Urea Reactor Integrity Evaluation Based on Failure Analysis

Multilayered pressure vessels tend to induce stress corrosion cracking (SCC) in the heavy weld. This conclusion is based on the recent ruptured urea reactor failure analysis. Finite element simulation proved that multilayered urea reactors have yielded zones at the heavy weld where the SCC crack initiated. Acoustic emission (AE) examination conducted for two in-service urea reactors revealed AE event clusters at the heavy weld and subsequent phased array reexamination confirmed the existence of propagating defects in the heavy weld. The results also showed that AE evaluation and phased array reexamination are sound combination methods to evaluate the integrity of multilayered urea reactors. Besides, they are superior to $γ$-ray inspection because of the uncertain propagation direction of SCC cracks.