Connect, no.163, November/December 2009, p.8

Variable amplitude fatigue testing of full-scale pipe joints

TWI's resonance fatigue testing laboratory

TWI has a total of seven resonance testing machines for full-scale fatigue testing of pipe joints accommodating diameters in the range 4 to 36" (100 to 914mm).

A rotating bending moment of constant amplitude is applied at the resonant frequency of the pipe, typically 25 to 30Hz, allowing high-cycle testing of riser girth welds to be carried out rapidly. In response to requests from clients, a method of reproducing the narrow band variable amplitude loading experienced by risers in deep water, has now been developed as shown in the diagram.

New control systems and software developed in-house, allow the required loading spectrum to be reproduced reliably at the resonant frequency of the full-scale pipe sample. This unique system is now being used for extreme high-cycle variable amplitude tests, up to 200 million cycles, on 16" (406mm) diameter pipe in a current Group Sponsored Project: 'Further study of fatigue damage to girth welds from low stresses in the loading spectrum'.

Other components such as pipe to forging joints, threaded pipe connectors or even solid components such as drive shafts can also be accommodated. Three of the machines have now been equipped for variable amplitude loading and are available for use by TWI Member companies.

Typical section of variable amplitude stress sequence for a riser

For further information, please contact structuralintegrity@twi.co.uk