What are the requirements for installing stainless steel welded air duct in underground garage for environmental protection ventilation project?

The core requirements of stainless steel welded air duct for environmental protection ventilation in underground garage are material compliance, reliable welding, corrosion and deformation prevention in installation, strict system, fire prevention and grounding standards, and strict compliance with GB 50243 and other specifications.

A, material and plate requirements

Material: 304 stainless steel is preferred, and 316L； is used in wet/corrosive environment; The plate conforms to GB 3280, and the surface is smooth, without scratches, corrosion and pits.

Thickness (when not required by design):

Rectangular long side ≤ 500mm: 0.5mm.

500–1000mm：0.75mm

1000–1500mm：1.0mm

＞1500mm：1.2mm

Accessories: flanges, bolts and gaskets are all made of stainless steel or anticorrosive materials; Carbon steel supports must be galvanized and padded with insulation/rubber. Direct contact with stainless steel is strictly prohibited (electrochemical corrosion prevention).

Second, the welding process requirements (core)

Welding method:

Thickness ≤1.2mm: manual TIG welding.

Thickness > ＞1.2mm: pulsed argon arc welding (reducing thermal deformation)

Splicing/flange shall be fully welded continuously. Spot welding and missing welding are strictly prohibited.

Process parameters:

Protective gas: argon purity ≥99.99%, flow rate 8–12l/min.

Current: 0.8 mm (30–50a), 1.0 mm (50–80a) and 1.2 mm (80–110a).

Interlayer temperature ≤60℃, control cooling rate to prevent intergranular corrosion.

Weld quality:

Appearance: silvery white/golden yellow, without cracks, pores and slag inclusion; Underbite ≤0.5mm, continuous ≤ 100 mm.

Inside: the back is protected by argon, and there is no incomplete penetration; The weld height meets the design.

After welding: slag removal, splash removal, pickling and passivation to restore corrosion resistance.

Personnel: Welders must hold relevant certificates.

Third, the production and molding requirements

Processing: plasma cutting, square folding machine forming; Rectangular priority joint corner bite, circular vertical bite.

Reinforcement:

Rectangular long side > ＞630mm: reinforced frame with stainless steel angle steel.

Length > ＞1.2m: longitudinal reinforcing bars are provided.

Flange:

Flatness clearance ≤2mm, diagonal error ≤ 1.5mm.

The bolt holes are even, the spacing is ≤150mm or less, and holes are set at the four corners.

Welding of flange and air duct: argon arc welding is used as backing, and the welding seam is flush with flange.

Four, installation and hanger requirements

Spacing between supports and hangers (horizontal):

Diameter/long side ≤ 400 mm: ≤ 4m

＞400mm：≤3m

The distance between the boom and the end is ≤1m, and a single straight pipe has ≥2 fixed points.

Installation deviation:

Level: ≤3‰, total deviation ≤20mm.

Vertical: ≤2‰, with total deviation ≤10mm.

Corrosion protection: carbon steel bracket+insulating pad; Stainless steel bolts are used between stainless steels, and silicone rubber and other corrosion-resistant materials are used for gaskets.

Crossing processing:

Crossing the fire compartment/floor: a steel protective sleeve ≥1.6mm shall be set, and the gap shall be sealed with incombustible flexible materials.

There shall be no air duct interface at the crossing.

Grounding: the system shall be grounded against static electricity, and jumper wires shall be set between flanges.

Five, rigor and system test

Light leakage method (low pressure): there is no continuous light leakage point in the dark.

Air leakage test (medium pressure/high pressure): According to GB 50243, the ventilation of underground garage is mostly medium pressure, and the air leakage is ≤ 10m/(hm2).

Strength test: Carry out water pressure/air pressure test according to the design pressure, and there is no deformation or leakage.

Six, fire prevention and environmental protection requirements

Fire damper: a 70℃ fire damper is installed at the place where it passes through the firewall, with correct installation direction and reliable operation.

Smoke exhaust system: in case of fire, the fan and smoke exhaust valve are linked together, and the response is ≤60s.

Environmental protection: welding waste gas and dust are treated up to standard; Centralized recycling of waste materials.

Seven, finished product protection

Transportation: special shelves, soft isolation, anti-collision and weld cracking.

Construction: wear clean gloves to prevent scratches and pollution; Avoid contact with carbon steel and chloride ions.

Identification: each section is marked with specifications, numbers and directions.

VIII. Basis of Core Norms

GB 50243 Code for Acceptance of Construction Quality of Ventilation and Air Conditioning Engineering

GB/T 31930 Specification for Stainless Steel Welding

GB 51137 Code for Construction and Acceptance of Waste Water and Waste Gas Treatment Engineering in Electronic Industry