Atmospheric corrosion studies in Kenya: past, present and future

Abstract

Despite the regular inspections and current contingencies made in the HF plant at Necsa, an isolated case where two mild steel vessels leaked HF during operation occurred without warning. The failure of both these vessels necessitated their premature decommissioning, and showed that better understanding the corrosion of mild steel used in the HF industry was needed. The failure of the mild steel was traced to nitric acid (HNO3) contamination in the sulphuric acid (H2SO4) feedstock which eventually concentrated in the technical grade HF product downstream. A study to simulate the industry corrosion conditions in a laboratory was required to better estimate the service life of the steels used in the HF plant because understanding the effect of HNO3 contamination on the plant’s steels and the determination of corrosion inhibition strategies was essential. Unfortunately, HF is an extremely hazardous chemical and concentrations above 70% HF have a fuming capacity, making it a potentially lethal chemical for corrosion experiments. Therefore, to safely work with HF, the safety risk for working with the chemical first had to be categorised and assessed. This entailed determining the internal hazards of handling HF and its consequences, the probability of exposure and then mitigating actions that would lower the risk to a point that corrosion experiments could safely be conducted. A regular safety risk assessment, a process description, a “what if” analysis, as well as an external hazard and operability study (HAZOP) was completed. This lead to the implementation of a specialized experimental setup that proved to be prepared for any HF exposure contingencies while still producing HF corrosion data comparable to literature. Moreover, preventative measures including the use of HF resistant PPE (Personal Protective Equipment), well ventilated facilities and HF resistant Teflon containers were put in place which eventually resulted in the safe execution of corrosion tests completed there.