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Chloride ions penetrate the passive oxide layer on stainless steel and initiate pitting corrosion in what is called localised depassivation. Once a pit initiates, the local chemistry within the pit becomes highly acidic (pH 2–3), creating an autocatalytic process that drives the pit deeper and wider regardless of the surface condition of the surrounding metal. 304 stainless steel, with 18% chromium and no molybdenum, is susceptible to chloride pitting at seawater concentrations. 316 stainless, with 16% chromium and 2–3% molybdenum, resists chloride pitting initiation at seawater concentrations through the passivating effect of molybdenum on the oxide layer.

Crevice corrosion occurs in the narrow gap between the sprocket hub bore and the shaft, where stagnant saltwater creates a depleted oxygen zone that cannot sustain the passive oxide layer. Even 316 SS can suffer crevice corrosion in tightly-fitted bore-shaft interfaces in continuous saltwater immersion. We address this through hub bore surface finish specifications that minimise the crevice geometry and through specifying a light interference fit rather than clearance fit at the bore-shaft interface.

When a stainless steel sprocket contacts a different metal — aluminium frame, carbon steel shaft, or bronze bushing — a galvanic cell forms in the saltwater electrolyte. The less noble metal (typically the steel shaft or aluminium frame) corrodes preferentially at the contact point. We specify 316 SS sprockets with compatible bore and hub materials to prevent galvanic couples, and recommend specifying the shaft material before confirming bore finish.

Marine barnacles, mussels, and biofilm organisms colonise stationary metal surfaces in aquaculture environments. The biofilm layer creates local anaerobic zones where sulphate-reducing bacteria produce hydrogen sulphide — a potent corrosive agent that attacks stainless steel through microbially induced corrosion (MIC). Regular cleaning cycles using food-safe descaling agents remove biofilm before MIC can initiate.

Drive the feed auger that conveys pelletised feed from the hopper to the distribution blower or direct discharge point. The auger operates intermittently — typically in 5–30 second discharge pulses — at moderate torque. These sprockets are in contact with dry pellet feed and moist coastal air, making 316 SS the correct specification. The auger drive is the most likely position to cause feed delivery failure if a sprocket corrodes and fails during a scheduled feeding cycle.

Drive the air blower that delivers pellet feed to individual cage feeding points through pneumatic pipework. These positions operate continuously at moderate speed. The blower is typically mounted on the main feeder barge in direct marine air exposure — 316 SS specification throughout is required.

Drive the agitator inside the feed hopper that prevents pellet bridging and ensures consistent feed flow to the auger inlet. These positions see low torque but are in direct contact with feed pellets and the moist, salt-laden air inside the hopper. Nylon (PA66-GF30) sprockets are an excellent specification here — they are completely corrosion-proof and food-safe, with no risk of metal contamination of the feed.

Drive the cable or chain systems that position the feeder relative to the fish cage. These are the lowest-load positions on the system but are continuously exposed to seawater spray and intermittent immersion during rough conditions. 316 SS with sealed bearing hubs is the recommended specification.

A Huon Valley salmon aquaculture operation running 12 automatic feeder barges replaced all feeder auger and blower drive sprockets with our 316 SS range after persistent corrosion failures with 304 SS and carbon steel components. “We had tried 304 SS and it pitted within 8 months in the Huon estuary salt environment — exactly as your CPT analysis predicted. Your 316 SS auger drive sprockets have been running for 22 months without a single corrosion indication on any tooth surface. This is the specification the aquaculture industry should have been using from the beginning.” ⭐⭐⭐⭐⭐

A Coffin Bay oyster operation running pontoon-mounted automatic feeders specified our 316 SS pontoon drive sprockets and PA66-GF30 nylon hopper agitator sprockets. “The nylon sprockets in the hopper agitator position are working perfectly after 18 months — no wear visible on the teeth and obviously no corrosion. The silent operation is an added benefit in the feeding area. The 316 SS pontoon drive sprockets are also performing as expected in the direct sea spray environment.” ⭐⭐⭐⭐⭐

A Norwegian Atlantic salmon operation running large-scale feeder systems sources our 316 SS auger and blower drive sprockets. “Norwegian aquaculture regulations require documented material specifications for all components in contact with fish feed or in the feeder water zone. Your 316 SS mill certificates and the PA66-GF30 food-contact compliance documentation satisfy our regulatory requirements without additional testing.” ⭐⭐⭐⭐⭐

A Los Lagos salmon farming operation running 30 feeder stations in high-salinity fjord conditions sources our full 316 SS feeder sprocket range. “The combination of cold fjord water, tidal variation, and the biological fouling in our operating area creates a very demanding corrosion environment. Your 316 SS sprockets with the molybdenum content confirmed on the mill certificate are the only specification we have found that provides reliable multi-year service in these conditions.” ⭐⭐⭐⭐⭐

A Port Lincoln abalone operation running land-based recirculating system feeders specifies our 316 SS auger drive sprockets and nylon distribution sprockets throughout. “Port Lincoln’s seawater is high-salinity even by Australian standards. Your CPT analysis correctly identified that 304 SS would fail here — 316 SS was the correct call and the performance has been exactly as your engineering team predicted.” ⭐⭐⭐⭐⭐