PV power stations are designed for 25‑year service life. Fasteners are continuously exposed to UV radiation, temperature cycling, rain and corrosive salt mist. Environmental aggressiveness varies greatly among inland mountain sites, coastal tidal flats and fish‑pv hybrid water‑surface plants. Many projects adopt uniform fastener specification for all scenarios, resulting in rusting, washer penetration and bolt seizing within 3‑5 years and raising high maintenance cost. Material and finish shall be selected according to site corrosion grade.
For ordinary inland mountain PV plants with low salinity, SUS304 stainless‑steel fasteners are sufficient for bracket flange bolts, T‑bolts and rail connections. It delivers balanced cost and stable supply. Note that surface rust stain may appear under acid‑rain or heavy industrial‑dust due to passivation‑film damage, without substrate penetration yet requiring regular site inspection. Ordinary electro‑zinc‑plated carbon‑steel shall not be used for main load‑bearing bracket joints for insufficient outdoor lifespan.
Coastal and island sites suffer heavy chloride‑ion attack. SUS304 is vulnerable to pitting corrosion. SUS316 stainless‑steel or sealed zinc‑flake coating (Dacromet / Geomet) with ≥800‑hour salt‑spray performance is recommended for sites within 10 km from seashore. Molybdenum additive in SUS316 greatly improves chloride resistance. Bolts, nuts and washers shall adopt identical material grade to prevent galvanic corrosion.
Fish‑pv hybrid floating plants represent the most aggressive corrosion condition with evaporating salt and ammonia from water body. Even SUS316 faces severe challenge. Critical load‑bearing connections prefer sealed zinc‑flake high‑strength bolts. Submerged positions need special evaluation; plain electro‑plated carbon‑steel is forbidden. EPDM‑stainless composite gaskets are applied to block crevice corrosion.
Common pitfalls: Mixing SUS316 bolts with SUS304 nuts/washers triggers galvanic corrosion; copying inland BOM directly for water‑surface projects leads to early pitting; using ordinary electro‑plated carbon‑steel for primary bracket load‑bearing joints.
All matching hardware including spring washers, flat washers, grounding serrated washers and clamp fasteners must share identical material and surface finish. EPDM weather‑resistant gaskets are suggested for flange joints to reduce moisture ingress into crevices.
Procurement checklist: Request salt‑spray reports for inland projects; require PMI spectral test report for SUS316 in coastal & fish‑pv sites; confirm top‑seal treatment and salt‑spray hours for zinc‑flake coating. Perform accelerated cyclic salt‑spray aging test during sampling. Clearly mark material and finish on drawings and BOM instead of vague term “stainless‑steel screw”.
Dimension compliance alone is not enough for solar fasteners. Corrosion grade is top priority during selection. Proper material‑finish matching ensures 25‑year lifetime alignment with PV modules and cuts expensive field‑replacement cost.