Since the launch of the earliest metal-hulled boats in the late 18th century, boat designers have made extensive use of steel and aluminium in watercraft of all sizes. Today, welding is the preferred technology for building metal hulls, offering greater integrity than traditional riveted construction. Testing welds to ensure that they are watertight can be labour-intensive, as the size and geometry of a boat generally rules out air pressurisation. Air hose testing and dye penetrant testing provide an acceptable degree of reliability without the need for sophisticated equipment.
- Skill level:
- Moderately Challenging
Things you need
- Wire brush
- Bubble testing liquid
- Compressed air hose with nozzle tip
- Metal marker
- Degreasing agent
- Dye penetrant test kit (dye, cleaner, developer)
Clean the front and reverse of the weld area to be tested. Use a wire brush to remove slag or other debris. Wipe the weld area with a rag.
Apply a thin film of bubble testing liquid to the reverse of the weld area in accordance with the manufacturer’s instructions. Station an observer at the reverse of the weld area to watch for bubbles.
Apply a stream of compressed air to the weld seam from close range. Hold the air nozzle as close as possible to the surface of the weld.
Check for any air bubbles that form on the reverse of the weld. These indicate leaks in the weld.
Mark the position of any leaks with a metal marker. Clean the weld area and retest once you have repaired the cracks.
Air Hose Testing
Clean the front and reverse of the weld area to be tested thoroughly. Use a wire brush to remove slag or other debris. Use degreasing agent to remove any surface contamination. Wipe dry with a clean cloth.
Apply dye penetrant to the front of the weld area according to the manufacturer’s instructions. Leave the penetrant for the manufacturer’s recommended dwell time to soak into any cracks.
Wipe off the excess dye penetrant with a rag. Clean any remaining penetrant from the surface of the weld using dye penetrant cleaner. Wipe the surface dry with a clean cloth.
Apply dye penetrant developer to both sides of the weld area according to the manufacturer’s instructions. Leave the developer for the manufacturer’s recommended dwell time to react with any remaining dye.
Inspect the weld area. Dye will be retained in any cracks in the weld area and will show up as coloured streaks on the surface of the developer. Positive indications on the front of the weld show leaks or small surface cracks, while those on the reverse of the weld indicate leaks.
Mark any cracks using a metal marker. Clean the weld area and retest once you have repaired the cracks.
Dye Penetrant Testing
Tips and warnings
- Small surface cracks may not result in leaks. However, it is good practice to repair all defects before relying on the integrity of the joint.
- Compressed air can be dangerous if used unsafely. Always use an air nozzle, and ensure that you and your observer wear suitable personal protective equipment for the duration of air hose testing.
- If you use a spray cleaner to remove the dye penetrant, do not spray too vigorously or you may remove dye that has lodged in any cracks.
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