The problem

A post-lay survey was performed after the installation of a 120km pipeline offshore Malaysia. The results of this survey revealed the presence of a number of spans whose length exceeded the allowable stress limits determined during the pipeline design process.

Our client asked us to assess the spans in order to determine the need for remediation works.

The solution

As the anomalous spans were discovered immediately after installation, assessment was required on the installed, flooded, hydrotest and operational conditions.

We reviewed the data and used finite element analysis (FEA) to determine span stresses and natural frequencies. The methodology defined in DNV-RP-F105 was utilised to assess the likely fatigue damage due to VIV.

Our team also performed local buckling analysis in accordance with DNV-OS-F101 of the pipeline spans, to investigate lay tension. A report was compiled comprehensively explaining the findings and their implications on the pipeline’s integrity.

The benefits

Our analysis concluded that although the longitudinal stresses were outside the allowable limits defined by ASME B31.8, the FE model was acceptable against DNV-OS-F101. As such, the pipeline was deemed suitable for flooding, hydrotest and operation without the need for any remedial work.

We provided our client with confidence the spans were fit-for-purpose in all of the conditions and scenarios considered.

Our timely completion of the analysis allowed our client to proceed with flooding and hydrotesting as per their rigid schedule.

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