Session: 08-07-01 Internal Flows & FIV

Submission Number: 153799

Analysis of Fatigue Caused by Flow Induced Pulsation in Subsea Jumper Dead-Legs 

Complex arrangements of high-pressure piping are used by oil and gas operators to transport working fluids from wells to topside equipment. Flow-Induced Pulsation (FIP) remains a widespread issue across multiple industries, particularly in gas transmission and chemical and process industries, leading to costly failures and shutdowns.

FIP occurs when high speed gas flows past a dead-leg entrance, where fluid is trapped and open to the flow path, and generates vortex shedding. These shed vortices create a relatively low frequency pressure pulsation excitation. If the frequency spectra of this pulsation source coincide with the acoustic natural frequencies of the dead-leg, then acoustic resonance can occur, which amplifies the pulsation pressures within the dead-leg. Should the resonant acoustic response frequencies be close to the structural natural frequencies of the dead-leg, a coupled vibro-acoustic response can result, leading to excessive vibrations. Such vibrations pose a significant risk for fatigue failure, noise, and damage to sensitive equipment.

Several industry accepted tools and guidelines are available to help designers and operators evaluate FIP risk, such as the Energy Institute (EI) Guidelines for the avoidance of vibration-induced fatigue failures (AVIFF) in process pipework. These guidelines provide a framework for the identification and mitigation of potential FIP issues. However, their reliance on empirical data and simplified assumptions may not fully capture the complexity of flow interactions. This can result in overly conservative predictions, especially in non-standard geometries or complex main line flows. Additionally, these tools often focus on avoidance rather than quantitative prediction, which can limit their usefulness in complex design and operational scenarios. Computational modelling and simulation can play a crucial role in complementing traditional tools to allow more quantitative approach to FIP assessments. Such approaches can support the verification of more complex flow scenarios or solve difficult operational troubleshooting problems. This study presents one such simulation-based methodology for characterizing pulsation  induced vibration response in piping systems and demonstrates this using case studies.

Our proposed computational FIP methodology uses a four-stage process.

1.      Advanced multiphase Computational Fluid Dynamics (CFD) is used to predict the vortex shedding and pulsation characteristics using Detached Eddie Simulation (DES) turbulence methods.

2.      Simulation of the acoustic response of the fluid trapped in the dead leg using the vortex shedding and pulsation characteristics as a boundary condition. This models propagation of the acoustic pressure wave through the dead leg and predict Power Spectral Density (PSD) on the inside surface of the dead leg.

3.      The interaction of this excitation with the structural model is then modelled using a vibro-acoustic Finite Element (FE) structural model to evaluate the system’s frequency-domain vibration response.

4.      The vibrational response can then be assessed against industry-standard vibration limits (e.g. API 618) or alternatively, a frequency-domain fatigue method can be used to predict system durability and assess this against design and operational requirements.

Through this analysis an effective and efficient method has been developed to quantify the fatigue life of dead leg pipework as a result of FIP. This approach provides added fidelity compared to the traditional EI approach. At the design stage this removes the need for over engineered systems, reducing upfront cost to suppliers and operators. Applying this methodology during in service operation also provides the opportunity to widen the operating envelope by either extending life or operate assets more harshly with a quantified deficit to life. This is a particularly powerful tool as new wells and systems are added to existing fields where system level physical testing is not feasible.

In summary, FIP poses a significant challenge in industry, but advances in modelling and simulation offer powerful tools to mitigate its effects. By integrating these advanced methodologies into both the design and operational phases, engineers can ensure safer and more reliable piping systems that are resilient to flow-induced pulsation-induced fatigue failures.

Presenting Author: Ed Hollis Element Digital Engineering

Presenting Author Biography: Ed has a background in fluids and thermal analysis including multiple years’ experience in multiphase flow and vortex induced vibration analysis of subsea structures.