Project mobilizations - welding on top of a fuel tank

Hey Mariners, engineers,

What do you all think about welding on top of a (MGO) fuel tank (with fuel inside)? Personally, I think it is dangerous, but due to commercial reasons (cost of venting and gas-freeing tanks), there is pressure to move ahead “with sufficient mitigation measures in place”. I referred to API 653, and it bars welding on tank tops as that’s the location where vapors are most likely to build up. I couldn’t get a copy of API RP 2009…

Just trying to see if there are any references / guides / recommended practices which give sufficient guidance on a methodology for safe welding on the top of tank with diesel inside…


CFR 46

§ 176.710 Inspection and testing prior to hot work.

(a) An inspection for flammable or combustible gases must be conducted by a certified marine chemist or other person authorized by the cognizant [OCMI) before alterations, repairs, or other operations involving riveting, welding, burning, or other fire producing actions may be made aboard a vessel:

(1) Within or on the boundaries of fuel tanks; or

  1. To pipelines, heating coils, pumps, fittings, or other appurtenances connected to fuel tanks.

Hi Sherman…

Isn’t this dealing with the part which requires venting, gas-freeing and subsequent certification that the space is safe to work?

What I mean is - following CFR 46 - we need to vent, gas-free and certify the space as gas free… correct?


That’s how I read this yes. No hot work on a fuel tank until a marine chemist gives the OK.

Here is an OSHA reference as well


Hot work shall not be performed:


In flammable or Potentially flammable atmospheres:


On or in equipment or tanks that have contained flammable gas or liquid or combustible liquid or dust-producing material, until a designated person has tested the atmosphere inside the equipment or tanks and determined that it is not hazardous; or

Save yourself a lot of trouble. You may be about to be inundated with all the “safe” ways to do this, complete with testimonials but the fact you posted this here indicates you’d be better off actually hiring a marine chemist or reputable contractor this time.

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You didn’t mention the specifics of the work but I have done it. There are basically 2 methods; fill the tank 100% so there is zero vapor space or blanket the space with CO2 or other inert gas. Keep the duration of welding to a minimum. I would prefer never to do it again.


A few years ago a welder died near my house welding an “empty” fuel tank at the boatyard, which if it was a gasoline tank is probably the most dangerous state of all. At the time I was wondering why they didn’t get a nitrogen or CO2 tank and stick the hose down the fill to keep it inert.

I’ve seen a gouge and fill repair done on a full tank as well as a nitrogen inerted dead space, but never an insert. All were approved by a CMC though.

I have to agree with KP Chief. Spend the money and get it done properly. Too much can go wrong here.


I’ve seen this before, if someone is trying to weld on top of a partially full diesel tank, to save money, they’re required to have a chemist. When I saw this happen, the guy basically showed up and said (in more professional language) he worried about how stupid we were for working for a company that was wasting his time with this and said it was not safe for hot work just based on the level and contents.

Don’t do it.


Welding on top of a properly inerted tank is substantially safer than welding just about anything else. I don’t know how many ‘gas free’ tanks that had been certed by a marine chemist that I’ve found flammable environments in. It is far easier to maintain something (inerting gas) that it is to maintain nothing (a gas free tank)

A good marine chemist will not only allow but encourage this. What separates a great marine chemist from a good one is the amount of steps they include to insure Murphy doesn’t bite.

Anyone telling you that you can’t do this is not interested in safety, they’re either ignorant or more interested in being a problem rather that being part of a safe solution.


Consider a no weld solutions first. Maybe you could use bolted joints or high strength epoxies.

Depends on how much diesel inside, the size of the tank and the amount of welding to be done. You can weld a leaking natural gas pipe if it is over the UEL and ventilation is restricted. A “marine chemist” can CYA.

If you have some more specifics on the repair that is being contemplated it would be easier to tell you procedures, precautions, and alternatives.


As has been mentioned, some more specific info would be useful. And not just on the type of repair/type of tank, but also under who’s jurisdiction do you fall. Whether or not the CFRs are applicable (ie: are you even US flagged or in US waters?) in no way negates the fact you shouldn’t just proceed unsafely for “commercial reasons”. I’d hope that if your SMS is worth a damn it covers hot work on/near fuel tanks/vents.

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In 1972 I was a new Ensign in the Engineering Dept of a major ship in Norfolk. We had a 1970 Ford Torino Squire station wagon and it had a leak in the seam on the gas tank, inside the left rear fender. I had tried various paste repairs, but no real success.

Leading Hull Technician (HT1) says give me your car keys and we’ll take care of it. I assumed drop tank, drain, bring to shop, inert, etc, and was concerned if it would be done that day.

He brings me keys in 90 minutes - all done. They enlarged the hole, drained the gas, emptied a CO2 extinguisher into the tank, then welded it. Poured the gas back in after it cooled, and no leak. On the pier, next to the ship.

I learned a LOT of life lessons that day. And never forgot them.


They drained it, inerteted it and got it done. Good plan. No way would I do it with fuel, whatever kind in the tank. Good for that big ass Torino. And the ship next to it.

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Thanks gents - your advice is well received. @shipengr SMS is clear on welding on fuel tanks - but SMS can be rewritten of course! Some of the (senior) mariners in my organization say “it has been done before”, and “can be done if done properly and carefully”… its harder to take the fight against mariners when they have a lead over you by 20 years.

The vessel is not US flagged, and not in US waters, so CFR is not applicable, but when it comes to welding API and AWS are still considered global standards. Vessel is in Brasil :slight_smile:


I have been around a long time and have heard these rationalizations more times than I can count. Just because it has been “done before” and nothing happens does not make it right or legal.

And go ahead, re-write your SMS…the lawyers will love that. Anywhere in the world, mind you. I am sure Brazilian lawyers will have a field day

The man who was killed in this incident linked below was a good friend of my dad’s. He is part of the reason why I never play games around tanks carrying any kind of flammable or explosive substance. He helped build my mom’s porch awning. All they could find of him were his shoes. The settlement was the largest ever in the state of Delaware. Won’t bring him back Don’t play around with tanks. Hire a contractor and pay them.


In the discovery phase of the suit, Kline said he and Casey reviewed more than 40,000 documents, took 39 depositions, and hired 14 experts, ranging from chemical engineers and metallurgists to an astrophysicist.

What expert testimony did they use the astrophysicist for? “Doctor Expert, can you describe what is Hydrogen, and how is it formed?”

“3.8 Billion Years Ago… take a seat, council, this is going to take a minute.”