SciAps True Demo Stories, Episode 8: Weld Inspection on Sydney Harbour Bridge
March 14, 2019
Going where no handheld has gone before
The historic Sydney Harbour Bridge is an icon of Australia itself. But the silicon steel structure is also extremely vulnerable to corrosion. How to get the best NDT results on a tight timeline and in tight spaces? Meet the Z-200 C+, the world’s only handheld analyzer for carbon. Sydney Harbour Bridge is a workhorse. Built in 1932 out of silicon steel, a precursor to modern structural steels, more than 160,000 vehicles and 200 trains cross it daily. The Roads & Maritime Service says protecting the bridge from corrosion is the most important factor in safety and conservation. But remediation has to be accurate, and fast. “They can’t shut down the bridge and train lines for testing any longer than necessary,” says Shaun Davis, engineer with Bureau Veritas. Shaun and a team were up on the bridge on a recent weekend in February, with the breakthrough SciAps Z-200 C+. AXT Australia had provided the demonstration unit. All rail traffic was halted, so testing steel grades had to move quickly. “They were planning on testing 5-8 locations, but after seeing the LIBS firsthand, they were looking at 50-plus,” says SciAps product specialist Ryan Clair, on hand to provide technical support.
Weighing in at just 4 lbs., the battery operated handheld analyzer miniaturizes the laboratory technique of laser induced breakdown spectroscopy. LIBS is very similar to spark OES, except it uses a pulsed laser, rather than a cumbersome high-voltage spark system, to create the plasma. Using a representative sample from the bridge, the team created a type-calibrated standard to dial in the calibration exactly as needed, and for each test, the instrument would automatically report the carbon equivalents. With five hours of battery life and a small argon canister in the handle ready for a hundred readings, they were equipped to accomplish up to 20 tests per hour. Compare that to original plan to bring a portable spectrometer with 20 kg tanks argon gas onto the bridge.
“We’ve got a portable spectro, but it’s like a little fridge on wheels. We’ve had it for ages, it’s very reliable. But today, we can be a lot more nimble, a lot more mobile, with confined spaces and constricted access,” says Roger Castanzi of Bureau Veritas. “I think that’s where the LIBS is easier to take on site. This is next level.”
In addition to a tight timeframe, tight spaces, and must-have repeatability, there was one more challenge to overcome. Working up on the bridge is an all-weather experience. In fact, it happened to be raining on one of the testing days, certainly suboptimal conditions for spark OES. “OES is not exactly waterproof, and with this light breeze, the wind would also blow out the UHP argon, and that would also cause additional problems,” Shaun said.
But the Z, with argon in the handle and a smaller sample window, performed beautifully. Inserting the nose of the analyzer between the rail ties to get the measurement on the exposed stringers, inspectors quickly tested each identified section of the rail bed to verify the material, collecting data that would allow them to later consult the proper welding technique for that particular metallurgy. All Weld Solutions and Sydney Trains had asked BV to analyze carbon composition in order to plan future infrastructure upgrades. As Constanzi summed up, “At the end of the day it’s about getting reproducible results, accurate results so they can go away and confidently write weld procedures for that material.”
Weather, time and tight space - all can be conquered with the handheld LIBS.
With the ease of point-and-shoot, the SciAps Z quantifies carbon, and other alloying elements, with enough precision to also report carbon equivalents.
The argon, sample prep, and calibration techniques are all familiar, just faster compared to OES. The Z-200 C+ can be used by more operators in the field, compared to the short supply of trained arc-spark OES operators.
In windy locations with spark OES, the wind blows away the argon purge, thus degrading the results. The combination of fast laser and reduced argon means wind is no problem for LIBS.
LIBS is a game-changer for places where you can’t lug around a 20kg can of argon, wheel something across scaffolding, or have to work without a power supply.
Lots of tests? No problem. Results can be stored in the machine, or shared with WiFi and Bluetooth on board. There’s also a place for test info, so you can keep track of test location, and the part and area that you’re testing.