Session: 3.5.1 - Coupled Multiphysics Simulation I

Paper Number: 158525

158525 - Coupled Multiphysics Simulation for Root Cause Analysis of Process Flow Vibrations in Piping Systems 

Abstract: 

This study investigates advanced numerical simulation methodologies for assessing flow-induced vibration (FIV) in critical plant equipment by integrating fluid-structure interaction (FSI), computational fluid dynamics (CFD), and finite element analysis (FEA). A comprehensive approach is presented to minimise uncertainties associated with broadband and tonal excitation caused by turbulent unsteady flows. A practical case study demonstrates the effectiveness of these methodologies as tools for both identifying and mitigating FIV in critical plant infrastructure.

The case study focuses on assessing FIV in thermowells located in a high-pressure (HP) steam line, undertaken as part of a debottlenecking project in a methanol plant. The debottlenecking initiative aimed to enhance plant efficiency by increasing the flow capacity of the HP steam line, posing significant challenges in terms of structural integrity and reliability. Initial evaluations using ASME PTC 19.3 Thermowells guidelines highlighted a high risk of FIV. These guidelines rely on decoupled calculations involving the Strouhal number to estimate vortex shedding frequencies and structural modes determined through beam calculations or finite element modelling. However, these methods can yield inconclusive results due to wake effects from closely spaced thermowells or line features.

Given that recent inspections revealed high-cycle fatigue cracking at the base of the thermowells, a redesign was deemed necessary to meet the operational requirements without compromising structural integrity. An FSI-based assessment procedure was proposed to provide greater certainty in the root cause analysis (RCA) of fatigue cracking and to offer robust assurance modelling for the proposed remedial measures.

The study also addressed the complexity introduced by thermowell placement within the HP steam line. Several thermowells were positioned near elbows and clustered together, creating conditions for wake interactions and increasing the uncertainty of traditional decoupled assessment methods. This configuration raised the potential for "lock-in" phenomena, where vibration frequencies align between thermowells, amplifying FIV effects. The application of FSI allowed for a more accurate and comprehensive analysis, confirming the presence of FIV under uprated conditions in several thermowells.

To resolve these issues, a revised thermowell design was developed and evaluated using both the FSI-based coupled approach and traditional methods. The new design substantially increased the thermowells’ fundamental structural frequencies, reducing their susceptibility to vortex shedding. Additionally, the modelling ensured that higher-frequency broadband excitations did not trigger resonance in higher structural modes. This integrated assessment approach provided greater confidence in the reliability and safety of the thermowell design under the new operational conditions. A discussion of the merits and applicability of different turbulence modelling approaches is also discussed for this application.

The findings underscore the value of combining FSI, CFD, and FEA in FIV assessment and demonstrate how these advanced methods can enhance the accuracy of RCA, enable effective mitigation strategies, and ensure the structural integrity of critical plant equipment.

Presenting Author: Paul Bosauder Sequence Engineering Ltd

Presenting Author Biography: Paul has 24 years of experience specialising in computational fluid dynamics (CFD) and non-linear finite element analysis (FEA). Paul brings well over two decades of CFD and FEA simulation experience. He is a NAFEMS registered Professional Simulation Engineer (PSE) with advanced accreditation for both flow and stress analysis. Paul also holds a current CPEng (Mech) registration with the practice area description (PAD) of computer-based flow and stress analysis for the design, code verification, and fitness for service (FFS) assessment of industrial and process plant and equipment.

Paul provides leading-edge delivery of CFD and FEA consulting services to customers around the globe. He brings significant experience from a wide range of industries, problem types, and analysis tools to each project he delivers or supervises. In addition to the practical application of numerical simulation, Paul has authored and presented professional education short courses, led business development for new technology fields, and maintained front-line technical support of advanced engineering analysis software.