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Welding a tank; why is it a bad idea?

Posted 10th April 2019

Welding a fuel tank might seem like a relatively simple and cheap process, especially when compared to the cost of a replacement tank.  However, many factors make welding a tank with residual oil, diesel or petrol dangerous.  Welding on a tank is the process of sealing a crack or split in its surface by heating the metal so that it rebinds together. Forming a strong joint that will no longer allow fuel to escape. The high heat and reaction taking place during this welding process, however, are unpredictable.

To control the reactivity of welding a tank you can fully empty a tank and clean it out prior to filling it with a noble gas.

Differences between welding different fuels

Whilst we don’t recommend welding any fuel tank there are certain elements to consider when undertaking a project like this if you do need to weld it.  Firstly, the volatility of some fuels can be much higher than others. This is entirely true of petrol and its fuel vapours.  A partially filled fuel tank, with air left in the tank will be full of vapourised gases.

These fuel gases, when exposed to a spark or flame, will ignite more aggressively than if they were liquid.  Much like a fuel air bomb, the extra oxygen in contact with the petrol allows for faster burning of the fuel.  This makes welding a petrol tank extremely dangerous to the user and the tank.

What are the uses of Argon gas?

Argon is the most commonly used of the inert gases in gas tank welding to stop any reaction from taking place. This lazy gas, like all the noble gases, is colourless and odourless. Argon is also used in the manufacture of fluorescent lighting.

What are the different types of welders?

There are multiple tools for welding a tank including TIG and MIG welders. They are similar methods with slightly different qualities and deciding which one to use is tough. Which gas metal arc welding method to use depends on the materials being used.

MIG welding

Metal inert gas (MIG) welding is a method of welding that utilises a filling metal. This metal doubles as the electrode used to heat the target pieces.  MIG welders are better at bonding thicker metals as it can join the two materials with an integrated filler.  This allows a strong connection to form without heating the metal thoroughly.  As the welding starts the filler material melts into the welding pool whilst shielding gas protects the weld.  By keeping the oxygen content low near the joint the welding machine prevents impurities from getting into the joint that might weaken it.

TIG welding

Tungsten inert gas (TIG) welding uses a fixed pure tungsten electrode to heat the joining metal.  A filler rod, made of a recommended type of metal, is then carefully introduced into the weld pool to fill the join.  Manipulating a rod by hand rather than being machine fed on a MIG welder makes TIG the slower method and requires both hands.

For sheet metal, using TIG makes controlling heat levels easier, therefore preventing the base and weld metal from melting too much.

Aluminum and stainless steel tanks

These are generally the tougher materials to weld.  Although it’s unlikely you’ll find a stainless steel tank for bulk fuel, I’ll cover it along with aluminium/aluminum. The first thing to do is to identify exactly what grade of material you are working with. Stamped onto the metal, there will be a number that will relate to what kind of filler rod to use.

After you have your materials ready, check your gas levels against the thickness of your target metals.  As your aluminium reaches over half an inch thick you’ll want to add helium to your argon to raise the arc temperature and improve the penetration of the join.  You’ll also need to consider the thickness of the tank.  Generally, about an eighth of an inch will require around 125 amps.


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