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Ultrasonic Testing of Welds

Updated: Feb 27, 2020

Introduction

It is not uncommon for a nondestructive testing ultrasonic technician to inspect structural welds according to the American Welding Society D1.1: Structural Welding Code – Steel (AWSD1.1), at least a few times in his or her career, and some inspectors use it daily. Completing a professional AWSD1.1 inspection, however, without the proper code specific training can be daunting. This article is designed to give the reader an introduction to the 2008 edition of Ultrasonic inspection per AWSD1.1 inspection procedure. The reader needs to be aware that some important (but routine) steps such as equipment qualifications have not been addressed here to allow the article to fit in available space. It is assumed that the reader has accomplished those tasks before proceeding on to transducer and wedge selection.

Transducer and Wedge Selection

AWSD1.1 recommends the weld metal be inspected using a 45o, 60o, or 70o degree shear wave in steel. The frequency range required by the code is 2-2.25 MHz. The active element inside the transducer must be square or rectangular with width in the 5/8” to 1” inch range and 5/8” to 13/16” in height. Major ultrasonic transducer suppliers sell complete AWS base and weld metal transducer kits that comply with the codes.


The next step is to determine the proper wedge for the weld inspection. The testing angle is selected using Table 6.7 in AWS D1.1 Chapter 6. The selection process requires knowledge of the weld type and plate thickness. Part of Table 6.7 is shown in Figure 1 to illustrate the wedge selection procedure. Supposing the inspection was performed on a 1.625” thick T-weld, the table shows the inspector “1” and “F” or “XF” in the Material Thickness column. The 1 is the shear wave angle from the table’s legend. In this case a 70 deg. shear wave is required for inspection of the top quarter, middle half, and bottom quarter of the weld. The “F” specifies the weld – base metal transition zone must be inspected further using a 45 deg., 60 deg., or 70 deg. degree wedge, whichever generates a shear wave closest perpendicular to the weld fusion line. The “X” specifies that inspection is required from Face C, which is defined in the legend of AWSD1.1 Table 6.7 for butt, corner, and T-joints.



Inspection Layout

Before the inspection of the welds could begin, there are a few simple steps that need to be taken to identify the area to be inspected using ultrasonic inspection and accurately report the location of any detected flaws.


Marking Skip Distance: The skip distance defines the zone of inspection. It is provided by a simple formula: Skip Distance = 2*T*tanθ, where T is the thickness of the part inspected and θ is the refracted angle of the shear wave in steel (45o, 60o, or 70o). Measure the thickness of the part that is to be inspected. Using a calculator, the skip distance can be determined easily. Mark the end of the skip distance from the edge of the heat affected zone (HAZ). The scanning distance is not measured from the weld centerline but rather from the edge of the HAZ. Identifying the skip distance from the edge of the HAZ ensures complete coverage of the weld when performing the angle beam ultrasonic inspection.Reference System: The reference system for flaw location must be setup before scanning with the calibrated unit so that the location of flaws may be reported accurately. First, the inspector should mark out the X- axis, which is the centerline of the weld as shown in Figure 2. Next, an edge or another well-defined reference point should be selected as the Y-axis. The inspector must select the +Y and –Y directions as well. In the example shown, +Y and –Y are to the left and right of the weld centerline, respectively.


Calibration