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What is Out of Chamber Electron Beam (EB) Welding?

   

Why Consider Out of Chamber Electron Beam Welding?

Out of chamber electron beam welding removes the constraint of component size, making thick section (>40mm) welding cost-effective for large structures.

What are the Benefits of Electron Beam Welding?

It is a rapid single pass welding process where a 200mm thick, 3m diameter canister (~9m weld length) can be welded within 4 hours, with no need for inter-pass inspection or cleaning. Cost-saving can be made as a result of less inspection and downtime. Also, wire and flux are not required, therefore further contributing to cost-savings.

Hydrogen cracking is usually eliminated as the welding is conducted in a vacuum.

Furthermore, it is an automated process and works best on a simple butt joint; therefore, it is a very repeatable and simple joint preparation. It is worth noting the tolerance is a little more demanding due to there being no filler materials.

How Does it Work?

The technology is enabled by TWI's reduced pressure electron beam technology, where the gun and chamber can operate at different pressures.

The chamber typically operates around 10-2mbar, whilst the electron beam gun operates at 10-7mbar.

Two types of out of chamber electron beam welding have been developed over the years at TWI and can be applied to thicknesses between 40-200mm. Local vacuum method can be applied through a local vacuum head and it is best for up to 80mm thickness; whilst the local chamber method is more suitable for thicknesses above 80mm.

TWI has recently developed a new local vacuum head for the Nuclear Advanced Manufacturing Research Centre under the INFORM project where a quality assurance station with a BeamAssure probe was integrated into a local vacuum head to reduce the setup time by 90%.

Local Vacuum system developed for Inform project in 2019.

out-of-chamber-eb-welding-(1)

Local Chamber for pipe laying developed in the 1990s 

out-of-chamber-eb-welding-(2)

What is the Quality Like?

The quality is the same as with conventional electron beam welding. The photo below shows the top bead of an 80mm thick mild steel canister made under the INFORM project, it is very similar to conventional high vacuum EB welding, but with more vaporised metal deposits due to the lower vacuum.

out-of-chamber-eb-welding-(3)

How Long do the Seals Usually Last?

For local vacuum systems, some commercially available seals can last for more than 10 hours; however, we recommend a new set of seals after every weld.

For local chamber systems, seals are not generally exposed to the high heat, and therefore normally last for a long time.

How Long does it Take to Change the Seals?

For local vacuum systems, it usually takes less than 10 minutes to replace the commercially available seals.

The seals in the local chamber system are considered as permanent seals, so will take longer to replace.

How Long does it Take to Pump Down?

This depends on the volume of the system; pump down can be as quick as 5 minutes for the local vacuum system.

How Long does it Take to Set Up the Machine for a Weld?

Coupled with a sliding quality assurance station, the set up should take less than 20 minutes.

How Fast Can it Weld?

It welds at the same speed as conventional electron beam welding. Typically, it can weld at ~100mm per min for 80mm thick steel.

Is Radiation Protection Required?

Yes, radiation protection is required. Welding can be carried out inside a lead clad steel enclosure similar to that employed by an X radiation inspection system.

Is it a Repeatable Process?

Electron beam welding is an automated process, therefore is very repeatable.

How Many Operators are Required?

One operator is required to operate the welding machine and a few more are required to assist with the loading and unloading of the workpiece. The operators do not usually require the same level of qualification as a manual welder.

Can the Weld be Repaired?

Small defects can be repaired by simply welding over the existing weld. Larger flaws may require extraction and repair using TIG welding. TWI has developed in-process ultrasound inspection technology that could identify flaws during the welding process so the weld could be brought to a controlled stop if necessary.

How Thick Can it Weld?

Up to 200mm thickness has been welded on C-Mn steel using single side welding. For thicker materials, double side electron beam welding can be achieved by using a second gun on the inside of the workpiece.

What is the Minimum Size of the Workpiece?

The technology is best suited to weld heavier structures. For lighter structures, bolting down may be required to prevent movement.

A minimum thickness of 40mm is best suited for this technology, as a thinner structure could warp under local vacuum. Moreover, thinner materials could be welded more economically with technologies such as laser welding.

Is it Commercially Available?

Yes, both local vacuum and local chamber machines are commercially available. A bespoke vacuum head/chamber may be needed depending on the geometry of the workpiece.

Is it only Suitable for Round Objects?

No, a local vacuum chamber can be mounted on a robotic arm for linear welds on large structures. Other shapes could be achieved by using the local chamber method. It is possible to feed wire to fill in to the gap, if a large joint tolerance is expected.

Typical Applications

Pressure Vessel Applications

Non-Pressure Vessel Applications

Hydrogen

Seismic resistant building columns

Oil refining

Bridge structures

Power generation

Electric pylons

Steam raising plant

Oil and Gas production and exploration platforms

Chemical plant

Molten Salt tanks

Olefins

Space propulsion

Fertiliser

Pharmaceutical plant

Pulp and paper

Agriculture

Gas production & storage

Wind energy

Space exploration

In Space welding

Vacuum vessels

 

Submarine and submersibles pressure hulls

 

 

How Can TWI Help?

TWI can support your organisation in the following areas:

Commercialisation of the Technology

  • Expanding regulatory codes and application standards 
  • Bringing the technology to higher TRL levels
  • Weld development
  • Repair strategy

Equipment Development

  • Design of low-cost interchangeable vacuum head
  • Integration of quality assurance systems, such as BeamAssure and in-process UT monitoring
  • Electron gun design

Inspections and Training

For more information please email:


contactus@twi.co.uk