Standard for Installation of Stainless Steel Ventilation Ducts in Food Processing Workshops

Below, the current national/industrial specifications, material standards, key points of manufacture and installation, hygiene and fire protection requirements of stainless steel ventilation pipes in food processing workshops are compiled into a version (including national standard number and key parameters) that can be directly compared with construction.

First, the core implementation specifications (must be observed)

GB 50243-2016 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering (national standard, mandatory)

GB 50738-2011 Code for Construction of Ventilation and Air Conditioning Engineering (Construction Technology)

JGJ/T 141-2017 Technical Specification for Ventilation Pipes (Special for Stainless Steel Ducts)

T/CCMSA 50212-2018 Technical Specification for Stainless Steel Ventilation Ducts (commonly used by trade associations and food factories)

Food Hygiene: GB 14881-2013 General Hygienic Standard for Food Production (SC Certification Core)

Second, the material standard (food grade, 304/316L)

1) Material brand

General wet workshop: 304(06Cr19Ni10)

Aquatic products/salting/high acidity and alkalinity: 316L(022Cr17Ni12Mo2) (chloride resistance)

2) Plate thickness (JGJ/T 141, GB 50243)

Circular duct (diameter d):

D ≤ 300mm：≥0.6mm

300＜D ≤ 800mm：≥0.8mm

D ＞ 800mm：≥1.0mm

Rectangular duct (side length b):

b ≤ 320mm：≥0.6mm

320＜b ≤ 800mm：≥0.8mm

b ＞ 800mm：≥1.0mm

3) Surface requirements (mandatory in food workshop)

Inner surface: polished Ra ≤ 0.4μm, without cracks, pits, scratches and dead corners.

External surface: wire drawing/polishing is acceptable, but it must be easy to clean and free from dust.

Third, the production process specification (sanitary level without dead ends)

1) Welding (full welding is preferred in food workshop)

Methods: TIG welding (thickness ≤1.2mm)/ pulsed TIG welding (> 1.2 mm).

Welding material: the same material as the base material (ER304 for 304 and er316L for 316l).

Weld requirements:

Full welding, no porosity, slag inclusion and incomplete fusion

After welding, the chromium oxide protective layer is formed by pickling and passivation (corrosion prevention and bacteriostasis).

Bite edge ≤0.5mm, continuous length ≤ 100 mm.

2) Pipe Fittings and Transitions

Elbow: circular arc transition, radius of curvature ≥1.5D (avoid material accumulation).

Tee/reducer: smooth transition, no acute angle and no groove.

Horizontal pipe: ≥1% slope, slope to the drainage end; The lowest point is provided with a food-grade drain valve (drain condensate/cleaning water).

3) Connection mode (general bite is prohibited in food workshop)

Priority: sanitary flange+food grade silicone/PTFE gasket (temperature resistance-40℃~200℃)

Second choice: quickly install the clamp (sanitary grade) for easy disassembly and cleaning.

Prohibition: ordinary rivets, bolts protruding inward, splicing gaps (easy to accumulate dirt and breed bacteria)

IV. Installation Specification (GB 50243+Food Hygiene)

1) Installation of supports and hangers

Spacing (GB 50243-2016):

Level: d/b ≤ 400 mm→≤ 4 m; ＞400mm → ≤3m

Vertical: ≤4m, with at least 2 fixed points.

Material: 304 stainless steel or carbon steel hot dip galvanized (contact with stainless steel must be insulated to prevent electrochemical corrosion).

Anti-sway: straight pipe > ＞20m anti-sway support; Strengthening fixation at elbow/tee

Height: the bottom of the pipe is **≥2.5m** from the ground, avoiding directly above the food exposure area (preventing condensation water from dripping).

2) Installation deviation

Level: ≤3‰, total length ≤20mm.

Vertical: ≤2‰, total length ≤10mm.

3) Sealing and pollution prevention

Through the wall/floor: add stainless steel casing, and the gap is sealed with food-grade sealant and incombustible filler to prevent insects, rats and dust from invading.

Crossing the fire zone: a 70℃ fire valve is set, and the space between the casing and the air duct is blocked with fire sealant+rock wool.

4) Tightness test (mandatory in food workshop)

Low pressure system (≤ 500 Pa): 1.5 times the working pressure, and there is no leakage after holding the pressure for 30 minutes.

Medium/high pressure: According to the classification test of GB 50243, the air leakage rate is ≤1%.

Inspection: Check whether there is oil stain/dust on the inner wall of weld and white cloth by endoscope.

Five, hygiene and cleaning requirements (GB 14881)

The air duct has no internal bolts, rivets and bulges, and all internal corners are in arc transition.

Sanitary manhole (every 6~8m) is provided, and the detachable pipe section is convenient for internal cleaning, disinfection and colony detection.

Thermal insulation: the food workshop must be externally insulated with a moisture-proof layer (anti-condensation). The thermal insulation material should be made of incombustible materials (such as rubber and plastic, rock wool), covered with stainless steel or waterproof aluminum foil, and the glass fiber should not be exposed.

Cleaning: it can withstand repeated washing with hot water at 85℃ and food-grade acid-base disinfectant, and does not rust or fall off.

Six, fire and safety

Stainless steel is a non-combustible material, which meets the requirements of fire-proof air duct.

Exhaust fume/high temperature area: full welding of flange to prevent oil leakage and fire.

Fan: damping base+soft joint to reduce vibration and noise; The exhaust outlet is away from the fresh air inlet/food area ≥10m.

Seven, food workshop special points (SC certification must be checked)

Material: 304/316L material certificate+spectrum test report.

Inner wall: polished+no dead angle+easy to clean.

Slope: ≥1%, drainage at lowest point.

Sealing: full welding+food-grade gasket, no air leakage, no condensation and dripping.

Test: air pressure tightness+inner wall cleanliness inspection