TWI Industrial Member Report Summary 879/2007
By P Moore, I Hadley and Y-H Zhang
The European FITNET consortium has recently prepared a new European fitness-for-service (FFS) procedure (FITNET, 2006), to cover assessment of flaws in welded and non-welded metallic structures. The procedure is intended to cover all industry sectors and all relevant failure/damage modes (fracture, fatigue, creep and corrosion). Further details of the project are given in the FITNET website (www.eurofitnet.org) and proceedings of the end-of-project conference (eg Koçak, 2006).
The fatigue assessment options within FITNET are divided into five different 'Routes'. Routes 1 to 3 are intended to assess the accumulated fatigue damage at critical locations in the absence of a pre-existing flaw. If real or postulated damage is present then Routes 4 or 5 are used. Route 4 is the appropriate approach for assessing planar crack-like flaws, and uses a fatigue crack growth analysis to calculate the growth of a pre-existing flaw for the purpose of making a safe FFS assessment. Route 5 is used only to assess non-planar flaws, and uses an S-N curve (stress versus number of cycles) approach.
In order to validate the FITNET FFS procedure (ie to test it against experiment and experience), case studies illustrating the application of the procedure to the results of full-scale tests are required. TWI has available the results of some laboratory fatigue tests on welds containing pre-existing flaws, which can be used to validate the fatigue assessment Route 4 from FITNET (to date, the FITNET procedure document does not contain any validation data for Route 4).
This report is one in a series of four TWI members' reports covering various aspects of the validation of FITNET, ie:
- Use of the Route 4 fatigue assessment procedures (this report).
- Effects of weld strength mismatch on fracture assessment.
- Use of Option 4 (FEA-based) fracture analysis.
- Application of the corrosion assessment procedures.
To validate the FITNET Route 4 fatigue assessment procedure against results of large-scale fatigue tests.