Sandvik’s bolts will keep Vasa’s hull stable for at least 150 years
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.
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. (Image, 788 kB)
- 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.
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. (Image, 554 kB)
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.
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. (Image, 539 kB)