ASSESSMENT OF OPERATING LIMITS FOR CRITICAL DISSIMILAR METAL WELDS IN A HYDROCRACKER

摘要

The risk of failure of ferritic alloy steel to austenitic stainless steel dissimilar metal butt-welds in a refinery hydroprocessing unit increases with operating temperature and shutdown cooling rate due to the combined effects of hydrogen diffusion and thermal fatigue. Operating limits of this type of weld were assessed with finite element modeling and simulation tests, and the findings from this work were supported by plant inspection results. As a result, both the maximum operating temperature and cooling rate constraints were relaxed for critical equipment and piping in a hydrocracker unit.