Design Examples

In the following examples were no thickness, size effect correction and no mean stress effects (e.g. R≤0.15) taken into consideration.

Example 1

The weld detail is categorised into FAT-Class 63 according to its characteristics. Stress range is 63 MPa @ 2 Million load changes (Fig. 8).

Through HiFIT Treatment the Class is improved by 4 steps (Fig. 7 blue arrow) to FAT 100. Stress range is 100 MPa @ 2 Million load changes.

The improvement is approx. 60%

At the same stress level (63 MPa) the fatigue life time improves from 2 Mio to 40 Mio load changes!

The Factor is 20! (Fig 8)

Example 2

The same weld construction is now from a steel fy ≥ 950 MPa. Will this not be treated the as welded status will not be changed and stays with a FAT Class of 63 (Fig. 9). There is no improvement just by using high tensile steel.

Through HiFIT Treatment the Class is now improved by 8 classes (Fig. 9 red arrow) to FAT 160. The stress range is now 160 MPa @ 2 Million load changes.

The improvement is approx. 150% (Fig. 10)

At the original stress level (63 MPa) the fatigue life time improves from 2 Mio to more then 100 Million load changes! Probably to the status that it will never brake! (Fig. 10)

Fig. 9: Improvement 8 FAT-Classes with the HiFIT Treatment

Fig. 10: S/N Diagram for fy ≥ 950 MPa; R ≤ 0,15

Practical Significance of the IIW Recommendation

The application of the IIW recommendations results in excellent improvements against weld fatigue for three different seam types.

Here are the comparisons between the HiFIT treatment and notchless grinding or TIG treatment.