A power company commissioned TWI to perform an engineering critical assessment (ECA) of three header welds where NDT indications had been reported during routine inspection.
- To determine the remaining life (margins of safety) of the header weld joints.
- Life assessment using a fracture mechanics methods in accordance with BSI PD6493:1991 Level 1 procedures. (PD 6493 has now been superseded by B7910), and TWI's software package 'Crackwise'.
- Sensitivity analysis in order to establish the effect of uncertainties generated by the use of assumed and estimated material property data.
- An understanding of the allowable stresses and defect sizes, so allowing the parts to continue in service with increased inspection monitoring.
- Replacement of the parts was no longer required, producing significant savings in both equipment and plant 'down-time'.
The probability of failure of the flawed welds was very low. However, the work highlighted the need for improved crack growth monitoring and some further investigation of the stresses within the component.