Failure investigation of a subsea pipeline

In-depth root cause analysis of a critical subsea pipeline failure to support insurer liability decisions.

Background

Aavir LLC received email notification of an incident of failure of a subsea pipeline from the Insurers wherein the root cause of the failure was a major cause of concern in determining policy liability requiring an in-depth root cause failure analysis.

Subsea pipelines serve as underwater arteries for petroleum developments. They transport oil, gas and other produced fluids from wells to production platforms and then on to a variety of onshore and offshore facilities. 


Whether the pipeline is rigid, flexible or composite, its structural integrity is fundamental for the performance of the subsea transportation network of hydrocarbons. Although a relatively infrequent event, pipeline failure can cause widespread physical and environmental damage, as well as resulting financial losses for operators, clients and dependents.

Common causes of failure include

Accidental damage

impact from anchors, other pipes, trawl boards and objects dropped from vessels.

Partial and total blockages

arising from the formation of hydrates, wax deposits and stuck tools or inspection gauges.

Corrosion

due to, inter alia, the presence of carbon dioxide (CO2), oxygen (O2) and hydrogen sulphide (H2S) in produced water.

Erosion

due to the abrasive properties of sand particles and other solids in the produced fluids.

Abrasion and wear

if the pipeline isn’t properly secured and allowed to move on the seabed.

Freespanning

where the seabed supporting the pipeline or overburden is washed away over time. This can cause fatigue damage due to vortex induced vibration, or buckling/hogging of the pipeline if it isn’t correctly restrained.

The Challenge

Due to the extreme nature of the environment in which this pipeline operated, the composition of the hydrocarbon it transported and the temperatures and pressure to which it was exposed, identifying the root cause of failure and its financial outcomes was extremely challenging and required specialist academic, technical and practical knowledge of the engineering discipline.

Investigation Methodology

The investigation methodology adopted by the Engineers at Aavir LLC on this occasion comprised of detailed inspection of the pipeline and comprehensive enquiries surrounding it which can be summarised as follows:

Inspection

  • External inspection of the pipeline was undertaken during an autonomous underwater vehicles (AUV) equipped with an array of sensors to look for issues such as anode wastage, damage to any weight coating, free spans, global buckling, marine growth and any evidence of an external force.
  • Internal inspection was undertaken using intelligent pigging wherein cameras and sensors were run through the pipe capturing data about its wall thickness, ovality and internal deposits which provided invaluable information about potential issues such as corrosion, erosion, hydrogen-induced stress cracking, metal loss and other abnormalities within the pipe.

Enquiries

  • Fluid being transported – What were the physical (state, volume, density) and chemical (corrosion/erosion resistance, toxicity, flammability) properties of the hydrocarbon being transported?
  • Materials used – What was the pipeline made from and was the material fit for transporting the hydrocarbon?
  • Age of the pipeline – How old was the pipeline? What was its expected lifespan? Was it well maintained?
  • Operational procedure – Was this being correctly adhered to in accordance with the design parameters?
  • Length of sections(s) affected – How many sections of the pipeline were affected and what was the length of each section?
  • Design of the pipeline – Was the design suitable for transporting the intended fluid? Was it approved by an appropriately accredited company?
  • Manufacturing process – How was the pipeline manufactured? Was it seamless or welded?
  • Location – What were the topographical and meteorological conditions? Was the location susceptible to natural catastrophes such as earthquakes, tsunamis or a shifting seabed?
  • Maintenance procedure – Was this being correctly adhered to in accordance with the operational procedures? This included periodic surveys of the internal and external surfaces of the pipeline and wall thickness measurements as well as any pipeline restraint system.

Conclusion

Although the root cause of failure of the pipeline could not be established on this particular occasion, detailed inspection of the pipeline and comprehensive enquiries surrounding it undertaken by us enabled Insures to rule out all concerned exclusions and form a definitive position on policy liability which was a favourable outcome for all the parties involved.