Residual Stress-Induced Cracking in Hot-Dip Galvanized Steel: Mechanisms, Prevention, and Liability Management

The Unexpected Crack: A Complex Multi-Factor Failure

Steel fabrications arriving at galvanizing facilities often harbor invisible vulnerabilities—residual stresses locked into material microstructure through fabrication processes including cutting, welding, bending, punching, and assembly. These internal stresses, ranging from moderate levels tolerable under ambient service conditions to severe concentrations approaching yield strength locally, exist in equilibrium within the steel structure until external forces or conditions disturb this balance. The hot-dip galvanizing thermal cycle—rapid heating from ambient temperature to 840-860°F (449-460°C) followed by controlled cooling—introduces substantial additional thermal stresses through differential heating rates, constrained thermal expansion, and metallurgical transformations. When pre-existing high residual stresses combine with galvanizing-induced thermal stresses, the cumulative stress state can exceed local material ductility, initiating brittle fracture manifesting as visible cracks typically discovered during or immediately after galvanizing immersion.

The frustrating unpredictability of residual stress cracking—identical designs successfully galvanized for years suddenly exhibiting failures—stems from the statistical confluence of multiple variables including subtle steel chemistry variations, fabrication sequence differences, welding parameter fluctuations, ambient temperature during fabrication, immersion angle and rate during galvanizing, and bath chemistry variations. Understanding the metallurgical and mechanical mechanisms generating high residual stress, recognizing fabrication details predisposing structures to cracking, implementing design and fabrication modifications reducing stress concentrations, and establishing clear pre-galvanizing communication protocols enables stakeholders to minimize cracking incidents while fairly allocating responsibility when failures occur despite reasonable precautions.

Residual Stress Fundamentals

Definition and Nature

Residual Stress:

Internal stresses existing within material in absence of external applied loads, locked into microstructure through:

• Non-uniform plastic deformation
• Thermal gradients during heating or cooling
• Metallurgical phase transformations
• Chemical processes (surface treatments, coatings)

Equilibrium State:

Residual stresses exist in self-equilibrating systems:

• Tensile stresses in some regions balanced by compressive stresses in others
• Total force and moment summation equals zero across structure
• Stable configuration under original conditions

Stress Magnitude:

Can approach or locally exceed material yield strength:

• Low residual stress: <10 ksi
• Moderate residual stress: 10-30 ksi
• High residual stress: 30-60 ksi
• Approaching yield: >60 ksi (for mild steel with 36-50 ksi yield strength)

Why Residual Stress Matters

Superposition Principle:

When external loads or thermal stresses apply to structure containing residual stresses:

Total Stress = Residual Stress + Applied Stress

Consequence:

Regions with high tensile residual stress reach critical stress levels under smaller applied loads than unstressed material would, reducing:

• Load-carrying capacity
• Ductility and toughness
• Fatigue life
• Stress corrosion resistance

Brittle Fracture Susceptibility:

High tensile residual stresses combined with:

• Reduced material ductility (from cold working, welding HAZ)
• Stress concentrations (notches, sharp corners, weld toes)
• Elevated temperature (galvanizing process)

Create conditions enabling sudden brittle fracture without warning.

The Galvanizing Thermal Cycle: Stress Generation

Understanding galvanizing-induced thermal stresses requires examining the thermal history experienced by immersed articles:

Temperature Profile

Immersion Sequence:

1. Pre-Heating (Optional): Some facilities pre-heat large articles to 200-400°F reducing thermal shock
   
   
2. Flux Application: Article coated with zinc ammonium chloride flux solution (ambient to 150°F)
   
   
3. Zinc Bath Immersion: Rapid heating from ambient (70°F typical) or flux temperature to zinc bath temperature (840-860°F)
   
   

Heating Rate Variables:

Material Thickness:

• Thin sections (<1/4 inch): Heat rapidly, seconds to 1-2 minutes to reach bath temperature
• Medium sections (1/4 - 1 inch): 2-5 minutes to equilibrate
• Heavy sections (>1 inch): 5-15+ minutes for full heating

Immersion Method:

• Complete immediate immersion: Maximum thermal shock
• Gradual immersion: Progressive heating reducing shock
• Angle of immersion: Affects which portions heat first

Bath Agitation:

• Stirring or circulation: Increases convective heat transfer
• Stagnant bath: Slower heating from boundary layer formation

Thermal Stress Mechanisms

Differential Expansion:

Steel coefficient of thermal expansion: ~6.5 × 10⁻⁶ per °F

Temperature rise of 770°F (70°F to 840°F): ΔL/L = 6.5 × 10⁻⁶ × 770 = 0.005 or 0.5% length increase

For 10-foot (120 inch) beam: Free expansion = 120 × 0.005 = 0.6 inches

If expansion is constrained: Compressive stress develops in heated member Tensile stress develops in restraining members

Stress Calculation:

If thermal expansion fully constrained: σ = E × α × ΔT

Where:

• E = Young's modulus (29,000 ksi for steel)
• α = Coefficient of thermal expansion (6.5 × 10⁻⁶ per °F)
• ΔT = Temperature change (770°F)

σ = 29,000 × 6.5 × 10⁻⁶ × 770 = 145 ksi

This theoretical stress far exceeds steel yield strength (36-50 ksi typical), meaning:

• Actual stress limited by plastic deformation (yielding)
• Permanent distortion occurs during heating
• Residual stresses lock in upon cooling

Temperature Gradients:

When different portions of structure heat at different rates:

Scenario 1: Thin plate welded to thick section

• Thin plate reaches 840°F in 30 seconds
• Thick section reaches 840°F in 5 minutes
• Thin plate tries to expand but is restrained by cooler thick section
• High compressive stress develops in thin plate during heating
• Upon equalizing, thin plate has undergone plastic compression
• Cooling reverses stress: Thin plate develops tensile residual stress

Scenario 2: Complex fabrication with enclosed spaces

• External surfaces heat rapidly from direct zinc contact
• Internal surfaces heat slowly through conduction
• Thermal gradients generate stress differentials
• Sharp corners and weld joints experience stress concentrations

Fabrication-Induced Residual Stress Sources

Multiple fabrication processes introduce significant residual stresses:

Welding: The Primary Stress Source

Welding Thermal Cycle:

Arc welding creates localized extreme heating:

• Weld pool temperature: 2,500-3,000°F
• Heat-affected zone (HAZ) temperature: 1,200-2,500°F
• Base metal adjacent to HAZ: <1,200°F

Residual Stress Generation Mechanism:

During Welding:

1. Local Heating: Weld metal and immediate HAZ heat to melting or near-melting temperature
   
   
2. Thermal Expansion: Heated region attempts to expand but is constrained by surrounding cooler base metal
   
   
3. Plastic Compression: Heated metal yields in compression because:
   
   
   
   • High temperature reduces yield strength
   • Expansion constraint generates compressive stress exceeding yield
   • Permanent plastic compression occurs
4. Cooling and Contraction: Weld metal and HAZ cool and shrink:
   
   
   
   • Solidification shrinkage (liquid to solid)
   • Thermal contraction (hot solid to cool solid)
   • Total shrinkage ~2-4% linear
5. Tensile Stress Development: As weld metal tries to shrink, surrounding base metal restrains contraction:
   
   
   
   • High tensile stress develops in weld metal and HAZ
   • Can approach or exceed base metal yield strength
   • Compressive stresses develop in regions away from weld balancing tensile weld stress

Typical Weld Residual Stress Pattern:

• Weld centerline: High tensile (40-70 ksi typical)
• HAZ: Moderate to high tensile (20-50 ksi)
• Base metal adjacent to HAZ: Low tensile to compressive
• Remote base metal: Low compressive balancing weld tension

Heat-Affected Zone (HAZ) Metallurgical Effects:

Beyond residual stress, welding alters steel microstructure in HAZ:

Grain Coarsening:

• Temperatures above 1,900°F cause austenite grain growth
• Upon cooling, coarse-grained transformed microstructure forms
• Larger grains reduce toughness and ductility

Hardness Increase:

• Rapid cooling rates in HAZ (especially thin sections)
• Formation of harder microstructures (bainite, martensite in medium-carbon or alloy steels)
• Reduced ductility, increased brittleness

Ductility Reduction:

• HAZ typically shows 20-50% reduction in ductility compared to base metal
• Reduced ability to accommodate stress through plastic deformation
• Increased susceptibility to brittle fracture

Combined Effect:

HAZ represents worst-case scenario:

• High tensile residual stress (from welding)
• Reduced ductility (from microstructure)
• Stress concentration (geometry of weld profile)

= Maximum cracking susceptibility

Thermal Cutting

Cutting Processes:

Oxyfuel Cutting:

• Combustion flame (5,500-6,000°F) preheat
• Chemical oxidation reaction cutting steel
• Significant heat input to cut edges

Plasma Cutting:

• High-temperature plasma arc (40,000-50,000°F)
• Rapid cutting with lower total heat input than oxyfuel
• Still creates HAZ on cut edges

Laser Cutting:

• Focused laser beam melting or vaporizing steel
• Minimal HAZ but very high local temperature

Residual Stress Generation:

Similar mechanism to welding but linear pattern:

• Cut edge heated to melting temperature
• Expansion constrained by surrounding cooler material
• Plastic compression during heating
• Cooling contraction creates tensile residual stress along cut edge

Stress Magnitude:

Can reach 30-60 ksi tensile stress along cut edge

Surface Roughness Factor:

Rough thermal cut surfaces create stress concentrations:

• Oxyfuel cutting: Drag lines, dross accumulation
• Plasma cutting: Roughness from kerf geometry
• Notch effect amplifies stress

Mitigation:

Grinding smooth thermal cut edges:

• Removes stress concentrations
• Partially relieves residual stress through material removal
• Improves cracking resistance substantially

Cold Working Operations

Definition:

Plastic deformation of steel below recrystallization temperature (typically <1,000°F for low-carbon steel):

• Bending
• Punching
• Shearing
• Forming
• Rolling

Residual Stress Mechanism:

Non-Uniform Plastic Deformation:

Cold working processes create plastic strain gradients:

Example: Plate Bending

Outer surface (tension side):

• Stretched beyond elastic limit
• Plastic tensile elongation
• Upon unloading: Elastic recovery creates compressive residual stress

Inner surface (compression side):

• Compressed beyond elastic limit
• Plastic compressive shortening
• Upon unloading: Elastic recovery creates tensile residual stress

Neutral axis:

• Minimal stress

Stress Distribution:

Residual stress pattern develops with:

• Tension on one surface
• Compression on opposite surface
• Gradient through thickness

Cold Working Hardening:

Plastic deformation:

• Increases dislocation density in crystal structure
• Raises yield strength and hardness
• Reduces ductility and toughness
• Increases brittleness

Severe Cold Working:

Heavy bends, deep stampings, or multiple forming operations accumulate:

• High residual stress (can approach 40-60 ksi)
• Significant work hardening
• Severely reduced ductility

Critical Concern:

Cold worked regions with high residual stress and reduced ductility are highly susceptible to cracking during galvanizing thermal cycle.

Punching and Shearing

Mechanical Cutting:

Punching holes or shearing edges creates:

Plastic Deformation Zone:

• Material adjacent to cut undergoes severe plastic deformation
• Work hardening and high residual stress
• Reduced ductility

Fractured Surface:

• Final separation creates rough fractured surface with microcracks
• Stress concentrations at surface irregularities

HAZ from Punching:

Unlike thermal cutting, no thermal HAZ but:

• Work-hardened zone extends 1-3 mm from cut edge
• Properties similar to thermal HAZ (hard, brittle, high residual stress)

Structural Configuration Factors

Beyond individual fabrication processes, overall structural design affects stress development:

Differential Thickness Members

Scenario:

Thin plate (1/4 inch) welded to thick section (1 inch):

During Galvanizing Immersion:

Heating Rate Difference:

• Thin plate: Reaches 840°F in 1-2 minutes
• Thick section: Requires 8-12 minutes to reach 840°F

Expansion Mismatch:

When thin plate is hot (840°F) and thick section is still cool (300°F):

• Thin plate thermal expansion: 0.5% length increase
• Thick section expansion: 0.1% length increase
• Differential expansion: 0.4% strain

For 12-inch dimension:

• Thin plate wants to expand: 0.06 inches
• Thick section allows: 0.012 inches
• Mismatch: 0.048 inches must be accommodated

Stress Consequence:

Thin plate cannot expand freely because:

• Welded to thick section providing rigid restraint
• Thin plate develops high compressive stress during heating
• Stress exceeds yield strength, causing plastic compression
• Upon cooling, residual tensile stress locks in

Weld Joint Stress Concentration:

Connecting weld experiences:

• Tensile stress from thin plate trying to expand
• Bending stress from differential expansion creating leverage
• Pre-existing weld residual stress
• Cumulative stress often highest at weld location

Constrained Assemblies

Framed Structures:

Configuration:

• Rectangular or trapezoidal frames
• Members welded at corners creating closed structure
• Diagonal bracing providing rigidity

Thermal Expansion Constraint:

During heating:

• Individual members want to expand freely
• Frame geometry constrains expansion
• Internal forces develop as members push against each other
• High stress concentrations at corner welds

Example:

Rectangular frame: 10 ft × 6 ft

Free thermal expansion at 770°F temperature rise:

• Long side: 120 inches × 0.005 = 0.6 inches
• Short side: 72 inches × 0.005 = 0.36 inches

If frame constrains expansion:

• Members yield locally accommodating expansion
• Permanent distortion (warping) may occur
• Residual stresses lock in upon cooling

Critical Locations:

• Corner welds (connection points)
• Mid-span of longest members
• Any additional bracing attachment points

Geometric Stress Concentrations

Sharp Corners:

90° corners or acute angles create:

• Theoretical infinite stress concentration (in elastic analysis)
• Actual stress concentration factor: 2-5× nominal stress
• Local plastic yielding limiting actual stress but creating residual stress

Notches and Cutouts:

Holes, slots, or cutouts create:

• Stress concentration at edges
• Factor depends on geometry (radius, depth, orientation)
• Amplification of both residual and applied stresses

Weld Profile:

Weld toe (junction between weld bead and base metal):

• Sharp angle creates stress concentration
• Typical stress concentration factor: 2-3×
• Combined with high weld residual stress = maximum stress location

Cracking Mechanisms During Galvanizing

Brittle Fracture Criteria

Crack initiation requires:

1. Critical Stress Level: Total stress (residual + thermal + applied) must exceed local material strength

2. Reduced Ductility: Material must be insufficiently ductile to accommodate stress through plastic deformation:

• HAZ embrittlement
• Cold work hardening
• Elevated temperature effects on some steels

3. Crack Initiation Site: Stress concentration providing crack nucleation location:

• Weld toes
• Sharp corners
• Rough thermal cut edges
• Pre-existing defects (inclusions, microcracks)

4. Crack Propagation Energy: Sufficient driving force for crack to propagate:

• High stress intensity at crack tip
• Low fracture toughness
• Brittle microstructure in crack path

Temperature Effects

Ductile-to-Brittle Transition:

Most steels exhibit temperature-dependent toughness:

Room Temperature (70°F):

• Good ductility and toughness
• Fracture requires high energy

Low Temperature (<0°F):

• Reduced ductility (ductile-to-brittle transition)
• Susceptibility to brittle fracture increases

Elevated Temperature (400-900°F):

Counterintuitive Behavior:

General expectation: Higher temperature improves ductility

Reality for Some Steels:

• Blue brittleness phenomenon (400-700°F range)
• Strain aging effects
• Dynamic strain aging reducing ductility

Galvanizing Temperature (840°F):

Near upper end of potential brittleness range for some steel compositions

Combination Effect:

Pre-existing residual stress + galvanizing thermal stress + potentially reduced ductility at temperature = cracking

The "Sometimes" Nature of Cracking

Explaining why identical designs crack occasionally but not consistently:

Variable Factors

Steel Chemistry Variations:

Silicon and Phosphorus Content:

• Higher silicon: Increased brittleness
• Higher phosphorus: Grain boundary segregation, embrittlement
• Variations within specification range (e.g., Si: 0.02-0.20% allowed) affect cracking susceptibility

Residual Elements:

• Sulfur, tin, antimony, arsenic
• Segregate to grain boundaries at elevated temperature
• Reduce grain boundary cohesion
• Minor concentration differences significantly affect cracking tendency

Fabrication Sequence:

Example: Beam Assembly

Sequence A (Less Stress):

1. Cut components
2. Fit-up with minimal clamping
3. Weld in balanced sequence allowing distortion
4. Final assembly

Sequence B (More Stress):

1. Cut components
2. Force fit-up requiring clamping and pulling
3. Weld in constrained condition
4. Release clamps - high residual stress remains

Identical final geometry, dramatically different residual stress

Welding Parameters:

Small variations in:

• Amperage
• Travel speed
• Electrode angle
• Preheat (or lack thereof)

Affect:

• HAZ width and properties
• Residual stress magnitude
• Likelihood of cracking

Ambient Temperature During Fabrication:

Cold Weather Welding:

• Higher cooling rates
• More severe HAZ hardening
• Increased residual stress

Warm Weather Welding:

• Slower cooling rates
• Softer HAZ
• Reduced residual stress

Galvanizing Immersion Variables:

Immersion Angle: Steep angle: One end heats first, high thermal gradient Shallow angle: More uniform heating, lower stress

Immersion Rate: Fast immersion: Thermal shock Slow immersion: Gradual heating, reduced shock

Bath Temperature Variation: Operating temperature may vary ±10-20°F day-to-day:

• Lower temperature: Slower heating, some stress reduction
• Higher temperature: Faster heating, increased stress

Bath Chemistry: Minor variations in aluminum, lead, or impurity levels affect:

• Wetting behavior
• Heat transfer characteristics
• Zinc-steel reaction kinetics

Statistical Probability

Cracking Threshold:

Structure cracks when cumulative stress exceeds critical value:

Crack occurs if: Residual Stress + Thermal Stress + Stress Concentration > Critical Stress

Variable Distribution:

Each contributing factor varies within range:

• Residual stress: 20-60 ksi depending on fabrication
• Thermal stress: 10-40 ksi depending on immersion
• Material toughness: Varies with chemistry and microstructure

Most Parts: Sum of factors stays below critical threshold → No cracking

Occasional Parts: Unfavorable combination of variables:

• High residual stress (cold weather welding)
• High thermal stress (fast immersion)
• Low toughness (high silicon heat)
• → Exceeds threshold → Cracking

Probability:

If each variable independently has 10% chance of being in unfavorable range: Probability of all unfavorable simultaneously: 0.1 × 0.1 × 0.1 = 0.1% = 1 in 1,000

Explains rare but repeated occurrence.

Prevention and Mitigation Strategies

Design Modifications

Reduce Constraint:

Allow Thermal Expansion:

Poor Design:

• Fully welded closed frame with no expansion allowance
• Rigid corner connections
• Heavy member cross-sections at connections

Improved Design:

• Slotted connection holes allowing movement
• Flexibility built into geometry
• Reduced section at connections reducing restraint force

Avoid Differential Thickness Connections:

Poor Design: 1/4-inch plate welded directly to 1-inch thick flange

Improved Design:

• Transition sections gradually changing thickness
• Intermediate thicknesses providing graduated expansion rates
• Separate thin and thick sections, bolt together after galvanizing

Minimize Stress Concentrations:

Sharp Corners:

Poor Design: 90° inside corners with zero radius

Improved Design:

• Radius corners minimum 1/2 inch radius
• Even larger radius (1-2 inches) for critical applications
• Provides stress concentration factor reduction from 5× to 2×

Weld Profile:

• Grind weld toes smooth blending into base metal
• Removes stress concentration
• Particularly important for highly stressed areas

Fabrication Improvements

Welding Best Practices:

Balanced Welding:

Poor Practice: Weld one side completely, then opposite side

Creates:

• Cumulative distortion pulling structure
• High residual stress from restraining distortion

Best Practice:

• Alternate welding between sides
• Short weld segments rather than long continuous beads
• Allows distortion to balance
• Reduces residual stress

Minimize Restraint:

Poor Practice: Clamp parts rigidly during welding, preventing any movement

Best Practice:

• Minimal clamping allowing some distortion
• Tack weld at intervals allowing parts to self-align
• Complete welding without forcing parts together

Preheat (When Appropriate):

For thick sections or high-carbon steels:

• Preheat to 200-400°F before welding
• Slows cooling rate
• Reduces HAZ hardening
• Lower residual stress

Thermal Cutting:

Grind Cut Edges:

Remove:

• Surface roughness creating stress concentrations
• Heat-affected zone on cut edge
• Burrs and dross

Method:

• Grinding removes 1/16 to 1/8 inch material
• Smooth surface significantly improves crack resistance

Cold Working:

Minimize Severity:

Poor Practice:

• Sharp bends with small radius (1× thickness)
• Multiple forming operations

Best Practice:

• Gentle bends with large radius (3-5× thickness)
• Minimize number of forming operations
• Anneal between operations if heavy forming required

Avoid Combinations:

Don't weld immediately adjacent to:

• Heavy cold work areas
• Sharp bends
• Punched holes

Spacing cold worked and welded areas reduces cumulative stress.

Stress Relief Heat Treatment

When design and fabrication modifications insufficient:

ASTM A143 Stress Relief Procedure

Standard Reference:

ASTM A143, "Standard Practice for Safeguarding Against Embrittlement of Hot-Dip Galvanized Structural Steel Products and Procedure for Detecting Embrittlement"

Paragraph 6.3: Stress Relieving

Procedure:

1. Temperature: Heat fabrication to 1,100-1,200°F (593-649°C)
   
   
2. Soak Time: Hold at temperature for 1 hour per inch of thickness (minimum 30 minutes)
   
   
3. Cooling: Cool slowly, typically in furnace or still air
   
   

Mechanism:

Elevated temperature enables:

• Dislocation rearrangement and annihilation
• Residual stress relaxation through creep mechanisms
• Partial recrystallization in cold-worked areas
• Stress reduction to 10-20% of original values

Effectiveness:

Properly executed stress relief:

• Reduces residual stress from 40-60 ksi to 5-15 ksi typical
• Substantially reduces cracking risk
• Improves subsequent galvanizing success

Practical Considerations:

Equipment: Requires furnace capable of:

• Accommodating fabrication size
• Uniform temperature control
• Controlled cooling

Cost: $200-2,000 per fabrication depending on size and complexity

Distortion: Some dimensional change may occur during stress relief:

• Locked-in distortions may relax
• Fabrication may shift slightly
• Usually acceptable tolerances but verify critical dimensions

Partial Stress Relief

Localized Heating:

For structures too large for furnace stress relief:

Method:

• Use oxy-fuel torches, induction heating, or resistance heating
• Heat critical high-stress areas to 1,100-1,200°F
• Slow cool wrapped in insulation
• Provides partial stress relief where most needed

Effectiveness: Less complete than full furnace treatment but often adequate

Pre-Galvanizing Inspection and Communication

Galvanizers can substantially reduce cracking incidents through proactive assessment:

Pre-Galvanizing Risk Assessment

Visual Inspection Indicators:

High-Risk Features:

• Differential thickness connections (thin-to-thick welded joints)
• Heavily constrained frames (closed rectangular with rigid corners)
• Evidence of forcing during assembly (bent members, weld spatter indicating difficult fit-up)
• Heavy cold work (sharp bends, stamped areas)
• Rough thermal cut edges without grinding
• Numerous welds concentrated in small area

Inspection Protocol:

Quality control personnel examine incoming work:

1. Identify high-risk fabrications
2. Document risk factors photographically
3. Flag for customer communication

Customer Communication

Proactive Notification:

When High-Risk Features Identified:

Contact customer BEFORE galvanizing:

"We've inspected your fabrication and identified features that may increase cracking risk during the galvanizing thermal cycle:

• [List specific concerns: differential thickness connections, constrained frame, etc.]

We can proceed with galvanizing as-is, but want you to be aware of potential cracking risk. Alternatively, we can discuss modifications or stress relief treatment before galvanizing to reduce risk.

Please advise how you'd like us to proceed."

Documentation:

• Written communication (email or form)
• Photographs highlighting concerns
• Customer acknowledgment and decision
• Protects galvanizer from unwarranted blame

Post-Galvanizing Inspection

Crack Detection

Inspection Timing:

Inspect fabrication after galvanizing and cooling:

• Visual examination all surfaces
• Focus on high-stress locations (welds, corners, connections)
• Before customer pickup or delivery

Crack Characteristics:

Appearance:

• Linear separation through coating and base metal
• Typically perpendicular to direction of maximum stress
• Often at weld HAZ or weld toe location
• May show branching

Detection Methods:

Visual Inspection: Most cracks readily visible to naked eye

Dye Penetrant Testing: For suspected hairline cracks:

• Apply penetrant dye
• Allow dwell time
• Remove excess
• Apply developer
• Cracks show as bright red lines

Magnetic Particle Testing: Alternative for crack detection in ferromagnetic steel

Immediate Customer Notification

When Cracks Discovered:

Contact customer immediately:

"Your fabrication was successfully galvanized, but we discovered cracking during post-galvanizing inspection. [Describe location and extent, provide photos]

Cracking appears to result from high residual stress combined with galvanizing thermal cycle. The cracked areas can be repaired through welding and coating touch-up.

We wanted to notify you immediately so we can discuss repair options and avoid potential issues if cracks were discovered later at your facility or job site."

Value to Customer:

• Early awareness enabling planning
• Repair at galvanizing facility potentially more economical than field repair
• Avoids embarrassment of customer discovering cracks on delivery
• Demonstrates galvanizer professionalism and quality commitment

Repair Procedures

Cracked galvanized fabrications are repairable:

Crack Repair Methodology

1. Crack Preparation:

• Grind out crack full depth
• V-groove preparation for welding
• Remove all cracked material
• Drill hole at crack terminus preventing propagation

2. Weld Repair:

• Use low-hydrogen electrodes (E7018 or similar)
• Proper welding procedure and parameters
• Multi-pass for thick sections
• Grind weld smooth blending to base metal

3. Coating Repair:

• Clean weld area removing scale and spatter
• Apply ASTM A780 repair materials:
  
  • Zinc-rich paint
  • Zinc spray metallizing
  • Zinc solder
• Achieve coating thickness matching adjacent galvanizing

4. Inspection:

• Visual examination confirming repair quality
• Dye penetrant if needed verifying complete crack removal
• Coating thickness measurement

Structural Adequacy:

Properly executed repairs restore:

• Full strength of original section
• Corrosion protection equivalent to original galvanizing
• Acceptable service life

Responsibility and Liability Allocation

The complex multi-factorial nature of residual stress cracking creates ambiguity regarding responsibility:

Contributing Party Responsibilities

Fabricator Responsibility:

Clear Fabricator Fault:

• Inappropriate welding procedures creating excessive HAZ hardness
• Forcing components together during assembly
• Heavy cold working without stress relief
• Ignoring known problematic details

Shared Responsibility:

• Standard fabrication practices that unknowingly create high residual stress
• Design specifications requiring problematic details

Galvanizer Responsibility:

Clear Galvanizer Fault:

• Excessively rapid immersion creating unnecessary thermal shock
• Failure to pre-heat large fabrications per established practices
• Dropping or impact damage

Shared Responsibility:

• Standard galvanizing procedures applied to inherently stress-sensitive fabrication

Owner/Engineer Responsibility:

Clear Owner Fault:

• Design specifications requiring inherently problematic geometry
• Rejecting stress relief treatment when recommended
• Demanding impossible tolerances requiring forcing during fabrication

Typical Reality:

Most cracking incidents involve:

• Standard acceptable design
• Proper fabrication methods
• Proper galvanizing procedures
  
  • Unfavorable combination of variables

= Shared responsibility among all parties

Allocation Strategies

Pre-Agreement Approach:

Contract Language:

"Fabrications containing high residual stress from welding, cold working, or constrained geometry may experience cracking during hot-dip galvanizing thermal cycle. Such cracking results from combination of fabrication-induced stress and galvanizing process thermal stress. Responsibility for repairs will be determined based on specific circumstances. Fabricator/owner will be notified of potential high-risk features before galvanizing."

Cost Sharing:

Common arrangements when cracking occurs despite reasonable practices:

• Galvanizer performs repair at cost (materials + labor, no markup)
• Fabricator/owner pays 50% of repair cost
• Other negotiated split

Prevention Investment:

Alternatively, agree before galvanizing:

• Owner/fabricator pays for stress relief treatment ($500-2,000)
• Eliminates cracking risk
• Eliminates responsibility disputes

Documentation Protection

Galvanizer Protection Measures:

1. Pre-Galvanizing Inspection Records:

• Photographs of incoming fabrication
• Notation of high-risk features
• Customer communication and acknowledgment

2. Processing Records:

• Immersion time and temperature
• Any unusual occurrences
• Operator notes

3. Post-Galvanizing Inspection:

• Documentation of any cracks discovered
• Immediate customer notification
• Repair authorization and execution

Purpose:

Demonstrates:

• Reasonable care in identifying risks
• Proactive communication
• Standard proper procedures
• Good faith in handling issues

Reduces galvanizer liability when cracking occurs despite proper practices.

Residual stress-induced cracking in hot-dip galvanized steel fabrications results from the cumulative effects of fabrication-generated internal stresses (welding residual stresses reaching 40-70 ksi in weld metal and heat-affected zones, cold working stresses from bending and forming creating 30-60 ksi tensile stress in severely worked regions, and thermal cutting producing 30-60 ksi edge stresses) combined with galvanizing thermal cycle stresses generated by rapid heating from ambient to 840-860°F producing theoretical constraint stresses of 145 ksi that drive local yielding and create permanent stress redistribution. Critical vulnerability locations include welded connections between thin and thick sections experiencing differential thermal expansion rates during galvanizing immersion, constrained frame assemblies where thermal expansion cannot occur freely generating internal forces at rigid corner welds, heat-affected zones adjacent to welds exhibiting reduced ductility from grain coarsening and hardness increases making material unable to accommodate stress through plastic deformation, and cold worked regions with work hardening and residual stress accumulation from multiple forming operations. The unpredictable "sometimes" nature of cracking—identical designs succeeding for years then suddenly failing—stems from statistical confluence of unfavorable variable combinations including steel chemistry variations within specification ranges (silicon, phosphorus, residual elements), fabrication sequence differences affecting residual stress patterns, welding parameter fluctuations influencing HAZ properties, ambient temperature during fabrication affecting cooling rates, galvanizing immersion variables (angle, rate, bath temperature), and bath chemistry variations, creating probability that occasional parts experience all factors simultaneously aligning at extreme values exceeding critical stress threshold. Prevention strategies encompass design modifications allowing thermal expansion through slotted connections and flexible geometry, differential thickness connection elimination or transitioning, stress concentration minimization through generous corner radii and smooth weld profiles, fabrication improvements including balanced welding sequences preventing cumulative distortion, minimal clamping during assembly avoiding forced fit-up, grinding of thermal cut edges removing stress concentrations, and controlled cold working minimizing severity and avoiding combinations with welding. ASTM A143 stress relief heat treatment at 1,100-1,200°F for 1 hour per inch thickness reduces residual stresses from 40-60 ksi to 5-15 ksi through elevated temperature creep mechanisms enabling dislocation rearrangement and stress relaxation, providing highly effective cracking prevention for identified high-risk fabrications justifying $200-2,000 treatment cost versus potential repair and dispute costs. Galvanizers substantially reduce incidents and protect against unwarranted liability through systematic pre-galvanizing risk assessment identifying differential thickness connections, constrained frames, evidence of forced assembly, and heavy cold working, followed by proactive customer communication documenting concerns and obtaining acknowledgment before proceeding, then post-galvanizing inspection immediately detecting any cracks and notifying customers enabling economical repair at facility rather than expensive field repairs or customer discovery after installation. Responsibility allocation for residual stress cracking typically involves shared responsibility among fabricator (introducing residual stresses through welding and forming), owner/engineer (specifying potentially problematic geometry), and galvanizer (applying thermal stresses during immersion), with fair resolution requiring recognition that standard proper practices by all parties sometimes produce unfavorable variable combinations exceeding critical thresholds, suggesting negotiated cost-sharing arrangements (50/50 typical) or pre-emptive stress relief investment eliminating disputes through prevention rather than attempting fault assignment for complex multi-factorial failures. To view the original AGA article on this topic, click this link.