Guide
How do you turn an ASHRAE wetted-materials list into material callouts on a liquid-cooling fitting drawing?
A wetted-materials list is the inventory of every material that touches the coolant in a liquid-cooled system, and data-center customers increasingly ask hardware suppliers to meet or declare one. Short answer: map each line of the list that applies to the machined part to one drawing note (alloy designation, condition, surface treatment, joining limits and traceability), declare anything the drawing cannot satisfy before quoting, and leave coolant-compatibility proof to the system owner, because a machine shop can control what the part is made of but cannot show that it suits a given fluid.
By Saola Manufacturing engineering team · Published · Updated
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What does ASHRAE mean by a wetted-materials list?
The ASHRAE TC 9.9 white paper (2019) defines a wetted material as any material in direct contact with the water-based cooling fluid, and tells designers to require a wetted-materials list from every component supplier. Its Table 2 records what manufacturers use today and is not an endorsement.
The paper stresses the “sheer number of materials” that touch the fluid and the due diligence needed to identify them across the whole loop, and it says the designer must understand the risk of each material and follow compatibility rules, local ordinances and best practice. A list therefore reaches the supplier as a flow-down: the customer has compiled it from its own loop, and each component supplier must show that its part fits the list. OCP’s UQD specification does the same one level down; its Section 12 requires the coupling materials to be compatible with the acceptable wetted materials in OCP’s two coolant guidelines, and its Table 8 adds a stainless requirement at the plug tip and cone.
For a machined fitting, the lines that matter are the body alloy, any surface layer such as a passivation film or plating, and the joining method if the fitting is assembled from pieces. Seals, hoses, thread sealant and filter media sit on the assembly bill of materials, not on the machined-part drawing.
Where do the ASHRAE, OCP and Lenovo lists agree and differ?
They agree on stainless steel, low-zinc brass and EPDM, and they differ on aluminum, plated brass, FEP and PTFE tape. The customer’s own list is the one the drawing must follow, because the three published references are not a single standard.
The ASHRAE TC 9.9 white paper (2019) is a 2019 survey of materials found in water-cooled servers. The OCP PG25 guideline (2026) is a 2026 guideline for propylene glycol-based coolants that describes its metals list as representative, not comprehensive. The Lenovo LP2018 standards page (2024) is a vendor’s own restrictive list, published in September 2024. Because they have different authors, dates and purposes, a material can be listed in one and prohibited in another, and the drawing should not choose between them on the customer’s behalf.
The table sets the positions side by side. It records what each source says in the pages read for this guide, and a blank or “not addressed” entry means the passage was not found, not that the material is acceptable.
| Material or practice | ASHRAE TC 9.9 (2019) | OCP PG25 (2026) | Lenovo LP2018 (2024) |
|---|---|---|---|
| Stainless steel | Listed as solution treated and passivated | 304L, 316L or higher grades preferred; most grades acceptable, including 303 and 410 | Low carbon, treated to improve corrosion resistance |
| Brass | Brass with under 15% zinc listed | Under 15% zinc preferred; above that, verify dezincification resistance per ISO 6509 | Copper alloys must be lead-free and under 15% zinc |
| Plated brass | Chrome-plated and nickel-plated brass listed as commonly found | Avoid plated quick connects until proven | Not addressed |
| Aluminum | Only with surface isolation from other wetted metals, or with a dielectric liquid | Not listed in the metals table | Not allowed |
| Carbon steel | Facility loop with inhibitor, in CDU implementations only | Not recommended | Avoid plain-carbon steel |
| FEP | Listed for the technology loop | Listed in the plastics and elastomers table | Not allowed |
| PTFE thread tape | Listed, to be used under best practice | Thread sealants not addressed | Teflon tape prohibited |
| Joining | No soldering; brazing for copper; neither for steels or stainless | Not addressed in the tables | Braze copper; weld stainless; no solder on wetted joints |
Which lines of the list reach a machined fitting drawing?
The lines for the metals and surface layers on the machined part reach the drawing, plus the joining limits and cleanliness conditions that affect it. Seals, hoses, sealants and filter media belong on the assembly bill of materials.
Take the elastomers as an example. The OCP PG25 guideline (2026) recommends peroxide-cured EPDM and warns that sulfur-cured EPDM can add sulfate to the fluid over time, which is a seal-purchasing decision for whoever assembles the coupling, not a note on a turned body. Hose lining, filter media and thread sealant are the same: relevant to the loop, but not to the part drawing. Mixing them into a body drawing creates notes the shop cannot act on.
What does belong are the facts a machined part carries: which alloy it is, what condition it is in, what has been done to its surface, whether it has been welded, and how it was cleaned. Those five facts are what a wetted-materials declaration from the shop should state for each part number.
How does each list line become a drawing note?
Each line becomes one note that names the alloy by designation, the condition or treatment, and the evidence the buyer expects, with a matching exclusion for every material the list bans. The table gives a starting set.
The stainless line deserves care. The ASHRAE footnote on stainless explains that 300-series steels get their corrosion resistance from a chromium oxide layer that high-temperature work such as welding can damage, and that a nitric acid treatment restores it, so passivation has to be considered whenever heat work is done on the stock. On a drawing that means the passivation callout is the last operation, and any weld forces a repeat. The passivation guide explains how the specification choices differ.
The brass line has to name the zinc limit and the lead-free requirement, because a shop that reads “brass” may default to a leaded free-machining grade. If the customer allows a higher-zinc alloy, the OCP PG25 guideline (2026) asks for dezincification resistance to be verified per ISO 6509 as a first pass, which is a test the buyer or the material supplier commissions; see the dezincification guide. For each exclusion (aluminum, plain carbon steel, plating), write the exclusion as a note too, so a substitution made for stock reasons is a visible deviation.
| List line | Drawing note | Evidence the shop can supply | Left to the buyer |
|---|---|---|---|
| Stainless steel, solution treated and passivated | Alloy by designation and condition named by the customer; passivate after all machining; re-passivate after any welding; record method and date | Material certificate with heat number; passivation record | Coolant compatibility of the grade |
| Brass under 15% zinc | Copper alloy by designation with a zinc maximum and a lead-free requirement; no substitute alloy | Material certificate showing zinc and lead content | Dezincification evidence for any higher-zinc alloy |
| Aluminum excluded | No aluminum on any wetted surface, including plugs and screws | Material certificate for every wetted part | Whether an isolation coating is allowed |
| Carbon steel excluded | No plain carbon steel in the wetted path | Material certificate for every wetted part | Corrosion inhibitor strategy |
| Plating or coating | None on wetted surfaces unless the list names it; if named, the specification and masking appear on the drawing | Plating record from the plating source | Plating wear and inspection |
| Joining | No solder; no brazing on stainless; welds followed by passivation | Process record for any joint | Joint qualification |
| Cleanliness | Cleaning and passivation steps completed before shipment declared on the packing documents | Cleaning record | On-site flushing |
What can a CNC shop provide, and what must the buyer test?
A CNC shop can supply the specified alloy with a material certificate and heat number, machine and clean to the drawing, and arrange passivation with a record. It cannot prove that a material suits a given coolant, which the PG25 guideline assigns to the material supplier, component maker, fluid supplier, operator or a test laboratory.
The OCP PG25 guideline (2026) describes compatibility verification at the maximum operating temperature of the system and repeats it for any later change of wetted material. Its corrosion test is a modified ASTM D8040 coupon exposure per ASTM D8040-18, run for two weeks at 88°C with continuous aeration, with limits for copper, brass, 304L and 316L. That is a fluid-and-metal test, and it is not something a part supplier runs for a drawing.
At Saola, CNC turning and milling of fittings, manifolds, adapters and plugs run at the lead plant (CNC turning, CNC milling), and the material certificate and heat number follow the lot; the certificate of conformance guide explains what to request. Passivation and any plating are arranged through partner plants that Saola manages, and the quote states where each step happens. The shop declares what the part is made of and how it was treated, and the customer decides whether that satisfies its list.
What should the RFQ ask for when the customer sends a list?
Ask for the list as a document with a revision date, map every line to a drawing note before quoting, and flag any line the drawing cannot satisfy, such as a part designed in aluminum or leaded brass. Settle the conflicting lines, such as plating and PTFE tape, in writing.
- Which list governs: the customer’s own, or one of the three public references. Get the revision or date.
- Conflicting lines: plated brass, FEP and PTFE tape are listed by one source and excluded by another, so ask which applies.
- Declaration format: part number, alloy designation, product form, condition, surface treatment, heat number, cleaning and passivation record.
- Change control: the PG25 guideline asks that any future change to wetted materials be re-verified, so agree that no alloy or finishing change is made without notice.
- Volume logic: at ten to twenty thousand parts a year, a declaration filed once per part number and revised only on change is easier to maintain than one produced for every lot.
If the list and the drawing disagree, resolve it before the first-article lot, since a material change after approval means repeating the customer’s compatibility work.
Frequently asked
Is ASHRAE Table 2 an approved materials list?
No. The paper says its list records the latest materials used by equipment makers and is not an endorsement. The designer must still assess the risk of each material.
Is the passivation film part of the wetted material?
ASHRAE lists stainless steel as solution treated and passivated, so the passivated surface is part of the listed material. Treat passivation state as a drawing requirement, not an option.
Can 303 stainless go on a wetted surface?
The OCP PG25 guideline says most stainless alloys should be acceptable, including 303, while preferring 304L and 316L. ASHRAE does not name grades, so the customer’s list decides.
Which source should govern when they disagree?
The customer’s own list. The three public references have different authors, dates and scopes, and the supplier cannot resolve their conflicts on the customer’s behalf.
What about PTFE tape at a threaded port?
ASHRAE lists both liquid sealant and PTFE tape, and the Lenovo page prohibits Teflon tape because particles can clog the loop. Port sealing is an assembly decision, so ask the customer which applies.
Sources
- 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
- 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
- Universal Quick Disconnect (UQD) Specification, Version 2.0.0, Open Compute Project, 2026