Will MIC develop on bare steel within (offshore) soil samples from the site?
Will MIC develop on steel coupons covered with a metallic coating exposed to (offshore) soil samples from the site?
– S355, metallic coating, zinc containing product which forms a non-toxic layer after the film layer is dry.
– Offshore sediment (North Sea), in-situ seawater (regular exchange), 6 months incubation
– Quantification of MIC relevant microorganisms in corrosion products (MPN, qPCR)
– SEM-EDX analysis of corrosion products
– Weight loss determination
– Pit analysis (3D microscopy)
Visual inspection of blank steel coupons after 6 months of incubation revealed rusty-brown corrosion products and tubercles in the area which was exposed to seawater whereas the area which was exposed to the sediment showed blackish brown corrosion products.
The zinc-coated coupons (with and without scratch) showed white precipitations at the water-sediment interface and in the area which was exposed to the sediment.
Only the corrosion products of the blank steel coupon showed presence of MIC relevant microorganisms: sulfate-reducing bacteria (SRB), acid-producing bacteria (APB) and iron-reducing bacteria (IRB). SEM-EDX analysis showed presence of Fe, O, which explains the rusty-brown color of iron(III)oxides and S was detectable which forms with Fe the black precipitations, iron sulfide (FeS).
Blank steel coupons showed a corrosion rate of 0.06 mm/year and pitting was found. The average pit depth was 34 µm on part of the coupon exposed to sediment and 240 µm on the water-sediment interphase. Presence of MIC relevant microorganisms, sulfur in the corrosion products and pitting corrosion is an indication that MIC is present and active on the coupon surface, especially in the water-sediment interphase.
The zinc containing product forms an oxide layer which protects the steel against (microbial) corrosion whereas the blank steel coupon showed (microbial) corrosion.
Offshore wind farm owner, engineering firm
Currently, in the planning of a new offshore wind farm in the North Sea, microbiologically influenced corrosion (MIC) is also taken into account as a possible corrosion mechanism in the context of a corrosion risk assessment for the foundation construction.
A complete microbial analysis was performed on cores to determine whether corrosion-relevant micro-organisms exist in the sediment on site. Endures uses a combination of two methods: the MPN method, which is based on the cultivation of bacteria, and q-PCR, a molecular technique that determines the composition of DNA.
Corrosion-related microorganisms were indeed found in samples from various locations in the planned offshore wind farm. Microbial activity was also determined at different depths in the sediment. On the basis of this data, an assessment was made of the possible corrosion risk for the metal structures to be placed at that location at a later date and advice was given on corrosion protection measures. In addition to microbiological research, Endures can also help you choose a suitable system for corrosion monitoring.
Samples were taken from various locations in the planned offshore wind farm
Conducting microbiological research at an early stage will significantly improve corrosion protection