Selection summary
Overview
G90 is the ASTM A653/A653M inch-pound designation for a minimum 0.90 oz/ft² total zinc coating weight on both sides. The heavier class can provide more zinc reserve than G60 under comparable conditions, but it is not a universal corrosion-life promise and does not replace exposure, substrate, surface or fabrication requirements.
This page separates standard-oriented limits from typical reference data. Purchase acceptance comes from the ordered specification and certified material test report.
Names and systems
Identity & standards
Similar designations across ASTM, EN, JIS, and other systems are not automatically interchangeable. Product form and ordered standard control chemistry, properties, dimensions, condition, and testing.
Reference chemistry
Composition
| Element | Reference range | Why it matters |
|---|---|---|
| Zinc coating | Designation-system controlled | Atmospheric corrosion protection for the coated sheet system |
| Steel substrate | Ordered separately | Carries strength, formability and dimensional requirements |
Concise grade-family reference only. Confirm every element limit against the current standard for the exact product ordered.
Condition matters
Reference properties
A designation is meaningful only with its governing standard, edition and product form.
Typical web values are screening information, not purchase acceptance limits.
Environment first
Corrosion behavior
Coating life depends on coating system, exposure, drainage, cut edges, fabrication damage and maintenance.
A coating designation does not establish universal service life or suitability.
Temperature, concentration, deposits, crevices, stress, surface finish, cleaning, and fabrication quality can change service performance.
Service limits
Temperature & service
Confirm temperature limits through the governing design code, product standard and complete material system.
Delivery condition
Heat treatment & condition
Do not infer heat treatment or temper from an incomplete designation.
State the ordered condition or temper and verify it on the certificate.
Process route
Fabrication
Qualify forming, welding, joining and surface-repair procedures for the ordered product form.
Preserve material or coating traceability after cutting and secondary processing.
Magnetic response: The steel substrate is ferromagnetic.
Decision boundaries
Comparisons & substitution
G90 carries 0.30 oz/ft² more minimum total coating weight than G60 within the ASTM system.
G90 and Z275 have a closely corresponding mass basis in published coating tables, but standards, test rules, substrate designations and order language still require a documented equivalence review.
Where it is used
Applications
Ordering scope
Product forms & standards
Continuously galvanized coil and cut sheet under ASTM A653/A653M
Decision support
Selection guidance
Choose this grade when
- ASTM A653/A653M G90 is explicitly specified for continuous galvanized coil or sheet.
- Exposure, drainage, cut edges, forming damage, paint and maintenance have been reviewed as one corrosion-control system.
Review another grade when
- Marine, immersed, chemical or persistently wet exposure needs project-specific corrosion engineering rather than a G90 label alone.
- The component is fabricated before galvanizing or relies on protected welds, fasteners and cut edges outside the coil coating scope.
Before ordering
Procurement checklist
State the coating standard, ordered edition and exact coating designation.
State substrate grade, delivery condition, thickness, width, tolerances and quantity.
State surface treatment, oil/passivation, spangle, intended forming and cut-edge controls.
Require coating evidence, substrate certificate, coil traceability, marking and dry export packing.
Verify G90 coating-weight evidence, local spot acceptance where applicable, surface treatment compatibility and repair requirements for damaged areas.
Traceable evidence