The structural integrity management of a deaerator feed water vessel approaching the end-of-life condition

Abstract

The present paper describes the integrity management of a deaerator feedwater vessel over a 20-month service period within which it approached the end-of-life condition. A series of four remnant life assessments were carried out using both Crackwise and the R6 failure assessment programmes which determined critical crack sizes for vessel failure and a leak-before-break event. Interestingly, actual crack growth data obtained from this particular feedwater vessel over a 12 year service period was used in the sub-critical crack growth rate assessments. Remnant life values were reduced from only 25% of the normal guideline period of two years to re-inspect repaired weld cracks to around 12% or only three months within a 30-month service period. Also at each inspection a large amount of cracks, which numbered over one hundred, were found. From this it was clear that the vessel was approaching an end of life condition and the final assessment deemed that the vessel should be removed from service and all the problematic weld runs be replaced with new welds.