The de Havilland DH 106 Comet hit the headlines half a century ago for two notable reasons. Firstly, it was the world’s first commercial jetliner. Secondly, it provided a catastrophic example of the phenomenon known as fatigue failure, which caused three of these passenger jets to break up mid-air and crash within a single year. Only a decade earlier, the World War II Liberty ships, the first all-welded ships, had a similarly catastrophic failure, with brittle steel fractures causing a number of the ships to break in half without warning, causing the loss of 10 lives.
Fatigue is the weakening of a material caused by repeatedly applied loads. Depending on the cyclic nature of the stress, material can fail quickly or over prolonged periods. Since the aforementioned incidents there have been other examples of infamous fatigue failures, which have cost limitless amounts of personal injury, machine down time and of course, bad PR! So for welded-steel structures subject to dynamic loading, and the engineers who design them, fatigue life is a top priority. Traditional methods such as hammer peening and burr grinding are successful in extending fatigue life, but welding consultancy company Technoweld is introducing a vastly more effective and efficient technique, relatively unknown in Australia, called Ultrasonic Peening (UP).
UP is a mechanical method that can be applied to a weld to reduce tensile residuals tresses and locally modify the weld geometry to improve fatigue performance and prolong fatigue life. Furthermore, it can reshape the appearance of welding toe and intensify the strength by surface engineering.
Technoweld Director Graham Fry says “the technology is unique as it induces a compressive stress rather than a tensile (or tension) stress. For material to crack, it needs to be in tension, it needs to be pulling apart. UP puts in a compressive stress at the toe of the weld, right where you have the highest stress. If something is in compression it can’t crack because it’s actually pushing together. That’s the difference between this method and all the other fatigue improvement methods.”
UP was developed in 1972 by two Russian scientists to enhance the fatigue and corrosion attributes of ship and submarine structures. It is now utilised in defence, aerospace, mining, offshore drilling, shipbuilding, infrastructure, automotive, energy production, construction, and other industry sectors.
The ability and the speed in which it can be applied is more efficient than Tig Toe remelting, and rotary burr methods, it is much more controlled and much more effective to improve fatigue performance and can save downtime of plant equipment assets which are often millions of dollars a day.
In order to implement UP technology locally, Graham has spent five years extensively researching and testing the technology. His research has put him in contact with one of the original Russian developers, who he is still talking with today. He has undertaken training in the US and brought US and European experts to Australia to learn their techniques. Of the extensive technology trials he has undertaken he says “we’ve had a number of different cases where items were in a high fatiguing environment, they were lasting about 12 weeks. Through this treatment we pushed it out to 24 weeks, then out to 36. We’ve got proven examples, not just theory, that this technology works.”
While there are limited suppliers of UP technology in Australia, Technoweld has a distinct competitive advantage, with their intimate knowledge of the technology placing them at the cutting edge. Learn more about how Technoweld implements Ultrasonic Peening here. As a training provider, their welders are trained to ensure they understand and can apply the welding methods to meet the stringent requirements of Australian standard AS 1554 part 5 – Welding of steel structures subject to high levels of fatigue loading. Graham is one of the few individuals that has achieved inspection qualifications by all the major welding institutes around the world.
“We can offer the whole solution. Offering the treatment itself is only one part of it. You have to provide the best possible starting point, otherwise you won’t end up with the best possible finishing point. You have to control how the weld is done prior to treatment. UP can be applied to get double the performance improvement, but at Technoweld, we start at a point that is already four times the performance improvement prior to treatment by ensuring that the weld is done correctly. Then we can double that four times improvement to eight times improvement and that is our real value add,” he says.
“The technology is there to be exploited and take advantage off. Based on all the research, in service application and real life studies it’s a market that’s going to grow. The technology is there to support the defence industry with the upcoming shipbuilding programs, aerospace programs, and all supporting infrastructure such as the Techport upgrade. It is there to support industry as a whole.”