Corrosion inhibitors are dual-track — yellow-metal protection (copper, bronze, brass) by triazole / thiadiazole chemistry, and ferrous rust protection by alkenyl-succinic acid (ASA), imidazoline and amine carboxylate. Together they pass ASTM D130 copper strip 1A-1B, IP 287 / ASTM D665 rust prevention, and IS 1115 emulsion stability. This guide covers CI chemistry families, treat rates by service, and Indian sourcing. The same inhibitor chemistry feeds our railway lubricant formulation, mining lubricant formulation, textile & spinning lubricant formulation and oil & gas lubricant formulation ranges.
| Service | Triazole % | ASA % | Imidazoline % | D130 Target |
|---|---|---|---|---|
| PCMO API SP / SN | 0.005-0.02% | 0.10-0.30% | 0 | 1B |
| HDD API CK-4 | 0.01-0.03% | 0.15-0.40% | 0.05-0.10% | 1B |
| Industrial Hydraulic HV / HVI | 0.05-0.15% | 0.10-0.25% | 0 | 1A |
| Turbine R&O ISO 32/46/68 | 0.02-0.10% | 0.05-0.20% | 0 | 1A |
| Gear EP GL-5 / MT-1 | 0.05-0.20% | 0.10-0.30% | 0 | 1B-2 |
| Metalworking Emulsion | 0.02-0.10% (water-soluble) | 0.20-0.50% (Na/K salt) | 0.10-0.30% | 1B |
| Marine Cylinder 70-100 TBN | 0 | 0.30-0.60% | 0.40-0.80% | 1B (detergent dominates) |
| Test | Method | What it Measures | Pass Target |
|---|---|---|---|
| Copper Strip Corrosion | ASTM D130 | Cu tarnish at 100 / 121 / 150 °C, 3 hr | 1A or 1B |
| Rust Prevention (distilled water) | ASTM D665A / IP 135 | Steel rod rust after 24 hr in oil-water | Pass (no rust) |
| Rust Prevention (synthetic seawater) | ASTM D665B | Salt-water rust resistance | Pass (no rust) |
| Humidity Cabinet Rust | ASTM D1748 | Steel panel coated with oil in humidity cabinet | No rust 7-30 days |
| Emulsion Stability / Corrosion (cutting fluid) | IS 1115 / IP 287 | Cast iron / steel chip corrosion in emulsion | No corrosion at 4% |
| L-33 Axle Moisture | SAE J2360 | Hypoid axle moisture resistance | Pass GM |
ASTM D130 (copper strip corrosion) rates a polished copper strip immersed in hot oil (typically 100 °C, 3 hr) on a scale 1A (slight tarnish, light orange) → 1B (slight tarnish, dark orange) → 2 (moderate tarnish) → 3 (dark tarnish) → 4 (corrosion). 1A is the best rating; 1B is acceptable for most engine oil and industrial. 2 fails most modern specs.
The 1A vs 1B difference is whether sulphur-EP / phosphate-ester / sulphurised additives in the formulation aggressive enough to start tarnishing yellow-metal at test temperature — fixed by raising triazole CI dose.
Benzotriazole (BTA) was the original yellow-metal inhibitor — works on copper, brass, bronze, zinc, silver. Cheap, effective, but limited oil solubility (max ~0.05% in oil). Tolutriazole (TTA, methylbenzotriazole) is the methyl-substituted variant — better oil solubility (up to 0.5%), same yellow-metal protection.
Cobratec TT-100, Cobratec 200, Reolube TT are TTA-based. Most modern lubricant formulations use TTA over BTA for higher dose capability. Both work by chemisorbing on the Cu/brass surface to form a passivation film.
Alkenyl succinic acid (ASA) and alkenyl succinic ester (ASE) protect ferrous metal from rust. Treat rate 0.05-0.5% in finished oil depending on service. PCMO uses 0.1-0.3% ASA for general rust protection. Industrial circulating uses 0.2-0.5% for severe-condition water-contaminated environments. Hydraulic uses 0.05-0.2%. Marine cylinder uses 0.3-0.6% — the dose tier we build into our automotive lubricant formulation and marine work.
ASA works by chemisorbing the carboxylic acid head onto the iron surface, forming a thin polar barrier that excludes water. Pass ASTM D665 (rust prevention with distilled or synthetic seawater).
ASTM D665B uses synthetic seawater for the rust prevention test — more aggressive than D665A (distilled water). Marine system oil, marine cylinder oil, and offshore hydraulic must pass D665B. Imidazoline-based CI (Naco 22 type, fatty-acid imidazolines) gives better salt-water rust protection than ASA — the imidazoline nitrogen heads bind to iron more strongly and the alkyl tails form a thicker hydrophobic barrier.
Marine CI treat rate 0.3-0.8% imidazoline plus 0.2-0.5% ASA for combined protection — see our marine lubricant formulation range.
Marine cylinder oil (70-100 TBN, used in two-stroke crosshead engines burning high-sulphur residual fuel) faces sulphuric acid attack on the cast-iron cylinder liner. Detergent (overbased Ca sulfonate or phenate at 500 TBN, 15-25% treat) neutralises the acid before it reaches the metal.
Plus traditional CI — imidazoline 0.4-0.8% — protects from residual moisture. The high TBN reserve does most of the CI job; ASA / imidazoline supplement is for water-contaminated phase between port calls.
Triazole — PMC Ouvry Cobratec TT-100 / TT-200, Wincom Tinuvin, Reolube TT. India landed ₹650-950 / kg. Thiadiazole (DMTD) — Vanderbilt Vanlube 887, Cuvan 826. ₹680-980 / kg. ASA — King Industries K-Corr 200 / 250, Vanderbilt ASA, Stepan Petronate. ₹380-540 / kg. Imidazoline — Stepan Amphoteric, Lubrizol R&O. ₹420-580 / kg.
Lubechem custom (LC-CI-TTA, LC-CI-ASA, LC-CI-IMID, LC-CI-COMBO) ₹250-540 / kg — 25-32% saving on branded. For the full picture see our lubricant additive suppliers guide.
Industrial hydraulic HV / HVI uses CI package combining triazole (Cu/yellow-metal protection of pump valves), ASA (steel rust), thiadiazole (additional Cu protection in high-pressure systems). Typical treat: TTA 0.05-0.15% + ASA 0.10-0.25% + thiadiazole 0.05-0.10%. Plus antioxidant additive for lubricants (DPA) 0.3-0.5%.
Custom Lubechem hydraulic CI (LC-CI-HYD-COMBO) at ₹290-410 / kg vs branded HiTEC 4951 at ₹360-480 / kg — 25% saving with same Denison T6H20C and Eaton 35VQ25 pump pass.
Triazole nitrogen atoms chemisorb onto the copper surface — the three N atoms of the triazole ring give strong coordination to Cu / Cu2+. This forms a passivation film 2-10 nm thick that excludes oxygen, acid and sulphur from reaching the bare Cu surface.
Without triazole, sulphur-EP additives and acidic combustion / oxidation products attack Cu, tarnishing rapidly. Triazole at 50-500 ppm in finished oil is enough to give D130 1A rating in most formulations. TTA preferred over BTA for higher solubility allowing higher treat dose.
Share your target service (PCMO, HDD, hydraulic, gear, marine, metalworking), D130 / D665 spec and volume. We respond within one business day with a CI blend plan and indicative cost.