Story by Jaap Weber
Repair parts of ship engines
At our company we repair parts of (large) ship engines. These can be pistons that need to be cladded or valves where a new layer needs to be added, but also covers of cylinders that are torn or otherwise have problems. We have been doing this for years and have built up a certain expertise in this area.
Standard working method
Because we are never entirely sure of the composition of the material to be welded, usually a C45, we always assume it is the most difficult to weld material. In these cases, we know exactly how to pre-treat the seams. We preheat to 250 degrees Celsius, know exactly how to cool such a workpiece and at which temperature it should be annealed. And that always works well. Almost always.
Sometimes it has to be different
A cylinder cover of a very large ship’s engine comes in. This engine produces 100,000 hp. For comparison, an average Ferrari engine delivers about 215 HP. The cover has a diameter of 1800 mm and a weight of 7000 kg. There are some cracks and a hole in the cover. We tackle this cover as we always do. Seam preparation, preheating, welding and cooling. The work seems to be going well. When we see the cover the next morning, we are shocked to learn that all the welds and the welded piece are completely torn out. And there are even more cracks than before. Now what?
Two solutions are possible. Either we supply the customer with a new cover, but that will cost us more than € 50,000. Or we will try to weld the cover again. After intensive internal deliberation, we decide on the latter option. But because it is now clear that we are dealing here with a very special material, we call in the help of an external company that performs an analysis of the material. It turns out to be a material with a carbon equivalent of 0.6, while the carbon equivalent for C45 is 0.7. It also contains 1% Cr and a few other alloying elements that don’t really make a welder happy.
We pre-treated the cracks and the hole in the same way as we always do and preheated the cover all night in an oven at 300 degrees Celsius. All night, because we wanted to be sure that the whole cover was 300 degrees Celsius. We have prepared a turntable so that the cover can be put on it the next morning. We will weld with three welders who will take turns, because we want to be welding continuously. Taking turns is also necessary because a welder does not last long at a cover of 300 degrees Celsius. The welding work lasts from 10.00 to 15.00 hours. Then the cover goes back into the oven to anneal. The complete finishing, turning, milling and so on, takes another two days. The non-destructive test that is then performed shows that everything is 100% as it should be.
This story clearly shows that it is unwise to assume that you know what material you are working on. Of course an analysis of the material costs money, but at the same time it will save you a lot of money and risk. Especially with complex projects.
Guest author Jaap Weber
Jaap has been working in the overhaul of ship engines for more than 40 years. Welding technology is a crucial component in this sector, especially cladding and repair welding. The diversity of problems and thus welding challenges keep it exciting and instructive to this day. Learning by doing and wanting to understand what you do could be Jaap’s motto. That is also the way in which he now coaches young welders.