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Bridge Pin Non-destructive Testing

TECHKNOWSERV CORP. (TKS) provides bridge pin non-destructive testing services to quantitatively assess cross-sectional area loss at hidden shoulders, barrels, and shear planes that are difficult or impossible to inspect visually. Our non-destructive testing engineering team has inspected bridge pins on over 100 bridges and other civil infrastructure assets over the last decade. This blog post summaries from of the insight gained for bridge pin nondestructive testing.

Bridge pin inspection is an important part of bridge fracture critical inspection programs. Bridge pins are steel cylinders produced by forging, casting, or cold-rolling processes. The most common bridge pin connection configurations include; bridge pin connected eyebars, bridge pin hangers, bridge bearing connections, hinge and bridge pin connections, bridge pin connected truss cord connections, and others.

The bridge pin connection can range in complexity from a simple system with two eyebar links or a multi-eyebar system with many links as shown in Figure 1. Due to the complexity of the bridge pin connection(s) is it absolutely essential to study the engineering drawing prior to bridge pin inspection and to identify the depth of shear planes, potential wear surfaces, shoulders and other changes in cross-sectional area. The pre-inspection effort is required to improve probability of detection of bridge pin defects while minimizing false positives bridge pin geometric features.

Figure 1 Steel bridge pin showing multiple connections points.

The objective of bridge pin testing is to inspect the volume of the bridge pin for cross-sectional area loss due to wear, corrosion, and in the worst case scenario fatigue cracks. Bridge pin non-destructive testing focuses particularly on the pin shear planes. Ultrasonic testing is accepted as the best non-destructive testing technique for bridge pins. X-ray testing has been used in the past but is rarely deployed these days, compared to ultrasonic bridge pin testing, due to safety issues associated with the radiation and the high cost.

These days there are four ultrasonic bridge pin testing options for the bridge owner: Straight beam ultrasonic pin testing, Angle beam ultrasonic pin testing, Phased array L-wave ultrasonic pin testing, Phased array shear wave ultrasonic pin testing

Nondestructive Testing of Bridge Pins with Straight Beam Ultrasound

This is the fastest and most economical nondestructive testing method for bridge pins and is typically performed in the 2.25 to 7.5 MHz range. This method provides a cross-sectional view of the pin and allows the user to size out internal reflectors in 2-dimensions to be passed on for engineering stress analyses. For a long bridge pin with a small diameter, it is the recommended method. Usually, the pin is inspected from a single side but to improve probability of detection (POD) it is recommended to inspect the bridge pin from both sides. Example data from a straight beam non-destructive bridge test is shown in Figure 2. On the left the bridge pin shown. The scanning face was 4” diameter. The steel bridge pin diameter beyond the shoulder was 5”. The shoulder was approximately 1.5” from the end of the bridge pin. The A-scan shown on the right displays the internal reflectors from the bridge. Starting from left to right, the main bang, shoulder, and pin end are observable. No bridge pin defects are observable.