Offshore Pipework Vibration Mitigation: From Diagnosis to Damping

Offshore Pipework Vibration Mitigation: From Diagnosis to Damping

Transient vibration in process pipework can be difficult to assess because the most damaging movement may not occur during normal steady-state operation.

That was the challenge facing a major oil and gas operator after concerns were raised about high vibration during process slugging events. Liquids being carried through with the gas were creating short-duration changes in loading, increasing movement within the main process line and raising questions about the integrity of the surrounding pipework and connected equipment.

The operator had already completed a pipework vibration survey, but the transient nature of the problem meant further investigation was needed to understand the scale of the risk and identify an appropriate mitigation strategy.

Investigating vibration under real operating conditions

AVT Reliability’s Asset Integrity engineers carried out a more detailed investigation using a combination of measurement and analytical techniques.

The assessment included:

• strain and vibration monitoring
• Motion Amplification
• Finite Element Analysis
• review of affected pipework connections and associated equipment

Using several techniques together provided a clearer picture than relying on vibration measurements alone.

Strain and vibration monitoring helped quantify how the pipework responded during operation, while Motion Amplification made the movement of the system easier to visualise. Finite Element Analysis then provided additional engineering insight into the behaviour of the structure and the areas most likely to experience increased stress.

This combined approach allowed the investigation to move beyond simply confirming that vibration was present and towards understanding where that movement could create an integrity risk.

Identifying the wider risk

The investigation confirmed that increased vibration within the mainline pipework was presenting a potential integrity concern.

Importantly, the problem was not limited to the primary line itself. Associated pipework connections and connected equipment were also being subjected to increased movement during slugging events.

This is an important consideration in offshore pipework vibration mitigation. The most visible movement is not always the only area of concern. Dynamic forces can transfer through supports, branches and connected equipment, creating fatigue risk elsewhere in the system.

For that reason, mitigation needs to be based on the behaviour of the wider system rather than simply restraining the point where vibration appears most obvious.

Moving from diagnosis to mitigation

Once the behaviour of the pipework had been established, the engineering team recommended a series of measures to reduce the risk.

One of the proposed solutions was the use of viscoelastic dampers to provide dynamic restraint during slugging events.

Unlike a rigid support, a correctly selected damping solution can reduce damaging dynamic movement while still allowing the pipework to accommodate the movement required during normal operation.

This makes damping particularly useful where vibration is intermittent or driven by changing process conditions.

The objective is not simply to make the pipework move less. Effective mitigation should reduce the dynamic response in a controlled way without introducing new stresses or restricting necessary thermal movement.

Why mitigation should follow investigation

There can be a temptation to address pipework vibration by adding additional supports or restraints as soon as excessive movement is observed.

That can create further problems if the underlying behaviour of the system is not understood first.

A structured investigation helps establish:

• where the vibration originates
• how the system responds during different operating conditions
• which components are carrying the greatest dynamic load
• whether fatigue risk extends beyond the visibly affected area
• which form of mitigation is appropriate

Only then can supports, dampers or other modifications be selected with confidence.

For this offshore application, combining physical measurements with visualisation and engineering analysis provided the evidence needed to move from a vibration concern to a targeted mitigation strategy.

A measured approach to pipework integrity

Process conditions change. Slugging, flow variation, pressure changes and transient events can all alter the way pipework behaves.

Where vibration becomes a concern, the most effective response is rarely to treat it as an isolated mechanical problem.

AVT Reliability combines pipework vibration assessment, strain measurement, Motion Amplification, Finite Element Analysis and fatigue assessment to understand how systems behave under real operating conditions and to identify proportionate mitigation measures.

Where dynamic restraint is required, solutions such as viscoelastic dampers can then be selected and applied based on measured behaviour rather than assumption.