Inspectioneering
Inspectioneering Journal

The Benefits of Laser-Based Inspection

By Connie LaMorte at EWI, and Jon Jennings at EWI. This article appears in the March/April 2015 issue of Inspectioneering Journal

Introduction

Lasers have been used in the welding industry for over 30 years for seam-tracking while welding, for inspection of weld surface quality, and for corrosion detection on existing structures. Today’s laser sensors are faster, have more resolution, and are smarter than ever. Weld inspection using lasers is not new, but doing it 75 meters inside a pipe or streaming inspection data wirelessly is new. As laser technology has improved, more industries such as oil & gas are beginning to require laser inspection as part of their specifications. This non-contact method can help catch an unacceptable condition before it becomes too late to remedy the weld.

Overview

Laser-based vision incorporates optical position finding to measure a surface in 3D. By scanning a laser line across a surface, measurements of the distance to the surface are accumulated, creating a contour map. This map can then be used to measure surface features such as weld bead height, mismatch, undercut, or cracks that are even a few mils in size. All of this technology can now be found in a single, smart package, but it wasn’t that way until recently. When the oil & gas industry first began using lasers for inspecting welds and corrosion on transmission pipeline surfaces, lasers were custom optical systems, not designed to operate outside a lab environment. These lasers had low measurement resolution and slow communication speeds, and required processing had to be completed using a computer with special processing cards. Furthermore, there were few laser sensor suppliers around and even fewer that provided sensors suitable for a welding environment. So what has changed in the past two decades?  Everything.

Smart lasers include their own processors now, so you do not need to connect to a computer. Blue lasers can measure glowing steel surfaces because their wavelength is unaffected by the irradiance of steel at certain temperatures. It is possible to measure underwater now as well, and the sensor hardware is commercially available. There are several laser sensor manufacturers now and each one has certain advantages and disadvantages. Common among all their products though are faster measurements, higher resolution, and smaller price tags than previous options.

Early laser line sensors used analog cameras, which limited the capture rate to 30 HZ generally, or double that if you used a few tricks like binning or processing every other line. Now, digital or smart cameras rule with Ethernet communication protocols and ever-increasing resolution. Lasers are more and more affordable as new manufacturers enter the market and veteran manufacturers continue to update their product offerings.

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