Reheat cracking in AGR boiler components

AGR header - courtesy Bristol University

The operator had experienced reheat cracking in thick-section welds in type 316 AGR boiler components - both pressure parts and support structures.

The objective of this work was to assess the integrity of specific welds in the boiler framework to assure safe operation for 30 years under steady state and cyclic operation, accounting for the effects of welding residual stresses and long-range fabrication-induced stresses.

A creep-fatigue crack growth assessment was performed, following the R5 procedure and using the results of a stress analysis carried out by the operator.

Residual stresses were evaluated for the range of welds assessed.  To provide confidence, sensitivity studies were performed based on the extent of cracking observed in different welds and the likely variation in materials properties.

It was concluded that certain welds might be at risk of cracking before the end of a 30 year life, but certain assumptions identified as conservative and further work was required to refine analysis.

Plant Integrity