Index of acronyms 

Creep is an in-service damage mechanism where a solid material deforms permanently over time under the influence of mechanical stress, which eventually leads to failure or stress rupture. It generally occurs in plant at elevated temperatures, such as superheater and reheater tubes and headers in conventional power station boilers. Creep always increases with temperature.

One type of creep-induced cracking is Type IV cracking. This occurs in ferritic steels in the ‘Type IV zone’ at the edge of the heat-affected zone. Creep causes the formation of voids in this zone. The voids grow and cracking occurs, joining up the voids. These cracks can grow rapidly. Ultrasonics is used to detect Type IV cracking as the cracking can form below the surface of the component.

For more information on creep see:

For more information on the use of TOFD and phased array detection of creep damage see:

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