Multispecies bacterial attachment to A106 GB industry-finished steel used in heat exchangers

Abstract

Multispecies bacterial attachment to industrial-finished alloys is not understood. It is not well understood as to why certain bacterial species selectively attach to differently finished steel surfaces. It is also a matter of curiosity as to why the attachment of certain bacteria influences corrosion. Bacterial attachment in heat exchangers leads to biofouling, corrosion, and downtime costs. This study evaluated the synergistic effect of bacterial attachment to smooth and rough (industrial standard) surfaces unique to the petrochemical industry. From the results there were no significant time-related differences in colonisation (p(perm)>0.05), and bacterial levels on the surfaces (p>0.05). However, quantification of surfaces using Atomic Force Microscopy (AFM) showed significant differences (p<0.05) in the root mean square surface roughness (RMS) of the differently finished surfaces, elucidating that bacterial colonisation was not proportional to surface roughness. It was observed that Clostridium sp. colonised the rough surfaces abundantly, and Pseudomonas sp. favoured the rough surface during early colonisation which influenced the corrosion rate. In bacterial presence, the corrosion rate on the rough alloy surface on day 3, exhibited corrosion resistance. This was owing to the synergistic behaviour of the bacteria which selectively attached to the rough surface and formed biofilm. Increased corrosion rates were then observed when compared to the smooth alloy. On the rough surface on day 6, the corrosion rate was observed to be the highest with 38.72 ± 0.15 mm/y. Smooth surfaces exhibited unusual corrosion rates on this day. On day 13 both surfaces exhibited a corrosion protection phenomenon. In light of the findings, it was i observed that there were significant differences observed on day 6, in the corrosion rate value between the rough and smooth surfaces (p<0.05). The growth model confirmed that exponential growth phase took place from day 6. Total Organic Carbon (TOC) results revealed that during bacterial growth, the bacteria utilised the carbon sources and produced acetic acid and lactic acid which played an important role in the corrosion process. Unlike sulfate-reducing bacteria (SRB), Clostridium sp. and Pseudomonas sp. described in this study are rarely reported in the petrochemical environment. These microorganisms are ubiquitous; however, their dominance in these systems showed that they play a significant role in steel corrosion. This study used next-generation sequencing with qPCR into microbial species colonising steel with AFM, which are rarely reported jointly in the literature. These bacteria can survive nutrient-depleted conditions for extended periods. The results provided a basis to explicate metabolic pathways. Long-term steel exposure to the bacterial consortia indicated steel protection rather than corrosion. Innovative insights on carbon-metal bonding were also determined, which could be a basis for future work. The synergistic behaviour of the bacteria provided a new dimension of thinking regarding the corrosion of carbon steel. In this study, the smooth-finished alloy performed best in this process system based on the corrosion evaluation.