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The average hardness of tube materials.
| Samples | Location Point | Average hardness (VHN) |
|---|---|---|
| Sample III (un-failed tube) | Inner surface | 153 ± 2 |
| Outer surface | 140 ± 3 | |
| Sample II (300 mm above bulging area) | Inner surface | 141 ± 3 |
| Outer surface | 120 ± 3 | |
| Sample I (bulging area) | Near crack tip (left) | 171 ± 4 |
| Near crack tip (right) | 164 ± 3 |
