How Lubricants Prevent Corrosion
1. Physical Barrier Protection
The lubricating oil or grease film forms a continuous barrier between the metal surface and the corrosive environment. This barrier prevents water, oxygen, and corrosive chemicals (salts, acids) from reaching the metal. The effectiveness of the physical barrier depends on film thickness, coverage completeness, and the lubricant's ability to resist water wash-off. Greases with good adhesion (tackiness) and water resistance maintain their barrier even under water spray or immersion.
2. Chemical Inhibition
Most industrial lubricants contain rust and corrosion inhibitors — polar molecules that adsorb onto metal surfaces, forming a protective monolayer. Common inhibitor types include: sulfonates (form a tenacious hydrophobic film), amine phosphates (neutralize acidic contaminants), and zinc dithiophosphates (ZDDP, multi-functional antiwear and corrosion inhibiting). The inhibitor package must be compatible with the base oil and thickener to remain effective throughout the lubricant's service life.
3. Water Displacement
Certain thickener types, particularly barium complex and aluminum complex, have a unique ability to shed and displace water from metal surfaces. This is distinct from water absorption — a water-displacing grease causes water to bead up and roll off rather than penetrating to the metal. Barium complex greases (KLÜBER Staburags NBU series) are renowned for this property, which is why they are the industry standard in steel mills subject to high-pressure water descaling spray.
Corrosion Test Standards
| Test | Standard | What It Measures | Pass/Fail Criteria |
| EMCOR | ISO 11007 / DIN 51802 | Corrosion on bearing under dynamic wet conditions | Rating 0-0 (no corrosion on either race) |
| Salt Spray | ASTM B117 / ISO 9227 | Corrosion resistance under continuous salt fog | No rust after specified hours (typically 48-240h) |
| Water Washout | ASTM D1264 | Grease resistance to water spray at specified temperature | % weight loss; < 10% at 79°C is good |
| Copper Corrosion | ASTM D4048 | Corrosivity toward copper and copper alloys | 1a or 1b rating (no darkening or corrosion) |
> Tip
When specifying a grease for wet or corrosive environments, request the EMCOR test result with distilled water AND with salt water (3% NaCl or synthetic seawater). A grease that achieves EMCOR 0-0 with distilled water may perform significantly worse with salt water. For marine and offshore applications, always specify the salt water EMCOR test.
KLÜBER Products for Corrosion Protection
- Staburags NBU 12 / NBU 8 EP — Barium complex greases with MoS₂ solid lubricants. Industry-standard in steel rolling mills, continuous casters, and marine applications. Exceptional water displacement and salt water corrosion protection. EMCOR 0-0 with salt water.
- Klüberfood NH1 94-301 — NSF H1 food-grade grease with aluminum complex thickener. Designed for washdown environments in food processing. Excellent corrosion protection combined with food safety compliance.
- Klüberplex BEM 41-141 — Special lithium complex grease with enhanced corrosion inhibitors for wet and dusty industrial environments. Cost-effective for applications not requiring barium complex performance.
- ISOFLEX TOPAS NB 52 — Barium complex high-speed grease. While engineered primarily for spindle applications, the barium thickener provides excellent incidental corrosion protection in humid machining environments.
Frequently Asked Questions
Q: What's the difference between rust and corrosion in a bearing context?
Rust specifically refers to the oxidation of iron and steel (ferrous metals), forming iron oxides. Corrosion is the broader term encompassing all material degradation by chemical or electrochemical reaction — including rust on steel, pitting on aluminum, tarnishing of copper, and oxidation of any metal. In bearing lubrication, both are concerns, but rust is the most common form because most bearings are manufactured from high-carbon chromium steel (AISI 52100 / 100Cr6).
Q: Can I apply an additional rust preventive over the grease?
Generally no — additional rust preventive coatings or oils can be incompatible with the grease, causing it to soften or lose adhesion. If extended shutdown corrosion protection is needed, use a grease specifically formulated for long-term preservation (KLÜBER Nontrop or Polylub series preservative greases) or apply a dedicated preservative compound that is compatible with the operating grease. Always verify compatibility before applying any secondary coating.