Ultrasonic Inspection of Welds with a Backing Bar

Introduction

• Presenter is wearing an NDT Hero shirt from Eddie Pompa.
• Using a weld test coupon, 0.5 inches thick with a single bevel backing bar.
• Inspection will be done using conventional UT (not phased array).
• Tools: Sun Test Wave on Olympus 5 MHz 70-degree transducer, millimeter ruler (using metric measurements).

Key Challenges in Backing Bar Weld Inspections

1. Backing Bar Signal

• Problem: Annoying signal on the screen caused by sound traversing through the joint and backing bar.
• Solution: Adjust the probe position and use X offset to measure from the front of the wedge, not the beam index point.
• Observation: Probe position aligns with the end of the backing bar.
• Tips: Watch for tack welds used to attach backing bars, as they can affect the signal.

2. Positioning and Reflectors

• Easier Positioning: Weld fusion provides a consistent reflector on the far side of the root, aiding in probe positioning.
• Demonstration: Moving the probe back and forth shows consistent reflector alignment.
• Technique: Push the probe to line up signals at the first line on the screen, oscillate probe for full two-leg inspection.

3. Defining the Center of the Weld

• Single Bevel Weld Challenge: Flat plate and angled plate create a large root gap, complicating center definition.
• Solution: Measure from the unbeveled edge for consistency.
• Example: Scan plan shows indication aligning around the 8mm mark from the unbeveled edge.

Conclusion

• Initial complexity in inspecting backing bar welds can be reduced with experience.
• Recognizable geometry signals aid in easier probe positioning.
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