Guide
Can nickel-plated brass quick connects be used in a liquid cooling loop, or must they be solid stainless?
Nickel-plated brass quick connects are brass-bodied couplings with a thin nickel layer over the base metal, and they show up in coolant-loop proposals because brass is easy to machine and plate. Short answer: the current OCP guideline says stainless steel quick connects should be used and that nickel-plated and chromium-plated ones should be avoided until they are proven satisfactory, so for a new liquid-cooling design specify solid stainless unless the system owner accepts plated brass in writing.
By Saola Manufacturing engineering team · Published · Updated
On this page
What does the OCP guideline say about plated quick connects?
The OCP PG25 guideline says quick connects made of stainless steel should be used, and recommends avoiding nickel-plated and chromium-plated quick connects until they are proven satisfactory. Its reason is that after many uses the plating can wear away and expose the underlying metal to the heat transfer fluid.
The OCP propylene glycol guideline (PG25, 2026) adds three points in a footnote to its metals table. Corrosion inhibitors may protect the exposed metal, but the galvanic couple between that metal and the plating may increase the tendency to corrode. Brass corrosion introduces zinc, and potentially copper, into the fluid, and the guideline says the consequences of dissolved zinc for the long-term performance of copper cold plates have not been determined. Acceptable plating thickness is declared outside its scope, and plated quick connects should be inspected regularly or as fluid analysis indicates.
This is a recommendation, not a ban, and it is written for propylene glycol-based fluids. The same table prefers brass with under 15 percent zinc, notes that higher-zinc alloys are more prone to dezincification, and says to verify dezincification resistance with ISO 6509 as a first pass and to consult the material maker. The dezincification guide explains that failure mode.
Does ASHRAE allow nickel-plated or chrome-plated brass?
ASHRAE TC 9.9 lists both nickel-plated and chrome-plated brass among the wetted materials commonly found in water-cooled servers, but it calls the list a record of what manufacturers use, not an endorsement. The same paper tells designers to require a wetted-materials list from every component supplier.
Table 2 of the ASHRAE TC 9.9 water-cooled servers white paper (2019) marks brass with under 15 percent zinc, brass chrome plated and brass nickel plated as found in both facility-water and technology-loop hardware, along with copper alloys that are under 15 percent zinc and lead free. The text says the designer must understand the risk of each material and abide by compatibility rules and best practice. So ASHRAE (2019) and OCP (2026) do not contradict each other so much as answer different questions: a survey of what is in the field, and a recommendation about quick connects written seven years later.
The Lenovo Neptune direct water-cooling standards (LP2018, 2024) restricts wetted metals to copper alloys and stainless steels, requires copper alloys to be lead-free with under 15 percent zinc, and does not allow aluminum. The page as read does not mention plating or quick connects. Typical free-machining brass contains lead and more zinc than that limit, so the common fitting alloy would not pass this list whether plated or not. The lead-free brass guide covers the alloy side.
| Source | Plated brass | Brass zinc and lead | Aluminum |
|---|---|---|---|
| OCP PG25, September 2026 | Use stainless quick connects; avoid nickel-plated and chromium-plated ones until proven | Under 15% zinc preferred; above 15% zinc, verify dezincification resistance per ISO 6509 and consult the material maker | Not listed in its metals table |
| ASHRAE TC 9.9 white paper, 2019 | Brass chrome plated and brass nickel plated are listed as commonly found; the paper says the list is not an endorsement | Brass with under 15% zinc is listed; copper alloys under 15% zinc and lead free are listed | Listed with a footnote: only if surface-isolated from other wetted metals, or in a dielectric loop |
| Lenovo LP2018, September 2024 | Not addressed on the page | Copper alloys must be lead-free and contain less than 15% zinc | Not allowed |
| OCP UQD v2.0.0, 2026 (Table 8) | Plug tip, shaft, cone and guide must be SUS 303, 304, 304L, 316 or 316L | Not addressed | Not addressed |
Does the UQD specification already settle the question for UQD couplings?
For a UQD or UQDB plug it largely does: Table 8 of the OCP UQD Specification v2.0.0 (2026) requires stainless steel at the plug external tip and shaft and at the cone and guide. A plated-brass tip would not meet that table, and the specification contains no plating-thickness or plating-wear test.
The specification does set a minimum coupling-cycle count of 5000 in its Table 6, and its mechanical cycling test (Section 9.2.3) is followed by a hydrostatic test with no visible leakage as the acceptance criterion. Those tests would catch a coupling that leaks after cycling, but they do not inspect for worn plating, which is the failure PG25 describes. The visual table in the same specification does reject rust or other evidence of corrosion on any zone.
In practice the commercial UQD range is stainless: the Danfoss Hansen UQD fact sheet (September 2026) lists 303/304 stainless steel as its standard material. For non-UQD fittings, adapters and manifold ports in the same loop, Table 8 does not apply and the question stays open, which is where the other documents matter.
Where does plating wear first on a turned quick-connect body?
Plating wears first where metal rubs against metal or a tool: sliding and locking surfaces, thread flanks under assembly torque, and wrench flats and edges. That is a machinist’s observation, not a figure from the guidelines, but it points at the surfaces PG25 is worried about.
Sealing shoulders and lands that an O-ring or poppet runs against see repeated sliding contact. Plated threads are torqued, backed off and torqued again, which polishes the plating off the flanks. Hex flats pick up wrench marks, and sharp external edges, where electroplate typically builds thicker, are the first places a chip or burr leaves bare base metal. Internal passages and thread roots typically receive the thinnest plating, and they are also the surfaces the coolant actually touches.
None of this can be quantified without a drawing, a plating specification and a wear test, and no published source gives a threshold, which is why the guideline leaves acceptable thickness open. What a machine shop controls is the base part: edge breaks and deburring before plating, a sealing-face finish the plater does not have to build up, and thread allowances that account for the coating (the threads after plating guide covers the allowance). Plating itself is arranged through a partner plant that Saola manages, and the surface finishing page describes the managed route.
What does a stainless redesign change in the machined part?
Moving from brass to stainless changes the cutting data, tool wear and deburring, and it removes the plating step, so the quote moves in both directions. How much depends on the part, and it should come from a quote on your drawing, not from a rule of thumb.
Stainless cuts slower than free-machining brass and is more prone to galling on threads and sliding fits, so the redesign is a review of tolerances, thread class and surface finish, not only a material swap. On the other side of the ledger, the plating line, its masking and its inspection disappear, and with them the risk that plating on a thread or seal land is out of tolerance. For a turned and milled part at ten to twenty thousand a year, ask the supplier to quote both versions on the same finish and inspection requirements so the comparison is honest. The C360 brass vs 303 stainless guide compares the two materials as machined parts.
The table below turns the three documents into an option guide. It is a summary of their positions, not a substitute for the customer’s own wetted-materials list, which overrides all of them.
| Option | Choose it when | What to watch |
|---|---|---|
| Solid stainless (303, 304L, 316L) | The default for any new design and for every UQD or UQDB part | Grade, passivation and traceability on the drawing; galling on threads |
| Unplated brass, lead-free, under 15% zinc | The system owner's list allows it and the part is not a UQD or UQDB coupling | Zinc entering the loop; PG25 says the effect of dissolved zinc on copper cold plates is not determined |
| Plated brass (nickel or chromium) | Only with the system owner's written acceptance, since PG25 says to avoid until proven | Plating wear, inspection interval and fluid analysis, all owned by the customer |
| Brass above 15% zinc, plated or not | Rarely; PG25 requires verified dezincification resistance, and Lenovo's list excludes it | ISO 6509 evidence and the material maker's confirmation |
| Aluminum | Only where the customer's list allows it with surface isolation | Galvanic attack of other wetted metals; Lenovo does not allow it |
What should an RFQ say if the customer insists on plated brass?
Get the customer’s wetted-materials list and plating specification in writing, and keep plating type, thickness and inspection with the customer. A machine shop can machine and mask to the drawing, but it cannot declare plated brass acceptable for a coolant loop.
The drawing and RFQ should state, at minimum, the following.
- Base alloy: the brass designation with a zinc maximum and a lead-free requirement, so the shop does not default to a leaded free-machining grade.
- Plating: the specification, type and thickness callout, written by the customer, plus which surfaces are masked (sealing faces and threads are the usual candidates).
- Sequence: deburr and clean before plating, with a stated edge-break requirement, because plating over a burr leaves a flake waiting to happen.
- Inspection: what is checked after plating, such as thread gauging and visual condition of sealing faces, and on what sample.
- Responsibility: fluid analysis and the in-service inspection interval that PG25 asks for sit with the system operator, so say so in the quote documents.
CNC turning and milling of the base part run at the lead plant, and the quote names the production site for each step. If stainless is still on the table, the CNC turning page and the CNC milling page describe what the lead plant runs.
Frequently asked
Is nickel-plated brass banned by OCP?
No. The PG25 guideline recommends avoiding nickel-plated and chromium-plated quick connects until they are proven satisfactory, and it recommends stainless ones. That is a recommendation, and the system owner decides.
Can unplated brass be used in a coolant loop?
The PG25 guideline prefers brass with under 15 percent zinc and asks for dezincification verification above that, and the Lenovo list requires lead-free copper alloys under 15 percent zinc. Whether it is acceptable still depends on the customer’s own list.
What about aluminum quick connects?
ASHRAE allows aluminum only where it is surface-isolated from other wetted metals or the liquid is dielectric, Lenovo does not allow it, and PG25’s metals table does not list it. Treat it as excluded unless the customer’s list says otherwise.
Why does zinc matter for cold plates?
PG25 says brass corrosion introduces zinc and possibly copper into the fluid, and that the consequences of dissolved zinc for the long-term performance of copper cold plates have not been determined.
Does a thicker plating solve the problem?
No published source sets a safe thickness. PG25 states that identifying acceptable plating thickness is outside its scope, so thickness is a customer decision backed by its own inspection.
Sources
- Guidelines for Using Propylene Glycol-Based Heat Transfer Fluids in Liquid Cooled Racks, Revision 2.0, Version 1.0.0, Open Compute Project, September 2026
- Water-Cooled Servers: Common Designs, Components, and Processes (white paper), ASHRAE Technical Committee 9.9, 2019
- Lenovo Neptune Direct Water-Cooling Standards (LP2018), Lenovo Press, September 2024
- Universal Quick Disconnect (UQD) Specification, Version 2.0.0, Open Compute Project, 2026
- Danfoss Hansen Universal Quick Disconnect (UQD) fact sheet, Danfoss, September 2026