The research and development cooperation between the museum and Sandvik, which it is estimated will take over 5 years to complete, will see the replacement of the majority of iron bolts, installed in the 1960’s, with unique bolts in highly advanced stainless steels from Sandvik, suited for the most demanding environments. The existing iron bolts were installed for their strength and durability, but have since been discovered to be reacting with the atmosphere and consequently causing chemical erosion, which is damaging the historic woodwork of Vasa.

Test different materials

Initial discussions between the Vasa Museum and Sandvik took place two years ago, leading to further investigations into the existing iron bolts and potential replacement materials.

The Vasa Museum was keen to test different materials on a sample of 200 bolts exchanged in order to test viability and suitability. The final choice came down to a decision between carbon fibre and high-alloyed stainless steels from Sandvik.

- We decided to go with the high-alloyed stainless steels from Sandvik because they proved to be the most suitable and versatile, and from our point of view the easiest to work with, explains Magnus Olofsson, Head of Vasa Unit.
- The carbon fibre option took longer to exchange the bolts, whereas there was a very good exchange using the Sandvik material

Analysis after 1,000 bolts

Sandvik and the Vasa Museum agreed that the first 1,000 bolts should be installed followed by a period of monitoring crucial factors including, the bolt itself, the wood around the bolt and the movement of the bolt in its position.

The results of this analysis can then be used to determine the ongoing progress of the project and if any adjustments are required.

- Having the opportunity to test our material in a meticulously controlled environment, as the one Vasa offers, is very important for us; the time frame for the project gives us a unique opportunity to follow the material in a way that would otherwise be nearly impossible to mimic, says Olle Wijk, R&D Director for Sandvik Materials Technology.

Complex procedure

The replacement of the bolts is a complex procedure because the Vasa Museum has to remain open and active at all times, to continue to bring in visitors who provide crucial revenue, so important in the continued preservation of the vessel.

During the process it is vital not to cause any undue movement in the ship that could compromise its structure. This makes bolt replacement a slow process.

- The replacement process time varies, explains Anders Ahlgren, Engineer and Project Coordinator, from the Vasa Museum.
- Many of the holes are at difficult angles. In some cases the wood around the bolt is damaged so this has to be cleaned and repaired before the bolt can be fitted.

Dr Marika Hedin, Vasa Museum Director, explains:
- Working in conjunction with Sandvik we aim to preserve Vasa for another 1,000 years, which should be completely feasible taking into account the preservation carried out on the timber structure of Norwegian churches of a comparable age.