The Weld.
Created | Updated Feb 14, 2008
I thought I would take this opportunity to write about something I spent fourteen years of life doing, welding. I once read somewhere that the definition of a weld was, a 100% defect joining two metals together, just how wrong could that be? Well, very wrong in fact as the total opposite is true. During my years in the oil construction industry I was a welder, then later a welding inspector, before teaching and becoming an instructor. The latter was in fact the most enjoyable for me, as it meant I could pass on the skills required as well as give the trainees a solid understanding of the more complex and theoretical side of welding, which may sound boring, but in fact it was one the more interesting side of it all for them. Many of my trainees were so impressed when I took them down to the met lab. (Mechanical Testing Centre) to show them the extent of the testing done on welds, even to the point of asking me if
they could make a return trip, as they were totally fascinated with it all. This trip down to the lab was always made towards the end of their intensive twelve week welding course. They would arrive at the training school with no welding experience what so ever, and we trained them up to ASME9 (American Standards in Mechanical Engineering) standard, where they had to pass the required welding test in order to be classed as coded welders. Once qualified they would be employed on the oil construction site where we built oil rig platforms and the modules that are placed of top of them. The art of welding during my years in the game as it were, progressed so much that it was hard to keep up with the progress and the technology of it all, a bit like me trying to keep with all this computer technology just now? I think that was what made it so interesting for me really. For example, when I first started in the industry it was common for the thickness of the main legs of an oil platform to be around four inches thick, which made the welding of a single “V” preparation very time consuming indeed, yet within a few years, this thickness and joint preparation would drop down to three quarters of an inch thick! With the new style "J" preparation. This was done by changing the complete formula in the forming of the steel, by adding more chemical compounds during the manufacturing of it at the smelter, which made it around ten times stronger and more ductile. Of course this also made a vast difference to the welding of it, as it made it ten times more complex to weld and the whole welding procedure had to be modified and tightened up.
The welding procedure itself is a complex thing, as it has to be carried out in such a way that the completed weld will be stronger, more ductile and even have better mechanical properties than the parent metal itself, (parent metal being the two pieces of metal being joined together forming the weld) The area of this parent metal which is effected by the heat of the welding process, is called the “heat affected zone” (HAZ) this is one of the most crucial areas of the weld, and its one of the main points where samples are cut from and tested in many ways. One of these tests was to freeze the small sample which had been from the weld in the HAZ area, then machined down to a regulation size, then frozen down to -40c, and then it is placed in a jig with the small V Notch which is cut in the centre of it, facing outwards, creating a weak spot. Then a pendulum type hammer is swung from a fixed arm right through it, breaking the sample, the amount of energy required to break this is recorded and it must fall within a preset scale. This test is called, the Charpy V Notch test, and is a uniformed test, known throughout the world When you consider that these tests used to carried out at -20c when I first started welding, gives you an idea of just how much the standards and chemistry make up of the steel had tightened up in that short time. There were many other similar mechanical tests carried out in the Lab, an "all weld tensile test" for example, which again is cut and machined a regulated shape and size, which has been removed from a section of the weld metal itself. This is machined to a pre-set size and placed in a vice type jig, where it stretched to breaking point; again the result of this must fall within a tight yield breaking point. The other type of tensile test, which is carried out in the same way, but is made up a “through sample” which has the weld metal in the centre and the end pieces are the parent metal from both sides of the weld. The result of this test is to prove that the “Weld Metal” is more ductile and stronger than the Parent Metal itself.
There are of course many other such mechanical tests carried out, but I just wanted to give you an idea of what is involved. Before any “Weld Procedure” mechanical tests are done, the weld (Which is going to be the actual weld procedure on completion of tests) has to pass stringent Non Destructive Testing (NDT) which include X-Ray and Ultrasonic Testing (similar to the tests carried out in hospitals on us humans?) and Magnetic Particle Inspection (MPI) This is a test where metal filings are excited by a magnetically charged force on a white painted background, this is a way of finding minute cracks on or near the welds surface. On the subject of cracks, which is the main concern during all welding, and the best way of preventing such cracking is by preheating-heating the parent metal prior to and during welding, this can be done by electric pads or gas flame, to a specified temperature which is decided by the carbon content of the parent metal and the combined thickness of it, and of course the ambient temperature at the time of welding. This actually slows down the cooling rate, which is very crucial, as this allows any hydrogen that may be trapped during welding, in the weld or parent metal, to escape. As it’s the force of the hydrogen escaping that causes the pressure, which would produce any cracking while the metal is being welded or while it is cooling down on completion. That is the main reason for using low hydrogen electrodes or any other welding consumable being used.
I have not covered the actual process of welding as I have only scratched the surface really. This could be done in another Snippet if required by anyone who may want to find out more about the subject.
I hope you found this little snippet on the art of welding of interest, as to be honest I quite enjoyed sitting here typing it, as it brought back so many memories of my days in the welding game, as we used to call it. We used to have a saying between us welders that went, “you are just like a Hollywood actor in this game”, as you are only as good as your last picture! (Your last picture, in this case, is the last X-Ray of your latest weld!
Smudger. 1/08
they could make a return trip, as they were totally fascinated with it all. This trip down to the lab was always made towards the end of their intensive twelve week welding course. They would arrive at the training school with no welding experience what so ever, and we trained them up to ASME9 (American Standards in Mechanical Engineering) standard, where they had to pass the required welding test in order to be classed as coded welders. Once qualified they would be employed on the oil construction site where we built oil rig platforms and the modules that are placed of top of them. The art of welding during my years in the game as it were, progressed so much that it was hard to keep up with the progress and the technology of it all, a bit like me trying to keep with all this computer technology just now? I think that was what made it so interesting for me really. For example, when I first started in the industry it was common for the thickness of the main legs of an oil platform to be around four inches thick, which made the welding of a single “V” preparation very time consuming indeed, yet within a few years, this thickness and joint preparation would drop down to three quarters of an inch thick! With the new style "J" preparation. This was done by changing the complete formula in the forming of the steel, by adding more chemical compounds during the manufacturing of it at the smelter, which made it around ten times stronger and more ductile. Of course this also made a vast difference to the welding of it, as it made it ten times more complex to weld and the whole welding procedure had to be modified and tightened up.
The welding procedure itself is a complex thing, as it has to be carried out in such a way that the completed weld will be stronger, more ductile and even have better mechanical properties than the parent metal itself, (parent metal being the two pieces of metal being joined together forming the weld) The area of this parent metal which is effected by the heat of the welding process, is called the “heat affected zone” (HAZ) this is one of the most crucial areas of the weld, and its one of the main points where samples are cut from and tested in many ways. One of these tests was to freeze the small sample which had been from the weld in the HAZ area, then machined down to a regulation size, then frozen down to -40c, and then it is placed in a jig with the small V Notch which is cut in the centre of it, facing outwards, creating a weak spot. Then a pendulum type hammer is swung from a fixed arm right through it, breaking the sample, the amount of energy required to break this is recorded and it must fall within a preset scale. This test is called, the Charpy V Notch test, and is a uniformed test, known throughout the world When you consider that these tests used to carried out at -20c when I first started welding, gives you an idea of just how much the standards and chemistry make up of the steel had tightened up in that short time. There were many other similar mechanical tests carried out in the Lab, an "all weld tensile test" for example, which again is cut and machined a regulated shape and size, which has been removed from a section of the weld metal itself. This is machined to a pre-set size and placed in a vice type jig, where it stretched to breaking point; again the result of this must fall within a tight yield breaking point. The other type of tensile test, which is carried out in the same way, but is made up a “through sample” which has the weld metal in the centre and the end pieces are the parent metal from both sides of the weld. The result of this test is to prove that the “Weld Metal” is more ductile and stronger than the Parent Metal itself.
There are of course many other such mechanical tests carried out, but I just wanted to give you an idea of what is involved. Before any “Weld Procedure” mechanical tests are done, the weld (Which is going to be the actual weld procedure on completion of tests) has to pass stringent Non Destructive Testing (NDT) which include X-Ray and Ultrasonic Testing (similar to the tests carried out in hospitals on us humans?) and Magnetic Particle Inspection (MPI) This is a test where metal filings are excited by a magnetically charged force on a white painted background, this is a way of finding minute cracks on or near the welds surface. On the subject of cracks, which is the main concern during all welding, and the best way of preventing such cracking is by preheating-heating the parent metal prior to and during welding, this can be done by electric pads or gas flame, to a specified temperature which is decided by the carbon content of the parent metal and the combined thickness of it, and of course the ambient temperature at the time of welding. This actually slows down the cooling rate, which is very crucial, as this allows any hydrogen that may be trapped during welding, in the weld or parent metal, to escape. As it’s the force of the hydrogen escaping that causes the pressure, which would produce any cracking while the metal is being welded or while it is cooling down on completion. That is the main reason for using low hydrogen electrodes or any other welding consumable being used.
I have not covered the actual process of welding as I have only scratched the surface really. This could be done in another Snippet if required by anyone who may want to find out more about the subject.
I hope you found this little snippet on the art of welding of interest, as to be honest I quite enjoyed sitting here typing it, as it brought back so many memories of my days in the welding game, as we used to call it. We used to have a saying between us welders that went, “you are just like a Hollywood actor in this game”, as you are only as good as your last picture! (Your last picture, in this case, is the last X-Ray of your latest weld!
Smudger. 1/08
