TWI Industrial Member Report Summary 512(II)/1995
N V Challenger, R Phaal and S J Garwood
BSI PD 6493:1980: 'Guidance on some methods for the derivation of acceptance levels for defects in fusion welded joints' was published by the British Standards Institute in 1980. Following recommendations of the BSI WEE/37 committee, the revised document PD 6493:1991 'Guidance on methods for assessing the acceptability of flaws in fusion welded structures' was published in 1991.
This report is the second in a series presenting the results of an appraisal of the fracture assessment procedures of PD 6493:1991. The objective of the work is to demonstrate the conservatism of the procedures and to indicate areas where the procedures could be improved.
This has been achieved by the use of fracture assessment procedures to predict the outcome of full scale tests (e.g. wide plates and pressure vessel tests) and service failures. The first in the series ('Appraisal of PD 6493:1991 fracture assessment procedures') covered the results of PD 6493:1991 fracture assessments on large scale tests (wide plates and pressure vessels) performed at TWI. Part III ('Appraisal of PD 6493:1991 fracture assessment procedures - Part III Assessment of actual failures'), presents similar assessments of actual service failures caused by fracture. This report presents PD 6493:1991 assessments of large scale tests reported by other organisations in addition to a number of further tests performed at TWI. In total over 600 individual fracture assessments have been performed covering 176 large scale tests. The tests include pressure vessels, pipe bending and pressure tests and wide plates (uniaxial and biaxial).
BSI committee WEE/37 has reconvened to consider further revisions to PD 6493, and the results from the analyses described in this series of reports will provide the committee with some guidance on areas where the procedure could be improved.
The objectives of this study are to validate the PD 6493:1991 fracture assessment procedures by comparison with large scale tests performed at TWI and elsewhere. In total, 176 wide plate, pressure vessel and pipe bending tests have been chosen from the published literature, covering a range of materials and applications, including pressure vessel steels, pipeline steels, stainless steels, parent materials and weldments. This is in addition to the 94 TWI tests covered by the previous report in this study.
Many features of the PD 6493 fracture assessment procedures have been investigated in over 600 individual fracture assessments described in this report, including Levels 1, 2 and 3 procedures, toughness inputs, residual stress assumptions, proof testing, stress intensity and net section stress solutions.