Avoiding vibration induced fatigue failure in refinery pipework
At Grangemouth Refinery, Xi Engineering Consultants combined measurement and finite element analysis to understand severe vibration in an agitator building, identifying fatigue hot spots and recommending structural improvements to protect foundations, steelwork and pipework.
The Challenge
An agitator building at Grangemouth Refinery housed four large mixing units on a mezzanine floor. During operation, high levels of vibration were felt and seen throughout the structure, accompanied by cracking in concrete foundations, damage to steel supports and concerns about fatigue in attached pipework. The refinery team suspected frequency matching between agitator running speeds and building resonances, but needed clear evidence and engineering guidance. They asked Xi to determine the building’s resonant behaviour, identify which machines were driving problematic vibration and recommend practical solutions that would minimise disruption to production.
Our Approach
Xi deployed low frequency geophones and accelerometers around the agitators and supporting structure to measure vibration levels and identify dominant frequencies. Analysis showed a strong response at around 7 Hz, indicating frequency matching between two agitators and a structural mode of the building. Using the measurement data, Xi developed and calibrated a finite element model of the building, then used it to calculate cyclic stresses and fatigue life for critical steel elements. Stress hot spots near the agitator bases and key connections were identified, and alternative support and stiffening strategies were tested in simulation before recommendations were made for targeted structural upgrades.
The Results
Why it matters
Process plants routinely mount heavy rotating machinery on steel frames and mezzanine structures, creating a risk of vibration induced fatigue in both steelwork and pipework. Following guidelines such as the Energy Institute’s recommendations is easier when supported by measured data and calibrated models. Xi’s approach helps operators move from concern to quantified risk and focused mitigation, reducing the likelihood of leaks, failures and costly outages.