Top Techniques Used in NDT for Aluminum Welding

Nondestructive testing (NDT) for aluminum welding includes two important techniques: ultrasonic and eddy current. Both methods can expose diverse flaw types and offer comprehensive probing measures. With eddy current testing (ECT) and ultrasonic testing (UT), you can scan larger areas in less time and obtain resolute data in the process. 

ECT works best on thin, aluminum plates and multi-layered structures, allowing users to probe for surface and near-surface flaws. UT probes on a volumetric level and can find parallel flaws using specialized procedures. This article will explain why ECT and UT are two of the best methods when inspecting aluminum welds.

The Benefits of Eddy Current for Aluminum Welding

ECT is tailor-made for conductive welds like aluminum and can measure the conductivity of the asset. With a wide-range frequency probe, analysts can measure the conductivity of an aluminum structure without additional equipment. Additionally, quality ECT equipment measures thickness variations of aluminum welds and can determine thinning caused by corrosion. 

Corrosion is a primary cause of thickness discontinuities in multi-layered assets, and welds with multiple layers tend to mask the presence of corrosion. Air gaps can hide corrosive anomalies and produce skewed data that can lead to imprecise maintenance scheduling. However, ECT provides a precise signal-to-noise ratio (SNR) that combats unneeded air signals stemming from air openings between the layering.

In addition to SNR, quality ECT equipment should include the following features:

• Quick setup times with no need for extensive calibration 
• A simple interface that matches consumer-oriented gadgets
• Handheld portability with no need for a constant electrical source

Other NDT techniques (i.e. magnetic particle testing) require an ever-present electrical outlet to work properly. In contrast, ECT equipment should have a battery-supported system that can last up to ten hours, and it should be light enough to carry without weighing down the user. Additionally, techniques like MPT require direct surface contact with an aluminum structure. In fact, MPT forces technicians to remove paint surfaces before testing and apply hazardous chemicals that are harmful to people, especially when used in enclosed quarters. 

ECT requires no chemicals or direct surface contact. Analysts can test an aluminum sub-layer with the painted surface intact. ECT also doesn’t require the use of couplants or chemicals during the testing process, as the device solely relies on eddy currents and magnetic fields to expose irregularities within the aluminum asset. 
For complex aluminum structures, there is also eddy current array (ECA), a system that can test complicated contours with multi-coil probes. The array capabilities provide detailed renderings of deviations, including minuscule cracks and other defects that are hard to find with other NDT alternatives. When coupled with array benefits, the ECT system can shorten inspection intervals by as much as 95 percent and provide data that is more reliable than other more traditional NDT means.

Flaw Detection Capabilities in Aerospace (white paper): Read case studies about how ECA technology applied using a high-quality signal to noise ratio ECA instrument can improve flaw detection speed, probability of detection and data recording.

The Benefits of Ultrasonic Testing for Aluminum Welding

Ultrasonic testing offers the same array strength in the form of phased array testing (PAUT). PAUT is a step above traditional ultrasonic testing, as it affords additional beaming angles and customizations. With conventional ultrasonic testing, technicians can only work with fixed beaming angles that may fail to find flaws entrenched in diverse positions. With PAUT, additional deviations can be found in a single campaign without additional probes or equipment. 

Overall, PAUT can offer the following benefits: 

• Extensive surface mapping that covers more ground in a single testing campaign
• Detailed flaw recording in real-time
• Tailor-made readiness on composite materials and complex structures

PAUT is especially useful for composite welds that consist of aluminum alloys, in addition to fiberglass, titanium, or steel. After the manufacturing process, a viable PAUT regimen can detect aberrations in the form of foreign agents, porosities, or delaminations. To maximize flaw-finding benefits on aluminum alloys and composites, technicians can combine PAUT with the time-reversal technique, which streamlines the inspection process and provides wider surface coverage. 

The time-reversal method works well for complex composite structures of varying thickness levels and eliminates alignment problems that stall testing campaigns. The process of time-reversal compensates for misalignment issues, and the features adapt to complicated geometries without hassle. Best of all, time-reversal could potentially enhance the signal quality even when the probe is not aligned properly. 

NDT for Aluminum Welding using ECT and UT

Even though eddy current and ultrasonic methods are ideal methods for aluminum welds, the array function adds a level of precision that finds additional flaws. ECT can detect indications within aluminum structures that have multiple layers and can measure thickness variations caused by corrosion. Ultrasonic can inspect aluminum welds using the phased array method, including aluminum composite welds that contain other materials. 

NDT for aluminum welding should consist of eddy current and ultrasonic, as both measures contain the most cutting-edge technologies within the industry. Both methods can be used to find infinitesimal defects that may escape the human eye using visual testing or fly under the radar with techniques such as MPT. Regardless of the industry, ECT and UT can find abnormalities in the making, allowing maintenance crews to commence the necessary repairs to maintain safety and operational cohesion.

Zetec is a major provider of ECT and UT equipment for industries such as aerospace, manufacturing, and oil and gas. Contact us today to get a custom inspection plan and further guidance on the best NDT equipment for your inspection endeavors.