Apollo has provided an overall assessment report of a flare tower structure. This supplied the client with the assurance for its current design integrity, validity for the previous fatigue assessment, and an accurate model that can be used to assist with future assessments, inspections, and repairs.
Summary
The flare tower is part of the original installation of the platform installed in 1982. The asset is at its late-life phase and the integrity of the structure is currently covered by in-service structural re-assessment. At the end of its original design life in 2007, the flare deck, together with the upper part of the flare tower, was removed and replaced.
As part of the flare tower’s integrity management, the client h
as a requirement for an in-place strength assessment to confirm that the structure meets current industry standards while accurately representing the current configuration and support stiffness of the tower. The study will provide the client with additional information which may be used in conjunction with the existing fatigue assessment to increase the efficiency of the inspection programme and assist with the assessment of any degraded areas.
Once complete, Apollo was able to provide commentary on the structure’s strength tolerability to degradation and defects. A working analysis model was also provided and can be used for future reassessments to inform the urgency of repairs for any future defects found.
Scope of Work
An overall assessment report was provided which details the natural frequency of the tower and the utilisation plots for all flare tower members. Apollo also provided a detailed analysis of the main flare tower structure and supporting module including all main ancillaries such as the flare tips, flare lines, and access stairs and platforms. The model included all the applicable loading, such as the flaring thrust loads, snow/ice, and latest wind data using BS EN 1993-3-1 load factors and combinations. As part of the analysis, the applicability of the Equivalent Static Method for towers and masts detailed in Eurocode has been assessed and applied to the wind loading to ensure that the dynamic response of the flare tower was accounted for.
One of the main challenges for this project was the complexity of the modelling required due to the configuration of the tower. To be able to carry out this out within budget and schedule, Apollo has utilised 3D CAD modelling of the tower and the main walkways and platforms and imported these into STAAD.Pro.
The flare tower structure has been designed using complex, non-conventional connections. In order to take some conservatism out of the assessment of these connections which are traditionally carried out by manual calculations, critical connections were modelled and analysed using IDEA StatiCa, which is a component-based finite element method (CBFEM) design software.
From the assessment, Apollo has given assurance that the flare tower meets code requirements. The natural frequency of the structure was found to be consistent with previous fatigue analysis. This gives confidence that the existing fatigue analysis remains valid for planning inspections targeted at low-fatigue locations. If future defects are identified, it should be possible to infer an impact on the strength and fatigue life of the tower from the modelling performed with the analysis model provided.
Benefit
- Assurance of the current integrity of the structure;
- A safe, pragmatic and cost-effective approach to the structural assessment;
- Confidence that previous fatigue assessments remain broadly valid for the current configuration and condition of the structure;
- Accurate analysis models are provided to the client, which can be used to assist with future assessments, inspections, and repairs.
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