Plasma Arc Gouging of 304 SS

Date 10-07-2015 18:21

Hello Mark, it is readily done. Now, for the bigger question, where, how, and in what sort of environment are you proposing to do this? There will be a lot of residual slag, sparks, smoke, etc. involved in this process. If you are gouging in a tight or enclosed area you will have to contend with all of the spatter, sparks, and other physical items that will want to stick to or somewhat embed onto the surface of the adjacent stainless steel. This could require special shielding requirements to prevent, or special cleaning of a mechanical type to resolve, does that fit into the plan for this work? Aside from the items that I have already mentioned, you will need to grind or otherwise prepare all of the gouged areas to be free of the oxidation that is produced by the gouging process, think in terms of time for all of this versus other possible options. Please continue to share your progress and decisions on this, I am sure others will be wondering too. Good luck and best regards, Allan

By marktski (**)

Date 10-07-2015 18:35

To answer your questions, small job shop, pressure vessel 7-8 feet dia.

I watched in curiousity as he experimented, he is using shop air as a gas,
60-80 amps, the SS is 0.5 inches thick and he will be back welding a 1 inch
full coupling into a head and back gouging.

My first impression is it is very messy, leaves a poor finish and will need a lot
of grinding.

Do many people choose this route rather than a GTAW root pass? This choice
was driven by time I'm told.

By aevald

Date 10-07-2015 19:20

Mark, simple answer is exactly that, time, and time is money. Is it easier and less costly to perform all of the grinding/cleaning after the fact, or is it easier to employ just a bit more time and utilize a copper backing shoe, some form of backing-gas segmented chamber, solar flux? That's the question. Hopefully others with direct experience might be able to provide some specific tips. Good luck and regards, Allan

By welderbrent (*****)

Date 10-07-2015 22:44

Hello Mark,

Let's make sure I am seeing this correctly:

A SS pressure vessel with 1/2" thickness in the area where a 1" coupler (1 3/8" ID, the dimension of the OD of 1" pipe, X about 2" OD so about 6-7" in circumference) is to be CJP welded. Weld one side then back gouge with PAC at 60-80 amps and shop air.

The amps are plenty high, may be a little cleaner to go about 50 amps. If your material were thicker you could go up since you are gouging and not cutting but then again, it is SS. Keep your air pressure down, too high makes a much larger mess and doesn't help. 60-80 should be plenty, 80-100 may push the limit but it is SS. For your purpose, I am wondering if a different gas would help instead of using the shop air. Make sure your air supply has a good filter for moisture, oils, and other contaminants. Use somewhere around a .078 gouging tip. Don't want too fine of a plasma stream.

Personal opinion, use the GTAW root with a well prepped joint so you can finish it out with what ever you want and only moderate clean up with a die grinder to make sure you are at sound metal from both sides. PAC is going to be a pain to clean before continuing the welding procedure.

Just my two tin pennies worth.

He Is In Control, Have a Great Day, Brent

By marktski (**)

Date 10-08-2015 12:06

I suggested the GTAW route and was told that only one person in the shop is certified and he is too slow.
That's a problem that should be fixed in my mind.
I suggested using a different gas yesterday, the were looking into as I left last night, we'll see what happens.
The GTAW time vs the PAC cleanup time should be looked at, I still think GTAW is the trick.

By fschweighardt (***)

Date 10-08-2015 22:18

H35 and N2 leave a pretty good groove, but you gotta pay attention to where the slag lands. If Jim Colt happens by, he will know WAY more about it. Of course you have to have a machine that will accept the H35 (35%H2, 65%Ar)

By kcd616

Date 10-09-2015 11:45

Mark,
gtaw root pass
what is the process for the root pass now for this possible fubar in the making?
my thoughts tell me first thing is need copper backing and heat sink due to small size and heat input
will lead to distortion on the coupling
meaning cut it out and start again
talk about time wasted
but the one of the real problems is an engineer is thinking :eek:

tell us the process for the root pass and we move forward
sincerely,
Kent

By pipewelder_1999 (****)

Date 10-10-2015 13:31

My primary concern would be airborne Hex Chrome. The process will generate significant amounts . maybe enough to warrant protection for those in the shop besides the ones doing the gouging.

As already mentioned, an alternative such as GTAW on the root or a process/joint design that minimizes the amount of metal to be removed would be ideal.

Have agreat day.

Gerald Austin

By Lawrence (*****)

Date 10-10-2015 15:15

I'm a BIG FAN of Plasma arc gouging (when contrasted with Carbon Arc Gouging)

But if I'm reading between the lines correctly there are two issues being put forward and a couple of questions that need to be answered.

1. Management is cheap and does not understand time/work/process control

2. Welder talent is limited for the scope of work being described (currently)
.
.

Questions:

1. What kind of production volume does this project represent?

2. What are future projections for similar work?

CJP welding on stainless pressure vessels or tanks is rarely done with backgouge in a manufacturing setting these days. Argon/Copper backers and advanced processes such as RMD, STT and Cold Metal Transfer can be purchased at relatively low cost and have been proven to consistently provide the following in similar situations.

1. CJP root passes with or without inert backing that pass the highest evaluation criteria.

2. Production rates exceeding 5X of what the best GTAW operator can accomplish.

3. A process learning curve SIGNIFICANTLY less than GTAW for similar joints.

Yes Hexavalent Chrome is an issue... And in my opinion the gouging should be limited to REPAIR of defects, unless you are making only one or two tanks.

If you are going to be seeing consistent work of the sort you are dealing with now... Step into the 21st Century and start making money!

This is not a criticism... Its an opportunity to do more work with less effort at a lower cost, even with the capital investment required to move forward.