Smudger Snippets
Created | Updated Dec 6, 2006
I suppose it's because I have so much time on my hands these days that all these memories come flooding back to me.
Interesting Programme
I recently saw a TV documentary about the sinking of the Titanic which researched all the different reasons why it sank. They covered all the ones that had been mentioned in the past, but they also did research on the actual rivets that held the outer plates together and this did, indeed, put the best suggestion forward that I have ever read about. It transpired that most of the riveting was done by machine, but the ones near the bow and just on the water line had to be done by hand as the machine was too bulky to get into position.
This meant that these rivets had to be struck by hand hammer and, in order for this to be done, they had to put more slag into the molten material that made the actual rivets. This slag was in all the rivets, but more had to added in order to hammer them down by hand as it made the metal more fluid and easier for them to shape.
This would have been perfectly feasible for normal sailing and would certainly have lasted for the life of the ship. It was not known at the time, however, that these rivets were weaker than all the rest and could not stand the same amount of pressure, especially that exherted when the ship struck the iceberg. The fact that these rivets were on and just below the water line sealed the fate of the ship as they burst open under the extreme pressure and allowed the sea water to rush in via the seam between them. Mind you, this was just yet another theory but, to my thinking, it was very good one.
What they actually did to test this theory was to have similar rivets made using the same ore as the originals, well as close as they could get using some of the material taken from the wreck of theTitanic some years earlier, and analysed it to gain its chemical composition. Then they constructed a section of the hull and put it under pressure until it burst. The result proved that the joint was a lot weaker that the rest of the hull was.
The reason this test interested me so much was the fact that I was a welder for some years prior to moving on to be a welding inspector and then an instructor later on in my career. During that time of some fourteen years that I spent in the oil construction industry, I saw some remarkable changes in both the raw materials that we used to weld as well as changes to the technique we used to weld them. One thing that never changed was the fact that we had to pre-heat all joints before we welded them. Although this was vital to the resulting strength of the weld, it made our job as welders a bit uncomfortable and awkward to say the least. The main reason we had to pre-heat the weld was, in fact, to slow down the cooling time in order to give all the hydrogen trapped within the weld time to escape. If this was allowed to remain within the welded joint it would build up unwanted stresses within the weld causing it to crack or burst when put under extreme pressure.
The temperature we pre heated to could rise up to 200°c, but the normal was around 160°c, so you can imagine the heat build this would cause when the weld area was enclosed by sheeting to protect it from the cold weather. In fact, part of the training for every trainee welder was to fully understand this, and we had to emphasise the importance of it as it was all too easy for them to push the heating pads away from the weld in order to gain better access to it, let alone obtain some relief from the intense heat they gave off.
Another process that we did on some welds after they were complete, was to stress relieve them. This process meant heating the weld up to around 600°c then cooling it down at a slow, controlled rate that had to be monitored very closely; this brought all the inherent stresses out from the weld. The joints that this was carried out on were the main load bearing ones; usually where a cluster of braces would join up in the structure. This area was called a node. The standard of welding on these nodes had to be of the very highest and had to pass very stringent non destructive testing (NDT).
Another area of change that I noticed during my time in the industry was the actual thickness of the steel which was used to construct these large jackets. In fact, as technology progressed, the thickness of the material we used was more than halved. This meant that, because more chemicals were used to increase the strength of the steel during manufacture, the welding procedures we used to weld them with became more difficult and the parameters became smaller. Then again, when you consider that the weld itself had to be a lot stronger and more ductile than the actual material being welded, it made sense that the welding process became more difficult.
For example a Charpy V notch test -a sample of material from or near the welded joint, cut to an exact size and frozen to a temperature of -20°c and then struck with a swinging hammer, which recorded the breaking point, to obtain its brittleness and ductile strength - was increased from -20°c to -50°c over the years, which of course made the actual welding a lot harder, so new procedures had to be drawn up and carried out to reach such high standards.
There were a lot of other parameters and tests which had to be modified over the years, but I will leave them for now as I do not want to bore you with the details. I just wanted to say that I thought the reason they put forward in the programme was, in fact, very feasible and I found it very interesting from a welding point of view.
