Subscribe to our newsletter to receive the latest news and events from TWI:

Subscribe >

Static strength of cracked tubular joints

Jacket structures for installation in offshore locations must be designed and constructed to withstand severe storm conditions. In particular, each joint must possess adequate static strength to withstand extreme loading. Design data for the static strength of tubular joint connections has mainly been produced for intact, uncracked joints. However, extreme loading could occur when undetected and unrepaired cracks are present in the structure. It is therefore essential that design data for cracked joints is available.

TWI addressed the problem with the following objective:

  • To develop guidance on the static strength of cracked tubular joints and to provide recommendations for in-service assessment of cracks using a failure assessment diagram (FAD) based approach.
Finite element model of a cracked joint. The model was loaded at the left of the picture, through the brace, and constrained at the right of the picture. Symmetry means that only half the joint needs to be meshed
Finite element model of a cracked joint. The model was loaded at the left of the picture, through the brace, and constrained at the right of the picture. Symmetry means that only half the joint needs to be meshed

The project objective was achieved by a combined numerical and experimental approach:

  • 3D finite element models were used to analyse uncracked and cracked tubular joints. The models were built and the results analysed using FAM. ABAQUS was used for the finite element analysis (FEA).
  • Experimental work on seven full size joints was carried out using a purpose built test rig to validate the numerical models. The test specimens were extensively instrumented in order to compare their behaviour with that predicted by FEA. The development of ductile tearing at the crack tip was also closely monitored.

The results of the project were encouraging:

  • Excellent agreement between the FEA and the experimental results enabled the numerical models to be used with confidence.
  • Failure assessment diagrams were developed for in-service assessment of cracks. Using this approach joint failure can be predicted for plastic collapse, fracture or a combination of the two.

The benefits of the FEA approach are summarised below:

  • Drastically reduced the number of physical tests that were needed.
  • Enabled crack tip fracture parameters to be calculated for the FAD.

This project was supported by:

Amoco (UK) Exploration Co., British Gas plc., Chevron UK, Conoco Inc., McDermott Engineering, Mobil North Sea Ltd., The Health and Safety Executive.

For more information, please email contactus@twi.co.uk.

Media /

Related Insights

View all insights
}