MISON® 25 (Ar + 25% CO₂ + micro O₂) maximizes penetration for heavy structural steel welding, delivering 30% deeper penetration than standard 18% CO₂ mixes while maintaining excellent mechanical properties. Essential for thick sections 12-50mm requiring single-pass capability and superior impact toughness in critical structural applications.

Heavy Structural

MISON® 25

Ar + 25% CO₂ + µO₂

High-penetration tri-mix gas engineered for heavy structural steel applications, combining maximum CO₂ content with controlled micro-oxygen for deep penetration and exceptional mechanical properties in thick sections.

Technical Specifications

Property	Value	Benefit
Argon Content	Balance (~74%)	Arc stability, manageable spatter
CO₂ Content	25%	Maximum penetration, heat input
Oxygen Content	1500-4000 ppm	Enhanced penetration profile
ISO 14175 Classification	M21-ArC-25-O	Heavy structural welding grade
AWS D1.1 Approval	Certified	Structural steel code compliance

PROOF Analysis: Why MISON® 25 for Heavy Structural

P - Problem: Heavy Section Welding Challenges

Lack of fusion: Insufficient penetration in thick structural sections
Multi-pass requirements: Increases distortion, time, and defect probability
Heat-affected zone: Wide HAZ reduces structural integrity
Impact toughness: Critical for seismic and dynamic loading applications
Productivity pressure: Need single-pass capability on thick sections
Code compliance: AWS D1.1/D1.8 requirements for critical structures

R - Research: High-CO₂ Tri-Mix Science

Penetration mechanics: 25% CO₂ provides optimal heat input for thick sections
Micro-oxygen effect: 0.15-0.4% O₂ optimizes metal transfer at high currents
AWS D1.1 testing: Qualified for seismic structural applications
Impact toughness data: Superior performance at -40°C compared to binary mixes
Metallurgical benefits: Refined microstructure from controlled oxidation
Fatigue performance: Enhanced crack growth resistance in cyclic loading
Single-pass capability: Full penetration up to 20mm thickness

O - Options: Heavy Section Gas Alternatives

Gas Option	Penetration Depth	Impact Toughness	Single-Pass Limit	Cost Index
MISON® 25	8.5mm @ 350A	85J @ -40°C	20mm	118%
Standard Ar/25% CO₂	7.2mm @ 350A	65J @ -40°C	15mm	100%
Ar/18% CO₂	6.1mm @ 350A	78J @ -40°C	12mm	95%
Pure CO₂	9.1mm @ 350A	45J @ -40°C	25mm	70%

O - Outcome: Structural Performance Validation

Penetration increase: 30% deeper than 18% CO₂ mixes (8.5mm vs 6.1mm)
Tensile strength: 640 MPa typical in as-welded condition
Impact toughness: 85J at -40°C (exceeds AWS D1.1 requirements)
Single-pass capability: Full penetration to 20mm thickness
Fatigue strength: 45% higher endurance limit vs pure CO₂
Productivity gain: 40% reduction in weld passes on thick sections
Defect reduction: 75% fewer lack-of-fusion rejections

F - Final Recommendation

Choose MISON® 25 for: Heavy structural steel applications requiring maximum single-pass penetration with code-compliant mechanical properties. Critical for bridges, high-rise construction, offshore platforms, and seismic-resistant structures where impact toughness and penetration are paramount.

Linde Product Code: MISON-25-O (structural grade certification)

Approval status: AWS D1.1, D1.8, CSA W59 certified for critical structures

Applications & Use Cases

Primary Applications

Structural steel construction (beams, columns, connections)
Bridge construction and heavy infrastructure
Offshore platform and marine structures
Seismic-resistant building frameworks
Heavy equipment manufacturing (mining, construction)
Pressure vessel and boiler construction

Material Compatibility

A572 Grade 50

High-strength structural steel

A572 Guide

A992 Wide Flange

Building construction beams

A992 Guide

A516 Grade 70

Pressure vessel applications

A516 Guide

S355 Structural

European structural steel standard

S355 Guide

Usage Guidelines

Recommended Parameters

Material Thickness	Gas Flow Rate	Current Range	Single-Pass Capability
12-16mm	18-22 L/min	300-380A	Full penetration
16-20mm	20-25 L/min	350-450A	Full penetration
20-30mm	22-28 L/min	400-520A	Multi-pass optimized
30-50mm	25-32 L/min	450-600A	Root/fill/cap sequence

Welding Position Guidelines

Flat (1G): Maximum penetration, optimal for single-pass thick sections
Horizontal (2G): Excellent for fillet welds, manage higher heat input
Vertical (3G): Reduce current 15-20%, use uphill progression
Overhead (4G): Not recommended for thick sections, use MISON 18

Code Compliance & Certification

Structural Welding Codes

AWS D1.1: Structural welding code - steel (certified)
AWS D1.8: Seismic supplement (qualified)
CSA W59: Canadian welding standard (approved)
EN 1090: European structural steel standard (compliant)
JIS Z 3211: Japanese structural welding (certified)

Mechanical Property Requirements

Property	AWS D1.1 Minimum	MISON® 25 Typical	Safety Factor
Tensile Strength	580 MPa	640 MPa	1.10x
Yield Strength	490 MPa	545 MPa	1.11x
CVN @ -29°C	20J minimum	85J typical	4.25x
Elongation	22% minimum	28% typical	1.27x

Advantages & Performance

Structural Benefits

Superior impact toughness for seismic and dynamic loading
Reduced susceptibility to brittle fracture
Enhanced fatigue resistance for cyclic loading
Consistent mechanical properties across weld cross-section
Reduced sensitivity to cooling rate variations

Production Benefits

Single-pass capability reduces welding time by 40%
Lower distortion due to concentrated heat input
Reduced grinding and preparation between passes
Enhanced productivity on thick structural connections
Fewer quality control rejections

Limitations & Considerations

Not Recommended For

Thin sections (<12mm) where heat input must be controlled
Overhead welding positions on thick sections
Applications requiring minimal spatter (use MISON 18)
Stainless steel or non-ferrous materials
Root passes in pressure vessel applications

Special Considerations

Higher heat input requires distortion control measures
May require preheat on high-carbon or thick sections
Enhanced spatter compared to 18% CO₂ mixes
Requires experienced operators for positional welding
Post-weld stress relief may be required on thick sections