ISO 20816-8 往復動型圧縮機の振動限界

What Is ISO 20816-8 and Why Does It Matter for Reciprocating Compressors?

ISO 20816-8 is the international standard that defines vibration severity evaluation criteria specifically for reciprocating compressors, including process gas, air, and refrigeration types. It establishes four vibration zones (A, B, C, D) based on measured velocity in mm/s RMS, helping engineers determine whether a compressor operates within acceptable limits or requires corrective action.

Reciprocating compressors are fundamentally different from rotating machines such as centrifugal or axial compressors. The piston-crank mechanism and pulsating gas forces inherent in reciprocating designs produce significantly higher vibration levels during normal operation. This is why ISO 20816-8 exists as a separate part of the ISO 20816 family — applying limits from rotating-machine standards (like ISO 20816-3) to reciprocating compressors would produce misleading and overly conservative assessments.

について 振動限界 - 往復動型コンプレッサー free online tool from this engineering toolkit implements ISO 20816-8 zone classification in a browser-based calculator. Engineers can input their measured vibration velocity, select compressor type and foundation type, and instantly receive the applicable vibration zone along with operational recommendations — no spreadsheets or manual table lookups required.

What Are the ISO 20816-8 Vibration Zone Boundaries for Rigid Foundations?

For reciprocating compressors mounted on rigid concrete or steel block foundations directly coupled to the building structure, ISO 20816-8 defines three zone boundaries: A/B at 7.1 mm/s RMS, B/C at 14.0 mm/s RMS, and C/D at 28.0 mm/s RMS. Zone A represents newly commissioned or excellent condition, while Zone D indicates vibration severe enough to cause damage.

ゾーン境界	Velocity Limit (mm/s RMS)	Operational Interpretation
A/B	7.1	Transition from newly commissioned (excellent) to acceptable for long-term operation
紀元前	14.0	Transition from acceptable to restricted operation — investigation recommended
CD	28.0	Transition from restricted to dangerous — risk of damage if operation continues

Rigid foundations are the most common installation method for large process gas compressors in refineries and chemical plants. The foundation mass and stiffness constrain frame motion, which is why the zone boundaries are lower compared to flexible (spring-isolated) installations. A reading of 12 mm/s RMS on a rigid-foundation process gas compressor, for example, falls within Zone B — acceptable for unrestricted long-term operation.

What Are the ISO 20816-8 Vibration Zone Boundaries for Flexible (Spring-Isolated) Foundations?

For reciprocating compressors mounted on spring-isolated or flexible foundations, ISO 20816-8 allows higher vibration limits: A/B at 9.0 mm/s RMS, B/C at 18.0 mm/s RMS, and C/D at 36.0 mm/s RMS. The increased allowances reflect the fact that spring isolation permits more frame motion while reducing vibration transmitted to the surrounding structure.

ゾーン境界	Rigid Foundation (mm/s RMS)	Flexible Foundation (mm/s RMS)	Increase Factor
A/B	7.1	9.0	×1.27
紀元前	14.0	18.0	×1.29
CD	28.0	36.0	×1.29

Spring-isolated installations are common for air compressors and refrigeration compressors in buildings where transmitted vibration to the structure must be minimized. The flexible foundation allows the compressor frame to move more freely at low frequencies, absorbing inertia forces rather than transmitting them. Engineers must correctly identify their foundation type before using the 振動限界 - 往復動型コンプレッサー tool; selecting the wrong foundation type can shift the zone classification by one full zone and lead to incorrect maintenance decisions.

How Do Reciprocating Compressor Vibration Limits Compare to Rotating Machine Limits?

Reciprocating compressors have significantly higher acceptable vibration levels than rotating machines. The Zone A upper limit for reciprocating compressors on rigid foundations is 7.1 mm/s RMS — roughly 2.5 times the 2.8 mm/s RMS typical Zone A limit for rotating machines under ISO 20816-3. This difference exists because the reciprocating mechanism inherently generates higher vibration that is considered normal operation.

パラメータ	Reciprocating Compressors (ISO 20816-8, Rigid)	Rotating Machines (ISO 20816-3, Group 2)	Ratio
Zone A/B boundary	7.1 mm/s RMS	2.8 mm/s RMS	2.5×
Zone B/C boundary	14.0 mm/s RMS	7.1 mm/s RMS	2.0×
Zone C/D boundary	28.0 mm/s RMS	18.0 mm/s RMS	1.6×
Primary vibration source	Piston-crank inertia forces, gas pulsation	Rotor imbalance, misalignment	—
Dominant frequency content	1×, 2×, and higher orders of running speed	Primarily 1× running speed	—

This comparison highlights a critical engineering principle: vibration limits are machine-type specific. Applying rotating machine limits to a reciprocating compressor would cause nearly every unit to be flagged for excessive vibration, leading to unnecessary shutdowns and wasted maintenance resources. Conversely, applying reciprocating limits to a centrifugal compressor could allow genuinely dangerous vibration to go undetected. The 振動限界 - 往復動型コンプレッサー tool ensures the correct standard is applied automatically based on the user’s machine selection.

What Do the Four Vibration Zones (A, B, C, D) Mean in ISO 20816-8?

The four zones in ISO 20816-8 classify vibration severity into actionable categories: Zone A represents excellent condition typical of newly commissioned machines, Zone B indicates acceptable long-term operation, Zone C means vibration has reached levels requiring investigation and restricted operation, and Zone D signals imminent damage risk requiring immediate action.

1. ゾーンA — Vibration levels typical of newly commissioned or recently overhauled reciprocating compressors. No action required. This is the baseline target for acceptance testing.
2. ゾーンB — Vibration levels acceptable for unrestricted long-term operation. Most compressors in routine service operate within this zone. Monitoring should continue at normal intervals.
3. ゾーンC — Vibration levels that are not acceptable for sustained operation. The compressor may operate for a limited period while corrective action is planned, but investigation into the root cause should begin immediately. Common causes include worn crosshead guides, loose foundation bolts, or gas pulsation resonance.
4. ゾーンD — Vibration levels severe enough to cause rapid damage to the compressor, piping, or foundation. Immediate shutdown or load reduction is recommended. Continued operation in Zone D risks catastrophic failure of bearings, crankshaft, or pressure-containing components.

The zone system provides a universal communication framework between operations, maintenance, and reliability engineering teams. Rather than debating whether a specific vibration number is “high” or “low,” teams can reference the ISO 20816-8 zone classification to make consistent decisions across different compressor types and installations.

Which Compressor Types Does ISO 20816-8 Cover?

ISO 20816-8 covers all major categories of reciprocating compressors: process gas compressors used in refineries and chemical plants, industrial air compressors for plant utilities, and refrigeration compressors used in HVAC and industrial cooling systems. The same zone boundary structure applies to all three types, differentiated only by foundation type (rigid or flexible).

• Process gas compressors — Typically large, multi-stage, slow-speed (300–600 RPM) machines handling hydrogen, natural gas, ethylene, and other process gases. Usually mounted on rigid reinforced concrete foundations. These machines represent the highest-consequence application due to flammable or toxic service.
• Air compressors — Medium to large reciprocating air compressors (typically 500–1800 RPM) used for plant air supply. Often mounted on either rigid or flexible foundations depending on installation requirements. Air compressor vibration issues frequently stem from valve degradation or unloader malfunction.
• Refrigeration compressors — Open-drive or semi-hermetic reciprocating compressors used in ammonia refrigeration systems, industrial chillers, and cold storage facilities. These may operate at higher speeds (900–1750 RPM) and are frequently spring-isolated to minimize noise and vibration transmission to occupied spaces.

について 振動限界 - 往復動型コンプレッサー tool supports all three compressor types with appropriate quick-preset values. For example, the tool includes presets of 12 mm/s for a process compressor on a rigid foundation (Zone B), 20 mm/s for an air compressor (Zone C on rigid, Zone C on flexible), and 8 mm/s for a refrigeration compressor (Zone B on rigid, Zone A on flexible).

Why Is Pulsation-Induced Piping Vibration Not Covered by ISO 20816-8?

ISO 20816-8 addresses only frame and bearing housing vibration on the compressor itself. Pulsation-induced piping vibration — often the most critical vibration concern for reciprocating compressor installations — must be assessed separately using standards such as the Energy Institute Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process Pipework or API 618 pulsation study requirements.

Reciprocating compressors generate gas pressure pulsations at multiples of the running speed and number of cylinders. These pulsations propagate through the connected piping system and can excite mechanical natural frequencies of pipe spans, small-bore connections, and instrument tubing. According to a 2019 Energy Institute survey, piping vibration fatigue accounts for approximately 20% of all hydrocarbon releases in the upstream oil and gas industry, making it a leading cause of loss-of-containment incidents.

The distinction is important: a compressor can have perfectly acceptable frame vibration (Zone A or B per ISO 20816-8) while simultaneously having piping vibration severe enough to cause fatigue failure within weeks. Engineers performing vibration assessments on reciprocating compressor installations should always evaluate both the compressor frame vibration per ISO 20816-8 and the associated piping vibration per applicable piping vibration standards.

How Do You Use the Free Online ISO 20816-8 Vibration Assessment Tool?

について 振動限界 - 往復動型コンプレッサー free online tool requires three inputs: compressor type (process gas, air, or refrigeration), foundation type (rigid or flexible), and the measured vibration velocity in mm/s RMS. The tool instantly returns the applicable vibration zone, the zone boundary values, and an operational recommendation based on ISO 20816-8 criteria.

1. Select compressor type — Choose from Process Gas Compressor, Air Compressor, or Refrigeration Compressor. While the zone boundaries are currently the same for all three types, this selection enables appropriate context for the recommendation text and supports future standard revisions that may differentiate by compressor type.
2. Select foundation type — Choose Rigid Foundation or Flexible (Spring-Isolated). This selection determines which set of zone boundaries applies. If uncertain, inspect the compressor mounting: rigid foundations have the frame bolted directly to concrete or steel; flexible foundations have visible spring or rubber isolation elements between the frame and the support structure.
3. Enter measured velocity — Input the overall vibration velocity in mm/s RMS as measured on the compressor frame or bearing housing. Measurements should be taken in the direction of maximum vibration, typically horizontal perpendicular to the crankshaft axis.
4. Review results — The tool displays a color-coded zone indicator (A = green, B = yellow, C = orange, D = red), the measured value relative to zone boundaries, and a specific operational recommendation.

Quick presets are available for common scenarios: a process compressor on a rigid foundation at 12 mm/s, an air compressor at 20 mm/s, and a refrigeration compressor at 8 mm/s. These presets allow engineers to quickly explore the tool’s functionality and understand how zone classifications work before entering their own measurement data.

What Measurement Practices Are Recommended for ISO 20816-8 Assessments?

ISO 20816-8 assessments require vibration velocity measurements in mm/s RMS taken on the compressor frame or main bearing housings. Measurements should be taken at steady-state operating conditions in all three axes (horizontal, vertical, axial), with the highest value used for zone classification. Broadband measurements covering at least 10–1000 Hz are recommended.

• Measurement parameter: Velocity, mm/s RMS (root mean square). Do not use peak or peak-to-peak values — these will overestimate severity by 40–100% depending on the waveform characteristics.
• Measurement locations: Main bearing housings, crosshead guide housings, and frame surfaces near the crankshaft centerline. Avoid measuring on thin covers, valve caps, or piping — these locations show local resonance amplification that does not represent frame vibration.
• 周波数範囲: Broadband measurement covering at least 2 Hz to 1000 Hz. Reciprocating compressors generate significant energy at low frequencies (1× and 2× running speed), so instruments with adequate low-frequency response are essential. Standard accelerometers with high-pass filters set above 10 Hz may miss critical low-frequency content.
• 動作条件: Measurements should be taken at normal, steady-state operating load. Vibration during startup, shutdown, or unloaded operation is not representative and should not be used for zone classification.
• Number of readings: Take at least three consecutive measurements at each point to verify repeatability. Reciprocating compressor vibration can vary with gas load, valve condition, and thermal state.

How Does ISO 20816-8 Fit Within the ISO 20816 Standard Family?

ISO 20816-8 is one of several machine-specific parts within the ISO 20816 family of vibration evaluation standards. Each part addresses a different machine category with zone boundaries calibrated to the vibration characteristics of that specific equipment type. The family replaced and consolidated the older ISO 10816 and ISO 7919 series.

Standard Part	マシンタイプ	Key Difference from ISO 20816-8
ISO 20816-1	一般的なガイドライン	Framework standard; does not provide specific zone boundaries
ISO 20816-3	Industrial machines (pumps, motors, fans, compressors > 15 kW)	For rotating machines only; significantly lower vibration limits
ISO 20816-5	Hydraulic turbines and pump-turbines	Covers both shaft and structural vibration on hydro generators
ISO 20816-8	往復動型コンプレッサー	Highest zone boundaries reflecting reciprocating mechanism forces
ISO 20816-9	ギアユニット	Accounts for gear mesh frequencies and tooth engagement forces
ISO 20816-21	風力タービン	Addresses nacelle and tower vibration under variable wind loads

Understanding where ISO 20816-8 fits within this family helps engineers avoid a common mistake: using the wrong part of the standard for their specific machine. A reliability engineer working in a refinery, for example, might need ISO 20816-3 for centrifugal pumps and motors, ISO 20816-8 for reciprocating compressors, and ISO 20816-9 for gearboxes — all within the same plant.

よくある質問

What vibration level is acceptable for a reciprocating compressor?

For reciprocating compressors on rigid foundations, vibration velocity up to 7.1 mm/s RMS is considered excellent (Zone A), and up to 14.0 mm/s RMS is acceptable for unrestricted long-term operation (Zone B) per ISO 20816-8. For flexible (spring-isolated) foundations, these limits increase to 9.0 and 18.0 mm/s RMS respectively.

Can I use ISO 20816-3 limits for a reciprocating compressor?

No. ISO 20816-3 applies exclusively to rotating machines. Reciprocating compressors generate inherently higher vibration due to the piston-crank mechanism, and their acceptable levels are approximately 2–2.5 times higher than rotating machine limits. Always use ISO 20816-8 for reciprocating compressors to avoid false alarms and unnecessary shutdowns.

What is the difference between rigid and flexible foundation limits in ISO 20816-8?

Flexible (spring-isolated) foundation limits are approximately 27–29% higher than rigid foundation limits across all zone boundaries. For example, the A/B boundary is 7.1 mm/s for rigid versus 9.0 mm/s for flexible foundations. This accounts for the additional frame motion allowed by the isolation system, which reduces transmitted vibration at the cost of higher machine-level displacement.

Does ISO 20816-8 cover piping vibration on reciprocating compressors?

No. ISO 20816-8 covers only compressor frame and bearing housing vibration. Pulsation-induced piping vibration — often the most critical concern — must be assessed separately using standards such as the Energy Institute guidelines or by performing an API 618 pulsation and mechanical response study during the design phase.

Should I measure vibration in displacement, velocity, or acceleration for ISO 20816-8?

ISO 20816-8 zone boundaries are defined in velocity, specifically mm/s RMS. Use broadband velocity measurements covering at least 2–1000 Hz. If your instrument measures acceleration, ensure it has software-based integration to convert to velocity with adequate low-frequency response, as reciprocating compressors produce significant energy at 1× and 2× running speed (often below 20 Hz).

How often should vibration be measured on reciprocating compressors?

While ISO 20816-8 does not prescribe a specific monitoring interval, industry best practice recommends monthly route-based measurements for non-critical compressors and continuous online monitoring for critical process gas compressors. Machines operating in Zone C should be monitored at increased frequency (weekly or continuous) until corrective action is completed.

What are common causes of high vibration on reciprocating compressors?

Common causes include worn crosshead or piston rod packing, loose foundation bolts, unbalanced opposing cylinders, degraded or leaking compressor valves, gas pulsation resonance in the piping system, misalignment between the compressor and driver, and crankshaft or bearing wear. The specific vibration frequency content (spectral analysis) helps distinguish between these root causes.

Is the Vibration Limits — Reciprocating Compressors tool free to use?

Yes. The Vibration Limits — Reciprocating Compressors tool is a free browser-based engineering calculator (Free Engineering Tool #024) that implements ISO 20816-8 zone classification. It requires no registration, software installation, or payment. Engineers can input their measured vibration values and receive instant zone classification with operational recommendations.