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Turning off vibration risk, turning on profitability

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LNG Industry,

In the long list of risks that pipeline operators face, vibration-induced fatigue is usually a low priority. Yet the consequences of a failure related to vibration can be catastrophic.

Of course, when pipework fails due to the effects of excessive vibration, safety is at stake. Entire production lines and plants may have to be shut down. Major repairs or overhauls may be required. Even if the threat is relatively minor, the costs of non-operation – in terms of lost revenue – add up fast.

Failures aside, the process of identifying and managing vibration risk is costly. The complexity of pinpointing threats across assets that extend over large areas, with multiple points that are physically unreachable, means operators sometimes resort to temporary, but often untenable, solutions.

In the case of one major LNG plant operator in the Middle East, this meant reducing production by limiting the throughput by around 20%. Over the course of four to five years, the unrealised revenue was piling up.

On top of this, the operator needed to bring a new gas field on stream to supplement the existing feed. So, not only did the current production limitations have to be addressed, but future constraints also had to be avoided.

When brains beat brawn: taking an analytical approach

Given the plant’s physical footprint, the operator sought a partner who could enable it to be more strategic with how it identified, managed and mitigated areas of vibration risk.

Wood was selected for its expertise in modelling and analytics, where operational data sets are used to map performance – and weaknesses – across the production plant.

The strength of this approach is that the majority of investigation can be completed from the office, rather than in the field. The operator used Veridian, Wood’s digital, risk-based vibration screening tool, to gauge the vibration integrity of the hydrocarbon process piping.

More than 2000 main process flow lines were assessed, measuring typical sources of vibration, including: flow-induced turbulence and pulsation, mechanical (machinery) vibration, pulsation due to reciprocating gas compressors, transient forces due to fast acting valves and rapidly changing fluid flows. These analyses measured performance of the pipe at its existing flow state and under simulated conditions.

Of those 2000 flowlines, 400 were identified as medium-to-high risk for vibration integrity, warranting further investigation. Factors like slugging and multiphase flow, liquid flashing and high flow velocity vibration were measured. Crucially, Wood ruled out areas that were previously perceived as high risk, concluding that only minor modifications were needed.

The next step was to run a more detailed integrity assessment, including dynamic stress measurements and on-site visual inspections, to quantify the vibration risk and prioritise vibration control measures.

Due to the significant gas inventory associated with the LNG plant, a relatively large number of flare system valves were flagged as a potential concern. Vibration reduction measures had been included in the original plant design; however, based on the latest industry best practices, specific design features were now seen as possible long-term integrity risks. Wood engaged its vibration engineers to identify short and long-term control measures, assessing the flare system for the risk of acoustic-induced vibration.

Piping dynamic stress assessments – in the form of defined finite element analysis – were carried out for the targeted lines to measure performance in current and future operating ranges. Where necessary, vibration control measures were then evaluated using Wood’s advanced computer models.

The various levels of analysis fed into an anomaly database – where the newly measured risks could be factored in to pinpoint 120 areas where immediate attention would deliver the greatest operational benefits. From the list of 120 anomalies, 10 were identified as having the highest priority for the introduction of the new gas stream. Wood’s software-led analysis was both thorough and fast. Ultimately, it helped reduce the plant’s vibration risk assessment time by up to 60%.

Maximising return on investment

Addressing just those 10 critical problem areas gave the operator the confidence to increase flow rates back to full design capacity – increasing annual revenue by half a billion dollars per year. This was achieved with a comparatively small investment of around US$500,000.

And that was just the start. With confidence in its ability to monitor, measure and manage risk, the operator has since been able to increase production beyond original projections by testing operational changes and modelling potential impacts on the LNG trains.

By assessing the true severity of each potential threat, the Veridian software has enabled the operator to make more strategic decisions about how, when and where to allocate its resources for vibration risk mitigation. The software continuously tracks and ranks the remaining areas of above-average risk, providing guidance on priorities and approach, whether it be a simple redesign or physical modification.

The modelling also provides a fully-auditable approach for minimising vibration failures. In the event that an unexpected issue occurs, the operator is able to rapidly assess whether it was caused by an abnormality or the result of changes to the physical or operational structure.

Ultimately, the vibration and acoustic mitigation has ensured the continued safety, integrity and viability of the plant’s piping systems. And importantly it has increased throughput and therefore revenues from the plant. Wood is now working with the operator to manage the integrity of future developments, while developing cost-effective solutions to address vibration and noise-related issues.

The collaboration demonstrates that addressing vibration-related risks with an intelligent modelling and analysis-led approach creates significant value, taking an asset from potential pitfall to profitability.

This article was written by Jonathan Baker, Principal Consultant, Asset Integrity Solutions, Wood.

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