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Manual Weld Inspection with Eddy Current


Introduction

Welds are present in many locations in different types of structures such as bridges, pipelines, and turbines. In structures subjected to loading cycles, cracks can form and grow during a weld’s service life. To help ensure the safety of infrastructure and society, welds must be regularly inspected in situ to look for cracks or defects. Olympus’ weld inspection eddy current (EC) kit is designed to facilitate these inspections using the NORTEC 600 (Figure 1).

Challenge

Conventional weld inspection methods, such as dye penetrant, can be used to detect cracks on welds, but any coating or paint over the weld must be removed and then reinstalled after the inspection. Eddy current is an effective tool to detect cracks on flat surfaces. Most of the time, welds are not completely flat but are, instead, composed of crests and crevices. This complicates the inspection because the EC probe cannot maintain consistent contact with the surface due to the topography, creating lift-off signals. However, using the proper inspection technique combined with the right EC tools greatly enhances the reliability of the inspection.

Solution

Olympus’ EC weld inspection kit contains

Item U8 Part Number Description
N600 Different configurations N600 NORTEC 600 eddy current flaw detector (basic)
Weld kit U8670016 NEC-8196 Weld inspection kit containing 1 ea.: WLD-5-63, WLD-8-55, NEC-2236 SRSM-51020S/WLD, WLD-SAMPLE & CN16-4L-6
Chest strap U8140055

EP4/CH

EPOCH series chest harness

Figure 1. The weld inspection kit (left) and NORTEC 600 (right).

Operation mode

The features of the NORTEC 600 combined with the eddy current weld kit and a proper inspection method considerably increases the detection and sizing capabilities of EC weld inspection.

Figure 2. Using the NORTEC 600 probe to inspect a painted weld with variable topography.

The proper EC weld inspection technique is described in the British Standard BS EN 1711: 2000 nondestructive examination of welds—eddy current examination of welds by complex plane analysis.

The technique consists of two steps:

  1. Paint thickness evaluation
    The EC probe is used to evaluate the thickness of the paint on the part that is going to be inspected. By comparing the shift of the operation point of the probe when it is sitting on the part, to the operation point curve produced when the probe is sitting on different shims, the operator can easily evaluate the paint thickness.
  2. Sensitivity calibration
    Once the paint thickness is defined, the operator can set the sensitivity of notches using the right quantity of shims on the calibration block (Figure 3). The NORTEC 600 enables inspectors to record the calibration amplitude to compare it against real indications. The reference signal can then be used as needed.

Figure 3. Reference signals of different notches.

Depth sizing

The detection amplitude is directly related to flaw depth. Therefore, the depth can be evaluated by comparing indication amplitudes to those of calibrated notches. Different weld areas (crest, crown, and toe position) have various operation points because of the lift-off conditions as illustrated below:

Figure 4. Peak-to-peak amplitude measurement with the NORTEC 600.

The NORTEC 600 has a Vpp (Peak-to-peak amplitude measurement) feature that provides accurate results independently of the weld zones.

Length sizing

The NORTEC 600 has a unique real-time reading that is useful for sizing the length of an indication using the -6 dB drop method. The length of the indication is then sized by moving the probe along the crack in both directions until the signal has dropped 6 dB.

Figure 5. Crack length sizing using the 6 dB drop technique.

The operator has to find the maximum amplitude of the indication and make note of it. Next, the user moves the probe along the crack until the signal drops off 6 dB (half the amplitude). At this point, the operator notes the position of the drop on the part. Repeat the same steps at the other end of the crack and use a ruler to measure the length of the notch.

Conclusions

Olympus’ weld inspection kit is designed to work with the NORTEC 600 to enable weld inspection through paint. By using the proper inspection techniques, inspectors can compensate for the lift-off due to paint thickness. The NORTEC 600 makes it easy to size the depth and length of cracks in welds.

Learn more about this application.

Olympus IMS

Products used for this application


NORTEC 600NEW

The new NORTEC 600 incorporates the latest advancements in high-performance eddy current flaw detection into a compact, durable unit. With its vibrant 5.7 inch VGA color display and true full-screen mode, the NORTEC 600 produces user-selectable, highly contrast eddy current signals.
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