HVAC Duct Machinery for Cleanrooms

Why cleanroom duct is different

A commercial office duct is graded on air leakage and dimensional accuracy. A cleanroom duct is graded on particulate contamination. Every surface inside the duct is a potential source of shed particles, and every crevice — overlapped seam, gasket groove, pop-rivet head — is a potential harbour for biological contamination that cannot be reached during washdown. The specification for cleanroom duct is therefore driven by cleanability, not leakage class. Material is 304 or 316 stainless steel. Seams are TIG welded with crevice-free fusion. Transverse joints are continuously welded or use full-gasket TDF with no exposed fasteners on the interior surface. Interior surface finish is specified to Ra values (usually Ra 0.8 µm or better for ISO Class 5 and cleaner).

These specifications translate into specific machine requirements: the auto duct line has to form stainless with no contamination of the base material, the longitudinal-seam station needs TIG welding capability instead of (or alongside) Pittsburgh-lock forming, and the finishing workflow has to include polishing or grinding to achieve the surface Ra specification. SBKJ covers this workflow with an SBAL-V stainless configuration plus an automatic TIG seam welder plus an orbital welding machine for transverse joints on the tightest ISO Class 5 projects.

The standards that govern cleanroom HVAC duct

• ISO 14644-1:2015 — Classification of Air Cleanliness by Particle Concentration. Defines Class 1 through Class 9 based on particle counts per cubic metre at specified particle sizes. Cleanrooms relevant to HVAC duct work typically fall between Class 5 (old Class 100) and Class 8 (old Class 100,000).
• FED-STD-209E — the older US federal standard, officially cancelled but still referenced on legacy projects. Class 100, Class 1,000, Class 10,000 and Class 100,000 map approximately to ISO Class 5, 6, 7 and 8 respectively.
• EU GMP Annex 1 — European Good Manufacturing Practice for sterile medicinal products. Grades A, B, C and D roughly correspond to ISO Class 5 (at rest and in operation), Class 5 at rest / Class 7 in operation, Class 7 at rest / Class 8 in operation, and Class 8 at rest respectively. The 2022 revision tightened a number of requirements and is now driving specification upgrades on existing facilities.
• SEMI F-series standards — semiconductor industry specific. SEMI F15 covers fab facility air, SEMI F21 covers categorised categories of classification, and SEMI F57 covers polymer materials for ultra-pure water — but for HVAC duct the most relevant requirement is typically the AMC (airborne molecular contamination) specification, which drives stainless or electropolished duct construction to avoid outgassing from adhesives and coatings.
• FDA cGMP and 21 CFR Parts 210/211 — US pharmaceutical regulations. Less prescriptive on duct construction than EU GMP Annex 1 but equivalent in practice.

Duct specification by cleanroom class

• ISO Class 5 and cleaner (Grade A/B, old Class 100) — Stainless steel 316L, TIG welded seam, continuously welded transverse joints or full-gasket TDF with sealed fasteners. Interior surface Ra 0.8 µm or better (electropolishing often specified for Grade A aseptic zones). HEPA or ULPA terminal filtration at every supply outlet. Very low duct leakage is implicit because the entire air-handling envelope is pressurised and monitored continuously.
• ISO Class 6 (Grade B/C, old Class 1,000) — Stainless steel 304 or 316, TIG welded seam. Transverse joints can use high-quality TDF with full gasket. Interior surface Ra 1.6 µm is usually acceptable. HEPA terminal filtration at supply outlets. SMACNA Seal Class A leakage.
• ISO Class 7 (Grade C, old Class 10,000) — Stainless steel 304 for pharma; galvanized steel sometimes acceptable for electronics. Pittsburgh-lock longitudinal seam acceptable if properly sealed. TDF flange with Seal Class A leakage. HEPA terminal filtration at most supply outlets, with some bypass return acceptable.
• ISO Class 8 (Grade D, old Class 100,000) — Galvanized steel typically acceptable (stainless still common in pharma for cleanability). Pittsburgh-lock or snaplock seam. TDF flange with Seal Class A or B leakage. HEPA filtration at final supply outlets only.

Why stainless steel is the default for pharmaceutical work

A pharmaceutical cleanroom is expected to survive repeated washdown with aggressive cleaning agents — hydrogen peroxide vapour (HPV) biodecontamination, peracetic acid, sodium hypochlorite and isopropyl alcohol at concentrations that would corrode galvanized zinc within months. Stainless steel 304 handles most of these; 316 is specified where chlorides are involved or where the facility is coastal. The duct has to be stainless not because the air inside needs to be stainless-clean, but because the walls need to survive the cleaning regime that keeps the cleanroom clean. This is the number-one reason first-time pharmaceutical buyers are surprised to find their ISO Class 8 project still specifying 304 stainless duct: the ISO class allows galvanized, but the cleaning regime does not.

A secondary reason is traceability. Pharmaceutical GMP requires documented material traceability back to mill certification, and stainless steel coil is much easier to document than galvanized steel of varying zinc coating thickness. SBKJ supplies stainless coil traceability documentation on request and can accept customer-supplied coil for projects with strict chain-of-custody requirements.

Why the TIG seam welder matters

Pittsburgh-lock longitudinal seam is the dominant construction technique for commercial galvanized duct. It is fast, cheap, and adequately sealed for Seal Class B or C air-tightness. But it creates a small interior crevice where the two sheets overlap and then lock together. In a cleanroom that crevice is a biological harbour, a particulate trap, and a source of periodic shed contamination as the locking profile flexes under pressure cycling. Pharmaceutical GMP projects consistently reject Pittsburgh-lock for ISO Class 5-6 zones for this reason.

The alternative is a continuously welded longitudinal seam: the two sheet edges are butt-joined and fused with a TIG welding torch, then the weld bead is ground flush and polished to match the interior Ra specification. Done well, the result is a seamless interior surface with no harbour points. SBKJ supplies an automatic TIG seam welding machine that integrates with the SBAL-V workflow — the auto line forms the duct body, the welder follows up on the seam, and the grinding/polishing station finishes the interior surface to the specified Ra. Total throughput drops to roughly 600–900 square metres per day from the 2,000–2,500 achievable on galvanized Pittsburgh-lock, but the specification is met end-to-end.

Recommended SBKJ machines for cleanroom work

• SBAL-V Auto Duct Production Line — stainless-capable configuration. Handles 0.5–1.5 mm 304 and 316 stainless steel, ±0.2 mm TDF flange tolerance, 1,000–1,500 m² per day stainless throughput (single shift). The standard recommendation for pharmaceutical and semiconductor cleanroom projects.
• SBAL-III Auto Duct Production Line — stainless-capable configuration. Lower throughput alternative for smaller cleanroom projects where the SBAL-V is over-spec. Still meets ISO Class 6-8 requirements comfortably.
• SBTF-1602 Spiral Tubeformer — stainless-capable configuration. Forms spiral round duct in 304 or 316 stainless, Φ80–Φ1600 mm range. The standard choice for round supply-air risers and return plenum in pharmaceutical fill-finish suites.
• SBPC Plasma Cutting Machine — for complex fittings, branch take-offs and custom transitions in stainless steel.
• Automatic Seam Welder — TIG longitudinal-seam welding for stainless cleanroom duct. The essential complement to the SBAL-V for ISO Class 5 and cleaner.

HEPA/ULPA terminal filtration and duct interface

Cleanrooms deliver filtered air to the working zone through HEPA (ISO Class 6-8) or ULPA (ISO Class 5 and cleaner) terminal filter housings installed at the ceiling. The duct connects to the terminal housing through a flanged spigot or a gasketed slip joint. The connection has to be leak-free under the differential pressure between the duct and the cleanroom, and the flange has to be dimensionally accurate enough that the terminal filter gasket compresses uniformly — unequal compression is a leak path and an immediate ISO-class failure.

This puts a specific tolerance requirement on the duct-side spigot: ±0.5 mm on outside diameter or rectangular width, with no burrs or sharp edges. The SBAL-V hits this tolerance as standard. The SBTF-1602 spiral tubeformer produces round spigots with ±0.3 mm diameter tolerance which is comfortably within the HEPA housing acceptance window for any major manufacturer.

Semiconductor fab AMC control

Semiconductor fabrication cleanrooms have a specific requirement that pharmaceutical cleanrooms usually do not: airborne molecular contamination (AMC) control. Organic vapours, acidic gases and base gases at parts-per-billion concentrations can cause photolithography defects and wafer yield loss, so the cleanroom HVAC system includes chemical filtration (activated carbon, ion exchange media) alongside the particulate HEPA/ULPA filters. From a duct construction perspective this typically means avoiding organic gasket and sealant materials in favour of stainless-faced EPDM or PTFE alternatives, and specifying stainless or electropolished interior surfaces to eliminate outgassing from zinc coatings.

SBKJ machines handle the specification side of this transparently — the SBAL-V and SBTF run stainless without modification — but buyers building fab cleanrooms should confirm gasket and sealant material selection with the machine supplier during quotation rather than leaving it to the installer. It is a surprisingly common source of first-article rejection on fab HVAC systems.

Daily volume and line sizing for cleanroom projects

Cleanroom projects are typically lower duct volume than data centers — the cleanroom envelope is smaller in absolute terms, even if the specification is tighter. A typical pharmaceutical fill-finish cleanroom suite of 1,500–3,000 square metres needs roughly 800–1,800 square metres of duct surface area total. A semiconductor fab is larger (10,000–50,000 m² cleanroom area) but the duct system is distributed over multiple sub-fabs and construction is usually phased, so peak duct demand is spread over 18–36 months.

At stainless-mode throughput of roughly 1,000–1,500 square metres per day, a single SBAL-V comfortably handles a single pharmaceutical project in 2–3 weeks of actual production. Most cleanroom contractors therefore run mixed-vertical shops — cleanroom work one week, commercial work the next — to keep the machine utilised year-round. The SBAL-V galvanized/stainless swap takes roughly 4 hours so the changeover is not prohibitive.

Surface finish and post-processing

ISO Class 5 pharmaceutical work routinely specifies interior surface finish Ra 0.8 µm or better, which is tighter than mill-finish stainless coil provides as-delivered (2B mill finish is typically Ra 0.3–0.8 µm, but the seam weld bead is much rougher until ground). The SBKJ workflow for cleanroom duct therefore typically includes: (1) form the duct body on the stainless-configured SBAL-V; (2) TIG weld the longitudinal seam on the automatic seam welder; (3) grind the weld bead with an orbital grinder; (4) polish the interior surface with progressively finer abrasive belts to meet the Ra specification; (5) passivate the polished surface with nitric or citric acid to restore the chromium-oxide layer.

Steps 3–5 are manual or semi-automatic workflow additions, not SBKJ machines. Contractors serving pharmaceutical tier-one projects usually invest in dedicated grinding and polishing stations and in an orbital passivation system, all of which can be sized against the SBAL-V throughput rather than independently of it. SBKJ engineering can advise on workflow layout during factory planning.

Common mistakes first-time cleanroom duct buyers make

1. Assuming galvanized is always acceptable for ISO Class 8. ISO allows it, the cleaning regime often does not. Confirm the cleaning-agent compatibility with the facility design team before quoting galvanized.
2. Specifying Pittsburgh-lock seam on ISO Class 5-6 pharma work. The interior crevice is a guaranteed GMP rejection. Budget for TIG seam welding from day one.
3. Omitting the polishing and passivation workflow from the capital plan. The auto duct line produces good stainless duct, but Grade A pharma work needs the finishing steps to hit the Ra specification. Plan for the additional stations.
4. Under-budgeting stainless coil lead time. 304 coil is readily available but 316L in cleanroom-grade surface finish can take 6–10 weeks to source. Order the coil in parallel with the machine rather than after delivery.
5. Ignoring AMC gasket compatibility on semiconductor fab projects. Standard EPDM gaskets outgas VOCs that trigger AMC alarms. Specify stainless-faced or PTFE gaskets before the first article.

Request a cleanroom duct workshop quotation →

Frequently asked questions

What ISO 14644 class needs welded-seam stainless duct?

ISO 14644 Class 5 and cleaner (the old Class 100 and below under FED-STD-209E) typically specify welded-seam stainless steel duct with crevice-free joints to eliminate particulate harbourage points. ISO 14644 Class 6 and Class 7 (old Class 1,000 and Class 10,000) can usually run galvanized steel with TDF flange and Seal Class A leakage, though pharmaceutical GMP projects often default to stainless regardless of ISO class because of cleanability and washdown requirements. ISO Class 8 projects typically accept galvanized steel with standard TDF construction.

Can the SBAL-V handle 304 and 316 stainless steel?

Yes, both grades. The SBAL-V is routinely supplied in stainless-capable configuration with upgraded forming rollers, reduced-speed cutting blades, and stainless-compatible lubrication. 304 is the default for most cleanroom and food work; 316 is specified for coastal or high-chloride environments and pharmaceutical projects with aggressive cleaning agents. Switching between galvanized and stainless takes roughly 4 hours of line setup time including roller swap, tension recalibration and test-cut verification.

Do I need a welding machine on top of an auto duct line for pharma projects?

For pharmaceutical GMP projects running ISO 14644 Class 5 or cleaner, yes. The SBAL-V forms the rectangular duct body and TDF flange to cleanroom tolerance, but the longitudinal seam on stainless cleanroom duct is typically TIG welded rather than Pittsburgh-lock to eliminate crevices. SBKJ supplies automatic seam welders and orbital TIG welding machines that integrate with the SBAL-V workflow. For ISO Class 6-8 projects the standard Pittsburgh-lock seam is usually acceptable, so the welder is optional.

How much more does a stainless-capable SBKJ line cost?

Stainless-capable configuration adds approximately 8–15 percent to the base SBAL-V machine price and 5–10 percent to the SBTF spiral tubeformer. Specific premium depends on the stainless gauge range and whether 316L is included. Lead time extends by 10–15 days because stainless rollers take longer to source and pre-test. See the pricing and lead time guide for full budget figures.

What cleanroom projects has SBKJ supplied?

SBKJ has supplied auto duct production lines and spiral tubeformers to contractors working on pharmaceutical, semiconductor and biotech cleanroom projects in China, Germany, Singapore, Malaysia and Australia. Specific project names are frequently subject to confidentiality and NDA requirements, but the SBKJ engineering team can arrange reference calls with peer fabricators under NDA for qualified buyers. An SBAL-V stainless configuration has been the standard recommendation for pharmaceutical tier-one projects for roughly a decade.

Other industries we serve

• HVAC Duct Machinery for Data Centers — SMACNA Seal Class A, hyperscale CRAH, AI infrastructure.
• HVAC Duct Machinery for Hospitals — ASHRAE 170, isolation wards, operating rooms.
• HVAC Duct Machinery for Food Processing — EHEDG, 3-A, FSMA, stainless hygienic duct.
• All industries served by SBKJ Group →