Acoustically Induced Vibration (AIV) & Flow Induced Vibration (FIV) Studies

Acoustically Induced Vibration (AIV)

This refers to the phenomenon where mechanical structures or components experience vibration as a result of exposure to acoustic or sound waves. It occurs when high-intensity sound waves or pressure fluctuations in a fluid medium interact with the structure, causing it to vibrate.

AIV can occur in various industrial settings, including oil and gas facilities, power plants, chemical plants, and transportation systems. It is particularly relevant in environments where high-pressure fluid flows, such as pipelines, valves, compressors, and process equipment. AIV is caused by high-pressure drops and high flow rates in vapor/gas services.

The vibration induced by acoustic waves can lead to several issues, including:

• Fatigue Failure: The repetitive vibrational stresses caused by AIV can lead to fatigue failure of the affected components, resulting in cracks, fractures, or structural damage over time.
• Performance Degradation: AIV can impact the performance and efficiency of equipment by affecting their dynamic behavior, causing disturbances, and reducing their operational lifespan.
• Noise Generation: AIV can generate additional noise in the system, leading to discomfort for operators or nearby personnel and potentially violating noise regulations.

It is important to note that the risk due to Acoustically Induced Vibration (AIV) can vary depending on the specific context and industry. However, here are some factors that could contribute to an increased risk of AIV:

• Increased Infrastructure Complexity: With advances in technology and industrial processes, infrastructure in various industries has become more complex. This complexity can introduce new sources of acoustic energy, such as rotating machinery, high-pressure systems, or specialized equipment, which may lead to increased AIV risks.
• Higher Energy Output: Industries such as power generation, manufacturing, and transportation have experienced increased energy demands. This has resulted in the construction of larger-scale facilities and the use of higher-power equipment. The increased energy output can generate higher levels of acoustic energy, intensifying the potential for AIV.
• Urbanization and Industrial Development: Urbanization and the expansion of industrial activities have resulted in a closer proximity between industrial facilities and residential or commercial areas. This proximity can increase the potential for AIV-related issues, as acoustic energy generated by industrial operations can affect nearby structures and communities.
• Modifications and Upgrades: Modifications or upgrades made to existing infrastructure can sometimes inadvertently introduce conditions that are more susceptible to AIV. Changes in equipment configurations, installation of new machinery, or alterations to system components can affect acoustic propagation and interaction with structures, potentially leading to increased AIV risks.
• Environmental and Regulatory Changes: Changes in environmental regulations or noise control standards can impact industrial operations. Compliance with stricter noise regulations may require modifications to existing systems or equipment, which could potentially alter acoustic characteristics and increase the risk of AIV.
• Aging Infrastructure: Older infrastructure in industries like oil and gas, transportation, and manufacturing may be more prone to AIV-related risks due to factors such as wear and tear, corrosion, or degradation of materials. As infrastructure ages, it may become more susceptible to vibrations induced by acoustic energy.

To mitigate the increased risk of AIV, industries should employ appropriate engineering practices, conduct thorough risk assessments, implement noise control measures, and regularly inspect and maintain infrastructure. Additionally, adherence to relevant regulations and standards can help minimize the potential impact of AIV on structures and surrounding communities. The severity of AIV depends on various factors, including the sound frequency, sound pressure level, structural characteristics, fluid properties, and operational conditions.

Understanding the causes and effects of AIV is crucial for designing, operating, and maintaining industrial facilities to prevent potential safety hazards, reduce maintenance costs, and ensure reliable operation. Mitigation strategies, such as equipment design modifications, flow control measures, structural damping, and acoustic treatments, can be implemented to minimize or control AIV in affected systems.

Flow Induced Vibration (FIV)

This refers to the phenomenon where fluid flow passing through a structure or around an object induces vibrations in the system. It occurs when the fluid flow interacts with the structure, causing it to oscillate or vibrate.

FIV can occur in various industrial systems and components, including pipes, heat exchangers, valves, offshore structures, and other fluid-carrying equipment. It is particularly relevant in situations where the fluid flow is turbulent, high-velocity, or has irregular characteristics.

The vibration induced by fluid flow can have several effects and consequences, including:

• Fatigue Failure: The cyclic loading caused by FIV can lead to fatigue failure of the affected components over time. The repeated vibration-induced stresses can cause cracks, fractures, or other types of structural damage.
• Performance Degradation: FIV can affect the performance and efficiency of equipment by altering their dynamic behavior, causing disturbances, and reducing their operational lifespan.
• Acoustic Emissions: The vibration caused by FIV can also generate noise and acoustic emissions, potentially leading to discomfort for operators or nearby personnel.

The risk due to flow-induced vibration (FIV) in the oil and gas industry has increased for several reasons:

• High Fluid Flow Rates: The demand for oil and gas has led to increased production rates, resulting in higher fluid flow velocities in pipelines and equipment. Higher flow rates can induce stronger fluid-induced forces, leading to amplified vibration amplitudes and increased risk of FIV.
• Complex Flow Conditions: Oil and gas facilities often encounter complex flow conditions, such as multi-phase flows, high-pressure differentials, or high-velocity flow regimes. These flow conditions can generate turbulence, flow instabilities, and flow-induced pressure fluctuations, which contribute to increased FIV risks.
• Aging Infrastructure: Many oil and gas facilities have been in operation for several decades, leading to aging infrastructure. Over time, equipment and pipelines may experience corrosion, erosion, or degradation, altering the flow characteristics and increasing the susceptibility to FIV.
• Extended Operational Life: In some cases, oil and gas facilities have extended their operational life beyond the originally planned duration. This extension can result in equipment and structures being exposed to flow conditions they were not initially designed for, making them more vulnerable to FIV.
• Increased Complexity of Equipment: Modern oil and gas equipment has become more complex in terms of design and functionality. Advanced designs, such as compact heat exchangers, subsea equipment, and riser systems, can introduce new challenges in terms of flow patterns and vibration response, increasing the potential for FIV.
• Non-Standard Flow Conditions: Oil and gas production often involves non-standard flow conditions, such as multiphase flow, slug flow, or intermittent flow regimes. These non-uniform flow patterns and fluctuations can significantly impact the dynamic response of equipment and increase the risk of FIV.
• Higher Operating Pressures and Temperatures: Oil and gas production processes are increasingly conducted at higher pressures and temperatures. Elevated pressures and temperatures can affect the flow properties of fluids, including changes in fluid density, viscosity, and thermodynamic behavior. These variations can lead to altered flow-induced forces and increased FIV risks.

Given these factors, it is crucial for the oil and gas industry to employ advanced FIV assessment techniques, implement robust design practices, conduct regular inspections, and apply appropriate mitigation measures to ensure the safe and reliable operation of equipment and structures in the face of increased FIV risks. The severity of FIV depends on various factors, including fluid properties, flow velocity, structural characteristics, presence of flow-induced turbulence, and system design.

Understanding the causes and effects of FIV is crucial for designing and operating fluid-carrying systems to prevent potential safety hazards, reduce maintenance costs, and ensure reliable operation. Mitigation strategies, such as structural modifications, flow control measures, dampening techniques, or use of vibration-resistant materials, can be employed to minimize or control FIV in affected systems. Additionally computational fluid dynamics (CFD) simulations and experimental testing can be used to predict and analyze FIV behavior and evaluate the effectiveness of mitigation measures.

During the initial design phase of a new plant or when modifying an existing plant, we provide a two-step approach to preventing vibration problems.

This strategy entails a qualitative evaluation and prioritization followed by a qualitative evaluation that yields actionable recommendations.

Step 1 – Qualitative assessment & prioritization

Using a meticulous methodology, we conduct a qualitative evaluation of all the primary lines in a process system in order to determine the potential excitation mechanisms. Then, we produce a report that identifies and ranks the potential excitation mechanisms that require quantitative analysis.

 Step 2 – Quantitative measurement & Solutions

Main lines: For each identified potentially risky excitation mechanism, a quantitative analysis is performed to determine the likelihood of vibration-induced pipe failure.

• Flow-induced turbulence
• Mechanical excitation
• Pulsation
• High-frequency acoustic excitation
• Surge/momentum change as a result of valve operation
• Cavitation and Flashing

The Methodology to carry out AIV & FIV Studies is as follows.

In the oil and gas industry, the study of AIV and FIV is essential for ensuring the integrity and reliability of equipment and structures. Here are some common methods used in AIV and FIV studies specifically tailored to the oil and gas industry:

1. Field Measurements: Conducting field measurements is crucial to understanding AIV and FIV in the oil and gas industry. It involves installing sensors and instrumentation on equipment such as pipelines, risers, valves, and other components to measure vibrations, acoustic levels, fluid velocities, pressure fluctuations, and structural responses under operational conditions. These measurements help identify the severity of vibrations and assess the potential risks.
2. Finite Element Analysis (FEA): Finite Element Analysis is widely used to simulate the behavior of oil and gas equipment subjected to AIV and FIV. FEA models can be created to represent the structures and components accurately. Acoustic loads, fluid flow conditions, and structural properties are considered to predict vibration levels, stress distribution, and potential failure modes. FEA can also help optimize the design of equipment to mitigate AIV and FIV.
3. Computational Fluid Dynamics (CFD): Computational Fluid Dynamics is employed to simulate fluid flow behavior around oil and gas equipment. CFD models can predict fluid velocities, pressure fluctuations, and flow-induced forces that can lead to FIV. These simulations assist in identifying critical areas of flow separation, vortex shedding, and fluid-structure interaction, enabling the design of mitigation measures to reduce FIV risks.
4. Experimental Testing: Experimental testing is conducted in laboratory or field settings to validate numerical models and investigate AIV and FIV phenomena specific to the oil and gas industry. It involves subjecting representative equipment or scaled-down models to controlled acoustic excitations or fluid flow conditions. Measurements of vibrations, acoustic levels, fluid velocities, and pressure fluctuations are collected to validate numerical simulations and provide insights into the behavior of the equipment.
5. Risk Assessment and Mitigation: AIV and FIV risk assessments are performed to identify vulnerable equipment and potential consequences. This involves analyzing the equipment design, fluid flow characteristics, acoustic environments, and structural properties. Mitigation strategies can include modifications to the equipment design, implementing flow control devices, adding damping materials, or changing operational parameters to reduce the likelihood and severity of AIV and FIV.
6. Standards and Guidelines: The oil and gas industry rely on industry-specific standards and guidelines to address AIV and FIV concerns. Organizations such as the American Petroleum Institute (API) provide recommended practices and design guidelines to mitigate AIV and FIV risks. Following these standards ensures that industry best practices are implemented during the design, operation, and maintenance of oil and gas equipment.
7. Monitoring and Maintenance: Continuous monitoring of equipment performance and condition is crucial to detect and mitigate AIV and FIV risks in the oil and gas industry. Implementing a monitoring system with sensors and instrumentation allows for real-time monitoring of vibration levels, acoustic levels, fluid flow parameters, and structural responses. Regular maintenance activities such as inspection, cleaning, and repairing or replacing damaged components can help prevent or mitigate AIV and FIV issues.

AIV and FIV have the same potential failure points, and fortunately, many of the solutions are identical. Every portion of the pipe system, from the source to the affected pipelines further downstream, is mitigated. Reduced speeds, thicker pipelines, and bending are all methods for addressing both issues. With each form of vibration, various options are discussed.

In the table below, the differences between the two types of sound are shown.

The combination of these methods and practices tailored to the oil and gas industry enables a comprehensive understanding of AIV and FIV behavior, assists in designing robust equipment, and ensures the safe and reliable operation of oil and gas facilities.