In Arlington, just outside Washington DC, the new and impressive monument comprises 3 stainless steel spires of a little over 80 metres in height. The monument honours all the men and women who have served in the United States Air Force. In its depiction of a flying manoeuvre for which the Thunderbird bomber has become famous, the monument symbolises precision. It also stands for the Air Force’s three core values of integrity, service and excellence.
The task of building the monument went to a Canadian company, Mariani Metal Fabricators. The challenges it faced were enormous. The spires in the 365 tonne monument are not only of unequal lengths, they are also triangular with a curve that results in the monument changing its appearance as the viewer switches viewing position.
James Ingo Freed, the world-renowned architect, designed the monument and imposed extreme demands as regards the surface finish. The three spires had to appear seamless and recall the “skin” of an aeroplane. They also had to be free of marks or defects and not give off any reflections that might dazzle pilots when flying over the monument in daylight. To avoid contamination of the surface, no carbon steel tools were allowed to come into contact with the monument while it was being built. Weld joints had to be straight and all exactly the same.
Specially ordered flux cored wire
Outokumpu’s plant in New Castle, Indiana, supplied the stainless steel – 316L with extra low sulphur content. The molybdenum alloyed stainless steel in the monument, which stands just 30 kilometres from the Atlantic, is expected to resist corrosion for an estimated one hundred years. Avesta Welding’s part in the project was to supply Mariani Metal Fabricators with filler metals for the welding and chemicals for pickling, passivation and cleaning.
“In all, assembling and erecting this stately monument took 3.6 tonnes of 1.6 mm, 316L FCW. As with the plate, the sulphur content of the wire was strictly controlled,” relates Ron Stahura, Technical/Sales representative at Avesta Welding in the USA.
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To solve problems arising during construction, Avesta Welding’s highly experienced welding instructors contributed good advice. Håkan Jansson, a welding instructor with 35 years of experience, was informed that welding with the specially ordered FCW was proving difficult. Thus, along with Ron Stahura and Tom Bush, sales manager at Avesta Welding in the USA, he went to Mariani Metal Fabricators’ plant in Toronto, Canada, to help their welders overcome the problem.
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Håkan Jansson, Tom Bush and Ron Stahura in front of one of the huge jigs that were devised for each of the three spires
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“When we arrived, they were welding the thick, triangular base plate and, on radiographic testing, had discovered slag inclusions. However, this wasn’t due to the consumables. The welders weren’t used to this type of welding where you have to get down into a deep joint. I showed them the trick of extending the tip so that you get deeper into the joint without the wire stick-out being so long. After grinding, I showed them how to angle the torch. We managed to sort out the repairs and they could then continue with their procedures.”
Surface treatment important
During Håkan Jansson’s visit to Canada, Mariani Metal Fabricators had suspended a spire segment from a crane and filmed it for 24 hours, from sunrise one day to sunrise the next. This was so that the architect could see what the surface looked like in different lights and decide which surface finish to use.
So that the architect could see how the light played on the spires and then choose the right surface finish, a segment was suspended from a crane and filmed for 24 hours.
“We reacted to them first pickling and then glass blasting the surface. I said that at Avesta Welding, where we’ve been working with stainless steel for 80 years, we do it exactly the other way around – first blast with olivine sand and then pickle. Otherwise, there’s the risk that any contaminants in the blasting sand will cause surface corrosion. That’s very expensive to correct. I referred them to our pickling manual, which I had with me, and I think that convinced them,” he explains.
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Pickling and passivation comprised first treating the stainless steel surface with 410 Rust Remover before pickling with RedOne 240 spray gel and finally rinsing with de-ionised water.
Avesta Finishing Chemicals' products for pickling, passivation and cleaning were used to give the spires the perfect surface finish. |
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Simple solutions that save time
In the summer of 2006, the monument was put together where it now stands, on a ridge near Arlington National Cemetery, overlooking the Pentagon and Washington DC. Håkan Jansson received yet another “emergency call” and travelled to the well-guarded area to give the benefit of his experience.
“This time there were pores in the welds. This wasn’t because the weather was windy. They had enclosed and sheltered the welding site properly,” he states. “We discovered that their gas hoses were too long. They let in air and created overpressure. Thus, I suggested that they should lift an ordinary gas bottle up onto the platform and have a two or three metre hose to the welding machine. This simple trick worked.”
The welders also had a bit of a problem welding the corners of the spires. “The welds had to be ground. To do this, the welders sat inside and used a rotating file, roughly like a dentist’s drill. I suggested that, instead, they should bend a copper pipe to shield the gas and then TIG weld the tip. This would mean no grinding. ‘Heavens above,” they said, “so simple and such a time saver!’”
Håkan Jansson has not seen the completed monument but, judging from the pictures and what he saw during construction, he feels it must be very impressive.
“It was truly a major project. An incredible construction with huge ‘canyons’ that had to be welded. It’s great that Avesta Welding was involved and that we were able to provide a little good advice,” concludes Håkan Jansson humbly.
Footnote:
Håkan Jansson also reveals that the first time Mariani Metal Fabricators’ welders examined the monument radiographically while it was being erected, two military jeeps and a police car pulled up. The radiation had been measured inside the Pentagon! After that, the welders had to give prior warning of when they would be switching the x-ray equipment on and off.