8 June 2016, 08:15
Half of the bolts installed in the historic Vasa ship during the 1960s have now been exchanged for specially designed, high-alloy bolts from Sandvik. Thanks to this, Vasa is now both lighter and more stable. The weight savings is a whole five tons — about the same as if a full-grown elephant had escaped from the ship.
Once the world’s most powerful warship, Vasa sank on her maiden voyage in 1628. When Vasa was raised from the ocean floor in 1961, the rivets that originally held the hull together had corroded away. Crews inserted new bolts where the old rivets had been, but now even these are corroding, causing serious problems.
“Replacing the bolts is essential to the ship’s future. Rust weakens the bolts and can cause chemical reactions in the ship’s timber hull,” says Lisa Månsson, Director of the Vasa Museum.
It’s been an extensive and tough job, but now the carpenters at Vasa Museum have exchanged half of the ship’s over 5,000 bolts.
“This is a particularly enjoyable and fruitful cooperation between a Swedish public museum and a worldwide high-tech engineering company that has enriched our respective businesses in many ways”
says Leif Grundberg, Senior Curator at the National Maritime Museums, the government body in which the Vasa Museum is included.
The cooperation between the Vasa Museum and Sandvik began in 2011, and together they developed the solution with specially designed, high-alloy bolts to replace the old, 1960s bolts, as well as tested them on the ship. During 2013, thorough evaluations measured movements and pressure and their effects on the ship. A full year of measurements showed that the new bolts exceeded expectations. Thanks to the bolts’ unique design and material, the ship is now more stable and five tons lighter — about the same as a full-grown elephant.
Symbolic elephant plaque
Today, as a sign of a successful collaboration, the Vasa Museum presented a symbolic elephant plaque to Petra Einarsson, President of Sandvik Materials Technology, the business area within Sandvik delivering the new bolt solution.
“We are delighted we’ve been able to lighten the load for Vasa. We’re also proud of our partnership with the Vasa Museum, and that we can contribute our materials expertise to help save one of our most important historical treasures,” says Einarsson.
The new bolts are made of Sandvik SAF 2707 HD™ and Sandvik SAF 2507®, also used in the most demanding environments in the oil and gas industry. The bolts are a combination of advanced, duplex stainless steel with dual properties: very high corrosion resistance and exceptional strength that can support the weight of Vasa’s 900-ton hull.
“The bolt construction also gives the advantage of being able to adjust the pressure with which each bolt is fastened in the hull, allowing for precise adjustments according to the ship's movements. Once all the bolts are changed, it will be at least 150 years before the next bolt replacement,” says Jan Haraldsson, director of development for products and processes in steel for machining at Sandvik.
Source: Sandvik