Data Center Glycol Inhibitor Chemistry Guide | OAT vs NOAT vs HOAT

What We Supply (Important Starting Point)

Alliance Chemical supplies pre-inhibited glycol solutions—complete and ready for service. We do not sell inhibitor packages separately, additive concentrates, or "booster" chemicals. Every glycol formulation we ship already contains a factory-blended corrosion inhibitor package matched to the base glycol type (EG or PG) and intended application.

What this approach means:

• ✅ Consistent chemistry: Inhibitor type, concentration, and metal compatibility are controlled at the manufacturing level
• ✅ No field mixing errors: You receive fluid ready to pump into your cooling loop—no dosing, blending, or chemistry calculations required
• ✅ Traceable quality: Every batch includes a Certificate of Analysis documenting inhibitor levels, pH, and reserve alkalinity
• ❌ No standalone inhibitors: If your existing system needs inhibitor "top-up," you'll need to drain and refill with fresh inhibited glycol rather than trying to dose additives

Mission-critical data center infrastructure depends on reliable cooling systems protected by properly inhibited glycol formulations

Understanding Inhibitor Chemistry: What Inhibitors Actually Do

The Corrosion Problem in Data Center Cooling Loops

Uninhibited glycol (pure ethylene glycol or propylene glycol without additives) will actively corrode a closed-loop cooling system. Here's why:

Electrochemical galvanic corrosion: Data center cooling systems contain dissimilar metals in electrical contact—carbon steel piping, copper heat exchanger tubes, aluminum CRAH/CRAC coils, brass fittings, and stainless steel components. When these metals are immersed in the same conductive fluid, they form galvanic couples where more anodic metals (steel, aluminum) corrode to protect more noble metals (copper, stainless). This process is accelerated by:

• Temperature: Corrosion rates roughly double for every 18°F (10°C) increase—data center chilled water loops operating at 60-80°F still see significant corrosion, while condenser loops at 95-105°F face extreme rates
• Dissolved oxygen: Even in "closed" loops, makeup water introduces oxygen that accelerates oxidation reactions
• Flow velocity: High-velocity flow (>4 ft/s) in undersized piping causes erosion-corrosion and removes protective oxide films
• pH drift: Glycol oxidation produces acidic byproducts (glycolic acid, formic acid, oxalic acid) that drive pH down below 7.0, massively accelerating corrosion

Without inhibitors, typical corrosion rates in uninhibited 40% glycol at 140°F:

Note: 1 mil = 0.001 inch. A 15 mpy (mils per year) rate means 0.015" wall loss annually—Schedule 40 steel pipe has only ~0.15" wall thickness, so uninhibited glycol could perforate pipe in 10 years.

Mixed-metal cooling systems require advanced inhibitor packages to prevent galvanic corrosion between dissimilar metals

How Inhibitors Work: The Three-Layer Defense

Effective inhibitor packages use multiple mechanisms to protect metal surfaces:

1. pH Buffering (Alkaline Reserve)

Inhibitor packages include pH buffers (typically alkali metal hydroxides, borates, or phosphates) that maintain pH in the slightly alkaline range (8.0-9.5). This serves two purposes:

• Passivation: Alkaline pH promotes formation of protective metal oxide films (Fe₃O₄ on steel, CuO on copper)
• Neutralization: Buffers neutralize acidic corrosion byproducts (glycolic acid, formic acid) that form as glycol slowly oxidizes over time

Reserve alkalinity is the measure of how much acid the inhibitor can neutralize before pH drops below the protective range. Fresh inhibited glycol has high reserve alkalinity (10-20 mL 0.1N HCl per 10 mL sample); when reserve alkalinity drops to 50% of the original level, the fluid should be replaced or recharged.

2. Anodic Inhibition (Passivating Films)

Certain inhibitor compounds—particularly organic carboxylates (sebacic acid, 2-ethylhexanoic acid), nitrites, molybdates, and azoles—adsorb onto metal surfaces and form stable, coherent oxide layers that physically separate the metal from the corrosive environment. These films are:

• Self-healing: If damaged by mechanical abrasion or cavitation, the inhibitor reforms the protective layer
• Metal-selective: Different inhibitors target different metals (azoles for copper/brass, carboxylates for ferrous metals, molybdates for aluminum)
• Nanometer-scale thin: Don't interfere with heat transfer but provide robust corrosion protection

3. Cathodic Inhibition (Oxygen Scavenging)

Some inhibitor systems (particularly those with nitrite) include oxygen scavengers that react with dissolved oxygen before it can participate in corrosion reactions. This is especially important in systems with frequent makeup water addition or air ingress through pump seals.

Inhibitor Types: Deep Comparison for Data Center Applications

Not all inhibitor chemistries are created equal for data center cooling applications. Understanding the differences helps you specify the right fluid—and recognize when a vendor is trying to sell you outdated or inappropriate technology.

Complete Inhibitor Technology Comparison

Regular laboratory testing of coolant chemistry ensures optimal inhibitor performance and early detection of corrosion problems

Why OAT and Molybdate-OAT Are Preferred for Data Centers

Data center cooling systems have unique requirements that make organic acid technology (OAT) the clear winner:

1. Low electrical conductivity

Water-cooled server racks, immersion cooling, and direct-to-chip liquid cooling require coolants with minimal electrical conductivity to prevent short circuits and galvanic corrosion in electronics. OAT inhibitors provide excellent corrosion protection while maintaining conductivity below 500 µS/cm (microsiemens per centimeter). Traditional IAT inhibitors with silicates and phosphates can exceed 2000 µS/cm—unacceptable for electronics cooling applications.

2. No scale or deposit formation

Data center heat exchangers—especially microchannel aluminum coils in CRAC units and brazed plate heat exchangers in free cooling systems—have extremely tight flow passages (0.5-2mm). Silicate gelation, phosphate scale, and other deposits from traditional inhibitors will foul these passages, reducing capacity and increasing pressure drop. OAT inhibitors contain zero silicates or phosphates, eliminating this failure mode entirely.

3. Extended service life (lower TCO)

Draining, flushing, and refilling a 10,000-gallon data center cooling loop costs $15,000-30,000 in fluid, labor, and downtime. OAT-inhibited glycol delivers 8-10 year service life when properly maintained, versus 2-3 years for traditional IAT formulations. Over a 20-year facility lifecycle, OAT saves 50-60% on fluid changeout costs.

4. Aluminum compatibility

Modern CRAC/CRAH units use aluminum microchannel coils for weight reduction and thermal performance. Molybdate-OAT formulations provide superior aluminum protection compared to standard OAT—molybdate forms a stable, protective MoO₃ film on aluminum oxide surfaces. For facilities with significant aluminum components, molybdate-OAT is the gold standard.

5. Mixed-metal system stability

Typical data center loops contain carbon steel pipe, copper brazed plate heat exchangers, aluminum coils, brass valves, and stainless steel strainers—five different metals in the same system. OAT carboxylates adsorb onto all of these surfaces, forming protective films that suppress galvanic coupling. The result: all metals corrode at slow, uniform rates without preferential attack on any one material.

EG vs. PG: Glycol Base Selection for Data Centers

Both ethylene glycol (EG) and propylene glycol (PG) can be formulated with excellent OAT or molybdate-OAT inhibitors. The choice comes down to thermal performance, toxicity profile, and system requirements:

Ethylene Glycol (EG): Maximum Thermal Efficiency

Choose EG when:

• Thermal performance is the top priority (lower viscosity = better heat transfer and lower pumping energy)
• Closed-loop industrial cooling where toxicity is not a concern
• Large systems (10,000+ gallons) where cost matters (EG is 20-30% less expensive than PG)
• Free cooling systems operating at low temperatures (-10°F to 40°F) where PG's higher viscosity becomes problematic

Thermal advantages of EG vs. PG at 30% concentration, 68°F:

What this means in practice: In a 500-ton chilled water system circulating 1200 GPM, switching from 30% EG to 30% PG increases annual pump energy consumption by ~15,000 kWh ($1,500/year at $0.10/kWh). Over 20 years, that's $30,000 in additional electricity costs—more than enough to offset PG's higher fluid cost.

Alliance Chemical EG products:

• 100% Ethylene Glycol Inhibited – OAT-inhibited concentrate for custom blending
• Ethylene Glycol Inhibited ACS Grade – High-purity formulation for critical applications
• Ethylene Glycol 60/40 – Pre-mixed for extreme cold protection
• Ethylene Glycol 50/50 – Standard pre-mix

Propylene Glycol (PG): Low-Toxicity Profile

Choose PG when:

• Building codes, insurance requirements, or corporate policy mandate low-toxicity coolants
• System has potential for drinking water cross-contamination (dual-use buildings with potable water and process cooling)
• Environmental sensitivity (PG is biodegradable and less toxic to aquatic life in case of spills)
• Food processing facilities or pharmaceutical clean rooms where FDA-compliant coolants are preferred

PG advantages:

• FDA GRAS status: Propylene glycol is Generally Recognized As Safe for incidental food contact—acceptable in facilities with food/pharma operations
• Lower acute toxicity: LD50 (rat, oral) is 20,000 mg/kg vs. 4,700 mg/kg for EG—approximately 4x less toxic
• Biodegradable: PG breaks down naturally in soil and water—easier environmental remediation if spilled
• Insurance/regulatory preference: Some jurisdictions or facility insurance policies require low-toxicity coolants in commercial buildings

PG disadvantages:

• Higher viscosity increases pumping costs 10-25% vs. EG
• Higher cost per gallon (20-40% premium vs. EG)
• Slightly reduced heat transfer efficiency

Alliance Chemical PG products:

• 100% Propylene Glycol Inhibited – OAT-inhibited concentrate
• Propylene Glycol Inhibited ACS Grade – High-purity formulation
• Propylene Glycol 50% USP Grade – Pre-mixed, pharmaceutical-grade
• Arctic Assist – PG-based antifreeze for extreme conditions

Concentration Selection & Freeze Protection

Glycol concentration determines freeze point, burst point, viscosity, and heat transfer efficiency. The "right" concentration balances freeze protection needs against thermal performance and cost.

Typical Data Center Concentration Targets

The Freeze Point Curve: More Isn't Always Better

One of the most common misconceptions is that "more glycol = more protection." This is only true up to about 60% concentration. Beyond that, freeze protection actually decreases because pure glycol has a higher freezing point than properly mixed solutions.

Ethylene Glycol Freeze Point by Concentration:

Burst point is the temperature where glycol solution becomes a solid slushy that can rupture pipes. Burst protection extends 10-20°F below freeze point.

How to Calculate Required Glycol Concentration

Example calculation:

• Location: Chicago, IL data center with free cooling
• ASHRAE 99.6% design dry-bulb: -7°F
• Safety margin: -7°F - 15°F = -22°F minimum protection required
• From table: 30% EG provides -10°F freeze point—not enough
• Next step: 40% EG provides -30°F freeze point—adequate
• Specify 40% ethylene glycol for this application

Precision cooling distribution units circulate inhibited glycol through liquid-cooled server infrastructure

Testing & Monitoring: How to Maintain Inhibitor Health

The best inhibitor package in the world won't protect your system if it's depleted, contaminated, or degraded. Regular testing is mandatory for data center cooling systems—treat coolant monitoring like oil analysis on your emergency generators: it's cheap insurance against expensive failures.

Critical Test Parameters & Frequency

How to Collect Representative Coolant Samples

Bad sampling = bad data = bad decisions. Follow these practices for accurate results:

• Sample from circulating fluid: Never sample from expansion tank, fill port, or dead legs. Sample from a system drain valve or install a sample port on the main circulation loop.
• Purge first: Flush 3-5x the sample line volume before collecting sample to ensure fresh fluid
• Use clean containers: Glass or HDPE bottles, rinsed 3x with the fluid being sampled
• Fill completely: Fill sample container to the top, minimizing airspace to prevent oxidation
• Label clearly: Include system name, sample location, date, and sampler initials
• Store properly: If not testing immediately, store samples at room temperature in dark location (UV degrades glycol)
• Test promptly: Analyze within 2 weeks of collection for best accuracy

In-House vs. Lab Testing

In-house testing (recommended minimum):

• Freeze point (refractometer): $50-150 tool, instant results, quarterly testing
• pH (digital meter): $100-300 tool, requires calibration, quarterly testing
• Nitrite (if NOAT): $25 test strips, quarterly
• Visual inspection: Free, quarterly

Laboratory testing (recommended annually):

• Complete coolant analysis package: $150-300 per sample
• Includes: pH, reserve alkalinity, freeze point, metals analysis (ICP-OES), chloride, conductivity, inhibitor levels
• Many coolant suppliers (including Alliance Chemical) can recommend partner labs or provide interpretation support
• Worth the cost for mission-critical systems—early detection of problems saves millions in avoided failures

Inhibitor Selection Guide: Choosing the Right Formulation

With a solid understanding of inhibitor chemistry, here's a practical decision framework for specifying coolant for new construction or replacing fluid in existing systems:

Quick Reference: Recommended Formulations by Application

Maintenance Best Practices: Keeping Your System Healthy

Initial Fill & Commissioning

When filling a new or drained system with inhibited glycol:

1. Pre-fill system cleaning: Flush new systems with water to remove cutting oils, welding slag, flux residue, and construction debris. Existing systems being refilled should be chemically cleaned if showing signs of corrosion, scale, or biological growth. Use manufacturer-approved cleaning chemicals, then flush thoroughly with clean water.
2. Verify system integrity: Pressure-test system to 1.5x operating pressure before filling with glycol (no sense filling with expensive coolant only to find leaks).
3. Fill with deaerated fluid: If possible, deaerate glycol before filling (especially important for high-temperature systems). Dissolved oxygen accelerates corrosion. Simple method: heat glycol to 180°F in vented drum, allow to cool—drives off most dissolved O₂.
4. Fill slowly, vent continuously: Fill at <10 GPM while venting all high points, air separators, and manual vents. Air pockets cause cavitation, noise, and flow problems.
5. Circulate before startup: Run pumps for 2-4 hours before bringing system online. This ensures complete air removal and uniform concentration.
6. Test, document, baseline: After circulation but before full-load operation, collect samples and test pH, freeze point, conductivity, and reserve alkalinity. Document these "time-zero" baseline values for future comparison.

Ongoing Maintenance

Quarterly checks (in-house testing):

• Visual inspection: Look for leaks, weeping fittings, corrosion stains on piping
• Test freeze point with refractometer at 3 locations in system (supply, return, expansion tank)
• Test pH with calibrated meter
• Test nitrite (if NOAT system) with test strips
• Check expansion tank level—frequent makeup indicates leaks
• Document findings in maintenance log

Annual comprehensive testing (lab analysis):

• Collect samples per proper procedure
• Send to coolant testing laboratory for complete analysis: pH, reserve alkalinity, freeze point, metals (Fe, Cu, Al, Pb), chloride, conductivity, inhibitor levels (nitrite, molybdate if applicable)
• Review results against baseline and manufacturer specifications
• Trend metal concentrations year-over-year (rising metals = active corrosion)
• Plan fluid changeout when reserve alkalinity drops to 50% or metals exceed action levels

When to Change Glycol (Replacement Triggers)

Don't wait for fluid to turn brown and pumps to fail. Plan fluid replacement based on objective test data:

Replace fluid when:

• Reserve alkalinity < 50% of original: Inhibitor protection is depleted
• pH < 7.5 or > 10.0: Outside protective range, indicates contamination or degradation
• Metal levels exceed limits: Fe > 50 ppm, Cu > 20 ppm, or Al > 20 ppm indicates active corrosion
• Freeze point rises > 15°F above target: Significant dilution from makeup water—indicates loss of freeze protection
• Nitrite (NOAT) < 300 ppm: Critical inhibitor depleted, protection compromised
• Molybdate < 20 ppm: Rare but indicates contamination or wrong fluid
• Service life reached: Even if tests look good, OAT-inhibited glycol has a 8-10 year maximum service life. Chemical breakdown products accumulate over time and some inhibitor components slowly deplete even in well-maintained systems.

Planned replacement schedule (ideal):

• Year 0: Fill new system, baseline testing
• Years 1-7: Quarterly pH/freeze point checks, annual lab analysis
• Year 8: Schedule fluid changeout during planned maintenance window
• Repeat cycle

Makeup & Top-Off Procedures

Critical rule: Always maintain concentration. When adding fluid to compensate for leaks or evaporation, you must add the same glycol/water ratio that's already in the system. Common mistakes:

• ❌ Wrong: Topping off 30% glycol system with pure water (dilutes concentration, reduces freeze protection)
• ❌ Wrong: Topping off with 100% concentrate (increases concentration, raises viscosity, wastes money)
• ✅ Correct: Top off 30% system with 30% pre-mix (maintains concentration)
• ✅ Correct: Calculate ratio and mix concentrate with water to match system concentration, then add

Better approach: Minimize makeup. Makeup water introduces dissolved oxygen, chlorides, and other contaminants. Every time you add makeup, you're adding corrosion risk. Instead:

• Fix leaks immediately: Don't band-aid problems with makeup—repair leaking fittings, weeping seals, and corroded components
• Monitor makeup rate: If you're adding > 2% system volume per year, you have a leak that needs finding
• Use deionized water for makeup: Never use tap water—minerals accelerate corrosion and deplete inhibitors. If you must add makeup, use only deionized or distilled water blended with concentrate to match system concentration.

Alliance Chemical Inhibited Glycol Products

Alliance Chemical supplies pre-inhibited heat-transfer fluids purpose-built for data center cooling systems. Every formulation includes factory-blended corrosion inhibitors matched to the base glycol and application.

Ethylene Glycol (EG) – Maximum Thermal Performance

• 100% Ethylene Glycol Inhibited – OAT-inhibited concentrate for on-site blending. Provides maximum freeze protection when mixed at 50-60% concentration. Ideal for large systems where bulk concentrate is economical. Available in 1-quart to 275-gallon totes.
• Ethylene Glycol Inhibited ACS Grade – High-purity, analytical-grade formulation for critical applications requiring ultra-clean coolant. Low metals, low chloride, tested to ACS specifications. Recommended for immersion cooling and direct-to-chip systems.
• Ethylene Glycol 60/40 – Pre-mixed to 60% glycol / 40% water for maximum freeze protection (-60°F). Ready-to-use for extreme cold climate free cooling systems or Arctic data center locations. No blending required.
• Ethylene Glycol 50/50 – Standard 50/50 pre-mix providing -37°F freeze protection. Balanced formula for general data center cooling applications. Most common concentration for chilled water loops with freeze margin.

Propylene Glycol (PG) – Low-Toxicity Profile

• 100% Propylene Glycol Inhibited – OAT-inhibited concentrate with low-toxicity FDA GRAS-rated base glycol. Blend to desired concentration on-site. Preferred for commercial buildings, food/pharma facilities, and applications where low-toxicity is mandated or preferred.
• Propylene Glycol Inhibited ACS Grade – High-purity, pharmaceutical-grade formulation meeting ACS specifications. Ultra-low metals and chloride for electronics cooling and immersion applications requiring minimal electrical conductivity.
• Propylene Glycol 50% USP Grade – Pre-mixed 50/50 formulation meeting USP (United States Pharmacopeia) standards. Suitable for applications requiring pharmaceutical-grade quality. Provides -26°F freeze protection.
• Arctic Assist – Propylene glycol-based antifreeze formulated specifically for extreme cold applications. Enhanced low-temperature flow properties. Ideal for outdoor equipment, emergency backup cooling systems, and portable cooling units in arctic environments.

Packaging & Ordering

Available sizes:

• 1 Quart: Perfect for testing, small top-offs, or spare inventory. Ships as DOT Limited Quantity (no hazmat fees—saves $30-50 per shipment).
• 1 Gallon: Standard size for maintenance inventory and small systems
• 5 Gallon Pail: Convenient for moderate makeup or small system fills
• 55 Gallon Drum: Most economical for large systems or annual maintenance inventory
• 275 Gallon Tote: Bulk pricing for hyperscale data centers and large system fills

Custom concentrations: Need a specific mix ratio not listed (e.g., 35% for your exact freeze point target)? We can blend to spec in drum or tote quantities. Minimum order applies for custom concentrations. Call (512) 365-6838 to discuss.

Documentation provided:

• Certificate of Analysis (COA) with every shipment—documents pH, reserve alkalinity, concentration, and lot number
• Safety Data Sheet (SDS) available for download on product pages
• Technical Data Sheet (TDS) with freeze point curves, physical properties, and dilution tables

How to Order

1. Browse products: Visit our Coolants & Antifreeze Collection to see all available formulations
2. Select specification: Choose glycol base (EG or PG), concentration (concentrate or pre-mix), and package size
3. Add to cart and checkout: Standard e-commerce checkout for stocked sizes
4. Need a custom spec? Call (512) 365-6838 or email sales@alliancechemical.com with:
   • System volume (gallons)
   • Target concentration (%)
   • Glycol type preference (EG or PG)
   • Inhibitor requirements (OAT, molybdate-OAT, etc.)
   • Delivery location
   We'll quote custom blends, bulk pricing, and provide technical recommendations.

Technical Support

Alliance Chemical provides complimentary technical support for coolant selection, system sizing, testing interpretation, and troubleshooting:

• Pre-purchase consultation: Help selecting the right inhibitor type, concentration, and package size
• Dilution calculations: Assistance calculating concentrate/water ratios for on-site blending
• Test result interpretation: Review your lab analysis and recommend actions
• Troubleshooting: Diagnose coolant-related problems (corrosion, fouling, freezing)
• Custom formulation: Work with our chemists to develop specialized formulations for unique requirements

Contact technical support: (512) 365-6838 | sales@alliancechemical.com