Welding a sealed vessel?

Spending the summers of my youth and well into my adulthood fishing in Bristol Bay Alaska, I was surrounded by commercial fishing boats.

The fleet was experiencing a transition from mostly wooden and fiberglass boats in the late 70’s to a new generation of Aluminum boats. We called them Tin boats.

Every year more and more new Tin boats would show up with innovative configurations and construction designs. Side note, there was a 32’ limit to the length of these boats so this prompted, what some would consider strange looking boats. They had overly wide beams, some up to 15’+ and the hulls were really tall.

One day I hit the beach after an opener and noticed a tin boat that had been pulled out of the water and was being worked on. Being nosy, I climbed the ladder and looked into the fish hold and it was more than obvious there had been a big explosion.
I noticed the fish hold had been partitioned. But these particular partitions were double walled, so instead of using a heavier plate like 3/8” for the partition they used lighter material and double walled it making it a sealed vessel. If I had to guess this boat was probably about 6 years old at the time.

The owner was wanting to add some brailer
hooks and as soon as the welder got it hot enough, Boom! I heard the welder was blown out of the fish hold and was hurt. This also happened again to the same type of boat but the second explosion was not as bad as the first one.

It was not from gasoline fumes. It had to be from hydrogen gas being released from the oxidation of the aluminum. I coincidentally became a metal fabricator and am very aware of this whenever I am welding on an aluminum sealed vessel.

My question is has anyone ever experienced this before?

 

I'm a bit younger so when I spent multiple winters cutting out poorly done double hulls in bay boats they were to old to be air tight. First was a laconner that was entirely double walled. Not a single bit of it was air much less water tight when patches were attempted. When we've done tanks, bulbs or built in keel coolers it's always been in conjunction with a threaded port that's open.

Never has a kaboom from that. Did sand blast and repair a seiner that in a previous life had been a tuna boat. It had diesel that was very old in between the hull and the hold skin. Was some wild flames on that one.

 

The oxidation of aluminum is as follow: ( at least according to the three of the sites that I looked for the actual chemical equation)

Al(s) + O2(g) ——— Al2O3
Basically, the aluminum reacts with the O2 in the air and forms aluminum oxide
I am curious where you think that H2 presents itself in this process

Can you back this statement up with a Hazardous Welding process bulletin?

Aluminum Welding Fumes: Composition, Risks & Solutions | Henlex https://www.henlex.com/aluminum-welding-fumes-composition-risks-solutions/#:~:text=When%20heated%20during%20welding%2C%20aluminum,and%20affect%20the%20nervous%20system.

The above link relates to gasses produced when welding aluminum. While ozone 03 which in high concentrations can be explosive in very high concentrations, it is very unstable and combines with air very quickly

 

It had to hydrogen was just a guess.

The reason I posted this form is because I’m not sure.

My question was, had anybody ever experienced this. If you have not experienced this why are we conversing?

 

Not sure why I have to justify the ability to offer a response as I basically put forth a simple question as to your assertation that the production of aluminum oxide produces
Hydrogen gas which is explosive.
The Alo3 can be present on the aluminum with normal air to aluminum interaction. In fact this is what make aluminum such a great boat building material.
From the equation, I do not see the H2 that you mention being formed.
The other possible availability will be perhaps H2 being produced by the welding process. Please read the link.

Responding to your comment " if you have not experienced this" you are correct in only one way. And that is that I have not welded inside an aluminum tank.
Certainly there are standards for "Welding in Confined Spaces" BUT, our 6 - 8 aluminum welders have welded literally miles of aluminum bead over 40 years, and I have
never ran into the concept of gases, H2 or o3, being produced to cause an explosion

The REASON for my post was to question your post, "it had to be from hydrogen gas"

I am open to your response as to the source of the H2 as I have been wrong before. (so she says)

 

Never heard of it. Worked at a yacht builders that produced many alloy boats, some with "double sealed" compartments.

Only boom i heard of was when someone was cleaning the inside of a tank cleaning with something like xylene, with no air extraction. Spark from an angle grinder set of the boom and a young worker was killed.

If its a problem on older alloy boats, first I have heard.

 

The bay is its own monster, I've crawled through and worked on more of those boats between work and owning them. It's sporadically the wild west of construction, lots of other reasons for an explosion.

Most impressive bay boat boom I saw was on a fat boy allpoints. They had been putting in a recess for a keel cooled oil cooler and shut off feed and retunt lines on the hydraulic pump. Martini thirty showed up before the project was done and they eventually fired up the main to test the flow. The dead headed pump eventually blew straight down cutting a 2 foot gash in the bottom of the hull. I was one boat over putting a rudder on and the bang left my ears ringing for a while.

 

Just to clarify this was not inside a tank. The partition was essentially a sealed vessel. The only thing I can think of is there was an explosive gas that was created by oxidization of the aluminum. I’m not thinking it was from heat pressure because it appeared that it was the first hook he had attempted to weld on, so I don’t think there would’ve been enough heat generated to cause enough pressure to burst it.
It looked like a stick of dynamite had gone off inside it. I have made several attempts to research this with no results. That’s why I posted it here to see if any one had ever seen something like this before.

 

It is standard practice in steel shipyards to drill a hole into any sealed welded structure for the lab technician to test for hydrogen before welding on them. Explosions happen welding on sealed rusted inside structures. Iron will pull the oxygen from a water molecule leaving hydrogen gas. Large void spaces between ship structures are filled with inert gas , argon and capped off. https://www.osha.gov/sites/default/files/publications/OSHA_FS_3586.pdf

 

It's a poorly worded question D Don.
Of course someone experienced it, YOU!
Members of the Forum read posts individually so speak to us individually.
Ex: "Have you ever experienced this?"

 

Crawled through quite literally hundreds of bay boats over the last 20 years. Cut the bottoms and rotted fish holds out of about a half a dozen including my own. Have crawled through and worked on Curry's, rozemas, All Points, La Conner's, Marcos, alfas, baywelds and kvichaks.

The Bay has historically been between 70% and 50% weekend warrior, There are professional fishermen but depending on the stage of the gold rush it can be a minority. Maintenance slips and jury rigging can be at a level most people can hardly fathom in the developed world. It's coming off a high right now where the boats have probably been in the best shape they've ever been because of the money from the last 7 years of big seasons. But go back to the late 90s and early 2000s after nearly a decade of disastrous prices and equally poor runs... there were some boats that probably were unsafe to be aboard. If I were to guess what caused the boat to blow up in those days I'd be looking for something other than airtight vessels...