Welding Screw Repair & Inspection Guide | Industrial Fastener Best Practices

Welding Screw Repair and Inspection Guide

This guide provides detailed procedures for repairing broken welding screws, performing surfacing welding, removing broken bolts, and inspecting the quality of welding screws in industrial applications. It is designed for engineers, maintenance teams, and quality assurance professionals.

1. Preparing and Drilling the Broken Welding Screw

1. Remove any oil stains from the surface of the broken      welding screw.

2. Use an electric drill with a 6–8 mm drill bit to      drill a hole at the center of the broken section. Ensure the hole is      drilled completely through the screw.

3. Replace the small drill bit with a 16 mm drill bit to expand      the hole, allowing proper access for subsequent welding.

2. Surfacing Welding Process

1. Use a welding rod with a diameter of less than 3.2 mm      and apply small to medium currents.

2. Begin surfacing welding from the inside to the outside      of the drilled hole. Start with half the length of the broken bolt,      avoiding overshooting the arc to prevent burning the outer wall.

3. Continue welding to the top end of the broken bolt, forming a cylinder      with a 14–16 mm diameter and 8–10 mm height.

3. Loosening the Broken Bolt

• After welding, hammer the end face lightly to cause      axial vibration.

• The heat from surfacing welding combined with vibration will loosen      the bond between the broken bolt and its threads.

4. Welding Nut Attachment

• Observe for minor rust leakage from the fracture.

• Place an M18 nut on the surfacing stud and weld it to      the stud.

5. Removing the Broken Bolt

• Allow the weld to cool slightly.

• Use a ring wrench to twist the nut back and forth while      optionally tapping the nut with a hand hammer to remove the broken      bolt.

6. Cleaning the Threaded Hole

• After bolt removal, use a suitable tap to clean the      threaded hole in the frame.

• Remove rust, debris, and sundries to ensure proper      engagement for replacement bolts.

Welding Screw Inspection Methods

Inspection ensures welding screws meet quality and safety standards before and after surface treatment.

1. Appearance Quality Inspection

• Examine screws for visual defects such as surface      irregularities, electroplating issues, and overall finish.

2. Coating Thickness Inspection

• Measuring Tool Method: Micrometers,      vernier calipers, and plug gauges.

• Magnetic Method: Non-destructive      measurement for non-magnetic coatings on magnetic substrates.

• Microscopy: Metallographic method      using a microscope and micrometer eyepiece.

• Timing/Flow Method: Dissolving      coating locally and measuring time to calculate thickness.

• Other methods include plating drop test and anodic dissolution      coulometric method.

3. Adhesion Strength Inspection

• Evaluate coating adhesion to the base metal using:

1. Friction polishing test

2. File method test

3. Scratch method

4. Bending test

5. Thermal shock test

6. Extrusion method

4. Corrosion Resistance Inspection

• Coating corrosion resistance is tested via:

• Atmospheric exposure

• Neutral salt spray (NSS)

• Acetic acid salt spray (ASS)

• Copper accelerated acetic acid salt spray (CASS)

• Corrosion paste and solution spot tests

• Immersion and interleaved corrosion tests