HSE material on plant design and failure modes shows that pressure vessels face much more than simple corrosion loss. Important deterioration and failure mechanisms include overpressure, overheating, mechanical and thermal fatigue, brittle fracture, creep and fabrication-related problems. A periodic inspection strategy that focuses only on thickness loss can therefore miss critical risks.
HSE’s research into historic welding failures also shows that weld defects and management weaknesses often appear together. Frequently observed issues include crack-like flaws, volumetric flaws, undersized weld geometry, inadequate supervision and insufficient inspection coverage. In practice, vessel inspection should combine visual review, record review, comparison with earlier NDT data and focused re-examination of critical weld regions.
Once a defect is found, the correct action boundary cannot be reduced to “keep running if possible.” The decision should consider defect type, size, location, process fluid, operating temperature and the remaining life assessment. For low-temperature service, cyclic loading or corrosive duty, the response threshold should be more conservative.