TWI Industrial Member Report Summary 512(III)/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/7 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 third 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 the 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 II (Published and additional TWI data), presents further assessments of large scale tests reported by other organisations, in addition to a number of further tests performed at TWI. The present report covers similar PD 6493:1991 assessments of actual service failures caused by fracture. In total, over 150 individual fracture assessments have been performed covering 14 failures. These include a bridge, ship, storage tank, pipe and HGV axle in addition to a number of pressure vessels. All but one, involved brittle fracture of ferritic steel structures.
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.