308A Metal Types and Properties 3

Question 1

What type of sheet metal is required for kitchen exhaust hoods handling grease-laden vapours?

Accepted Answer

Minimum 18-gauge stainless steel (Type 304 or 316) for grease resistance and fire safety

Answer

Kitchen exhaust hoods require stainless steel (typically Type 304 or 316) at a minimum of 18 gauge for grease resistance, cleanability, fire resistance, and compliance with fire codes. Galvanized steel is not permitted.

Question 2

What is 'G90' coating designation on galvanized steel?

Accepted Answer

The zinc coating weight — 0.90 ounces of zinc per square foot of sheet (both sides combined)

Answer

G90 indicates the zinc coating weight is 0.90 ounces per square foot (total for both sides). This is the most common coating weight for HVAC ductwork, providing good corrosion protection for normal environments.

Question 3

Why is Type 316 stainless steel specified instead of Type 304 for certain sheet metal applications?

Accepted Answer

Type 316 contains molybdenum which provides superior resistance to chloride and chemical corrosion

Answer

Type 316 stainless steel contains 2-3% molybdenum, which provides significantly better resistance to chlorides, acids, and other corrosive chemicals. It is specified for marine, chemical, and coastal environments.

Question 4

What is 'terne-coated' steel and what was it historically used for?

Accepted Answer

Steel coated with a lead-tin alloy, historically used for roofing and architectural sheet metal

Answer

Terne coating is a lead-tin alloy applied to steel. Historically used for roofing, it provided excellent solderability and corrosion resistance. Modern terne alternatives use tin-zinc coatings due to lead health concerns.

Question 5

What physical property of metal is described by 'ductility'?

Accepted Answer

The ability to be stretched, formed, or drawn into shapes without fracturing

Answer

Ductility is the ability of a metal to be deformed (stretched, bent, drawn, or hammered) without breaking. Highly ductile metals like copper, aluminum, and mild steel are well-suited for sheet metal forming operations.

Red Seal Sheet Metal 308A Practice Test

Red Seal Sheet Metal 308A Practice Test

308A Metal Types and Properties 3