Cast Iron Failures in Sulphuric Acid Plant

The first part of this article (February issue) dealt with a failure in a boiler raising steam by using heat from a 7% SO2‐in‐air mixture; the protective corrugated cast iron shell round the boiler tubes opened, exposing them to oxidation. The present case concerns cracking of a 22‐in. connecting main between two SO3 absorbers; this was found to be caused by SO3 passing into the cast iron through the graphite flakes and attacking the adjoining ferrite.