TWI’s resonance testing laboratory has seven TWI-designed resonance fatigue test machines which can test pipes and mechanical connectors with outer diameters ranging from six to 36 inches in rotating bending.
Tests can be conducted with:
- zero mean stress
- a tensile axial mean stress introduced by internal pressurisation with water (up to 10,000psi)
- a tensile axial mean stress introduced mechanically (up to 2000kN)
Operators choose TWI for our expertise (especially in interpretation of results), our experience and our capability.
The need for reliable testing
Small changes in welding process or parameters can greatly influence the geometry and properties of girth welds, and so can affect their fatigue strength. Where high reliability is required, validation fatigue testing of new welding procedures is therefore specified to ensure safety of these systems.
The resonance technique is a quick and efficient means of fatigue testing the full circumference of girth welds and mechanical connectors in full-scale pipes.
Resonance fatigue testing for the oil and gas sector
This type of testing is mainly used by the oil and gas industry for testing girth welds in risers, pipelines and flowlines to generate S-N curves. Connector designers use resonance fatigue testing to verify finite element predictions of fatigue life and of the mode and location of fatigue failure.
Resonance tests typically run at 30Hz, so samples can be tested to failure quickly. Tests are run continuously, achieving 2.5 million cycles per day. Resonance fatigue testing has become the industry standard method of testing full-scale girth welds for high integrity pipes and risers, and is also widely adopted for fatigue testing mechanical connectors and other subsea components.
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