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Rack densities have outgrown air cooling. A liquid loop moves far more heat through the same cross-section than an air stream can, which is why data center liquid cooling now reaches cold plates, coolant distribution units and immersion tanks in mainstream data center design. The change brings a materials question with it: every wetted part in a closed loop has to stay sound for the life of the facility, and every joint has to stay tight.
A liquid cooling system is a set of components that each put different demands on the metal they are made from. The parts that are usually specified are the ones where the material choice is driven by corrosion behavior and by the cost of a leak.
| Component | What it does | Where the material is usually specified |
|---|---|---|
| Cold plate | Sits on the processor and takes heat into the loop | Copper, because the heat has to cross the wall into the fluid |
| Coolant distribution unit | Pumps, filters and exchanges heat between the rack loop and the facility loop | Stainless manifolds, with CuNi coil tube in the heat exchanger |
| Manifolds and quick disconnects | Distribute coolant to the racks and allow a rack to be serviced without draining the loop | Stainless, for strength at the joint and resistance to the coolant |
| Immersion tank | Holds servers in a single-phase or two-phase fluid | Stainless for the tank, with nickel-bearing materials on wet surfaces that see the fluid directly |
| Secondary loop tubing | Carries fluid between the distribution unit and the facility | CuNi coil tube and stainless, where the loop chemistry or a mixed-metal joint calls for them |
Four drivers decide the wetted material at any position in the loop, and they pull in different directions.
| Driver | What it rules in | What it rules out |
|---|---|---|
| Coolant chemistry | Alloys that keep a passive surface in the fluid the loop runs on | Carbon steel, and any pairing that puts an active metal against a passive one |
| Mixed-metal joints | Materials that stay sound when copper, stainless and brass share the same fluid | Combinations that leave one metal as the sacrificial half of the pair |
| Leak tolerance | Wetted parts chosen for how they behave in crevices and under deposits | Thin-wall choices where a weep inside a rack becomes an outage |
| Heat transfer | Copper for the thermal path, where the coolant side is not the problem | A nickel-bearing surface sized on conductivity alone |
Coolant is not plain water, and the fluid a loop runs on behaves differently towards each metal it touches. A closed loop is by definition a mixed-metal system, where copper parts and stainless manifolds can end up sharing a fluid with brass fittings and an aluminium heat sink. Where two metals sit in the same circuit, the less noble one corrodes, and the choice at that joint decides whether the loop survives ten years of service.
Heat transfer sets the limit on the other side. Copper alloys conduct heat faster than nickel, so where a nickel-bearing surface is specified for corrosion reasons, the wall thickness and the flow path are sized to move the heat anyway. Pure nickel itself conducts 70.2 W/m·K, well below copper, so it is chosen where the fluid side of the duty is the problem and the thermal side is not.
Each position is settled by whichever driver dominates there, and the decision is then confirmed against the loop chemistry and the drawing on the order.
| Position | What decides it | What the order has to confirm |
|---|---|---|
| Cold plate | Heat flux across the wall | The plate material and the flatness or surface requirement |
| Coolant distribution unit | The small-bore tube and the brazed joints | Tube grade, wall thickness and the coolant the tube will see |
| Manifolds and quick disconnects | Strength at the joint, and resistance to the coolant | Material, wall thickness and the connection form |
| Immersion tank | Long wet contact over a large area | Tank material and the wetted parts inside it |
| Secondary loop tubing | Loop chemistry and any mixed-metal joint | Tube grade, and the length or volume in the delivery |
A liquid cooling installation is normally two circuits, and the material question splits with them. The rack loop runs from the cold plate to the distribution unit and is closed and controlled. The facility loop carries the heat away from the distribution unit and out of the building, and its water quality is set by the site. The same alloy can be correct on one side and wrong on the other.
| Item | Rack loop | Facility loop |
|---|---|---|
| What it carries | Coolant between the cold plate and the distribution unit | Heat from the distribution unit to the plant water or to atmosphere |
| Materials usually specified | Copper cold plates, stainless manifolds and quick disconnects | Stainless and CuNi exchanger tube, with wetted parts chosen for the plant water |
| Chemical control | Treated fluid held to a specification | Water quality and filtration set by the site |
| What the order fixes | Grade, wall thickness and the connection form | Exchanger tube grade, and the coolant it sees on each side |
| If a joint fails | A rack is taken out of service | The loop is derated while the leak is traced |
Cooling hardware is ordered in the forms the drawing calls for, and the standard follows the form.
| Form | Why it is ordered for cooling work | Standard the lot is released to |
|---|---|---|
| Coil tube | The exchanger surface, where wall thickness sets the heat path | ASTM B161 and B163 with GB/T 2882-2023 |
| Tube | Distribution runs, where the bore and the joint decide | ASTM B161 and B163 with GB/T 2882-2023 |
| Strip | Brazed assemblies, where the strip thickness sets the gap | ASTM B162 with GB/T 2072-2020 |
| Plate | Fabricated parts sized from the drawing | ASTM B162 with GB/T 2054-2023 |
| Bar | Machined fittings and connections | ASTM B160 with GB/T 4435-2010 |
Cooling hardware is specified twice: once by the equipment builder who owns the thermal design, and once by the material supplier who owns the analysis and the release. Where the two disagree, the disagreement shows up as a certificate that does not match the drawing.
| Item | Specified by the equipment builder | Confirmed by the material supplier |
|---|---|---|
| Alloy family or grade | The service condition at the part: the coolant and the running temperature | The grade and analysis window that meet it, and the standard behind the release |
| Size and wall thickness | The heat path, and the pressure the part has to hold | The tolerance the form can hold, and how it is measured |
| Surface and cleanliness | Whether the part is brazed, welded or sealed | The surface condition supplied, and how residue is controlled |
| Quantity and staging | The build schedule, and how many racks go in per phase | The lot sizes, and the batch records that keep each phase traceable |
The drawing carries the geometry. Five things about the duty do not sit on the drawing, and they are the ones that change the material:
CuNi coil tube, stainless and copper for the wetted parts, with pure nickel, Inconel, Hastelloy and Monel available where the fluid or the temperature rules out the simpler choice. The selection is confirmed against the loop chemistry and the drawing on each order.
The form, the grade or UNS number, the size and wall thickness, the tolerance, the condition, the quantity and the document package. Where the coolant is not water, naming it at the enquiry stage saves a second round of quotations.
Tube follows ASTM B161 and B163 with GB/T 2882-2023, strip and plate follow ASTM B162 with GB/T 2072-2020 and GB/T 2054-2023, and bar and wire follow ASTM B160 and ASTM B164. Copper-nickel is supplied to the composition agreed on the order and confirmed on the mill test certificate.
Every lot is released with an EN 10204 3.1 mill test certificate issued for the heat it came from, which is what keeps a staged delivery traceable when a project is installed over several months.
The coolant and the other metals in the circuit are written into the order, and the material is then confirmed against them. A glycol mix, a treated fluid and deionised water do not behave the same way towards the same alloy, so the fluid is part of the specification and not a site detail.
Tube and coil tube start at 10 kg, and 3 kg for N4. Cut parts and manifolds are quoted from the drawing, because the quantity that suits the run is set by the nesting, not by a package size.
Liquid cooling puts corrosion, leakage and heat transfer in the same component, and the material at each position is chosen for whichever of the three dominates there. Cold plates are copper for the thermal duty. Manifolds are stainless for the joint. Heat exchanger tube and the wet surfaces behind it take nickel-bearing materials where the coolant chemistry, the temperature or a mixed-metal joint makes the cheaper option short-lived.
DLX has supplied nickel and copper-nickel products to thermal management builders since 2002, from a plant rated at 10,000 t/yr and certified to ISO 9001 with SGS audits. Coil tube, manifolds and cut parts are quoted from the drawing. Send the drawing and quantity for a confirmed quotation.
Property values are nominal and are not acceptance limits. Acceptance follows the ordered specification and the tests agreed on the order, with copper-nickel supplied to the composition fixed on the order and reported on the certificate for the heat.
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