Understanding API 684 Standard

Devices

Portable balancer & Vibration analyzer Balanset-1A

$2,335.73 Izvorna cijena bila je: $2,335.73.$2,010.50Trenutna cijena je: $2,010.50.

Parts

Vibration sensor

$106.44 Izvorna cijena bila je: $106.44.$82.79Trenutna cijena je: $82.79.

Parts

Optical Sensor (Laser Tachometer)

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Devices

Balanset-4

$8,045.54

Parts

Magnetic Stand Insize-60-kgf

$54.40

Parts

Reflective tape

$11.83

Devices

Dynamic balancer “Balanset-1A” OEM

$2,051.89 Izvorna cijena bila je: $2,051.89.$1,773.97Trenutna cijena je: $1,773.97.

Definition: What is API 684?

API 684 (American Petroleum Institute Standard 684: “API Standard Paragraphs Rotordynamic Tutorial: Lateral Critical Speeds, Unbalance Response, Stability, Train Torsionals, and Rotor Balancing”) is a comprehensive tutorial document providing guidance, recommended practices, and theoretical background for performing rotor dynamics analysis on turbomachinery. Unlike prescriptive specifications, API 684 is educational—explaining how to analyze critical speeds, predict unbalance response, assess stability, evaluate torsional vibration, and establish balancing requirements for equipment covered by other API standards (API 610 pumps, API 617 compressors, API 612 steam turbines).

API 684 serves as the theoretical foundation and analytical guide supporting the vibration requirements in other API equipment standards, providing the “how and why” of rotor dynamic analysis methods, acceptance criteria derivation, and troubleshooting approaches for rotating equipment engineers and analysts.

Standard Structure

Part 1: Tutorial on Lateral Rotor Dynamics

• Critical Speed Analysis: Methods for calculating lateral critical speeds
• Unbalance Response: Predicting vibration from unbalance
• Stability Analysis: Assessing rotor stability margins
• Modeling Techniques: Finite element and transfer matrix methods
• Acceptance Criteria: How to judge if analysis acceptable

Part 2: Tutorial on Train Torsional Analysis

• Torsional Natural Frequencies: Calculation methods
• Forced Response: Prediction from excitation sources
• Transient Analysis: Startup, shutdown, fault conditions
• Acceptance: Stress limits, separation margins

Part 3: Tutorial on Rotor Balancing

• Balance Criteria: ISO balance grades application
• Shop Balancing: Procedures and tolerances
• Field Balancing: In-situ methods
• Flexible Rotor Balancing: Special considerations

Key Concepts Addressed

Separation Margins

• Operating speed should be ±15-20% from critical speeds minimum
• Larger margins for low-damping systems
• Guidance on evaluating adequacy

Damping Requirements

• Minimum damping levels for safe operation
• Log decrement criteria
• Amplification factor limits at critical speeds

Stability Criteria

• Analysis methods for predicting onset of instability
• Threshold of stability determination
• Bearing selection for stability

Practical Application

Design Phase

• Perform rotor dynamic analysis per API 684 methods
• Predict critical speeds and response
• Document analysis in vendor documentation
• Purchaser reviews and approves

Commissioning

• Compare actual vibration to predictions
• Verify critical speeds within predicted range (±15%)
• Confirm unbalance response matches calculations
• Validate Campbell diagrams

Troubleshooting

• Use API 684 guidance for problem diagnosis
• Modify rotor dynamic models based on test data
• Evaluate proposed modifications
• Predict effects before implementation

Relationship to Other API Standards

API 617 (Compressors)

• References API 684 for rotor dynamics requirements
• Specifies that analysis must follow API 684 methods
• Acceptance criteria derived from API 684 principles

API 610 (Pumps)

• Critical speed and rotor dynamics requirements reference API 684
• Balancing specifications based on API 684

API 612 (Steam Turbines)

• Rotor dynamics analysis per API 684
• Lateral and torsional analysis requirements

Benefits and Value

Standardized Approach

• Common methodology across industry
• Consistent analysis quality
• Facilitates communication between parties
• Enables comparison between vendors

Educational Resource

• Tutorial format explains concepts
• Not just requirements but understanding
• Training tool for engineers
• Reference for best practices

Proven Practices

• Based on decades of industry experience
• Incorporates lessons learned
• Reduces risks from inadequate analysis
• Improves equipment reliability

Implementation

Who Performs Analysis

• Equipment manufacturers (OEMs)
• Engineering contractors
• Specialized rotor dynamics consultants
• End-user engineering departments
• Requires specialized software and expertise

Deliverables

• Rotor dynamics report
• Campbell diagrams
• Unbalance response predictions
• Stability analysis
• Torsional analysis (if applicable)
• Recommended operating speed ranges

API 684 is the authoritative tutorial and guidance document for rotor dynamics analysis in petroleum and power industries. By providing comprehensive methodology, acceptance criteria, and educational content for lateral and torsional analysis, API 684 ensures consistent, high-quality rotor dynamic assessments supporting reliable, safe operation of critical turbomachinery worldwide.

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