What material is used in the air duct for the installation of fire ventilation in the underground parking lot? How to choose galvanized and stainless steel?

Underground garage fire ventilation (mechanical exhaust+fire smoke exhaust) air duct: galvanized steel sheet VS stainless steel selection guide (according to GB51251-2017, JGJ/T141).

Garage air ducts are divided into two systems: normal exhaust (daily exhaust) and fire smoke exhaust (fire smoke exhaust). Hot dip galvanizing is the first choice for inland conventional garages. Stainless steel (304/316L) for coastal/high humidity/corrosive conditions.

1. Comparison of core parameters of two materials

1. Hot-dip galvanized steel plate (hot-dip galvanized Z80, zinc layer ≥80g/㎡, the mainstream of the project)

Advantages: low cost (about 1/3 of 304 stainless steel), common flange bite, fast processing, fire acceptance compliance and sufficient supply;

Disadvantages: garage condensed water+automobile exhaust (sulfide and nitrogen oxides become weak acid when meeting water), flange and bite rusted and perforated in humid environment for 3 ~ 6 years, and the zinc layer rusted quickly after being damaged;

Fire-resistance: the fire-resistance limit (GB51251) of garage smoke exhaust ≥0.5h can be met by outsourcing fire-proof coating.

2. Stainless steel air duct (304/316L, mainly full argon arc welding)

304: Resistant to inland humidity, weak acid of common tail gas, and not resistant to salt spray of chlorine ion at the seaside, with a service life of 15 years+;

316L: It is specially used for garages with coastal areas, high salt fog, diesel exhaust gas and wet accumulated water, and is resistant to chloride ion and organic acid corrosion;

Advantages: smooth inner wall, small wind resistance, no corrosion, no air leakage, no post-corrosion maintenance and high temperature resistance;

Disadvantages: high cost (3 times for 304≈ zinc plating and 4.5 times for 316L≈ zinc plating), only full welding and long processing period.

Second, the application scenario of galvanized steel plate (90% inland residential quarters/shopping malls garage standard)

Choose zinc plating conditions (use zinc plating when all conditions are met).

Inland non-coastal areas (more than ＞10km away from the coastline), underground garages of ordinary commercial houses and shopping malls, well ventilated, free from long-term water accumulation, and free from tail gas from diesel engine room;

Garage ventilation design is perfect, dehumidification is in place, and there is no large area condensation and dripping;

Regular budget, real estate housing construction projects (cost-effective priority).

Common thickness of galvanized sheet garage (long side dimension)

Long side ≤ 500: 0.6 mm hot dip galvanizing (exhaust branch pipe)

500 ~ 1000: 0.75 ~ 0.8 mm (main exhaust/exhaust pipe)

> 1000 directors: 1.0mm

The smoke exhaust duct must be wrapped with fireproof board/coating to meet the fire resistance limit of 0.5h; The exhaust duct does not need fireproof coating.

Galvanizing forbidden scene

Coastal linhai garage, underground perennial water accumulation, diesel generator room smoke exhaust garage, chemical park supporting garage.

Third, stainless steel (304/316L) selection scenario (forced optimization in harsh environment)

1, choose 304 stainless steel scene.

Garage with high humidity along the river and long-term condensation and dripping underground, underground closed air defense garage (poor ventilation and heavy humidity);

The garage partially passes through the vicinity of the equipment room and garbage room (the exhaust gas is sour);

High-end commercial/hotel garage requires 15 years of maintenance-free and less maintenance.

304 thickness: 1.0mm for conventional main pipe and 1.2mm for large section > 1000, all of which are fully welded.

2. Choose 316L stainless steel scene (3 required).

The garage of coastal project within 5km along the coast (sea breeze and salt spray+tail gas chloride ion), 304 has been used for 2 ~ 3 years for pitting perforation;

The garage is equipped with a diesel generator exhaust pipe, and the exhaust from the boiler room passes through the garage (high temperature+acidic waste gas);

Pre-embedded air duct in underground pipe trench, perennial water bubble pipe, and supporting garage of chemical industrial park.

Fourth, quick selection formula

Inland dry ordinary garage → hot dip galvanizing (Z80)+ fireproof coating (the best cost);

Inland damp, airtight civil air defense garage →304 stainless steel;

Garage beside coastal/coastal and diesel engine rooms →316L stainless steel.

V. Supplementary Details (Acceptance & Construction)

It is strictly forbidden to substitute cold galvanized and 201 stainless iron, which will lead to failure of fire control acceptance and short-term rust;

The same garage can be mixed: stainless steel in the wet section of the main pipe and zinc plating in the dry branch pipe (cost reduction);

Galvanized flange and bite are the high-risk points of corrosion, and the flange under wet working conditions needs to be brushed with antirust paint to strengthen corrosion protection.