RE: [PSUBS-MAILIST] Seeing a pro welder at work

Alec, I think you did a good thing. My specialty is welding. I put myself through college as a certified welder only to get an engineering degree in metallurgy. So, I would say I am qualified to at least give my opinion.

I agree with every step of his porcess, from correcting the gap between the plates, to puting the final touches on the cap ( or the weld that is on top). The only thing that I didn't follow is the retracing his weld without removing the slag at the overlaps when he had to change rods. This is a tricky process, and unless you are experienced; it would not be advisable. Slag can be traped when going back over a weld that has cooled, causing a void of slag, or even air. This is bad in any weld that matters. I don't want to doubt your guy, becuase I am sure he knows what he is doing, because when eveything is right the slag will just fall off. In the case where you have to beat your slag off, you may want to bump the heat up, just a touch...

I just wanted to express my opinions, because retracing a weld is a tricky thing. My suggestion for the group is to do exactly what Alec did. For the external welds, I would go with a person that has put his reputation on it for a few years. It seems like a lot to pay a guy that amount, but implosion is not a pretty thing I am sure!

Brad

>From: Alec Smyth

>Reply-To: personal_submersibles@psubs.org

>To: "PSUBS (E-mail)"

>Subject: [PSUBS-MAILIST] Seeing a pro welder at work

>Date: Wed, 8 Aug 2001 12:45:41 -0400

>Last night I saw some interesting things I thought I'd share with the group.

>Sorry if this is old news to the experienced folks.

>I can "stick metal together", but I'm no professional welder. I'm doing most

>of my welding, but decided not to chance it when it comes to the pressure

>boundary seams. Those I'm having done by a pro. So I called a local welding

>supply store and they put me in touch with a gentleman who is a certified

>pressure vessel welder and pressure vessel inspector, with 30 years

>experience. Last night he came by and did the longitudinal seam on the

>pressure hull. This is the single largest weld on the boat.

>1) The starting point was a cylinder 94" in length, of 516 gr 70 plate 3/8"

>thick. Per welder's instructions, I had ordered this with a double beveled

>edge. The first surprise was that he prefers the edges not to touch. The

>seam was just how he liked it, with a small gap about 1/16th between the

>beveled edges. The reason for the gap is he wants to know he has filled it,

>and without a gap he would be hoping (but not certain) that the metal had

>melted to the center of the material.

>2) He started by doing a continuous weld on the inside with 7018 rods, 1/8".

>Its interesting seeing the technique. When the rods were still long, he

>actually held them with both hands -- two fingers were near the hot end, to

>keep it perfectly steady. Sometimes he'd just be going straight down the

>seam, other times going side to side "depending on what the puddle is

>doing". The end result looked like it had been made by a machine. An

>interesting detail was what he did at the ends of the seams. He'd get to the

>end and then back up again and redo the last 2-3 inches, all in one movement

>without removing the slag. He said this "avoids an end of the weld on the

>end of the seam", which would be a potential weakness.

>3) He then went at the outside with a blowtorch and a 90 degree nozzle. He

>"torch-gouged" the beveled channel turning the V into a wider sort of U,

>about 1/2" wide. He took it down so the material at the bottom of this U was

>the inside weld. This also removed the tack welds, but was not limited to

>the tack welds (he did the whole length). This step could have been done

>with a grinder, but the torch was a noise reduction tactic -- I live in a

>quiet residential neighborhood and try to minimize grinding on the driveway.

>4) He finished the channel with a light grinding. The result was a shiny and

>very solid looking channel without discontinuities of any sort. This did get

>one neighbor out onto the street, but fortunately she was one of the

>friendly ones. Did I mention his welding equipment was gas powered and 1963

>vintage? About as subtle as a locomotive.

>5) He welded the whole length from the outside. This weld filled the channel

>to half its depth but covered its entire width.

>6) Removed slag, wire brushed, and laid another bead along the whole length

>to bring it flush with the surface.

>One interesting thing is that there was almost no spatter, and the slag just

>fell off almost on its own. He had a whole truck full of welding equipment,

>but did not posess a chipping hammer... no need apparently. The slag

>required at most a brush of the glove or a scrape with the end of a rod to

>remove. For some reason I have to pound my welds.

>The entire process took 4 hours, working efficiently and without a break.

>His rate was $65/hour which included all equipment and consumables. He

>turned up with this self-contained welding-shop-on-a-truck and did

>everything right there on the driveway. Boy do I have no regrets about this

>one, the peace of mind is well worth it!

> >/>