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Vibration Monitoring and Risk Analysis for Process Piping

Vibration-induced fatigue is one of the most common causes of failure in process piping systems. The resulting unexpected hydrocarbon release may lead to financial losses and impact both health and safety and the environment. Data published by the UK’s Health and Safety Executive (HSE) for the offshore industry has shown that in the UK sector of the North Sea, fatigue and vibration failures account for 21% of all hydrocarbon releases.

The likelihood of failure of a piping system when flow-induced turbulence is the excitation mechanism is governed by two conditions: flow-induced vibration factor (Fv) and dynamic pressure (ρv2).

The flow-induced vibration factor is calculated from the geometric properties of the pipe being inspected. The external pipe diameter (Dext) and the wall thickness of main pipe (T) are used to calculate the  and  for a particular piping support arrangement, as specified in the aforementioned EI guidelines.

The dynamic pressure is determined from the flow properties of the fluid system. It depends on parameters such as density or fluid velocity.

The likelihood of failure for flow-induced turbulence is then calculated using equation 1.

The calculated LOF for the respective piping system is then integrated with online measurement data to determine the effective LOF. This is done by measuring the vibration level against the predefined natural frequency, as in equation 2.

The objectives of this project were as follows:

  • identify the excitation mechanisms
  • provide detailed screening of main pipework (and possibly small-bore connections)
  • assess the likelihood of fatigue crack initiation using vibration analysis.

The condition monitoring system developed for the project is capable of incorporating vibration analysis. This is in contrast to existing systems, which are unable to link vibration analysis of pipework to the likelihood of fatigue crack occurrence.

The market-dominating piping vibration management system relies on a desktop assessment by specialist engineers. However,  the system developed by TWI offers operators a portable device that screens the vibration signal into either of two options:

  • an acceptable vibration signal that passes the first stage of assessment/screening described in the EI guidelines
  • an unacceptable vibration signal that then requires a risk-based assessment by specialist engineers.

Therefore, the present system achieves the following for plant owners/operators:

  • easy operation: the first screening method can be undertaken by a non‑specialist engineer/inspector
  • low cost: the first screening method can achieve cost savings since specialist vibration management vendors are only required to investigate piping sections that failed the first level of screening.

The resulting LOF is combined with a consequence of failure (COF) value to quantitatively determine the risk associated with the pipeline’s condition. This provides quantitative risk management, calculating asset integrity and informing maintenance activities.

The system strategy is described in Figure 1:

The testing environment, as defined by the operator, will determine which parameters are used. These could include the external pipe diameter, support span length, wall thickness of main pipe, fluid velocity, gas dynamic viscosity and fluid density.

The system prototype comprises a vibration signal sensor and an assessment module. A touchscreen interface allows the operator to enter the pipe and fluid details. Once the vibration data is acquired, the functions can be calculated either in real-time or using offline advanced data processing.

The system is able to plot both the acceleration and the frequency spectrum, enabling the detection of dominant peak frequencies. This allows the initial vibration assessment to be determined and the LOF for flow-induced turbulence to be calculated and plotted on the risk-based inspection matrix (Figure 2).

The developed system can be used for fluid-carrying pipework deployed in the following environments:

  • oil and gas upstream production/processing offshore plants
  • oil and gas downstream chemical processing plants
  • power generation plants
  • water/waste water plants
  • pharmaceutical plants

 

Research leading to these results has received funding by TWI’s Core Reach Programme. For further information, please email contactus@twi.co.uk

Figure 1: The different modules of the system including the user interface and the MEMS Accelerometer ADXL325
Figure 1: The different modules of the system including the user interface and the MEMS Accelerometer ADXL325
Figure 2: Display of the LOF in the risk matrix for vibration induced by rotating motor with embedded unbalance
Figure 2: Display of the LOF in the risk matrix for vibration induced by rotating motor with embedded unbalance
Avatar Ángela Angulo Senior Project Leader – Condition and Structural Monitoring

Ángela has an MEng degree in industrial engineering from the University of Navarra in Spain and an MSc in structural integrity from Brunel University.

Ángela joined TWI in January 2013, in the Integrity Management Group, which provides cost savings and reliability assurance through the development and application of advanced innovative inspection, assessment and risk management solutions for industry sectors including oil and gas. Within the condition monitoring section, Ángela works on the following areas of expertise: strategic health monitoring using vibration analysis, acoustic emission, modal analysis and guided ultrasonic waves.

Ángela has experience in forecasting for economic and societal impacts of project results, exploitation strategy and plan, and market route and opportunity identification.

For more information please email:


contactus@twi.co.uk