Chemical Plant Workers Fall From Unsafe Catwalk

This case involves two workers who fatally fell from scaffolding at a chemical plant after the catwalk collapsed. The scaffolding at this plant was made out of zinc and located near tanks that emitted hydrogen sulfide. An expert in corrosion engineering was sought to discuss corrosion hazards associated with wastewater treatment and determine if facility conditions had caused the zinc to rust.

Question(s) For Expert Witness

1. Please describe your experience in corrosion engineering.

2. What corrosion hazards do chemicals / microbes cause?

3. How are corrosion hazards in facilities mitigated?

Expert Witness Response E-144531

I have been engaged in corrosion research for 43 years and served as a consultant on corrosion-related failures for 32 years. A significant portion of my work involves corrosion associated with wastewater. The specific hazards depend on the specific chemicals. Hydrogen sulfide reacts strongly with iron (e.g., carbon steels and low alloy steels) and generates a solid corrosion product film that might slow down subsequent corrosion. However, the solid sulfide film is often non-protective for several reasons, resulting in significant corrosion of the steel. Zinc is also susceptible to corrosion by hydrogen sulfide. Both iron and zinc typically suffer significant corrosion when exposed to sulfuric acid. Mitigation techniques include: control of oxidizers (such as dissolved oxygen and chlorine); adjustment of pH; addition of organic inhibitors; cathodic protection; electrically insulating coatings (e.g., polymers); sacrificial anodes. I have considered several instances of corrosion caused by hydrogen sulfide and corrosion caused by sulfuric acid.