Sandvik’s bolts will keep Vasa’s hull stable for at least 150 years

Ship carpenter Åsa Egerquist uses a hammer during bolt work on the ship. Photo: Anneli Karlsson, Swedish National Maritime Museums.

The royal warship Vasa has so far had 1000 new bolts inserted in the hull. Careful measurement and evaluation has been ongoing for a year in order to measure movement, pressure and impact on the ship. The result is gratifying: movement is only very slight and a further 4000 bolts will now be replaced in Vasa.

Conservation technician and Ove Olsen ship carpenter Monika Ask working on a bolt replacement. Photo: Anneli Karlsson, Swedish National Maritime Museums. (Image, 788 kB)For a whole year, the replacement bolts were measured and logged around the clock with sophisticated instruments that measured to an accuracy of a hundredth of a millimeter. It has now been confirmed that the calculations and tests carried out beforehand and the methods used for the insertion of the bolts were correct.

- The evaluations show that we are on the right track and can continue to switch the bolts. Our fears that the hull would not hold together or that the bolts would compress the hull, can be dismissed. In collaboration with Sandvik, we have managed to cope with the delicate balancing act of finding the smallest possible pressure from the bolts so that they hold the hull together without damaging it, says Anders Ahlgren, engineer at the Vasa Museum.

Work with replacing bolts requires precision. Ship carpenter Åsa Egerquist makes accurate measurements. Photo: Anneli Karlsson, Swedish National Maritime Museums. (Image, 554 kB)In 2011 Sandvik and the Vasa Museum joined forces in what has proven to be a successful research project where expertise and experience has been exchanged. 5000 rusting, low alloy steel bolts from the 1960s are gradually being replaced in Vasa's hull with new, specially designed bolts in high alloy stainless steel.

The environment inside Vasa's old oak wood is chemically complex and Sandvik has delivered two of its strongest and most corrosion resistant alloys, Sandvik SAF 2507™ and Sandvik SAF 2707 HD™. The new bolts contain 27% chromium, 7% nickel, along with additional alloying elements and iron.

Ship carpenter Robert Jonsson working on the insertion of a new bolt. Photo: Anneli Karlsson, Swedish National Maritime Museums. (Image, 539 kB)All 5000 bolts are planned to be replaced by 2017 and the old bolts will be transported to Sandviken, where they will be melted down to become new alloy steel. The new bolts are expected to hold Vasa together for at least 150 years.

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Sandvik's Vasa site