Why Crack Detection Matters

Surface cracks in bolts, screws, and studs reduce load capacity by up to 90% and cause 80% of fastener failures in critical applications. This guide covers industry-proven NDT (Non-Destructive Testing) methods to identify defects before they compromise structural integrity.

The 4 Core Crack Detection Methods

(Selection Depends on Material & Defect Type)

1. Magnetic Particle Testing (MT): For Steel Fasteners

How It Works

1. Magnetize fastener → Crack disrupts magnetic field → Magnetic particles cluster at defect

2. UV light reveals fluorescent particle patterns

Optimal Use Cases

• Carbon/alloy steel bolts (Grade 5/8, A325)

• Head-to-shank fillet areas

• Thread root cracks

JM Hardware® Pro Tip:

*"For high-strength bolts >10.9 grade, use DC magnetization. AC won't detect subsurface flaws."*

2. Liquid Penetrant Testing (PT): Universal Surface Checks

4-Step Process

1. Clean: Remove oil/grease (ASTM E165)

2. Penetrant: Apply red dye/fluorescent fluid (5-30 min dwell)

3. Developer: Draw out penetrant from cracks

4. Inspect: Under white/UV light

Ideal For

• Stainless steel fasteners (A193 B8)

• Complex geometries (e.g., socket heads)

• Field inspections

Limitation Alert: Cannot detect sealed or subsurface defects.

3. Ultrasonic Testing (UT): Deep Defect Detection

Technical Procedure

• Transducer sends 1-10 MHz sound waves

• Crack reflection creates echo patterns

• Time-of-flight calculates depth

Critical Applications

• Anchor bolts in concrete

• Large-diameter flange studs

• Aerospace fasteners (NASM specs)

Data You Get:
✓ Crack depth ✓ Orientation ✓ Length

4. Visual Inspection (VI): First Line of Defense

Enhanced Techniques

Inspection Zones to Target:

• Under bolt heads

• Thread run-out sections

• Stress-corrosion prone areas
  

  
  
  Method Selection Guide: Match Technique to Need
  
  
  
  
  

  Why Trust JM Hardware® Fasteners?

  We implement 3-layer quality assurance:

  1. Raw Material Scan: PMI (Positive Material Identification)

  2. Process Control: Inline UT during cold forging

  3. Final Verification: 100% MT for ferromagnetic fasteners

  Certifications: ISO 9018, ASTM E1444/E1417, NADCAP AC7114

  
  
  Request Our Inspection Reports:
  ✉️ Email:  jminfo@jm-industry.com
  📱 WhatsApp: +8613681923533