Project Description
316L Stainless Steel Square Tube Liquid Cooling Manifold
The liquid cooling manifold — also referred to as a liquid separator, branch pipe, or coolant distributor — is a precision-fabricated stainless steel square tube assembly that serves as the arterial backbone of modern data center liquid cooling systems. Built from 316L (UNS S31603 / EN 1.4404) austenitic stainless steel square tubing, the manifold evenly distributes cooling fluid from a central supply line to multiple server cold plates and collects heated return fluid, forming the critical interface between the cooling distribution unit (CDU) and the IT equipment.
The square tube geometry offers distinct advantages over conventional round tube designs for manifold applications: flat external surfaces simplify mounting to server rack frames, provide stable platforms for precision CNC-drilled branch ports, and enable tighter packing density within confined rack enclosures. The uniform wall thickness inherent in cold-formed square tubing ensures consistent pressure-bearing capacity across all four faces.
At Fushun Steel Tube, we manufacture these manifolds from 316L austenitic stainless steel square tube stock, chosen for its molybdenum-enhanced pitting and crevice corrosion resistance — critical when operating with chloride-containing coolants or in coastal data center environments. The low-carbon “L” grade (C ≤ 0.03%) virtually eliminates the risk of intergranular corrosion after welding, allowing as-welded manifold assemblies to enter service without mandatory post-weld heat treatment. Typical deployments include high-density GPU and CPU server racks in hyperscale data centers, edge computing facilities, and enterprise HPC clusters.
Product Image
Applications
As a Square Tube Distribution Component
- Direct-to-chip liquid cooling distribution in GPU-accelerated AI training racks (NVIDIA H100/H200/B200 platforms)
- CPU cold plate coolant supply for high-frequency trading server clusters
- Immersion cooling tank fluid distribution and return header assemblies
- Heat exchanger primary/secondary loop branch connections in modular data centers
- EV battery pack thermal management coolant distribution rails
- Power electronics liquid cooling for IGBT modules in renewable energy inverters
- Medical imaging equipment (MRI/CT) closed-loop cooling circuits
- Laser system chiller distribution networks in industrial cutting and welding installations
Specifications & Standards
The manifold body is fabricated from 316L stainless steel square tubing that conforms to the following international standards. We supply tube stock certified to any of these specifications depending on project requirements, end-use jurisdiction, and customer preference.
| Standard | Description | Product Form |
|---|---|---|
| ASTM A213 / A213M | Seamless ferritic and austenitic alloy-steel boiler, superheater, and heat-exchanger tubes | Seamless round tube |
| ASTM A269 / A269M | Seamless and welded austenitic stainless steel tubing for general service | Seamless & welded round tube |
| ASTM A312 / A312M | Seamless, welded, and heavily cold worked austenitic stainless steel pipes | Seamless & welded round pipe |
| ASTM A554 | Welded austenitic stainless steel mechanical tubing — square, rectangular, and round | Welded square & rectangular tube |
| EN 10216-5 | Seamless steel tubes for pressure purposes — Stainless steel tubes (grade 1.4404) | Seamless round tube |
| EN 10296-2 | Welded circular, square, and rectangular steel tubes for mechanical and general engineering purposes (grade 1.4404) | Welded square & rectangular tube |
| GB/T 14976 | Seamless stainless steel pipes for fluid transport (grade 022Cr17Ni12Mo2) | Seamless round pipe |
| GB/T 3094 | Cold drawn shaped steel tubes (grade 022Cr17Ni12Mo2) | Cold-drawn square & rectangular tube |
| JIS G3459 | Stainless steel pipes (grade SUS316L) | Seamless & welded round pipe |
| JIS G3446 | Stainless steel pipes for machine and structural purposes (grade SUS316L) | Welded square & rectangular tube |
Fabricated manifold assemblies can be supplied with EN 10204 3.1 or 3.2 inspection certificates. Additional compliance documentation for pressure equipment directives (PED 2014/68/EU) is available on request.
Available Sizes & Delivery
316L Stainless Steel Square Tube Stock (Manifold Body)
| Dimension | Range |
|---|---|
| Side length (S × S) | 10 mm × 10 mm – 150 mm × 150 mm (0.394″ × 0.394″ – 5.906″ × 5.906″) |
| Wall thickness (WT) | 1.0 mm – 8.0 mm (0.039″ – 0.315″) |
| Length | Up to 6,000 mm (custom cut-to-length available) |
Rectangular Section Options
| Dimension | Range |
|---|---|
| Cross-section (A × B) | 10 mm × 20 mm – 100 mm × 200 mm |
| Wall thickness | 1.0 mm – 8.0 mm |
Standard manifold body sizes for data center applications are typically 30 mm × 30 mm or 40 mm × 40 mm square sections, with wall thicknesses ranging from 1.5 mm to 3.0 mm. Flat side surfaces provide a stable platform for precision CNC-drilled branch ports and simplify mounting to rack infrastructure. Port count, spacing, and connection type are engineered to customer specifications.
Delivery & MOQ
- Standard square tube sizes in 316L stock: Ready-stock available, shipment within 7 working days.
- Custom dimensions or non-standard port configurations: MOQ from 2–3 metric tons, lead time approximately 25–35 working days.
- Small-batch trial orders: Accepted; we encourage prototype and pilot runs before series production.
- Large-volume project orders: Significant price advantages available; delivery schedules can be coordinated to match project milestones.
Contact us with your manifold specifications for a detailed quotation and delivery timeline.
Chemical Composition
The manifold body is fabricated from 316L (UNS S31603 / EN 1.4404 / SUS316L) molybdenum-bearing austenitic stainless steel. The addition of 2.0–3.0% molybdenum significantly enhances resistance to pitting and crevice corrosion in chloride-containing environments compared to standard 304 grades. The ultra-low carbon content (max 0.03%) of 316L is a defining advantage for welded square tube manifold fabrication — it effectively suppresses chromium carbide precipitation along grain boundaries during welding, preserving full intergranular corrosion resistance in the as-welded condition.
| Element | ASTM A213/A269/A312/A554 | EN 10216-5 / EN 10296-2 1.4404 | GB/T 14976 / GB/T 3094 022Cr17Ni12Mo2 |
|---|---|---|---|
| Carbon (C) | ≤ 0.030 | ≤ 0.030 | ≤ 0.030 |
| Manganese (Mn) | ≤ 2.00 | ≤ 2.00 | ≤ 2.00 |
| Silicon (Si) | ≤ 1.00 | ≤ 1.00 | ≤ 1.00 |
| Phosphorus (P) | ≤ 0.045 | ≤ 0.045 | ≤ 0.035 |
| Sulfur (S) | ≤ 0.030 | ≤ 0.015 | ≤ 0.030 |
| Chromium (Cr) | 16.0 – 18.0 | 16.5 – 18.5 | 16.0 – 18.0 |
| Nickel (Ni) | 10.0 – 14.0 | 10.0 – 13.0 | 10.0 – 14.0 |
| Molybdenum (Mo) | 2.00 – 3.00 | 2.00 – 2.50 | 2.00 – 3.00 |
| Nitrogen (N) | — | ≤ 0.10 | — |
Manufacturing Process
Steelmaking Route
316L stainless steel for manifold square tubing is produced through the following refining path:
- Standard: Electric Arc Furnace (EAF) → Argon Oxygen Decarburization (AOD) → Ladle Furnace (LF) → Continuous Casting
- Enhanced purity (on request): EAF → AOD → LF → Vacuum Degassing (VD) → Continuous Casting
- Ultra-clean or nuclear-grade: VIM + VAR double-melt route available
The AOD process is essential for achieving the precise ultra-low carbon control (≤ 0.03%), desulfurization, and inclusion cleanliness required in 316L austenitic stainless steel.
Square Tube Manufacturing & Manifold Fabrication
Square tube production: Flat strip from cold-rolled 316L coil → slitting to width → continuous roll forming into square profile → longitudinal welding (TIG / laser / plasma) → in-line bead conditioning → sizing and straightening → solution annealing in controlled-atmosphere furnace → pickling & passivation → cut-to-length. For enhanced dimensional precision, the as-welded square tube can undergo a subsequent cold-drawing pass through a shaped die.
Cold-drawn square tube (precision grade): Welded square tube hollow → intermediate annealing → pickling → cold drawing through square die profile → final solution annealing → straightening → cutting → end finishing. For round branch port tube stock, we apply cold Pilger rolling techniques to achieve tight dimensional tolerances.
Manifold assembly: Precision-cut square tube sections → CNC drilling/milling of branch ports on flat side faces — the square geometry provides an inherently stable workpiece surface, improving machining accuracy and reducing setup complexity compared to round tube → deburring & edge conditioning → fit-up of branch stubs / quick-disconnect bosses → orbital TIG welding → helium leak testing → final inspection.
Customers can work with our engineering team to select the optimal square tube forming route and manifold fabrication sequence based on pressure class, wall thickness, and surface finish requirements.
Mechanical Properties
The following mechanical properties apply to 316L stainless steel square tube stock in the solution-annealed condition at room temperature.
| Property | ASTM A213/A269/A554 | EN 10216-5 / EN 10296-2 1.4404 | Remarks |
|---|---|---|---|
| Tensile strength, Rm | ≥ 485 MPa (70 ksi) | 500 – 700 MPa | — |
| Yield strength, Rp0.2 | ≥ 170 MPa (25 ksi) | ≥ 200 MPa | Room temperature |
| Elongation, A | ≥ 35% | ≥ 40% (longitudinal) | Gauge length per standard |
| Hardness | ≤ 90 HRB / ≤ 200 HBW | — | — |
| Impact toughness | Not normally specified at ambient | — | Excellent down to cryogenic temperatures |
316L stainless steel retains excellent toughness at sub-zero temperatures and does not exhibit a ductile-to-brittle transition. It is routinely specified for cryogenic service down to −196 °C. For manifolds serving low-temperature coolant loops, impact testing at the design minimum temperature can be performed on request.
Heat Treatment
316L stainless steel achieves its corrosion-resistant, fully austenitic microstructure through solution annealing.
| Treatment | Temperature Range | Holding Time | Cooling Method |
|---|---|---|---|
| Solution annealing | 1,040 – 1,100 °C (1,900 – 2,010 °F) | 1 min per mm wall thickness (min 30 min for weldments) | Rapid water quench or rapid air cool |
Due to the ultra-low carbon content (≤ 0.03%), 316L is inherently resistant to sensitization and intergranular corrosion in the as-welded condition. For the majority of data center liquid cooling applications, post-weld solution annealing is not required — the as-welded 316L square tube manifold can enter service directly after fabrication and testing, reducing lead time and cost. Where full solution annealing is specified for highly aggressive coolant chemistries, it is performed in controlled-atmosphere or vacuum furnaces to prevent surface oxidation and molybdenum depletion.
Surface Finish & Tolerances
| Processing State | Surface Description | Typical Ra (Internal / External) |
|---|---|---|
| As-welded & pickled | Matte, scale-free, passivated; weld bead conditioned | ≤ 6.3 μm / ≤ 3.2 μm |
| Cold-drawn square (bright) | Smooth, metallic bright finish on all four faces | ≤ 1.6 μm / ≤ 0.8 μm |
| Honed / skived & roller burnished (ID) | Mirror-like internal surface for branch ports | ≤ 0.4 μm (ID) |
| Ground (external faces) | High-precision ground finish on flat square faces | ≤ 0.8 μm |
| Electropolished | Maximum surface cleanliness, enhanced passivation | ≤ 0.4 μm |
Dimensional Tolerances
- Welded square tube side length: ±0.5% (min ±0.3 mm); WT: ±10%
- Cold-drawn square tube side length: ±0.10 – 0.20 mm; WT: ±5 – 8%
- Square tube corner radius (external): ≤ 2.0 × WT (standard); ≤ 1.5 × WT (cold-drawn)
- Straightness: ≤ 1.5 mm/m (cold-drawn); ≤ 3 mm/m (as-welded)
- Twist: ≤ 1° per meter
- Port center-to-center spacing: ±0.15 mm (CNC-machined on flat square face)
For data center manifolds with quick-disconnect coupling interfaces, the flat faces of the square tube provide an inherently superior sealing surface for O-ring face-seal connections compared to the curved surface of round tube. Fushun Steel Tube’s stainless steel square tubing is manufactured to the precision required for mission-critical coolant distribution.
Quality Assurance & Testing
Every 316L stainless steel square tube liquid cooling manifold undergoes a comprehensive quality control process from incoming material to final assembly.
Incoming Material Inspection
- Chemical composition verification by optical emission spectrometry (OES) on every heat of tube stock, with molybdenum content confirmed
- Positive material identification (PMI) using handheld XRF for grade confirmation (Cr/Ni/Mo verification)
- Square tube dimensional check: side length, wall thickness at center of each face, corner radius, straightness, and twist
In-Process Inspection
- Online wall thickness and side length measurement during square tube forming and cold-drawing
- Weld parameter monitoring and recording (orbital TIG / laser)
- Dimensional check of port positions after CNC machining on flat square faces
Final Product Testing
- Hydrostatic pressure test: Performed to 1.5× design pressure or per customer specification
- Helium leak test: Leakage rate ≤ 1 × 10−9 Pa·m3/s; this is the primary integrity test for every manifold assembly
- Ultrasonic testing (UT): Seamless tube stock and weld seam per applicable ASTM / EN supplementary requirements
- Eddy current testing (ET): Available for thin-wall precision tube sections
- Dye penetrant testing (PT): Weld surface inspection per ASME Section V
- Mechanical testing: Tensile per heat treatment lot; hardness per tube
- Intergranular corrosion test: ASTM A262 Practice E or EN ISO 3651-2 on request
- Pitting corrosion test: ASTM G48 Method A on request for chloride-heavy coolant chemistries
Certification & Third-Party Inspection
- EN 10204 Type 3.1 inspection certificate issued as standard
- EN 10204 Type 3.2 with independent third-party verification available (SGS, TÜV, Bureau Veritas)
- Fushun Steel Tube is ISO 9001:2015 certified
Packing & Shipping
- Each manifold is individually wrapped in VCI (volatile corrosion inhibitor) film or anti-rust paper to protect 316L stainless steel surfaces.
- All ports are sealed with plastic protective caps or plugs to prevent ingress of foreign matter.
- The square tube profile simplifies stacking and securing within crates — flat faces distribute contact pressure evenly.
- Assemblies are secured in custom-fitted plywood crates with internal foam or EPE cushioning. Steel-frame crates available for heavy manifolds.
- Each crate is clearly labeled with part number, purchase order reference, gross/net weight, and handling instructions.
- Custom packing specifications, including customer-specific labels, barcodes, and shipping marks, are fully supported.
Shipping is available by ocean freight, air freight, or international courier. We work with major logistics partners to deliver to data center project sites worldwide.
Frequently Asked Questions
- Why use 316L square tube instead of 304 round tube for a liquid cooling manifold?
- 316L offers two key advantages over 304: molybdenum-enhanced pitting resistance for chloride-containing coolants, and the ultra-low-carbon “L” grade eliminates sensitization risk after welding, often removing the need for post-weld heat treatment. The square tube profile provides flat surfaces that simplify mounting, improve CNC port drilling accuracy, and create better sealing interfaces for O-ring connections.
- Can you fabricate a manifold with non-standard port count or custom spacing?
- Absolutely. All manifolds are fabricated to customer specifications. The square tube’s flat faces provide an ideal reference surface for precision CNC-machined ports at any required position. Provide us with your port count, center-to-center spacing, port thread type or quick-disconnect coupling model, and overall envelope dimensions. Our engineering team will prepare a fabrication drawing for your approval before production begins.
- What is the maximum operating pressure your 316L square tube manifolds can handle?
- The pressure rating depends primarily on the wall thickness, cross-section size, and branch connection design. For standard data center liquid cooling applications operating at 1–10 bar, our standard wall thickness selection is more than adequate. For higher-pressure applications, our engineering team will perform cross-section stress analysis per your operating parameters and recommend the required wall schedule, with hydrostatic testing conducted at 1.5× the rated pressure.
- What documentation do you provide with each shipment?
- Every shipment includes an EN 10204 Type 3.1 material certificate covering 316L chemical composition (including molybdenum verification) and mechanical properties, hydrostatic and helium leak test reports for each manifold, dimensional inspection reports covering square tube side length, wall thickness, straightness, and twist, and a certificate of conformance. Type 3.2 certificates with third-party witness testing are available on request.
- Can you support a small prototype order before volume production?
- Yes, we actively encourage prototype and pilot runs. Single-unit or small-batch orders in 316L square tube are welcome, with no minimum order quantity for initial qualification. Our engineering team will work closely with yours during the prototyping phase to refine the design for manufacturability.
Request a Quote
Whether you need a single prototype manifold or a production run for an entire data center deployment, Fushun Steel Tube has the 316L square tube manufacturing capability and manifold fabrication expertise to deliver. Contact our engineering team today with your specifications — we will respond with a detailed quotation and lead time within 24 hours.
