TWI Industrial Member Report Summary 1082/2017
By Emily Hutchison, Emilie Buennagel, John Wintle, Warren Bath and Museok Kwak
Many ageing pressure vessels were designed with a notional 25 year design life using standards such as BS 1515, which did not require fatigue assessment. This means that the fatigue lives of these vessels have never been calculated. Offshore operators seek a methodology for justifying life extension for vessels designed to older codes through fatigue assessment and a campaign of risk based inspection. Therefore, fatigue assessment is a critical part of the life extension process.
The report outlines the principles for fatigue reassessment of long service pressure vessels and demonstrates these principles by means of a case study on a vessel that has been in service since the 1970s.
The case study demonstrated the principle of reassessment based on detailed modelling and inspection of an example vessel. Five necessary phases are:
- Examination of benchmark vessel;
- Compliance with standards, including analysis of fatigue loading;
- Commonality between vessels;
- Engineering critical assessment (if necessary);
- Inspection plan.