Habitable Controlled Atmosphere Chambers for Welding

It is difficult to imagine anything high-tech or even space-related in the profession of a welder until the task involves something large, yet lightweight, completely non-magnetic, corrosion-resistant, and capable of withstanding temperature fluctuations of more than one hundred degrees Celsius.

Obviously, such challenges are common in the aerospace industry. The difference is that there they are still relatively unique projects. In aircraft manufacturing, however, welders often have to take on the role of astronauts and deep-sea divers almost every day. Slightly less often, but still quite actively, welders also put on “space suits” at shipyards.

It All Comes Down to Spacecraft, Aircraft, and Submarines

The problem is simple: both aircraft and submarines contain numerous assemblies and large components that require exceptional strength. Titanium is an ideal material for such applications. However, both aircraft wings and submarine hull structures use multilayer backing surfaces that cannot be accessed from the reverse side with welding equipment. As a result, welding has to be performed only from the outside, reducing joint strength by more than two times.

There is, of course, a solution. Titanium alloys and alloying additives help improve performance, but one fundamental issue remains unavoidable: despite its chemical inertness, titanium retains its stability only up to approximately 450–500°C. At around 500°C, Ti begins actively absorbing everything present in the surrounding atmosphere or on its own surface. It not only readily undergoes “amorphous oxidation” in the presence of oxygen, but also absorbs hydrogen, forming brittle structures similar to clathrates — TiH2. In theory, this could be avoided by directing a carbon dioxide jet into the welding area, but this obvious and inexpensive solution is not suitable. Titanium reacts readily with carbon in CO2, separating it from oxygen. This results in the formation of a eutectic structure consisting of titanium and titanium carbide, which is significantly stronger than the base metal itself but becomes unsuitable for high-quality welding because of its increased brittleness.

Self-Isolation Inside a Gas Chamber

This chamber serves as the welder’s workplace, while the control panel on the right is the workstation of the operator-controller.

The most interesting solution is the “space-inspired” one. It involves creating a sealed volume completely filled with inert gas, where the purity parameters of the internal atmosphere are continuously monitored. Essentially, it is a large pressure chamber with controlled gas supply and monitoring of pressure and temperature. Welding operations are carried out inside this environment.

Surprisingly, helium and neon are not suitable as filling gases. Titanium actively absorbs surrounding substances already at 500°C, and at the plasma temperatures reached during arc welding, even inert gases such as helium and neon can easily penetrate the titanium crystal lattice due to their small atomic size. Argon, however, is ideally suited for this purpose.

It is also necessary to maintain the purity of the internal atmosphere. Even Grade A argon must be passed through a regeneration system equipped with anion exchange resins, cation exchange resins, and fine particulate filters.

And finally, the welder-operator himself cannot breathe argon, which means he has to wear a real protective suit. It differs from a space suit mainly in that it usually does not need to withstand a pressure difference of one atmosphere between the internal and external environments.

It is clearly visible that the gloves are connected to the sleeves using sealed locking rings.

There is another important aspect. Even after the most thorough purification of argon, the concentration of impurities inside the chamber atmosphere can be reduced further in a simple and cost-effective way — for example, by half. This can be achieved by maintaining the internal pressure at approximately 0.5 atmospheres. The price of such a solution is a slightly reinforced protective suit and highly flexible glove material (or gloves equipped with articulated supports that follow the movement of finger phalanges). However, there are applications where an almost complete vacuum is required, and this already approaches true space technologies.

Welder-Astronaut

One atmosphere is not much. Such a pressure difference can easily be tolerated not only by professional divers but even by recreational swimmers at a depth of 10 meters. Therefore, from the perspective of scale, there are virtually no limits to the size of pressure chambers.

However, human physiological capabilities still have to be taken into account. Frequent breaks during welding are highly undesirable because an uneven weld seam would eliminate all the advantages of chamber welding. That is why welders require approximately two weeks of preparation. Although “selection” would be a more accurate term: candidates simulate all their work operations while wearing the suit for 4–5 hours every day. Of course, this is not diver training according to ACUC/PADI standards, and certainly not astronaut preparation at Star City. Still, highly qualified welders are dozens or even hundreds of times more common than test pilots. Cynical as it may sound, not everyone is capable of spending half a day inside a protective suit.

This is a fairly typical chamber — there is nothing especially gigantic about it. Some chambers are built as multi-level structures.

Gas Purging or Vacuum — Different Approaches to the Same Task

On the other hand, besides these large systems, there are chambers compact enough to fit into an ordinary garage. There are two main types:

• chambers with inert gas purging;
• vacuum chambers.

Since these systems are often designed for specific operations, they may vary significantly in appearance, although their operating principles remain essentially the same.

Typical argon-purged chamber.

For example, a classic frame-type chamber with argon purging has a very straightforward design: the gas is supplied into the chamber from below, while the exhaust valve is located at the top. Small parts intended for welding are loaded through a side access hatch, whereas larger components are inserted through a large hatch in the upper section of the chamber. The only critical parameter that must be monitored continuously is the argon supply pressure. Typically, a slightly elevated pressure of about 1.1 atm is maintained to ensure complete displacement of air.

Vacuum chambers differ mainly in their higher structural strength. They also use special glass instead of inexpensive acrylic panels.

Our engineers have extensive expertise in all these specialized systems and can tell you much more than this brief overview. Whether you choose a standard model or require a custom solution designed for specific dimensions and technical requirements, our specialists will handle your project without difficulty.