How BBQ Gas Bottles – Propane Tanks – Are Made

How BBQ Gas Bottles – Propane Tanks – Are Made

The manufacturing of BBQ gas bottles – propane tanks – requires excellent quality control to assure long life and safe use.

Most users expect a minimum of 20 years of use, so premium materials and quality manufacturing are a must.

But how are they made?

How LPG Cylinders are Made? How Propane Tanks Are Made?

An LPG cylinder or propane tank, is most commonly made of welded steel.

Two half cylinder shapes are welded together, with foot and neck rings added, to form a single steel cylinder.

In recent years, there has also been an influx of composite cylinders.

Composites use the combination of  an inner liner of polyethylene (HDPE), wrapped glass fibers and resin, and a polyethylene (HDPE) outer casing.

Starting with the Cylinder Body

The process starts with a coil of sheet steel.

The sheet is fed through a strong punch press, creating circular blanks of about 48cm (19 inches) in diameter (image below).

Steel disc blanks for forming the cylinder body

The circular blanks then go through a powerful hydraulic press, as shown below, which draws the steel disc into the shape of a half of a cylinder.

Steel disc pressed into half of a cylinder

An automated trimmer gives it a clean edge so the two halves can be welded together evenly, without any gaps.

Cylinder Add-Ons

A hole is punched into the top of the cylinder and a threaded valve flange is inserted, as shown.

Valve flange for screwing in the valve

An automated welding station, shown in the following image, fuses the flange to the top of the tank.

Valve flange is automatically welded in place

This provides a secure sealed opening for screwing in the tank valve.

Steel strips are punched and formed into the circular foot rings.

The foot rings (below) are welded to the bottom of the tank with another automated welding machine.

Foot ring is welded in place

In a similar process, the neck ring is punched and formed from another strip of steel and welded to the top half of the tank.

The difference is the secondary bending that is done to form the gas bottle handle.

About the Valve

Brass valve for BBQ gas bottleThe main valve on a BBQ tank is made out of brass.

Why brass? 

Brass is considered to be "non-sparking", so there is less chance of any accidental ignition.

The valve also has an integral Pressure Relief Valve (PRV).

The PRV is the single most critical safety feature on an LPG cylinder. 

It is incorporated within the main valve and appears as the protrusion opposite the main connection. 

Pressure relief valves are designed to relieve excess pressure that might result from overfilling or exposure to excessive heat or fire. 

The function of a PRV is to keep a cylinder from rupturing in the unlikely event of excessive pressure build-up.

The pressure relief valves are held in the closed position by the force of a powerful spring inside.  

As long as the pressure is less than that of the spring, the valve will remain closed. 

Stamped On Information

The neck ring contains a lot of important information that is stamped into the steel.

This information typically includes:

• Cylinder manufacturer name

Country of manufacture

Date of manufacture, which is important for the tank re-testing date reference

Test station identification

Tare weight – empty weight of the cylinder

Water capacity, which is indicative of volumetric capacity

A hydraulic stamp is used to embed this information into the steel of the neck ring.

Space also remains on the neck ring for additional date stamps, required when the cylinder is retested in the future.

 Final Assembly

The two tank halves come together and are welded in a special rotary welding station (shown below).

Two cylinder halves are welded together

Entire tank is then heat tempered, in a furnace (as shown below), to provide for the correct hardness required for the expansion and contraction that occurs during pressurisation.

gas cylinders going through a tempering oven

Tanks are painted on an automated electrostatic paint line with electrostatically charged powdered paint, as seen in this image:

Eloectrostatic painting of the gas bottles

This process helps assure full and even paint coverage.

The last assembly step is the valve insertion (below) and tightening.

Inserting the valve for tightening

Testing

There are a number of tests performed to assure a quality product.

Testing is done on the weld seams to assure that they are as strong as the adjacent steel.

A water pressurisation test is done to test for expansion.  This assures that the heat tempering was properly done.

Prior to valve insertion, the tank undergoes an internal inspection, using a small video camera, to look for contamination or corrosion inside the tank.

The final test involves the air pressurisation of the tanks, whilst they are submerged (see below), to test for leaks.

Water pressurisation test

Final Thoughts

Most people don't realise how much goes into making a BBQ gas bottle.

Quality is paramount to ensure long life and safety.

 

 

 

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All images courtesy of Worthington Industries

The information in this article is derived from various sources and is believed to be correct at the time of publication. However, the information may not be error free and may not be applicable in all circumstances.

 

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