The physical laws for welding processes came to the test when the steel hull of a 100 metre long ship was to be straightened up.
Sometimes there is a difference as to what is described in the world of theory and as to what reality actually offers. The two worlds often agree, but not always. Testing the theory may be the only way to get a final answer.
Gunnar Sørensen with FORCE Technology faced such a challenge, when he was contacted by the Danish consultancy firm, ShipTech Marine Consultants, who were in the middle of restoring a 100 metres long double hulled steel ship. The outer steel plates had been replaced at the shipyard, but not without damage to the hull’s harmonious lines.
”As the plates were welded together, deformation occurred due to thermal impact on the steel plates. Contraction in the plates caused so much distortion of the upper deck that the cargo hatches could no longer be shut tight”, explains project manager Gunnar Sørensen from FORCE Technology.
Seeking Advice
The shipping owner had ShipTech on the sideline as advisor during the restoration, and naval engineer, Alex Hjortnæs wished to consult FORCE Technology on certain welding issues related to the correction of the distortion.
”To begin with we had decided to cut some very long slits into the double bottom and thus force the sides in correct position. We were seeking advice on the welding processes and we asked which deformation could be expected during the process, but instead FORCE Technology suggested another method that sounded simpler and much more cost-efficient”.
Extra seam
Based on practical weld tests through the 1960’s and again in the 1990’s FORCE Technology has developed theories and formulas to describe occurrence and extent of weld distortion in various materials. Additionally, FORCE Technology may also depend on gained experience from work with huge welded steel structures such as bridges.
”We suggested that ShipTech simply add an extra number of weld seams alongside the inner hull to provoke simultaneous contractions from the inner and outer hulls, which should be able to straighten up the ship”, explains Gunnar Sørensen.
Steering the right course
No sooner thought than done, even if specialists at the shipyard were somewhat sceptical about the idea.
”It is always a good thing to get an experienced specialist’s opinion. However in this case we were pretty sure we would succeed, and when the shipyard had welded the first seams, it was obvious that the method was water-tight. There is no doubt that this has saved us a lot of time and money” concludes Alex Hjortnæs from ShipTech.
