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Publication Number: FHWA-HRT-04-042
Date: July 2004

Guidelines for Ultrasonic Inspection of Hanger Pins

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Table of Contents

FOREWORD

In June 1983, a failed hanger pin initiated the tragic collapse of one span of the Mianus River Bridge on the Connecticut Turnpike near Greenwich, CT. This incident resulted in the deaths of three motorists. Following the collapse, there was an immediate increase in interest in the inspection and condition evaluation of bridge hanger pins.  Ultrasonic inspection is one of the most reliable methods used to inspect hanger pins, and it has become the primary method of performing a detailed inspection of an in-service hanger pin. 

This report provides background information regarding hanger pins in general and discusses the field ultrasonic techniques, including methods, results, and limitations of each method. The report provides a comprehensive document describing the fundamentals of ultrasonic hanger pin inspection and can be used by State transportation agencies that are either inspecting pins themselves or contracting for inspection services.  In addition, a limited experimental program was utilized to emphasize, and more completely explain, some important aspects of ultrasonic pin inspection.  This report will be of interest to bridge engineers, designers, and inspectors who are involved with the inspection of hanger pin assemblies used in our Nation's highway bridges. 

T. Paul Teng, P.E.
Director, Office of Infrastructure
  Research and Development

NOTICE

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange.  The U.S. Government assumes no liability for its contents or use thereof.  This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers.  Trade and manufacturers' names appear in this report only because they are considered essential to the object of the document.


Technical Report Documentation Page

1.  Report No.
HRT-04-042

2.  Government Accession No.

3.  Recipient's Catalog No.

4.  Title and Subtitle
Guidelines for Ultrasonic Inspection of Hanger Pins

5.  Report Date
July 2004

6.  Performing Organization Code

8.  Performing Organization Report No.

7.  Author(s)
Mark Moore, P.E., Brent M. Phares, Ph.D., Glenn A. Washer, P.E., Ph.D.

9.  Performing Organization Name and Address
Wiss, Janney, Elstner Associates, Inc.
4165 Shackleford Road, Suite 100
Norcross, GA 30093

10.  Work Unit No. (TRAIS)

11.  Contract or Grant No.
DTFH61-98-C-00050

13.  Type of Report and Period Covered
Final Report
January 1998–September 2001

12.  Sponsoring Agency Name and Address
Nondestructive Evaluation Validation Center
Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, VA 22101-2296

14.  Sponsoring Agency Code

15.  Supplementary Notes
FHWA Contracting Officer's Technical Representative (COTR):  Glenn A. Washer, P.E., HRDI-10

16.  Abstract

A failed hanger pin initiated the tragic collapse of one span of the Mianus River Bridge in Greenwich, CT on June 28, 1983, resulting in the deaths of three motorists.  Following the collapse, there was an immediate increase of interest in the inspection and condition evaluation of bridge hanger pins.  Ultrasonic inspection has become the primary method of performing detailed inspection of in-service hanger pins.

The document describes the fundamentals of ultrasonic testing and general inspection requirements that can be used by State transportation agencies or by others performing ultrasonic hanger pin inspection.  In addition, five hanger pins, with known defects, were inspected to emphasize and more completely explain some important aspects of ultrasonic hanger pin inspection.

Items included in the fundamental review are the pulse-echo technique, pitch-catch technique, decibel scale, piezoelectric effect, beam diffraction, beam absorption, beam spread (beam divergence), beam centerline location, and distance amplitude correction.  Items included in the general inspection requirement section are cleaning and coupling requirements, interpretation of signals, defect sizing techniques, effect of wear grooves, phenomena of acoustic coupling, inspection documentation, data collection, and inspector qualifications and certifications.

Results from the experimental program include beam diffraction graphs, distance amplitude correction curves, sensitivity analysis of straight and angled beams, defect sizing analysis, and verification of the acoustic coupling phenomena.

17.  Key Words
Ultrasonic, Bridges, Pin, Nondestructive Evaluation

18.  Distribution Statement

19.  Security Classif. (of this report)
Unclassified

20.  Security Classif. (of this page)
Unclassified

21.  No. of Pages
107

22.  Price

Form DOT F 1700.7 (8-72)     Reproduction of completed page authorized


TABLE OF CONTENTS

1.  INTRODUCTION

      1.1.      BACKGROUND

      1.2.      OBJECTIVE

2.   GENERAL INFORMATION

      2.1.      ULTRASONIC TESTING EQUIPMENT

                  2.1.1.   Fundamentals of Ultrasonic Waves

                              2.1.1.1.   Pulse-Echo Technique

                              2.1.1.2.   Pitch-Catch Technique

                  2.1.2.   Decibel Scale

                  2.1.3.   Transducers

                  2.1.4.   Ultrasonic Beam Characteristics and Important Formulae

                              2.1.4.1.   Beam Attenuation

                                            2.1.4.1.1.   Beam diffraction

                                             2.1.4.1.2.   Beam absorption

                              2.1.4.2.   Beam Spread (Beam Divergence)

                             2.1.4.3.   Beam Centerline Location

                  2.1.5.   Distance Amplitude Correction

      2.2.      GENERAL HANGER PIN INSPECTION REQUIREMENTS

                  2.2.1.   Cleaning and Coupling Requirements

                  2.2.2.   Scanning Patterns

                  2.2.3.   Application and Sensitivity of Straight and Angle Beam Transducers

                  2.2.4.   Interpretation of Ultrasonic Testing Signals

                  2.2.5.   Defect Sizing Techniques

                              2.2.5.1.   Probe Movement Techniques

                                             2.2.5.1.1.   The 6-dB drop technique

                                            2.2.5.1.2.   The 20-dB drop technique

                                             2.2.5.1.3.   The time-of-flight diffraction technique

                              2.2.5.2.   Amplitude Techniques

                                             2.2.5.2.1.   The comparator block technique

                                             2.2.5.2.2.   The distance amplitude correction technique

                                             2.2.5.2.3.   The distance grain size technique

                  2.2.6.   Wear Grooves

                  2.2.7.   Acoustic Coupling

      2.3.      INSPECTION DOCUMENTATION

                  2.3.1.   Physical Measurements

                  2.3.2.   Visual Assessments

                  2.3.3.   Ultrasonic Testing Data Collection

      2.4.      INSPECTOR QUALIFICATIONS AND CERTIFICATIONS

3.   EXPERIMENTAL PROGRAM

      3.1.      INTRODUCTION

      3.2.      INSPECTION SPECIMENS

                  3.2.1.   Side-Drilled Hole Test Block

                  3.2.2.   Manufactured Cracked Pins

                  3.2.3.   Pin/Hanger Mockup

      3.3.      TESTING PROGRAM

                  3.3.1.   Beam Diffraction

                  3.3.2.   Distance Amplitude Correction

                  3.3.3.   Angle and Straight Beam Sensitivity to Cracks

                  3.3.4.   Defect Sizing

                  3.3.5.   Acoustic Coupling

4.   EXPERIMENTAL RESULTS

      4.1.      BEAM DIFFRACTION

      4.2.      DISTANCE AMPLITUDE CORRECTION

      4.3.      ANGLE AND STRAIGHT BEAM SENSITIVITY TO CRACKS

      4.4.      DEFECT SIZING

      4.5.      ACOUSTIC COUPLING

5.   CONCLUDING REMARKS

LIST OF FIGURES

Figure 1.     Model of an elastic material

Figure 2.     Longitudinal wave

Figure 3.     Shear wave

Figure 4.     Basic principle of pulse-echo technique

Figure 5.     Sketch of a typical ultrasonic A-scan

Figure 6.     Influence of distance on reflected ultrasonic signal

Figure 7.     Influence of shadow effects on ultrasonic signal

Figure 8.     Influence of defect orientation on ultrasonic signal

Figure 9.     Influence of defect size on ultrasonic signal

Figure 10.   Schematic of direct pitch-catch technique

Figure 11.   Schematic of indirect pitch-catch technique

Figure 12.   Piezoelectric effect

Figure 13.   Schematic of a straight beam piezoelectric ultrasonic probe

Figure 14.   Schematic of an angle beam piezoelectric ultrasonic probe

Figure 15.   Concept for generating distance amplitude correction curves

Figure 16.   Typical pin/hanger assembly

Figure 17.   Application of a straight beam transducer

Figure 18.   Application of an angle beam transducer

Figure 19.   Typical physical measurements

Figure 20.   Sample ultrasonic test data

Figure 21.   SDHTB details

Figure 22.   Photograph of the SDHTB

Figure 23.   Typical pin geometry

Figure 24.   Pin 1 defect details

Figure 25.   Pin 2 defect details

Figure 26.   Pin 3 defect details

Figure 27.   Pin 4 defect details

Figure 28.   Pin 5 defect details

Figure 29.   Pin/hanger mockup details

Figure 30.   Beam diffraction results for 8-degree, 5-MHz, 12.7-mm diameter transducer

Figure 31.   Beam diffraction results for 0-degree, 5-MHz, 12.7-mm diameter transducer

Figure 32.   Beam diffraction results for 0-degree, 2.25-MHz, 25.4-mm diameter transducer

Figure 33.   Beam diffraction results for 11-degree, 2.25-MHz, 12.7-mm diameter transducer

Figure 34.   Beam diffraction results for 14-degree, 2.25-MHz, 12.7-mm diameter transducer

Figure 35.   Beam diffraction results for 8-degree, 2.25-MHz, 19-mm square transducer

Figure 36.   Distance amplitude correction curve for 8-degree, 5-MHz, 12.7-mm diameter transducer

Figure 37.   Distance amplitude correction curve for 0-degree, 5-MHz, 12.7-mm diameter transducer

Figure 38.   Distance amplitude correction curve for 0-degree, 2.25-MHz, 25.4-mm diameter transducer

Figure 39.   Distance amplitude correction curve for 11-degree, 2.25-MHz, 12.7-mm diameter transducer

Figure 40.   Distance amplitude correction curve for 14-degree, 2.25-MHz, 12.7-mm diameter transducer

Figure 41.   Distance amplitude correction curve for 8-degree, 2.25-MHz, 19-mm square transducer

Figure 42.   Pin 1 testing results

Figure 43.   Pin 2 testing results

Figure 44.   Pin 3 testing results

Figure 45    Pin 4 testing results

Figure 46.   Pin 5 testing results

Figure 47.   Photograph of pulse-echo setup using 14-degree transducer

Figure 48.   UT scan utilizing pulse-echo technique with a 14-degree transducer

Figure 49.   Photograph of pitch-catch setup using 0-degree transducers

Figure 50.   UT scan utilizing pitch-catch technique using 0-degree transducers

Figure 51.   Photograph of pitch-catch setup using 0-degree receiving and 14-degree transmitting transducers

Figure 52.   UT scan utilizing pitch-catch technique using 0-degree and 14-degree transducers

LIST OF TABLES

Table 1.      Defect size data

Table 2.      Defect sizing error

Table 3.      Absolute value of defect sizing error

1.  INTRODUCTION

1.1.  BACKGROUND

A failed hanger pin initiated the tragic collapse of one span of the Mianus River Bridge in Greenwich, CT, on June 28, 1983, resulting in the deaths of three motorists.  The collapse sparked an immediate increase of interest in the inspection and condition evaluation of bridge hanger pins.  Ultrasonic inspection has become the primary method of performing detailed inspection of in-service hanger pins.

1.2.  OBJECTIVE

The research objective is to develop a document describing the fundamentals of ultrasonic hanger pin inspection that can be used by State transportation agencies that are either inspecting pins themselves or contracting for inspection services.  In addition, a limited experimental program is utilized to emphasize, and more completely explain, some important aspects of ultrasonic pin inspection.

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