The North American Galvanizing Standards Landscape
ASTM A123, "Standard Specification for Zinc (Hot-Dip Galvanized) Coatings on Iron and Steel Products," serves as the predominant industry standard throughout North America, establishing coating thickness requirements, appearance criteria, and quality assurance protocols for batch hot-dip galvanized steel. The specification's widespread adoption by galvanizers, fabricators, and specifiers across the United States, Canada, and Mexico creates consistent expectations and evaluation criteria throughout the continent.
However, an alternative standard—CSA G164, "Hot Dip Galvanizing of Irregularly Shaped Articles"—occasionally appears in project specifications, particularly for Canadian projects or applications involving electrical and communications infrastructure. Understanding the substantial differences between these standards, their respective strengths and limitations, and practical implications for material specification and quality evaluation enables informed standard selection while avoiding specification conflicts that can complicate procurement and inspection.
Historical Context and 2018 CSA G164 Revision
CSA G164's previous revision dated to 1992, creating a 26-year gap without updates during a period of substantial evolution in galvanizing technology, metallurgical understanding, and industry practices. This extended dormancy reduced the standard's market relevance, with most North American projects defaulting to ASTM A123 even in Canada.
The 2018 revision substantially modernized CSA G164, incorporating contemporary practices and addressing specific industry needs:
Major 2018 Updates:
- Addition of references to electrical and communications infrastructure standards
- Conversion from coating weight values to coating thickness values (aligning with international practice)
- Revised material classifications and associated minimum coating thickness requirements
- Inclusion of alternative galvanizing methods (thermal diffusion galvanizing, mechanical galvanizing)
- Updated sampling procedures referencing CSA C83 protocols
- Modernized language and formatting
These revisions renewed CSA G164 as a viable specification option, though substantial differences from ASTM A123 remain.
Scope and Industry Focus Differences
While both standards address batch hot-dip galvanizing of irregularly shaped steel articles, subtle but significant scope differences distinguish their primary applications:
ASTM A123 Scope
ASTM A123 maintains broad, general-purpose scope covering:
"...zinc (hot-dip galvanized) coatings applied by the hot-dip process to iron and steel products made from rolled, pressed, and forged shapes, castings, plates, bars, and strips."
This general language encompasses structural steel, industrial fabrications, infrastructure components, architectural metalwork, and essentially any batch-galvanized product without specific industry targeting.
CSA G164-18 Scope
The 2018 revision introduced industry-specific language:
"This Standard specifies the requirements for zinc coating (galvanizing) by the hot-dipping process on iron and steel products intended or primarily for use in electrical and communication systems made from rolled, pressed, cast iron, or forged shapes such as structural sections, plates, bars, pipes, or sheets 1mm thick and thicker." [emphasis added]
This scope modification targets utility infrastructure—transmission towers, distribution poles, substation structures, communications antenna supports, and related electrical and communications hardware.
Implications of Scope Difference
The electrical/communications focus influences several CSA G164 provisions:
Reference Standards: G164 explicitly references CSA C83, "Communication and Power Line Hardware," establishing specific requirements for utility line hardware including dimensional tolerances, performance criteria, and inspection protocols beyond basic coating quality
Material Priorities: Electrical infrastructure priorities (high strength, precise dimensions, fatigue resistance) may differ from general structural steel priorities
Application Context: The standard assumes expertise with utility-specific fabrication and installation practices
For general structural steel, industrial fabrications, or non-utility applications, ASTM A123's broader scope provides more appropriate guidance.
Zinc Bath Composition and Purity Requirements
Historical versions of these standards specified different zinc bath composition requirements, creating potential confusion. The 2018 CSA G164 revision eliminated this discrepancy:
Current Alignment
CSA G164-18: "...the galvanizing bath shall contain not less than 98.0% zinc by mass"
ASTM A123: "...the galvanizing bath shall contain not less than an average value of 98.0% zinc by weight"
The terms "by mass" and "by weight" are functionally equivalent in standard usage—both specify the same concentration requirement based on mass percentage rather than volume percentage.
Zinc Specifications Referenced
CSA G164: References ASTM B6 (Prime Western, High Grade, and Special High Grade zinc specifications)
ASTM A123: References ASTM B6 AND ASTM B960 (recycled zinc specification)
ASTM A123's acceptance of B960 recycled zinc reflects environmental sustainability emphasis and acknowledges that properly refined recycled zinc performs equivalently to virgin zinc. CSA G164's omission of B960 represents a minor difference with minimal practical impact, as recycled zinc meeting B6 purity requirements remains acceptable under the "not less than 98.0%" provision.
Material Categories and Coating Thickness Requirements: Critical Differences
The most substantial and practically significant differences between the standards involve material classification systems and associated minimum coating thickness requirements:
ASTM A123 Material Categories
ASTM A123 Table 1 establishes seven material categories reflecting distinct product forms and typical steel chemistries:
- Structural Shapes (wide-flange beams, angles, channels)
- Strip and Bar (flat bars, strip, sheet)
- Plate (flat plate material)
- Pipe and Tubing (hollow sections, HSS)
- Wire (drawn wire products)
- Reinforcing Bar (concrete reinforcement)
- Forgings and Castings (forged or cast products)
Each category specifies minimum average coating thickness varying by steel thickness range, with requirements calibrated to achievable coating thicknesses based on typical steel chemistries for each product form.
CSA G164-18 Material Classifications
CSA G164 Table 1 employs broader, more generalized classifications:
- Castings (iron and steel castings—all sizes)
- Rolled, Drawn, Pressed, or Forged Steel Articles (encompasses most wrought steel products with sub-categories by thickness)
- Screws, Bolts, Nuts, Rivets, Nails, and Similar Fasteners (<12.7 mm diameter)
- Bolts, Nuts, and Threaded Fasteners (≥12.7 mm diameter)
This consolidation creates a simpler classification structure but sacrifices the nuanced product-form-specific requirements that reflect metallurgical realities.
Coating Thickness Requirement Comparison
For Steel Thickness 1.6-3.2 mm (approximately 1/16 to 1/8 inch):
Product Type ASTM A123 Minimum CSA G164 Minimum Difference
Structural Shapes 65 μm (2.6 mils) 65 μm (2.6 mils) Match
Pipe and Tubing 45 μm (1.8 mils) 65 μm (2.6 mils) 44% higher requirement in G164
Strip and Bar 65 μm (2.6 mils) 65 μm (2.6 mils) Match
For Steel Thickness 6.4-16.0 mm (approximately 1/4 to 5/8 inch):
Product Type ASTM A123 Minimum CSA G164 Minimum Difference
Structural Shapes 100 μm (3.9 mils). 100 μm (3.9 mils) Match
Pipe and Tubing 75 μm (3.0 mils) 100 μm (3.9 mils) 33% higher requirement in G164
Strip and Bar 75 μm (3.0 mils) 100 μm (3.9 mils) 33% higher requirement in G164
The Achievability Problem
The higher CSA G164 requirements for pipe/tubing and strip/bar create practical compliance challenges. As discussed extensively in related technical literature:
Pipe and Tubing Metallurgy: Pipe and hollow structural sections are predominantly manufactured from aluminum-killed steel with silicon content below 0.02%. This low-reactivity chemistry produces characteristically thin coatings—typically 1.5-2.5 mils (38-64 micrometers)—through fundamental metallurgical limitations rather than process control inadequacies.
Strip and Bar Similar Issues: Many strip and bar products similarly employ low-silicon steel chemistries for formability and surface quality, producing coating thicknesses that naturally fall in the 2-3 mil range.
CSA G164 Compliance Challenge: The 65 μm (2.6 mils) CSA G164 requirement for thin-section pipe/tubing and the 100 μm (3.9 mils) requirement for thicker sections exceed typical coating formation for aluminum-killed steel. Meeting G164 requirements would necessitate:
- Custom steel specification with controlled silicon content (0.04-0.08%)
- Pre-galvanizing abrasive blast cleaning (adding $0.50-2.00/lb cost)
- Extended immersion times risking thermal distortion
- Special processing adding substantial cost and schedule
For routine pipe, tubing, strip, and bar products, CSA G164 coating thickness requirements may prove difficult or impossible to achieve without extraordinary measures not reflected in normal pricing or lead times.
Coating Thickness Measurement and Acceptance Criteria
Both standards recognize identical test methods for coating thickness determination:
Approved Methods:
- Magnetic or electronic thickness gauge (most common)
- Weigh-galvanize-weigh method
- Weigh-strip-weigh method
- Microscopic examination of cross-sections
However, the standards differ substantially in measurement quantity requirements and acceptance criteria:
ASTM A123 Measurement Approach
Measurement Quantity: Minimum three measurements per test article, averaging results
Acceptance Criteria:
- The average of measurements on an article must meet or exceed the minimum thickness in Table 1
- Individual articles may average one coating grade below Table 1 requirement (as specified in Table 2) without rejection, provided lot average meets requirements
Philosophy: Recognizes natural coating thickness variation across articles and within article surfaces. Focuses on lot-average performance while allowing individual article variation within defined limits.
CSA G164-18 Measurement Approach
Measurement Quantity: Five measurements minimum
Acceptance Criteria:
- ALL individual measurements must be at least 90% of the minimum required thickness
- The average of five measurements must equal or exceed the minimum requirement
Philosophy: More stringent approach requiring tighter uniformity. Individual measurements below 90% of minimum cause rejection regardless of average.
Practical Implications
CSA G164's "90% minimum for all readings" creates stricter acceptance standards:
Example Scenario: Steel article requiring 75 μm minimum coating thickness
ASTM A123 Results: Measurements: 82, 78, 71, 75, 79 μm Average: 77 μm → PASSES (average exceeds minimum)
CSA G164 Results: Same measurements: 82, 78, 71, 75, 79 μm 90% of minimum = 67.5 μm 71 μm measurement is only 95% of minimum (above 90% threshold) → PASSES But if any reading were below 67.5 μm → FAILS regardless of average
The stricter individual measurement criterion in CSA G164 increases rejection probability for articles with localized thin areas common in complex geometries.
Sampling Procedures
ASTM A123 Sampling
Paragraph 7 establishes lot-based sampling:
Lot Definition: Articles of similar size and shape galvanized in the same production run
Sample Size:
- Lots ≤1,000 kg (2,200 lbs): Examine 1 article
- Lots 1,000-2,500 kg: Examine 2 articles
- Lots 2,500-5,000 kg: Examine 3 articles
- Lots >5,000 kg: Examine 5 articles minimum
Sample Selection: Random selection from the lot
CSA G164-18 Sampling
The 2018 revision modified sampling by referencing CSA C83 Annex B:
Reference Standard: CSA C83, "Communication and Power Line Hardware," Annex B provides detailed sampling plans including:
- Lot size definitions
- Sample size determination
- Statistical sampling approaches
- Range plans and variance analysis
Complexity: CSA C83 Annex B presents more elaborate statistical sampling protocols than ASTM A123's straightforward approach
Applicability Concern: CSA C83 sampling procedures are optimized for electrical hardware production runs. Their appropriateness for general structural steel or diverse fabrications is questionable.
As discussed in related technical literature on coating thickness variation and range plans, statistical sampling plans designed for normal distributions may inappropriately reject galvanized coatings that meet functional requirements but exhibit the skewed thickness distributions inherent to the galvanizing process.
Finish and Appearance Requirements
CSA G164 Appearance Criteria
Requires coating be free from: "...imperfections such as blisters; gritty or uncoated areas; acid, black spots, or dross particles adhering to the coating" [emphasis added]
The prohibition on "any dross particles" represents an extremely strict standard. Dross—zinc oxide and zinc-iron alloy particles that form on molten zinc bath surfaces—occasionally adheres to galvanized surfaces despite galvanizer quality control efforts.
Practical Reality: Small dross inclusions (1-5 mm size) occur occasionally on complex geometries or in recessed areas. These inclusions typically do not compromise corrosion protection and are cosmetic rather than functional defects.
Rejection Risk: CSA G164's absolute prohibition on any dross particles creates rejection potential for articles that would pass ASTM A123 and perform adequately in service.
ASTM A123 Appearance Criteria
Requires coating be free from: "...uncoated areas, blisters, flux deposits, and gross dross inclusions" [emphasis added]
The modifier "gross" provides practical flexibility. Small, isolated dross particles are acceptable; only substantial dross deposits that compromise coating integrity or function cause rejection.
Additional ASTM A123 Provisions:
Surface Smoothness: "The coating shall be reasonably smooth" acknowledging that hot-dip galvanizing produces texture variations based on steel chemistry and processing
Color Variation Acceptance: Recognizes that bright, matte gray, or mixed appearance results from steel chemistry rather than processing deficiencies
ASTM A123's more realistic appearance expectations reduce disputes over cosmetic issues while maintaining functional quality standards.
Adherence Testing
Both standards employ similar adherence verification:
Stout Knife Test (Both Standards)
Procedure:
- Use a sturdy knife blade to attempt coating removal
- Apply moderate force attempting to pry coating from substrate
- Examine whether coating detaches or steel substrate gouges
Pass Criteria: Coating should resist removal, with the knife gouging steel substrate before separating coating
Failure Indication: Coating that flakes, peels, or detaches easily indicates inadequate bonding
The test provides qualitative adherence assessment suitable for field inspection without specialized equipment.
Embrittlement Testing
ASTM A123 Approach
References ASTM A143, "Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement"
Comprehensive Guidance: A143 provides detailed information on:
- Steel conditions increasing embrittlement risk
- Safeguarding practices
- Bend test procedures
- Result interpretation
Hydrogen Embrittlement Focus: A143 primarily addresses hydrogen embrittlement—the most relevant embrittlement mechanism in galvanizing
CSA G164 Approach
Provides strain-age embrittlement test procedures directly in Paragraph 7.5:
Bend Test: Cold bending galvanized specimen through specified angle and examining for cracking
Impact Test: Striking galvanized specimen with specified energy and examining for coating damage or fracture
Limitation: G164 does not explicitly address hydrogen embrittlement testing despite this being the primary embrittlement concern in galvanizing
The self-contained test procedures provide convenience but lack the comprehensive guidance of A143.
Touch-Up and Repair Provisions
Both standards reference ASTM A780, "Standard Practice for Repair of Damaged and Uncoated Areas of Hot-Dip Galvanized Coatings," for repair procedures but differ in allowable repair area limitations:
Maximum Repairable Area at Galvanizing Plant
Common Requirement (Both Standards):
- Maximum dimension: <25 mm (<1 inch) in narrowest dimension
- Maximum area: 0.5% of surface area
CSA G164 Exception: "Any area larger than this may be renovated if mutually agreeable to the galvanizer and purchaser"
This flexibility clause allows negotiated acceptance of larger repairs by agreement.
ASTM A123 Additional Limit: "0.5% of accessible surface area or 36 in² per short ton [256 cm² per metric ton] of piece weight, whichever is less"
The weight-based alternative limit prevents excessive absolute repair area on heavy articles where 0.5% might otherwise allow substantial bare areas.
CSA G164 Ambiguity: References "surface area to be coated" versus ASTM A123's specific "accessible surface area"
The "accessible" qualifier in A123 clarifies that interior surfaces of hollow sections or inaccessible areas don't count toward the repair percentage calculation.
Field Repairs After Shipment
ASTM A123: Explicitly states "once the parts have left the galvanizing facility there shall be no limit on the size of the area subject to renovation"
This clear provision acknowledges that field welding, installation damage, or in-service repairs may require large-area touch-up beyond plant repair limits.
CSA G164: Does not explicitly address field repair size limits
The silence creates ambiguity. The "mutual agreement" clause might apply, or field repairs might be unlimited by default.
Alternative Galvanizing Methods
CSA G164-18 includes a new Informative Annex E describing alternative galvanizing processes:
Thermal Diffusion Galvanizing (TDG)
Process Description: Articles heated in zinc dust-filler powder mixture, causing zinc diffusion into steel surface
Reference Standard: ASTM A1059, "Standard Specification for Zinc Alloy Thermo-Diffusion Coatings (TDC) on Steel Fasteners, Hardware, and Other Products"
Characteristics:
- Produces zinc-iron diffusion coating
- Excellent coating uniformity including threads and complex shapes
- Higher processing cost than hot-dip galvanizing
- Typical applications: Fasteners, small components
Mechanical Galvanizing
Process Description: Zinc powder mechanically impacted onto steel surface in rotating barrel with glass beads
Reference Standard: ASTM B695, "Standard Specification for Coatings of Zinc Mechanically Deposited on Iron and Steel"
Characteristics:
- No heat exposure (benefits heat-sensitive materials)
- Excellent thread coating without dimensional issues
- Limited to small articles fitting in barrel
- Lower coating thickness than hot-dip galvanizing
ASTM A123 Position
ASTM A123 does not address alternative galvanizing methods. The standard exclusively covers hot-dip galvanizing, with other zinc coating processes governed by their respective specifications.
Practical Implications for Specification Selection
Understanding the differences informs specification decisions:
When ASTM A123 Is Preferred
General Structural Steel: Broad applicability and realistic requirements for diverse product forms
Pipe, Tubing, Hollow Structural Sections: Achievable coating thickness requirements aligned with aluminum-killed steel chemistry
Strip and Bar Products: Similar achievability advantages
Complex Fabrications: More flexible appearance and repair provisions reduce rejection risk
Widespread Adoption: Most galvanizers default to A123, simplifying procurement
Clear Field Repair Provisions: Explicit unlimited field repair allowance
When CSA G164 May Be Appropriate
Electrical/Communications Infrastructure: Standard designed specifically for utility applications
Canadian Projects Requiring CSA Standards: Some Canadian jurisdictions mandate CSA specifications
Fastener Specifications: Explicit fastener requirements not in A123 (though A153 provides similar guidance)
Uniform Coating Requirements: Stricter individual measurement criteria when thickness uniformity is critical
Alternative Coating Methods: Projects considering thermal diffusion or mechanical galvanizing
Mixed Standard Specification Risks
Specifying both standards or mixing requirements creates confusion:
Problematic Language: "Hot-dip galvanized coating shall meet ASTM A123 and CSA G164 requirements"
Conflicts:
- Which coating thickness table applies?
- Which sampling procedure governs?
- Which appearance criteria control?
- What repair limitations apply?
Resolution: Specify ONE standard as governing with others referenced for information only.
Recommendations for Specifiers
Default to ASTM A123
For most North American projects, ASTM A123 provides appropriate requirements with achievable coating thicknesses, realistic appearance expectations, and widespread industry familiarity.
Specify Material Category Explicitly
When using ASTM A123, identify material category:
"Hot-dip galvanized coating on hollow structural sections shall meet ASTM A123 requirements for the Pipe and Tubing material category"
CSA G164 Use Requires Careful Evaluation
If CSA G164 is required:
Verify Coating Achievability: Confirm that aluminum-killed pipe, tubing, strip, or bar can meet the higher thickness requirements, or specify steel chemistry control enabling thickness achievement
Understand Stricter Criteria: Recognize that individual measurement minimums and appearance provisions increase rejection potential
Address Field Repairs: Clarify repair size limits for post-shipment damage
Galvanizer Capability: Confirm galvanizer familiarity with CSA G164 and associated CSA C83 sampling procedures
Steel Chemistry Specification
When coating thickness is critical:
"Steel for galvanizing shall contain 0.04-0.08% silicon per ASTM A385 to enable achieving specified coating thickness"
This proactive approach prevents coating thickness deficiencies from metallurgical causes.
Communication and Coordination
Regardless of standard selected:
Pre-Bid Clarification: Discuss specification requirements with galvanizers during project planning
Mill Test Reports: Request steel chemistry documentation before galvanizing
Sample Galvanizing: For critical or high-volume projects, galvanize sample articles to verify coating achievability under specified standard
Inspector Training: Ensure quality inspectors understand the applicable standard's requirements and acceptance criteria
ASTM A123 and CSA G164-18 both provide comprehensive specifications for hot-dip galvanizing but differ substantially in material classifications, coating thickness requirements, acceptance criteria, and application focus. The most critical practical difference involves coating thickness requirements for pipe, tubing, strip, and bar products, where CSA G164 specifies minimums 25-45% higher than ASTM A123—requirements often difficult or impossible to achieve on aluminum-killed steel with characteristic low silicon content that produces inherently thinner coatings through metallurgical limitations rather than process deficiencies. CSA G164's 2018 revision modernized the standard and introduced focus on electrical and communications infrastructure through references to CSA C83, while adopting more stringent individual measurement minimums (all readings ≥90% of minimum requirement) and stricter appearance criteria (no dross particles permitted) compared to ASTM A123's more realistic provisions. ASTM A123 remains the predominant North American standard with broader applicability, achievable requirements across diverse product forms, extensive industry familiarity, and explicit field repair provisions, making it the appropriate default selection for general structural steel and industrial fabrications. CSA G164 suits specific applications in Canadian electrical/communications infrastructure where standard requirements align with project needs and specifiers can ensure steel chemistry control or supplemental processing enabling the higher coating thickness achievement. Mixed-standard specifications create conflicts requiring resolution through explicit designation of one governing standard, while successful projects require early communication among specifiers, fabricators, and galvanizers regarding standard selection, coating thickness achievability, steel chemistry requirements, and inspection acceptance criteria. To understand further, read the original AGA resource on this topic.
