Master Project Presentation: Copper Backing Shoes

Master Project Presentation: Copper Backing Shoes

Good morning everyone. I am Clandia. Today I am going to talk about my
master project which is the damage of copper backing shoes during root pass in GMAW. And i also bring one of my test specimen today so if you want to pass around to see Notice the pits along the weld So the aim of today presentation is to
identified what factors cause the damage of copper backing shoes and we will be going through the background, what is ILUC, copper backing shoes, copper inclusion and moving on to the method, on
material preparation, welding and examination after that, we will be
discussing the key results and summary So ILUC is used in offshore pipeline welding. It is used for the root pass to avoid misalignment, it is usually made up with copper or ceramic shoes as you can see from the picture here and i’m going to show you a video
on the operation of ILUC to give you better understanding Copper back up clamp have two major functions. Lining up the pipe end, and providing copper back up for the external root pass There are 4 steps for the operation of the clamp First, is to align the copper shoes with the bevel edges, Second, is the aligning of the pipe ends The third steps is to clamp up the pipes and making the weld Four is moving the clamp from pipe joint to pipe joint. Ok, so the problem with copper backing shoes is that it gets damage after a degree of usage and the damaged copper shoes have to replace according to DNV rules However, there is no a clear statement saying that hoe much damage is acceptable or not Therefore, it made a good research study for it. Here is some pictures on the damaged copper backing shoes another problem is copper inclusion. Which is common defect listed in DNV rules it is probably associated with copper contamination cracking Some research had been done on CCC in the late 1970s and early 1980s But it is not for copper inclusion CCC and copper inclusion are two different things There are 4 conditions that made CCC happen So the first is tensile stress plastic deformation and a solubility gradient Melting point gradient and no intermetallic compound between the liquid and solid metal And in this case, the copper backing shoes made fully contact with the steel, which made a strong foundation on these two and my
project will focus on the copper oxide which is the intermetallic compound part Moving on to the method, first we have to prepare a number of 1m long steel stripe With V-45 beveling Also 1m long copper block and machine it to create different level of gaps As you can see from the picture here Then the steel will sit on top of the copper and start welding. At the same time, the temperature will be monitor by 4 thermocouples placed inside the copper block Here is the picture on the set up for the experiment the sheilding gas that use for welding is a mixture of Argon, CO2 and Oxygen. And the electrode that use is E70S6 copper coated steel wire Its the same as what they use offshore 4 welds had been conducted so far moving onto the methods straight after the welding, pictures has been taken on oxide formation on the copper surface and then the copper block will examine under the microscope And record the number of pits and the surface area of the damage so the first key result is the oxide formation actually become less as increase number of weld and i’m going to show you an
animation on the picture i taken in a reasonable speed. But you have to pay attention on it okay? First, second, third, forth weld, okay? is everyone got it? That the oxide became less. Do you want me to replay it? i move on to the key result 2 the number of pits and the area of damage is actually usually increase as increase number of weld However, there is some case that the number of pits is decrease but the total damage is increased because the pit’s size is increased But there is one exception. Which is part 10 it is either an error or it is just because it is a rougher surface Key result 3, it is actually, hardly see any relationship between the gaps and the damage However, after the weld, it seen like for 0.4mm to 1mm gaps, it has an average of 75 number of pits and in term of total damage area, 0.2mm gaps has the highest damage And for the last and very important key result is the molten bits started to form after the forth weld. it is actually quite obvious, and they are always much smaller and within the previous mentioned oxide pits You see in the picture And to summarize, on repeating weld, it give increase number of pits and area of damage increase and less oxide layer formed The heat that suppose to generate the oxide is used being use to form the molten bits after the forth weld So it ended up easier to get copper inclusion So in the coming weeks before the submission of the report I need to convert the unit of px to mm Because it then make more sense and then, i also need to input the weld number 4 result in more effective way Because the damage of the copper shoes is much larger than expected it is hard to record the result under the same microscope the mass of oxide and the depth of damage was planned part of the project However, because the limitation of the equipment, it is now not included So further improvement is needed if these two are important and then future research
will moving towards relating copper inclusion and CCC and to find out whether a solution for CCC is a solution for Copper inclusion and it will be also interesting to know what happen increase number of weld to more than 4 or to do a full scale model as offshore pipeline which means thicker plate and circular joint And also interesting to know, to do a non-destructive test on the steel plate. it will be another great project. Thank you for listening, any question? Q1: The copper, is the copper coming from the backing plate or is it coming from the shielding weld rod? You said the welding rod has copper on them A1: Yep, but we only examine the damage on the copper shoes. So there is no anything to do with the electrode Q2: so you are looking at specifically the damage on the material holding the two bits in place? A2: Yep yep. Q3: You talked about varying some parameters, by varying parameter you get more molten bits on surface and then you seen to jump saying that the more molten bits, the more copper inclusion that you will get do you have any prove that is the case? It is more likely to get (copper inclusion), because the molten bits is formed. if there is no molten bits, it will not get (into steel), because it will all solid, and not cause CCC. its what i think. Q4: How is (dust inclusion) different from copper inclusion? You mean inclusion and copper inclusion? yeah different between slag inclusion and copper inclusion. A4: Copper inclusion will specifically for copper, that coming from either the electrode or the backing shoes But for slag inclusion, that will just be a spatter get into the weld There is one question and one comment, Clandia. First the question is, Are you sure that the steel wasn’t going when you do the weld? Q5: Are you sure it wasn’t changing shape when you do the weld? Oh yes! yes, i can show you. So this is the experiment setting. So they (the welder) placed a heavy block that sit on top of it (the steel). so it will always be flat when doing the welding So it started here and then stopped, and then continue and removing this. Do they attached it? And they also attached it before the weld. Just the comment. which is you have a little bit of confusion to the audience because you have a very wide scope which is content. and i just advised you to stick with what happening on the copper And although, you can make comment on your discussion. About how that might led to copper inclusion and copper cracking try to kind of keep that as content rather than your investigation your investigation is going to tell you what damage is Thank you.

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