A silent threat in a pressurized recirculation line.
Inspection is not a snapshot.
Sometimes, you read the life story of a weld… and uncover a ticking time bomb.
This case involves a WB36 pipe (⌀ 298.6 × 23 mm), operating at 375 °C and 346 kgf/cm².
During a routine inspection, I detected a subtle MT indication in one of the welds.
Further investigation revealed:
A transgranular crack propagating from the inside, initiated at a notch in the root pass.
Causes & Findings
- Crack initiated at a sharp angle caused by excessive root penetration
- Partially filled with oxides, likely formed during or shortly after welding
- No anomalies in hardness or microstructure (200 HV10, compliant with WB36)
- Mechanism: Thermal stress, not pressure-induced
Lesson:
Even with properly stress-relieved weld metal, geometric stress concentrations combined with thermal cycling can initiate critical cracking.
Inspection means understanding.
It’s not just about what you see, but what it’s becoming.
Your Turn
In your experience, which geometries deserve special attention in weld design or inspection?
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