A plasma seam welder for vessel longitudinal seams.

When fabricators produce components for nuclear power plants, safety is a top priority. They ensure safety by selecting and using high-quality materials, complex production processes, and the highest quality standards. All things considered, and as in any industry, production costs are particularly important. The global market leader in mechanized and orbital welding, Polysoude, tailored a welding solution for a Russian supplier of pressure-vessels to bring the operation into line with the required productivity and security.

This Russian manufacturer fabricates pressure vessels for nuclear power plants, and exports 80 percent of its finished goods. As such, it attaches great importance to the ability to achieve and maintain short delivery schedules.

A joining system was developed using standard mechanized components, and the optimal welding technique. It is a procedure that is available to address any wall thickness, any diameter and any material type.

A precision lathe used with the plasma process: precision lathe.

The system that Polysoude prescribed uses either plasma or TIG welding, or both combined. With large diameters the operators even have the choice to weld from the outside to the inside, or vice versa. For some vessels this constitutes a very interesting alternative. In any case, an integrated camera allows visual control of the welding process.

A plasma torch with a trailing box.

Polysoude’s installation included a Power source 600 PC; a plasma torch with a wire feeder; a TIG hotwire torch, with wire feeder; a camera; a column and boom system with a motorized compound slide rest for Arc Voltage Control (AVC) and Torch Oscillation Control (OSC); and a positioner/rotator.

In the plant’s production process, the fabricated sections are made from low-alloyed or austenitic steel. Their lengths range between 1,000 and 3,000 millimeters, their diameters vary between 800 and 1,500 mm, and their wall thicknesses run between five and 40 millimeters.

Polysoude defined the procedure so that the fabricators can recognize exactly the most productive process for every application, and it developed the corresponding welding programs to follow.

A TIG torch with three alternative filler metals available.

The strengths of TIG welding are revealed when welding low-alloyed, thin-walled sections – heat input and the addition of filler wire can easily be piloted and controlled.

For components with butt weld preparation and wall thicknesses up to eight millimeters, the plasma welding with cold wire is the right choice.

For greater wall thicknesses, the procedure combination takes effect: the root is welded with plasma/cold-wire process, the filler and cap pass with the hot-wire TIG process. Depending on material and material thickness, welding speeds range between 60 and 250 millimeters per minute; the number of welding passes is small, and the controlled heat input is assured at any time.