Purge Welding

Introduction: Purge Welding

Purge Welding Stainless Steel

By. Dr. Hunter Riley

1. Measure, cut pipe

2. File pipe

3. Put purge plugs in pipe

4. Fill pipe with argon

5. Fit pipe together

6. Tack them together

7. Weld pipe

8. Look at your dime of a weld

Step 1: The Art

Today what I will be teaching is the art of purge welding
stainless steel. It’s a tough process that not many people can do. Purge welding prevents the roots pass from becoming “sugared” which basically means its contaminated, looks like crushed gravel and will not pass inspection. The argon cleans the weld and if done properly can have products such as dairy run over the top of it and not contaminate the batch. This process is one that they do in every factory that deals with products that are meant for consumption by anyone or anything.

Step 2: Items Needed

The things needed for a good purge weld is not that long of
a list. Items consist of: welder, saw, file, purge plugs, argon, and welding hood. These items will insure that the weld is clean, presentable, and will definitely pass the inspection.

Step 3: Before the Weld

Before
the welder make sure to have a proper cut in the pipe. Always read the parameters on a blueprint for the cut never try and guess on it. If the cut is bad it will cause a bad fit up which leads to a garbage weld that will not pass inspection. I personally follow the rule measure twice cut once which insures that there is a good cut and allows for a bomb weld.

Step 4: Good Fit Up

Next is also a very import detail to get a good fit up and
weld on the pipe and that is to file the pipe. There are little burrs that are left on the pipe from the saw cutting it that has to be filed off. If left on the pipe can contaminate the weld and the inspectors will make the welder cut out the weld and do it again which is no fun. Filing the pipe also makes the fit up nice because the little burrs and imperfections from the saw are ground off and makes the surface smooth and perfect very easy to fit up at that point.

Step 5: Purge Plugs

Purge plugs need to be put into the opposite side of the
pipe and taped off so they don’t fall out. The purge plugs are thick pieces of rubber with holes on them to allow a small amount of argon to bleed out so the pressure doesn’t build inside the pipe and cause the weld to blow out. In one of the holes there needs to be a small hose shoved into it that is hooked up to the argon tank so it can pump argon directly into the pipe. Argon is heavy so imagine that it is like water filling up the pipes so the hose pumping in the argon always goes to the bottom of the pipe unless the weld is on a flat pipe.

Step 6: Argon

The Argon now needs to be put on the correct flow to fill
the pipe. The pressure I like to use is two psi (pounds per square inch). Argon flows slowly so wait a second before welding the pipe generally waiting until air pressure comes out the open hole on the other side is a good rule of thumb. This is very important to get right because too much argon blows out the weld not enough argon causes sugaring in the weld which all results in a failed weld.

Step 7: Fit Up

Now that you have argon flowing through the pipes fit them
together. The fit up is the most important part even more important than the weld because if there is a bad fit up there will definitely be a bad weld. Making sure the pipe runs smoothly no high lows is crucial. Very simple just run your hands across where the pipes meet and make sure it is smooth no bump in it.

Step 8:

Tacking the pipe comes next which is an art in itself. After
the pipe is fit up perfectly tack the pipes together with small tacks that can be welded over. When running tacks never stay in one spot strike your arc and continue to move or else sugaring can be caused or the tack will be too big to run over the top of. Four to eight tacks are needed in the pipe anything two inches or under only needs four tacks anything over two needs eight tacks. The reason for so many tacks is the pipe will warp and bend if not tacked a bunch.

Step 9: Welding

The
fun part comes next which is put in a fire weld. The weld is very important choose either walking the cup or free handing it. Walking the cup is what is most commonly used in the field because it is easier, faster, and looks better. Walking the cup is just what it sounds like you have to put the ceramic cup of the tig torch on the metal and walk it, the best way to picture it is like walking a soda cup across a table. Sometimes if in tight corners or against the wall walking the cup cannot be done and free handing must be done which works and if done right can look just as good as walking the cup. To free hand all that’s is required is subtle back and forth motions without the tig torch touching the metal.

Step 10:

Finally
step back and look at that dime of a weld. Inspection of the weld is required because if flaws are found they need to be fixed or the weld could fail and cost the company a lot of money and time. It is the easiest part to do just look for pin holes lack of fusion or not enough penetration. After that the pipe can be hung and product can begin to flow through it.

Step 11:

If
all my steps are followed a great fully passable weld should be the result. All the steps are very important and need to be followed no exception or shortcuts or else a terrible failure of a weld will be the result. Purge welding is in a league of its over and can be messed up very easily so take the time to make sure all the steps are done properly and a great purge welder will be the outcome.

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    4 Discussions

    I've seen a few welding projects today - was this done for a class? This is a good write-up, regardless. Thank you for sharing what you know! :)

    1 reply

    So there is gas coming out all the time ? how do you turn the pipe with the gas feeds on??

    1 reply

    There is gas constantly flowing while you are welding the gas line is usually taped in so you can spin it and it will not come out