Introduction: The Hidden Threats Within the Loop
While liquid cooling brings unprecedented thermal management capability to high-density AI data centers, it also introduces a set of risks that traditional air-cooling systems never faced. Pressure excursions, corrosion, and contamination are regarded as the three “invisible killers” of liquid cooling piping. If left unchecked, the consequences range from compromised cooling efficiency to the complete failure of entire racks.
Industry guidance from ASHRAE identifies coolant cleanliness as a key requirement for reliable direct-to-chip liquid cooling operation . This means performing regular maintenance and monitoring to prevent deterioration of the fluid and damage to servers and infrastructure. Having a “fill it and forget it” mindset about liquid cooling can cause significant problems .
Excessive Pressure: From Slow Fatigue to Sudden Rupture
The Pressure-Temperature Coupling Effect
Excessive system pressure triggers a cascade of failures. ASHRAE TC 9.9 technical guidance emphasizes that pressure ratings of all components of a Technology Cooling System (TCS) must be understood as part of the design process . If the pressure in any part of the system exceeds the ratings of that component, it may result in a failure condition—especially true of IT equipment, where the risk is costly failure .
A hydraulic model is recommended to ensure the pressure cascade is understood at all points in the system . Pressure analysis must include conditions outside of normal, steady-state operation, including flush and fill pressures, static height of the system, maximum pressure set by system pressure relief valves, expansion tank pre-charge pressures, and pressure excursions during connection or disconnection of equipment .
Temperature-pressure coupling is equally important. In high-density compute scenarios, a positive feedback loop can form: load rises → temperature rises → pressure rises → system stress increases → failure risk rises.
Pressure Relief and Safety Requirements
IEC 62368-1 (4th Edition) requires a hydrostatic pressure safety test of 1.5x the rated maximum working pressure . The system’s pressure relief valve must be set lower than the rated maximum pressure, which IT equipment manufacturers should specify in their product’s thermal template . Many CDU manufacturers provide customization for pressure relief valves, which must be selected and aligned to the requirements of the system .
In practice, CDU internal piping systems are typically pressure-tested at 1.5x operating pressure . Vesfil, for example, verifies wall thickness and performs stress analysis per ASME B31.3, safeguarding operation under high pressures up to 25 bar (360 psi) .
Prevention Strategies
Corrosion: The Chronic Erosion of Electrochemical Reactions
Material Compatibility as the First Line of Defense
Corrosion is the most persistent threat to metal piping. In a CDU, one drip can cause a severe shutdown . Material selection is critical: 316L stainless steel is used as the standard material for most regular applications, featuring good compatibility with deionized water and water-glycol mixtures .
For chloride-containing environments or fluorinated fluid/mineral oil media, 316L or higher grades are required . If working with seawater or other aggressive chlorides, SMO254 stands up where standard stainless steel may start to crack; titanium presents an ultimate choice for extreme corrosive conditions .
The draft standard T/CAEE (征求意见稿) specifies that for aqueous coolants (water, glycol solutions), 06Cr19Ni10 (304) is recommended, while chloride-containing environments or fluorinated fluid/mineral oil media require 022Cr17Ni12Mo2 (316L) or higher grades .
Passivation: The Critical Surface Preparation
Proper passivation is essential for corrosion resistance. ASHRAE TC 9.9 guidance emphasizes that a piping system component that is NOT passivated can jeopardize the entire system’s operation . Passivation can be performed in factory/shop conditions (controlled cleaning, chemical passivation with nitric or citric formulations, thorough rinsing, drying, and packaging) or in the field (controlled cleaning, chemical passivation, neutralization, thorough rinsing) .
Passivation verification should confirm removal of free iron and acceptable surface condition using accepted methods such as ASTM A380/A967 guidance . For stainless steel piping, electropolished internal surfaces to Ra ≤0.6 μm (or even down to 0.2 μm) provide better sealing and stronger resistance to chemical attack .
Sealing Material Compatibility
Seals and gaskets are often overlooked corrosion risks. The draft standard requires that seal materials (O-rings, gaskets) be compatible with the working medium. After immersion in the specified coolant (temperature × time), volume change should be between -5% and +10%, with hardness change not exceeding ±5 Shore A .
Prevention Strategies
Cleanliness: A Full-Lifecycle Challenge from Installation to Operations
The Particulate Threat
Liquid cooling systems have far lower tolerance for contamination than air-cooling systems. Cold plate microchannels are incredibly small and sensitive; microscopic particles can clog these channels and compromise cooling performance, or worse, damage chips or cause downtime .
Research on heat exchanger fouling has shown heat-transfer degradation of up to 14% and pressure-drop increases of up to 45% as contaminants accumulate . Because modern AI servers rely on precise coolant flow and heat removal, even minor fluid-quality issues can increase the risk of thermal throttling, equipment degradation, and unplanned downtime .
Cleanliness Standards and Testing
The draft standard T/CAEE specifies cleanliness level requirements according to ISO 4406 for solid particle contamination in the fluid . Vesfil uses DI water flush and particle count tests before delivery . Each assembly is tested with helium mass spectrometry (≤1×10⁻⁶ mbar·L/s) and hydrostatic testing at 1.5x operating pressure .
For stainless steel piping, automated orbital welding produces uniform, full-penetration, gas-purged welds that minimize contamination . For polymer systems, infrared (IR) welding is a non-contact process that creates homogeneous molecular bonds without filler materials or welding gases, eliminating contamination risks .
Coolant Monitoring and Filtration
Industry best practice recommends coolant testing at three minimum intervals: at commissioning to establish a baseline, annually during normal operation, and semiannually for systems supporting high-density AI GPU workloads . Periodic coolant testing is much like routine bloodwork for humans—it helps identify developing issues before they impact performance or reliability .
Filters are critical for maintaining cleanliness. In closed-loop liquid cooling, filters are located in multiple places, including CDUs and Rear Door Heat Exchangers (RDHx) . Disposable “sock filters” are often used during installation and cleaning/rinsing cycles, while reusable metal filters are used during normal operation and can be cleaned .
Prevention Strategies
Conclusion: A Holistic Risk Management Approach
The three “invisible killers”—pressure, corrosion, and cleanliness—are interconnected. Corrosion products can increase particulate contamination; pressure excursions can accelerate fatigue and failure at corrosion-weakened points; contamination can accelerate corrosion by creating localized galvanic cells .
A holistic approach requires:
As one industry source notes, a well-defined liquid cooling fluid management regime prevents these scenarios . The investment in proactive management is modest compared to the potential cost of downtime in high-density AI environments.
Post time: Aug-25-2026