Stress Corrosion Cracking in SA304 Stainless Steel Phenolic Resin Reactors

Aging phenolic resin reactors built in the 1960’s were constructed of SA304 stainless steel, many of which were originally fabricated to ASME Section VIII standards and were never registered as such nor with the National Board. Some of these reactors have been exhibiting stress corrosion cracking, (SCC) in the shell plate where external carbon steel structural components such as support legs and vacuum rings are attached. The problem is observed primarily at the interface of support legs where reinforcing pads or “poison” pads have not been installed.Of the vessels inspected to date approximately 50% have been identified as having SCC.

Newer vessels are typically fabricated with reinforcing pads beneath the support legs in order to reduce the stresses induced in the shell plate and therefore minimizing or eliminating the potential for SCC. Insufficient historical data has been collected on new vessels to date to provide a determination on the effectiveness of new practices for reinforcing pads with respect to decreasing the probability of cracking.

Initiating at the root of the external attachment weld and propagating into the shell plate material, advanced forms of the cracking have been known to propagate through the shell at almost a laminar direction and in some cases working their way through wall. In most instances, the problematic reactors can be identified before the development of the cracking leads to failure or leaking with the use of proper nondestructive testing (NDT) techniques applied from the interior of the vessel.