Process, standard and indicative SST selection guide
The ranges below are practical Neutral Salt Spray Test (NSS / SST) selection windows, not guarantees or service-life predictions. Unless noted otherwise, the stated endpoint is first red rust or base-metal corrosion on a correctly prepared steel part. Final hours, thickness, passivation, top coat, specimen condition and acceptance criteria must be agreed in the RFQ.
| Treatment | Primary technical reference | Indicative NSS / SST performance | RFQ information that adds value |
|---|---|---|---|
| Zinc electroplating | ISO 4042 for electroplated fasteners; ISO 19598 for Cr(VI)-free zinc and zinc-alloy coatings on iron or steel | Typically 240–480 h to red rust for zinc with a suitable trivalent passivate and sealer; higher-performance combined systems must be separately qualified | Part identity, substrate / strength, passivation or colour, thickness / designation, significant surfaces, performance and report requirement |
| Zinc-nickel plating | ISO 4042 for fasteners; ISO 19598 for zinc-alloy coatings on iron or steel with supplementary Cr(VI)-free treatment | Typically 720–1,000 h to red rust with an approximately 8 µm zinc-nickel layer, passivation and compatible sealer / top coat | Alloy coating designation, passivation, sealant / top coat if required, thickness, corrosion test and acceptance criterion |
| Zinc-flake coating | ISO 10683 for non-electrolytically applied zinc-flake systems on steel fasteners | Typically 720–1,000 h to base-metal corrosion at about 8–10 µm; selected thicker or top-coated systems can exceed 1,000 h | Fastener type, substrate / strength, top coat, lubricant / friction requirement, coating requirement and test evidence |
| Hot-dip galvanizing | ISO 10684 for threaded fasteners; ISO 1461 for fabricated iron and steel articles | No reliable universal SST range. Continuous salt spray is not representative of normal hot-dip galvanized service; specify coating thickness / mass and service environment instead | Component route, material, dimensions / weight, threads and masking, thickness requirement, inspection and handling |
| Tin plating | ISO 2093 for nominally pure tin on fabricated metal articles | No universal SST range. Tin is normally selected by substrate, undercoat, thickness, porosity and solderability / contact function rather than a generic red-rust target | Substrate, significant surfaces, bright or matte finish, thickness, undercoat and functional / test requirement |
| Electroless nickel | ISO 4527 for autocatalytic nickel-phosphorus alloy coatings | High-phosphorus Ni-P can provide about 500–1,500 h at roughly 10–30 µm; substrate finish, porosity, phosphorus level and heat treatment strongly affect the result | Substrate, heat treatment if specified, coating designation / phosphorus requirement, thickness, significant surfaces and tests |
| Silver plating | ISO 4521 for engineering silver and silver-alloy coatings | No universal SST range. Engineering silver is normally qualified by undercoat, thickness, adhesion, electrical / contact performance and tarnish requirements | Substrate, basis-material finish, undercoat, significant surfaces, thickness and electrical / functional tests |
Indicative ranges are based on published coating-system performance data, including MKS Atotech zinc, zinc-nickel and zinc-flake systems and SKF high-phosphorus Ni-P data. They are comparison guidance only. ISO 9227 does not convert laboratory hours into outdoor service life, and the customer specification remains the final acceptance authority.