Check out our process on how we pre–form a carbon steel Tig pipe weld to meet piping code tested with an x-ray machine that can see any flaw inside, outside, and anywhere in between (literally)
First off I want to state that there are many different ways and techniques that can and may apply in this process and it all depends on personnel preference. In other words, you or someone may do it differently or disagree and that is fine, but this is how we and others in our company have done it successfully for 20+ years and counting. Also I am / this is a welder writing this not a professional writer, so bear with me. I would rather it come straight from the source and be realistic. Now let’s get started!
In this case we are going to be using a factory beveled piece of pipe and a factory beveled 90 degree fitting. Both of these come standard with a flat spot on the bevel, which we like to call a landing that is used to face the fitting AKA make it true and square by the factory / manufacturer. They also both come painted or coated to keep from rusting.
Step one – Preperation:
If there is one thing I can’t stress enough it is PREPERATION IS KEY. Here we will show you how we prepare our parts to weld. When prepping for a Tig weld we take a flapper wheel/sanding pad on our angle grinder and sand down the landing (the flat surface on the bevel) until it has a nice even sharp bevel all the way around which helps break down that edge and allows the weld to consume and help break down the metal on each side (we will address this process further in step ) We then take a flapper wheel on our end grinder and remove all of the paint / coating one – two inches back from the bevel inside and outside. This helps prevent porosity / contamination of the weld. We will do this to both the pipe and fitting.
Step two – Fitment:
Next is fitment, you want to make sure you get the two bevels aligned as close as possible. Use a nice straight piece of angle-iron to help properly align faster and easier. Chain clamp it to the piece of pipe while leaving a few inches over hanging. We then take a 5/32” Tig rod, bend it in half and cut it to proper length depending on size of pipe and use it as a spacer. In this case we are using a 1/8” ER70S-6 Filler rod to put the root in so therefore the 5/32” spacer gives enough space to maneuver your filler rod while making your root pass. (first pass) Double check and make sure that both sides, top and bottom of the fitting / pipe are all flush with each other (inside the pipe as well)
Step three – Root Pass:
Tacking and preparing for root pass. When making your first tack on the top of the pipe with the 90 degree fitting facing up, put a tack about ¾” long (more info in step 4) This allows enough give to still square up or level the 90. Next remove your 5/32” spacer and the piece of angle iron and tack the bottom side once you have it level/square. Now that you have tacked top and bottom, look at the gap on each side of the fitting and use either your 1/8” or 5/32” to judge and determine whether one side it tighter than the other. If so, slightly tap it over with a small hammer. Once you have an even gap on each, put a ¾” tack on each side. Keep in mind and take into consideration, after you tack one side that tack is contracting as it cools down so the faster you get the other side tacked the better. Now that you have four tacks all the way around, take your angle grinder with a 1/8” thick grinding disk and slightly tapper each end of all the tacks to insure you have good clean tie in points.
Step four – Filler Rod:
Root pass (the most important) if this one is no good then there is no point in continuing to the next pass until properly addressed (unless your just practicing). When you are putting in the root pass (also when tacking) we like to back feed the rod. Which means we place the filler rod on the back side of the bevel while welding. Now when you go to take off or start up again, start towards the middle of the tack or around 3/8” away from the end. Once you start walking the cup towards the end it will start to break down the edge of the tack (where you ground to a tapper) that Is when you will start to apply the filler rod. The main thing you are looking for is as you go you are catching / melting both sides of each bevel, breaking it down and consuming it in your puddle. Now when you start coming up to your tack about to tie in and you can no longer have your filler rod on the back side, slow down a little bit and just dab your filler rod into your puddle while making sure you are walking back and forth to each side breaking down that edge to the bevel. After making your root pass inspect it for any flaws. If you see something you want to fix do it now before filling it up.
Step five – Hot Pass:
Hot pass, this is where your going to crank up the machine and run good and hot. The point of this is to try and melt / consume any parts of the root pass that have not been fully melted, broke down, and fused together, and also has the potential to burn out any porosity the was not seen when putting in the root. Keep in mind, you are still adding a nice even amount of filler rod, your just not trying to fill the whole thing up. You’re basically putting in just enough to keep from blowing a hole through your root (yes it happens). I am still using a 1/8” filler rod for this pass as well.
Step six – Filler Pass:
Filler pass, now that you have a good amount of weld in there you don’t have to worry about blowing a hole you can take a little more time going a little slower and adding more filler to it. Some people like to “flush it out” in one pass (stack enough weld in the bevel to bring it flush to the surface of the pipe and ready to cap). Some people also like to do two passes that are faster speed and less filler material going in at once. Whichever route your choose, what you want to be watching for is that as you are bringing it flush to the surface of the pipe you are stacking an even amount all the way around and that you are just barley going to the edge of the bevel. If you are going above and beyond the edges of the bevel, all you are doing is giving yourself a wider cap and more weld then necessary.
Step seven – The Cap:
The cap, this is the one everyone sees and the one the Certified Weld Inspector (C.W.I.) looks at so make it count! The key things to look for when making your cap, make sure as you are walking the cup side to side you are fully covering your previous pass and tying into each side of the pipe, make sure you are laying an even amount of filler rod to make your cap even and smooth, and when you make it to your tie in point and are about to stop, slowly bring your tungsten / electrode further away from the pipe by rolling your wrist / tig torch backwards and breaking the arch either in the middle of your weld (unless you’re using a foot pedal and can slowly start dropping down the temperature). This helps prevent leaving a small pin hole that comes from a fast pull out while having a complete puddle (as you get the tungsten further away while still walking the cup you can watch your puddle get smaller and smaller).
Step 8 – Finish & Inspect:
Finish & inspect, if there is a little flaw from pulling out you can take a file and lightly blend it as long as it doesn’t go deep into the weld and is just on the surface. Be sure to look over each edge of the weld looking for any undercut or showing bevel. If you do happen to find some you can slightly file it out or run back over it with some more filler material. Depending on specs you can either wire brush is once you are all finished or leave it.
Side Notes and additional info– We believe that “walking the cup” technique is the most effective and efficient way to make these welds. That does not mean you have to do it this way. There are multiple techniques and ways to tig weld this is just the way we prefer. We like to wire brush after each and every pass to keep it as clean as possible. If you are performing these welds out side make sure to have a wind block, tent, or some sort of protection from the wind otherwise you can potentially get some porosity in your weld and if your not familiar with it you probably wont even see the porosity happen. This applies to people making these welds in shops as well if the doors are open allowing gusts of wind coming through or big fans causing a breeze. Another thing to do is cover the one end of the pipe (or both considering all circumstances). Depending on the pipe size you can tape it, put a cap over it, or for bigger pipe put a tarp over it and tape around it. When a gust of wind comes through it takes away your Argon that’s flowing through your tig torch (kind of like using a lighter in the wind) you need that gas to perform a clean weld. We have welded pipe as small as 1/2” and up to 66” in diameter, a variety of different thicknesses from 3/32” thick up to 1-1/2” in thickness. All of these are what play a role to determine how many amps or volts you should be running. That could be a whole other post itself, everyone is different on how fast they move, how much they stack in there, what size of rod they prefer, and what kind of a gap they have. Each machine runs a little hotter or colder than others. The main thing is finding that right temperature for you and getting comfortable with it. If your told cold your going to fight melting the filler rod and you’ll leave chunks of “cold rod” in your root (pieces of filler rod that did not completely melt). If you are too hot then you’ll struggle with your root pass falling out, drooping down, and eating away to much of the bevel making it wider then it needs to be.
I hope this helps some of you guys and girls out there, if you have any questions, concerns, or something you would like us to cover feel free to email us anytime. We are going to continue to keep doing our best to provide you with useful information and tips in the welding and fabrication industry. Because there is so much that actually goes into making these welds and it might be slightly difficult to take it all in by reading this, we will be making a video with all the information and detail in the near future. Thank you guys for reading and look forward to hearing from you and sharing more information with you all!