Welding Tips and Tricks

I am here to ask for advise because I know that I do not know. I was taught that if you do not know ask someone who knows more than you.

I was a frame maker/ restorer for some 30 years. I have always gotten my hands dirty. I have been designing a hermetically sealed box filled with argon gas for the storage and display of art and artifacts for the past 5 years. This box (enclosure) is similar technology to the enclosures used to store the Constitution and Bill of Rights, etc. at the National Archives. If you have seen the movie National Treasure, you would see a Hollywood version of the enclosure. The enclosures were produced by NIST at a cost of approx. $1,000,000 each. I have made some adjustments in designing an enclosure to bring the cost to less than $5,000. My design has been reviewed by several museum people who have given me a go ahead on the changes.

My question is: What type of certification should I require of a welder to fabricate these rectangle boxes and shoebox style cover made from 18ga 304 stainless steel sheet? The sheet would be plasma cut (one piece top and one piece bottom) and bent on a box brake.

JFeig wrote:I am here to ask for advise because I know that I do not know. I was taught that if you do not know ask someone who knows more than you.

I was a frame maker/ restorer for some 30 years. I have always gotten my hands dirty. I have been designing a hermetically sealed box filled with argon gas for the storage and display of art and artifacts for the past 5 years. This box (enclosure) is similar technology to the enclosures used to store the Constitution and Bill of Rights, etc. at the National Archives. If you have seen the movie National Treasure, you would see a Hollywood version of the enclosure. The enclosures were produced by NIST at a cost of approx. $1,000,000 each. I have made some adjustments in designing an enclosure to bring the cost to less than $5,000. My design has been reviewed by several museum people who have given me a go ahead on the changes.

My question is: What type of certification should I require of a welder to fabricate these rectangle boxes and shoebox style cover made from 18ga 304 stainless steel sheet? The sheet would be plasma cut (one piece top and one piece bottom) and bent on a box brake.

I don't know about certifications, unless you want to use a certified welder for posterity's sake. Any welder that does sanitary stainless work (kitchen repairs, process piping for a milk plant) should be able to take care of what you need. Most of them are self certified through their work, meaning their work says that they are qualified to make a repair on certain pipe/plate size/joint configurations. We weld 18-22ga stainless and aluminum at work, and no welder here is "certified" in the sense that they have an ASME or AWS certification, but all would be qualified to make the weld.

My personal recommendation would be get in contact with some welders in your area, and then provide them with a smaller sample piece of the same thickness and configuration as the full scale model, and when you find a welder that can meet your aesthetic requirements, negotiate a price with him as far as the cost to weld a full size one for you.

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A suspect the 'hermetically sealed' bit is something to focus on as far as welder qualifications go..

You'll need welder(s) that are experienced in welding stainless pressure or vacuum vessels that get tested to very low to 0 ppm leaks. Probably want the welds tested/checked afterwards too with X-ray or ultrasound and then the whole containers pressure tested for any leaks.

At least I assume that these storage containers are expected to keep a noble gas (argon, etc.) charge as long as possible and keep out any contaminations like moisture, fungus spores and such.

Bye, Arno.

Welcome...

Arno,
You are right on with 0% leak over a period of time. I am looking for a leakage rate of less than 5,000 ppm oxygen over 10 years. Conservators have to keep their jobs! The NIST specifications are for less than 5,000 ppm oxygen leakage over 150 years. NIST used 6" plate for the titanium top cover and aluminum bottom that was CNC milled.
My current testing procedure is the bubble test with 60psi internal pressure.
The concept of someone who has pressure vessel welding experience is the info that I appreciate.

Thank you all.

Jerry

Or refrigeration exp. lots of refrigerant pipe is tested at 200 -800 psi depending on use and material.

Jerry,

I regularly do welds that would meet the NIST specifications, and I have to prove them with helium leak detection. If it won't leak helium in a quantity I can detect (and I can measure in the nanoliter range), it won't leak oxygen.

I highly recommend the helium leak detection as your final proof.

I don't suppose you're anywhere near New Orleans?

Steve S