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Ultrasonic Testing of Steel Bridge Pins: Conventional Ultrasonic and Phased Array Ultrasonic Testing

Conventional ultrasonic testing (UT) and phased array ultrasonic testing (PAUT) of steel bridge pins is important for several reasons, primarily related to ensuring the structural integrity and safety of the bridge [1,2]. Some of the key reasons why ultrasonic testing is crucial for steel bridge pins include:

  • Detection of Flaws and Defects: Ultrasonic testing can detect various flaws and defects in steel bridge pins, such as cracks, voids, inclusions, and corrosion. Identifying these defects is essential to prevent potential failures or weaknesses in the bridge structure.

  • Safety Assurance: Bridges are critical infrastructure, and the safety of the people who use them is paramount. Ultrasonic testing helps ensure that bridge pins are in good condition and capable of supporting the loads they are subjected to, reducing the risk of accidents or structural failures.

Figure 1: Access to bridge pins performed using rope access, snooper trucks, and standard high reach manlifts.
Figure 1: Access to bridge pins performed using rope access, snooper trucks, and standard high reach manlifts.

Maintenance Planning: By identifying defects early through ultrasonic testing, bridge owners and operators can plan maintenance and repair activities more effectively. This proactive approach helps extend the lifespan of the bridge and reduces the overall cost of maintenance.

  • Regulatory Compliance: Many regions and countries have regulations and standards in place that require regular inspections and testing of critical infrastructure, including bridges. Ultrasonic testing helps bridge owners comply with these regulations and demonstrate their commitment to safety.

  • Long-Term Performance: Steel bridge pins play a crucial role in the overall performance of a bridge. Detecting and addressing issues early can extend the lifespan of the pins and, by extension, the entire bridge structure.

Ultrasonic testing of steel bridge pins is crucial for ensuring the safety, longevity, and cost-effectiveness of bridge infrastructure. By identifying defects and weaknesses early, bridge owners and operators can take appropriate actions to maintain and improve the structural integrity of their bridges. Over the last decade or so, phased array ultrasonic testing (PAUT) has emerged as non-destructive testing technique that can improve the bridge pin inspection process.


Steel Bridge Pins


A steel bridge pin, also known as a bridge bearing pin or bridge pivot pin, is a structural component used in the construction of bridges. It plays a vital role in the functionality and safety of the bridge. A steel bridge pin is a cylindrical or rod-like component made of steel that serves as a pivotal connection point within a bridge's superstructure. These pins are typically installed at critical locations where movement or rotation is required, such as expansion joints, hinge points, or bearing locations. Bridge pins are designed to transfer loads from the bridge deck and superstructure to the bridge substructure, which includes abutments and piers. They allow for controlled movement, expansion, contraction, and rotation of bridge components in response to various forces, including temperature changes, traffic loads, and seismic activity. Shown below is a common steel bridge pin and eye bar configuration that is tested with conventional ultrasonic and phased array ultrasonic testing. In this case the pin is approximately 24” long and 9” diameter and intersects with 10 different eye bars. Each intersection is a potential for wear, outside diameter corrosion and fatigue cracking. These areas are therefore critical to reach with conventional ultrasonic and phased array ultrasonic testing.


Figure 2: Example pin and eye bar configuration showing side view on left and top view on right.
Figure 2: Example pin and eye bar configuration showing side view on left and top view on right.


Example Longitudinal and Shear Wave Phased Array Ultrasonic Testing Data


Longitudinal and shear wave ultrasound are commonly used for bridge pin inspections. Similarly, conventional ultrasonic testing (UT) and phased array ultrasonic testing (PAUT) are also commonly deployed depending on the complexity of the inspection and the desired outcomes. Shown below in Figure 3 is example longitudinal wave PAUT data. The PAUT longitudinal wave S-scan on the right scan is setup from -10 degrees to + 10 degrees with 1 degree resolution. The A-scan on the left shows the active angle in the S-scan. The pin tested is approximately 8” long and a strong backwall is observed at this distance. The pin body to thread transition is detected at approximately 6.5” from the pin face from which phased array data were acquired. In between the start of the threads and the opposite pin face, the individual threads are observed. The data correlates well with a simple reflection amplitude analysis. The transition from the pin body to the threaded section provides ultrasonic reflections in the 20 – 40 % full screen height (%FSH) range. The underlying threads, while discernable, produce lower amplitude ultrasonic reflections. The pin end provides a very strong ultrasonic reflections greater that 100 %FSH. The test data from multiple pin face locations concludes that no significant diameter reduction or cracks are present.


Figure 3: Phased array ultrasonic testing of steel bridge pin example longitudinal wave data. Active focal law A-scan shown on the right. -10 degrees to + 10 degrees with 1 degree resolution longitudinal wave S-scan shown in the right.

Figure 4: Phased array ultrasonic testing of steel bridge pin example shear wave data. Active focal law A-scan shown on the right. 40 degrees to 70 degrees with 1 degree resolution shear wave S-scan shown in the right.


Figure 4 is example shear wave PAUT data. The PAUT shear wave S-scan on the right scan is setup from 40 degrees to 70 degrees with 1 degree resolution and is targeting the near surface threads for any root cracks. The A-scan on the left shows the active angle in the S-scan. The individual threads are surveyed and with each thread aligning vertically and the thread pitch rough the vertical distance between the thread faces. The test data from multiple pin face locations concludes that no significant diameter cracks have initiated and propagated in the threaded area.


Summary


Steel bridge pins are critical components in the construction of bridges, providing structural support, load transfer, and the ability to accommodate movement and rotation. Their proper function and maintenance are essential for the safety, stability, and longevity of the bridge, making them an important consideration in bridge design and maintenance practices. Longitudinal and shear wave phased array ultrasonic testing (PAUT) provide full volumetric inspection of the near surface threaded area, shoulders, and pin body.



References

  1. FHWA-HRT-04-042 – Guidelines for Ultrasonic Inspection of Hanger Pins

  2. American Society for Testing and Materials, ASTM 388/A 388M, Standard Practice for Ultrasonic Examination of Heavy Steel Forgings

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