity and shaft relative displacement measurements.

ISO 20816-2 Zones A/B/C/D >40 MW

Results

Vibration Zone

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Measured Value

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Recommendation

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Zone	Boundary	Description

ISO 20816-2 Scope

ISO 20816-2 specifies vibration evaluation criteria for steam turbines and generators exceeding 40 MW output, operating at speeds between 1500 and 3600 RPM (50/60 Hz power generation). It covers both bearing housing vibration and shaft relative vibration.

Bearing Housing Vibration

Broadband vibration velocity is measured on the bearing housing (pedestal) in mm/s RMS, typically in the frequency range 10–1000 Hz.

Zone Boundary	Velocity (mm/s RMS)
A/B	2.8
B/C	5.3
C/D	8.5

Shaft Relative Displacement

Shaft vibration is measured with proximity probes, expressed as peak-to-peak displacement in μm. These values are simplified for general application.

Zone Boundary	Displacement (μm p-p)
A/B	50
B/C	100
C/D	165

ℹ️ Note: Shaft displacement limits may vary with operating speed. The values above are simplified for general use. For exact speed-dependent limits, consult the full ISO 20816-2 standard.

⚠️ Important: Both bearing housing and shaft vibration should be monitored. A machine may show low bearing housing vibration but high shaft vibration, or vice versa. The worse of the two assessments governs the overall evaluation.

Vibration Limits for Steam Turbines & Generators | ISO 20816-2

Published by Nikolai Shelkovenko on February 15, 2026 March 5, 2026

Results

ISO 20816-2 Scope

Bearing Housing Vibration

Shaft Relative Displacement