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ASME B133.8-2011 (2017) — Gas Turbine Installation Sound Emissions
🔊 ASME B133.8-2011 (2017) is the landmark standard for gas turbine installation sound emissions. After most B133 standards were withdrawn in favor of the ISO 3977 series, B133.8 was retained because of sustained interest in U.S. industry; in 2008 the ASME PTC 36 Committee (Measurement of Industrial Sound) took over its revision, producing the 2011 edition, which was reaffirmed in 2017. This Standard provides methods and procedures for specifying the sound emissions of gas turbine installations for industrial, pipeline, and utility applications, including guidelines for making field sound measurements and reporting field data. Users and manufacturers may use it to write specifications and to determine compliance with a specification after installation.
💡 Noise limits are a key constraint in gas turbine project environmental review and community relations. B133.8 turns the vague question “how loud is it” into a technical specification with defined measurement points, weighting networks, and report formats, giving acceptance disputes an objective basis.
1. Object and Scope 📌
Section 1-1 states the object: to provide methods and procedures for specifying the sound emissions of gas turbine installations, including guidelines for field sound measurements and field data reporting. Users and manufacturers may use the Standard to write specifications and to verify compliance after installation. Nonmandatory Appendices A and B provide guidance for estimating expected community reaction to noise and for determining installation sound emission levels compatible with the sound environment of a neighboring sensitive receiver such as a residential community.
Section 1-2 defines the scope: the Standard is applicable to land-based, or shore-side, barge-mounted gas turbines in single or multiple arrangements, for indoor or outdoor stationary installations. Applications include, but are not limited to, gas turbine-driven generators, compressors, or pumps, in simple-cycle gas turbines or combined-cycle gas turbines with simple-cycle bypass capability. (The full list of included/excluded applications is given in the Standard.)
⚠️ Scope boundaries: B133.8 targets stationary land-based/shore-side installations. Gas turbines on earth-moving machines, agricultural and industrial tractors, vehicles, and aeropropulsion units are excluded, and unconventional heat-source applications (e.g., nuclear or chemical process heat) may need appropriate modifications.
2. Main Improvements in the 2011 Edition 🔧
Building on the 1977 framework, the 2011 edition makes six substantive improvements (per the Foreword):
- Near-field measurement specification: added a near-field measurement specification along a prescribed near-field source envelope contour.
- Combined-cycle clarification: clarified the gas turbine acoustical specification for combined-cycle applications in both near field and far field.
- Measurement positions and distance corrections: clarified definitions of measurement positions and distance corrections.
- Measurement methodology: added guidance regarding measurement methodology.
- Reflective surface effects: clarified treatment and evaluation of reflective surface effects.
- Updated references: added and updated references, including Nonmandatory Appendix B on low-frequency airborne sound.
💡 Low-frequency airborne sound (rumble down to tens of hertz) attenuates slowly over long distances and is a frequent source of community complaints — this is why the 2011 edition emphasizes it. Do not evaluate only the A-weighted total; also examine octave-band and low-frequency content.
3. Sound Emissions Specification Procedures 📝
Section 2 defines the procedures and formats for sound emissions specifications, covering both environmental (far-field) and near-field paths:
| Procedure | Measurement Location | Content | Use Case |
|---|---|---|---|
| Procedure A: total sound level | ~400 ft (120 m) from the installation boundary | A-weighted total sound level of the whole installation at contract conditions | A single number representing far-field impact |
| Procedure B: octave-band sound pressure levels | ~400 ft (120 m) from the installation boundary | Octave-band sound pressure levels at contract conditions | Frequency distribution and noise-control effectiveness |
| Near-field specification | Points along a prescribed near-field source envelope contour | Near-field level distribution to identify major source regions | Source localization, enclosure and mitigation verification |
Writing an acoustical specification is difficult because the sound power of the same machine is not constant across load and ambient conditions, and is affected by ground reflection, obstacles, and wind gradients. The specification must therefore fix the baseline duty, measurement distance, weighting network (A/C), meteorological limits, and measurement period — exactly what B133.8 formalizes.
4. Field Sound Measurement Guidelines 📏
Section 3 provides complete operational guidance for field measurement:
| Element | Key Requirements |
|---|---|
| Qualifications (3-2) | Personnel competent in acoustics and familiar with instruments and site conditions |
| Gas turbine operation (3-3) | Run at contract load and conditions; record load, fuel, ambient data |
| Acoustic environment (3-4) | Assess background noise, reflecting surfaces, and meteorology; limits must be satisfied |
| Instruments (3-5) | Conforming sound level meters/analyzers; acoustic calibration before and after measurement |
| Microphone locations (3-6) | Far-field points at specified distance and height; near-field points along the envelope contour (see Figs. 3-6-1/3-6-2/3-6-3) |
| Sound measurements (3-7) | Record sufficient sample time over stable operation; exclude anomalous events |
| Data reporting (3-8) | Report measured values, ambient conditions, and corrections in a uniform format |
| Average and maximum levels (3-9) | Compute average levels by the specified energy-average method; apply reflecting-surface corrections (Table 3-9.4-1) |
| Comparison with specification (3-10) | Compare corrected measured levels with specified values to determine compliance |
🚨 Reflecting-surface correction is the most error-prone part of acceptance: ground, walls, and enclosures near the microphone add reflected sound and inflate readings. Table 3-9.4-1 gives corrections for different reflecting conditions; the measurement report must state that they were applied, otherwise the comparison is invalid.
5. Engineering Practice Essentials 🛠️
- 📋 Specify first: set the baseline sound level or octave-band specification at the concept stage and define the 400 ft (120 m) positions and near-field envelope contour to avoid acceptance disputes later.
- 💡 Integrated noise control: inlet silencers, exhaust silencers, enclosure acoustic treatment, pipe lagging, and base isolation are the main measures; allocate contributions per source in the specification.
- 📊 Combined-cycle plants: additional sources such as heat recovery steam generators and bypass stacks must be covered in the specification and evaluated with the clarified B133.8 method.
- 🌤️ Meteorological corrections: wind and temperature gradients refract sound paths; record conditions and note them in the report, re-testing when necessary.
- 🔄 Acceptance flow: follow Section 3 step by step — qualification, calibration, duty records, measurement, reporting — and compare corrected data item by item against the specification.
6. Frequently Asked Questions ❓
❓ Q: What is the difference between B133.8 and B133.9?
A: B133.8 covers the specification and measurement of sound (noise) emissions from gas turbine installations — an acoustics topic; B133.9 covers measurement of pollutant emissions (NOx, CO, SO2, particulates, etc.) in the exhaust of stationary gas turbines — a flue-gas/environmental chemistry topic. They address “noise” and “exhaust” constraints respectively.
A: B133.8 covers the specification and measurement of sound (noise) emissions from gas turbine installations — an acoustics topic; B133.9 covers measurement of pollutant emissions (NOx, CO, SO2, particulates, etc.) in the exhaust of stationary gas turbines — a flue-gas/environmental chemistry topic. They address “noise” and “exhaust” constraints respectively.
❓ Q: What are near-field and far-field measurements each used for?
A: Far-field points (e.g., 400 ft/120 m) evaluate impact on external sensitive receivers and map to environmental and community noise limits; near-field points along the envelope contour identify dominant sources and verify the actual performance of enclosures and silencers. Use both to control the “impact area” and the “source” together.
A: Far-field points (e.g., 400 ft/120 m) evaluate impact on external sensitive receivers and map to environmental and community noise limits; near-field points along the envelope contour identify dominant sources and verify the actual performance of enclosures and silencers. Use both to control the “impact area” and the “source” together.
❓ Q: Why measure at a specified distance (e.g., 400 ft) rather than next to the machine?
A: That distance represents a typical sensitive receiver — a community or site boundary — so specification values map directly to regulatory limits at the boundary/sensitive point, and the fixed distance keeps data comparable across machines and projects.
A: That distance represents a typical sensitive receiver — a community or site boundary — so specification values map directly to regulatory limits at the boundary/sensitive point, and the fixed distance keeps data comparable across machines and projects.
🔍 Q: What does the 2017 reaffirmation mean?
A: ASME periodically reviews each standard; if no revision is needed it issues a reaffirmation declaring the standard remains in effect. B133.8-2011 was reaffirmed in 2017, so all technical content of the 2011 edition remains valid for specification and measurement.
A: ASME periodically reviews each standard; if no revision is needed it issues a reaffirmation declaring the standard remains in effect. B133.8-2011 was reaffirmed in 2017, so all technical content of the 2011 edition remains valid for specification and measurement.
