Technology

The Trueflaw production method is based on controlled thermal fatigue damage mechanism and produces natural thermal fatigue cracks with realistic residual stress fields. Produced cracks give a realistic simulation of mechanical and thermal fatigue cracks and good simulation of stress corrosion cracks. As an advantage of the method, different crack characteristics (e.g. opening, surface roughness, branching) can be controlled during the production.

Production is based purely on temperature changes so, that machining, welding or mechanical loading is not needed. Surface breaking cracks are produced to ready-made specimens without any extra treatments. Crack size is controlled during the production by controlling the crack growth rate.

Representativeness of True flaws

True flaws are natural thermal fatigue cracks and have similar characteristics than service induced cracks have. For example, produced flaws are tight, rough and have small crack tip radius. Figure 1 shows two different True flaws with differently controlled crack propagation. The other crack exhibit more tortuous propagation than the other one, but both cracks follow the natural and realistic propagation path in the microstructure.

Figure 1. Two True flaws produced with different crack production parameters.

Dye penetrant indication

Typical dye penetrant test results (Figure 2) show, that True flaws can be produced as single and separate cracks without any notable secondary indications.

More information about the method and crack characteristics are given in the enclosed print of an article published in the Journal of Nuclear Engineering & Design September 2003. This article includes also information about NDT response of True flaws.

Figure 2. Typical dye penetrant (PT) indications of True flaws in different materials.

Real components

The Trueflaw method can be applied practically to any shape or size of a component. As an example, Figure 3 and Figure 4 show different real components where True flaws have been produced.

Figure 3. Different real components: a) PWR nozzle specimen, b) PWR collector head and c) pressure vessel nozzle specimen with welded austenitic stainless steel cladding.

Figure 4. BWR Core spray nozzle safe-end.