Welcome Weldinstructor!
As a retired Boilermaker/Tube Welder/Mechanic one of the first things I had to learn to do with GTA welding otherwise also known as TIG welding, was to practice how to strike an arc without using any Hi-frequency and without a foot pedal because just about every job I have been on, the machines and torches are set-up that way and only once in a while would a contractor have torches with start and amperage/current control either built in or adapted to work with these accessories...
So I would start out by teaching your students how to scratch start an TIG arc by first explaining how it works and then to demonstrate how to go about doing do with out contaminating the joint with W/
Tungsten inclusions (See below for a factoid on W/
Tungsten)... How you do this is really simple and it would be best to show you than to try and describe this technique to you in written form... Since they have some experience already in TIG welding from what you have taught them so far which means that you're training them how to start a weld differently from what they're already used to and you're not re-inventing the wheel so to speak... They shouldn't have a problem adapting to this method of starting a GT Arc to Weld...
I'll try to give you a simple enough description but a picture or video is worth a thousand or more words so, I'll begin with explaining that with the foot pedal method of starting a GT Arc to Weld, the power output from the power source/welding machine to the torch is off when the student doesn't have the foot pedal depressed... However, when using the scratch start method of starting an Arc to TIG weld or GTAW (Gas
Tungsten Arc Welding) the power output from the power source is always live if the power source/welding machine is turned on so, one must be much more careful of how to handle the torch around ant metal that's connected to where your work cable is attached to or or any metal the
tungsten electrode makes contact with that's also making contact with any metal the power source's work (Not ground!) clamp is attached to and this is really important to drill this into their heads to be aware of...
In fact, many torches in the field are now fitted with an on/off switch so that it's a lot safer to use a live torch in confined spaces however for the most part, pipe GTAW is done out in the field with "live" torches... Once they're extremely aware of this - you can then continue to begin to show them the very simple technique of scratch starting a TIG weld root on pipe...
To do this, place the filler wire that is usually 3/32" or 1/8" diameter into the pipe joint in between the members that has a 1/8 root opening and make sure the wire is making contact with both members of the joint, and then scratch the end of the wire towards the other end to a distance of about 1/16" or less and with a height between the
tungsten and the filler rod of about at lease 1/4 - 3/8" then once the arc is started and without hesitation move the torch towards the one of the 2 bevels inside the joint as closest to the land as possible and back to the beginning of the filler wire to start building up the molten metal and begin to fuse the beginning of the puddle on to the bottom of the bevel as close as possible by feeding the rod and then manipulating the torch in a circular motion and forming the puddle for the root of the the weld... Now remember that all of what I just described must be done within 2 to 3 seconds the most! So you want to make sure that you have set the power source output current to easily melt the filler and penetrate through the root opening in order to have adequate root of the weld reinforcement...
It's a whole lot easier to show somebody how to do this as opposed to attempting to describe it with words or just audio without any visual aid so pay attention to the video's especially where the welder is shown starting the arc and forming the puddle and you can do that by placing your cursor right where the bar below the video shows you how much time in the video has already been shown and repeatedly going back and forth with your mouse to see in slow motion so you can see how the arc, puddle and the weld is started in the root opening of the pipe joint... Never scratch start the arc on the base metal because you then contaminate the weld with
tungsten inclusion(s) which will show up on an X ray shot!
They'll need to practice the root pass a few times in order to sharpen their technique in how to deposit root passes that will have the necessary build up inside of the joint @ the root of the weld and once they get that down, you can go through the positions especially 5G, 2G, and 6G joints which will end up being the majority of configurations they'll be welding on in the field with 5G being the most likely out of those 3 positions and 6G to be used for testing and some 2G joints also... If they're in a shop, they will more than likely be welding a lot of the joints in the 1G position usually and a welding turntable/positioner but, Boilermaker/ Welders don't find themselves doing that kind of gravy work out in the field so don't spend too much time with that position and instead focus more on training the students to become proficient in welding in the 5 & 6G positions instead with 2G rounding out the course if they're able to become proficient enough with the first two positions...
You could teach them how to weld the root pass free-hand otherwise known as lay wire & the other key-holing/walk the cup method, and then once they become proficient with the root pass, and some Boilermakers are taught to use the filler and feed in through the pipe whereby they look into the pipe joint and monitor the root of the weld as it's forming inside the joint while walking the cup in order to maintain consistent weave pattern on the outside of the joint in between the bevels... Now this is a little tricky at first but, once they get the hang of it, their confidence in their welding skills will improve and sometimes dramatically...
You could teach them how to use the "walking the cup" technique for the hot and all of the other passes also because once they go out into the field, they will have to know how to do both and some contractors will not even give you a test if you don't know how to walk the cup... What you will be teaching them will be just enough for your students to be proficient enough to take a weld performance test however, there's sooooo much more to being a Boilermaker/ tube welder apprentice which is what they will more than likely start out as for their first few years... And during that time, they will be going through sooooo much more training in various subject related to being a Boilermaker/Tube Welder/Mechanic/Journeyman...
As a fully experienced Boilermaker/tube welder/ mechanic/journeyman, one must know how to perform all sorts of other tasks besides welding such as fitting, tube preparation, be proficient in interpreting engineering drawings, rigging, Quality control, NDT methods, inspection etc... And they must also put in the years (For me it was 5 years) in order ot gain the necessary experience to be relied upon with confidence that they can do the work to best quality required and with minimal supervision... So let them know right off the bat that you're only preparing to get them prepared to take a tube test and that they will have to go through much more training after they get into the union and the same will be true even if they do shipyard work or non-union work also...
So if I got you confused, I apologize and maybe these video's will make it up to you so have fun watching them okay? Good luck and all the best!
https://www.youtube.com/watch?v=0h5yw-qrl9chttps://www.youtube.com/watch?v=QYYkPELEBRU https://www.youtube.com/watch?v=UKaPIpxIneEhttps://www.youtube.com/watch?v=PPKstOZSZughttps://www.youtube.com/watch?v=rzrfrSMEOo4https://www.youtube.com/watch?v=dRoxXTlRa_IWell, that's about it for now... I hope this post and the video's can help you out training your students to learn how eo GTAW C/Stl. pipe in both 2" nominal and 6" OD.
Respectfully,
Henry
P.S., Here's the factoid below regarding
Tungsten or Wolfram and the history of those 2 names:
What's in a name? From the Swedish words tung sten, which mean "heavy stone."
Tungsten's chemical symbol comes from its eariler, Germanic name, Wolfram. The name Wolfram comes from the mineral wolframite, in which it was discovered. Wolframite means "the devourer of tin" since the mineral interferes with the smelting of tin.
Say what?
Tungsten is pronounced as TUNG-sten... History and Uses:
Tungsten was discovered by Juan José and Fausto Elhuyar, Spanish chemists and brothers, in 1783 in samples of the mineral wolframite ((Fe, Mn)WO4)... Today,
tungsten is primarily obtained from wolframite and scheelite (CaWO4) using the same basic method developed by José and Elhuyar...
Tungsten ores are crushed, cleaned and treated with alkalis to form
tungsten trioxide (WO3)...
Tungsten trioxide is then heated with carbon or hydrogen gas (H2), forming
tungsten metal and carbon dioxide (CO2) or
tungsten metal and water vapor (H2O)... Pure
tungsten is a light gray or whitish metal that is soft enough to be cut with a hacksaw and ductile enough to be drawn into wire or extruded into various shapes... If contaminated with other materials,
tungsten becomes brittle and difficult to work with.
Tungsten has the highest melting point of all metallic elements and is used to make filaments for incandescent light bulbs, fluorescent light bulbs and television tubes...
Tungsten expands at nearly the same rate as borosilicate glass and is used to make metal to glass seals...
Tungsten is also used as a target for X-ray production, as heating elements in electric furnaces and for parts of spacecraft and missiles which must withstand high temperatures...
Tungsten is alloyed with steel to form tough metals that are stable at high temperatures.
Tungsten-steel alloys are used to make such things as high speed cutting tools and rocket engine nozzles...
Tungsten carbide (WC) is an extremely hard
tungsten compound. It is used in the tips of drill bits, high speed cutting tools and in mining machinery...
Tungsten disulfide (WS2) is a dry lubricant that can be used to temperatures as high as 500°C...
Tungsten forms compounds with calcium and magnesium that have phosphorescent properties and are used in fluorescent light bulbs.
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