Overview of Piping Vibration Risk Assessment

What is Piping Vibration Risk Assessment

Vibration in pipelines and piping systems can result from various factors, including Flow Induced Turbulence (FIT), Flow Induced Pulsation (FIP), Acoustic Induced Vibration (AIV), Small Bore Connection (SBC), etc. To mitigate the risk of vibration-related failure, a systematic evaluation process, known as piping vibration risk assessment, is conducted to identify, analyze and mitigate the potential risk associated with vibrations in pipelines and piping systems.

Why Perform Piping Vibration Risk Assessment

Excessive vibration in piping systems can lead to fatigue failure, elevated maintenance costs, and significant safety risks. A piping vibration risk assessment is essential to identify the sources of vibration and evaluate their severity using both quantitative and qualitative methods. This systematic approach ensures the mechanical integrity and operational reliability of pipelines and piping systems, reducing the likelihood of failures, minimizing downtime, and maintaining safe, efficient operations.

Piping Vibration Risk Assessment Methodology

Energy Institute published the ‘Guidelines for the Avoidance of Vibration Induced Fatigue Failure in Process PipeWork’ in 2008, commonly referred to as the EI Guideline 2008, to provide a comprehensive methodology for conducting piping vibration risk assessment. The guidelines outline a staged approach that includes identifying vibration sources, conducting risk-based assessments, performing quantitative and qualitative analyses, implementing mitigation techniques, and establishing continuous monitoring protocols.

In addition to the EI Guideline 2008 which covers the most common excitation mechanisms which occur in oil and gas industry, various industry standards and procedures are available to address specific types of vibration, allowing for tailored approaches based on the nature of the vibration under consideration.

Flow Induced Turbulence (FIT) Assessment

What is Flow Induced Turbulence (FIT)

Flow Induced Turbulence (FIT) exists in most piping systems with dominant sources of turbulence associated with major flow discontinuities in the system such as bends, partially closed valves, tees, and reducers. These major discontinuities generate potentially high levels of kinetic energy, which is a function of pipe size, fluid density, viscosity, velocity and structural support. This broadband energy, mainly concentrated at low frequency (below 100 Hz), can lead to the excitation of the low frequency vibration modes of the pipework if it coincides with the natural mechanical frequencies of the pipe.

Flow Induced Turbulence at Tee
(Resourced from EI Guideline 2008)

FIT Assessment Methodology

The VibTech quantitative assessment tools were developed in accordance with the EI Guideline 2008 to evaluate the likelihood of failure (LOF) due to FIT. Based on the assessment findings, appropriate mitigation measures are proposed to eliminate the vibration risk.

An example of FIT assessment is provided below.

Flow Induced Turbulence Assessment Results

Flow Induced Pulsation (FIP) Assessment

What is Flow Induced Pulsation (FIP)

Flow Induced Pulsation (FIP) is caused by flow past a closed side-branch in a piping system, which creates vortices to be shed at specific frequencies. If these vortex shedding frequencies coincide with the acoustic natural frequency of the side-branch, amplification of the vibration can occur.

FIP at a Closed Side Branch
(Resourced from EI Guideline 2008)

FIP Assessment Methodology

The VibTech quantitative assessment tools were developed in accordance with the EI Guideline 2008 to evaluate the likelihood of failure (LOF) due to FIP. Based on the findings of FIP evaluation results, a frequency sweep along all the relative lines is conducted to identify if the acoustical resonances are observed. The acoustical models used for the frequency sweep were created using Bentley PULS software. Based on the calculated Strouhal Numbers and the vortex shedding frequencies at the mouth of each deadleg, the acoustical analysis frequency sweep was conducted with a range of ±20% of the shedding frequencies. By using this analysis method, the acoustical resonant frequencies within the ±20% range of shedding frequencies were identified, the associated shaking forces along the deadlegs were calculated as well.

An example of FIP assessment is provided below.

FIP Assessment Results

Acoustic Induced Vibration (AIV) Assessment

What is Acoustic Induced Vibration (AIV) Assessment

Acoustic Induced Vibration (AIV) refers to high-frequency excitations typically ranging from 500 Hz to 2000 Hz. These excitations are generated by pressure-reducing devices, such as relief valves, control valves, and orifice plates. In gas systems, AIV can lead to shell mode vibrations that can cause rapid failures, sometimes occurring within hours, in addition to generating excessive noise concerns.

AIV Assessment Methodology

The assessment of AIV is performed using the VibTech quantitative assessment tools, following the flowcharts outlined in the EI Guideline 2008. This systematic approach ensures a thorough evaluation of AIV risks, enabling the identification of potential vibration issues and the implementation of appropriate mitigation strategies.

AIV Assessment Flowchart
(Resourced from EI Guideline 2008)

Small Bore Connection (SBC) Vibration Assessment

What is Small Bore Connection (SBC)

A small bore connection (SBC) refers to a piping connection with a relatively small diameter, typically less than 50 millimeters (2 inches). These connections are commonly utilized in various industrial applications to link smaller instruments, control lines, or auxiliary systems to larger piping systems.

SBC are particularly susceptible to vibration issues due to their design and support limitations. Often, SBCs are inadequately supported or poorly designed, which increases their risk of experiencing vibration-related problems, even if the main piping line is properly supported.

SBC Assessment Methodology

The VibTech quantitative assessment tools were developed in alignment with the EI Guideline 2008 to evaluate the likelihood of failure (LOF) due to SBC. This assessment is conducted to identify poorly designed and supported SBCs. Based on the findings, appropriate modifications are proposed to improve SBC design, including bracing them to the main pipe securely and reducing the length of SBC as much as possible.

An example of SBC assessment and its mitigation measures are provided below.

SBC without Brace Support

SBC with Brace Support

Vibration Risk Assessment

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