Corrosion of Ferritic Stainless Steel Weldments

1 Leaking Welds in a Ferritic Stainless Steel Wastewater Vaporizer 

A nozzle in a wastewater vaporizer began leaking after approximately three years of service with acetic and formic acid wastewater at 105 °C (225 °F) and 414kPa (60 psig). 

The shell of the vessel was weld fabricated in 1972 from 6.4mm ( /4 inch) E-Brite stainless steel plate. The shell measured 1.5 m (58 inches) in diameter and 8.5 m (28 ft) in length. Non-destructive 

An internal inspection of the vessel revealed that portions of the circumferential and longitudinal seam welds, in addition to the leaking nozzle weld, displayed intergranular corrosion. At the point of leakage, there was a small intergranular crack. 

The evidence indicated weldment contamination therefore, effort was directed at finding the levels of carbon, nitrogen, and oxygen in the various components present before and after welding. The averaged results were as follows  

---