Ethylene Oxide Reactor Engineered Weld Repair Case History

Abstract

Abstract A pair of ethylene oxide reactors have been in service for approximately twenty years. The shell material of construction is SA-543, Grade B, CL.1 They were designed according to ASME Section VIII Div.2. A temporal repair work was engineered to remove cracks and reweld. One-side welding approach was qualified per ASME Section IX. It is widely accepted that tensile residual stresses can be detrimental to the integrity of welded components. A combination of weld residual stress simulation and measurement was performed to predict and characterize the weld residual stresses. Generation and analysis of the models followed established best practice for computational welding mechanics. The weld residual stress profiles were optimized after several interactions and mockup coupons were prepared. The approach included the generation a representative computational welding mechanics model; calibration the free parameters in the model against test data; and then validation of the predictions of residual stresses against various experimental residual stress measurements. The residual stress states in both the original weld mock-up and the as-repaired weld were determined using two different experimental techniques: Air-abrasive Centre Hole Drilling (ACHD) for surface residual stresses and incremental Deep Hole Drilling (iDHD) for through-thickness residual stresses. Mechanical testing included tensile and impact testing along with hardness profiles. Controlled deposition approach was implemented to lower hardness. Extensive temporary repairs were successfully executed. New reactors with lower strength steel and post weld heat treatment are being fabricated for permanent replacement.