Brittle Fracture of Thin Wall Pressure Equipment

Even for ferritic materials, it has been assumed that no consideration for the brittle fracture at low temperature is necessary on condition that the wall thickness of pressure equipment is less than roughly half an inch (12.7mm) from industrial experience. Nevertheless, brittle fracture incident occurred at a welded joint of a carbon steel pipeline used for transportation of crude oil at low temperature of −6°C in one of our refineries recently. The pipeline was 12.0 mm in thickness and it was found that significant crack-like flaw existed along inside of the welded joint. In this study, the assessment of the brittle fracture of thin wall welded joint with crack-like flaw was performed in accordance with Section 9 in API RP 579 (2000). Then it was concluded that brittle fracture assessment is necessary regardless of the wall thickness when significant crack-like-flaw is detected in pressure equipment, especially at low temperature condition.