SINTEF and Equinor Develop Method to Predict Subsea Riser Fatigue

A new large-scale transparent riser test by SINTEF and Equinor reveals how internal flows and external wave motion interact to drive fatigue, which could lead to safer, more cost-effective riser design and lifetime extension. Subsea risers are large pipes carrying resources from seabed wells to surface facilities, exposed to external loads from waves and currents and internal loads from fluids. The research tested slug-flow and wave loading together, addressing uncertainty in current engineering practice.

 

Details of the Research

 

SINTEF and Equinor have developed a method. It predicts subsea riser fatigue. It uses a transparent riser test. This is a large-scale test. It reveals how forces interact.

The method addresses a key challenge. Risers carry resources from wells. These go to surface facilities. They face external and internal loads. These create fatigue over time.

 

The Fatigue Challenge

 

Riser fatigue is a significant issue. It is prevalent with multiphase flow. This combines gas, liquids and solids. These form alternating slugs and pockets. This is called slug flow.

The resulting forces cause fatigue. Changing pressure generates fluctuating forces. These affect critical points. These include the hang-off and touchdown areas. This drives wear and tear.

 

The Limitations of Current Practice

 

Current practice has limitations. Load processes are assessed separately. Their contributions are then combined. This uses simplified methods. These contain considerable uncertainty.

These methods can mislead. They can underestimate combined fatigue. Other approaches are too conservative. Simply adding damage is questionable. This can underestimate total damage.

 

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The Testing Approach

 

The research used a novel approach. The team built a scaled riser. It completed three test categories. These covered slug and wave loading. Combined loading was also tested.

The approach isolated the processes. Wave motion was introduced. Slugs were injected separately. Sensors recorded the response. The scale makes it among the largest of its type.

 

The Transparent Innovation

 

A key feature was transparency. The pipe was transparent. Cameras recorded internal flows. This occurred during motion. This was a distinctive feature.

This enabled simultaneous observation. The team observed flow and response together. Company leadership cited this value. Image processing quantified the flow. This related internal flow to structural response.

 

Significance of the Research

 

The research provides a benchmark. It offers controlled data. This assesses numerical models. It couples structural and flow modelling. This validates the coupled approach.

The research improves prediction. Company leadership stressed the evidence base. Better representation aids decisions. This covers new designs. It also predicts remaining lifespan. The method could extend to more complex combinations.