Pipe cladding

With pipe cladding as well as cladding accessories, all king of piping can be clad with rapidity, quality and minimal to no measurable distortion. Polysoude can design various types of cladding installations, to meet customer requirements. Hot Wire TIG welding is a benchmark in high-quality cladding operations, especially those involving complex shapes, where there are space constraints, or a higher level of automation is required.

TIG welding cladding applications

Cladding operations using the TIG process generate good results in the following types of application:

  • repair of worn parts in service or following a manufacturing anomaly,
  • preventive cladding operations for particular hazards (wear, corrosion, etc.),
  • buttering operations as part of a more complex welding process for heterogeneous joints.

Part repair operations - the most frequent and easiest to identify - concern homogeneous components subject to attack. Those simply require a machining or equivalent operation to eliminate the damaged areas (fissuring, cracking, erosion, etc.) followed by a cladding phase by redepositing materials identical to the composition of the substrate. In most cases, these operations are performed on high value-added stainless-steel parts. Clad welding does not fundamentally change the metallurgical characteristics of the parent materials but does increase the stress level in the repaired part.

pipe cladding welding column and boom of nuclear reactor head for TIG GTAW heterogenous weld overlay
Welding overlay installation to realise a buttering operation on nozzle-end-piece in preparation for a heterogeneous weld in Nuclear Industry

This situation is, for example, very common for piping used in the nuclear reactor environment or in gigantic pipelines in the oil and gas industry.

Pipe cladding handbook white paper for automated tig gtaw weld overlay cladding
Cover page of the Polysoude handbook about the automated TIG weld overlay cladding. the picture shows a flat clad welding and an internal pipe cladding.

Dilution

The main difficulty encountered with pipe cladding relates to controlling the dilution rate to guarantee the chemical analysis of the deposits. In general cases, the dilution principle characterises the result obtained after deposition on a substrate of another grade. The alloys used for cladding welding are in fact listed for the specificity of their chemical analysis and their capacity to withstand external stress. In most cases, performance is only guaranteed in a non-dilution condition, which means with a chemical analysis that corresponds to the classification of the grade.

However, in the scope of the welding operation, the filler product is melted completely and deposited on the parent metal (substrate) which is itself molten under the impact of the arc. The mixture of filler metal and parent metal characterises the dilution rate resulting from the cladding operation.

principle scheme of weld dilution tig gtaw pipe cladding deposition rate
Scheme of cladding operation in two layers on an unalloyed steel (or low-alloy steel) substrate. The dilution percentage decreases due to overlaying. In this example, the first layer reaches 12% dilution rate ; the second layer only 2.5%.

The search for a compromise between melting a minimum of parent metal while guaranteeing the quality of the bond with the deposit remains the major difficulty in defining operating procedures to ensure a balance between the compactness and the chemical analysis of the deposit. The percentage dilution reflects the change to the chemical composition of the cladding alloy resulting from the mixture with the molten parent metal, or a layer that had already been deposited.

Pipe cladding power sources and equipment

The TIG welding power source is the heart of a weld overlay installations. Via interface with the operator, Polysoude’s multifunction, computer-programmable welding power sources are designed for precise control of current intensities and movements. The Smart Welding Stations offer:

  • 100% duty cycle of between 300 and 550 A according to the particularities of the applications
  • high-performance programming systems, able to create application programs with features suited to cladding
  • the capacity to control the peripherals required for automated welding systems.

The open-ended structure of the Polysoude PC range of power sources makes it possible to adapt and add extra axes to control and programme all movements, both linear and circular, in automated cladding. The instrumentation and control system are designed to steer the installation through all phases of the automated cladding welding process.

The axes controlling peripheral or external units include printed circuit boards designed to control:

  • turntables
  • positioners
  • booms
  • rotary collector cladding welding heads
  • real-time data acquisition systems
  • coolers
  • oxygen control devices
  • Rotation counters – for the development of programme loops, in repetitive operations such as cylinder cladding
  • AVC slide – comprising a powered slide, measuring system and closed-loop regulation
  • Oscillation slide – used for positioning prior to welding, oscillating during welding or to enable reset/ offset (step over).

Other PCBs equipped with input and output ports can be programmed as logic circuits to disable or enable equipment operation.

Polysoude can recommend a range of standard equipment, to cover the diversity of applications; provide assistance regarding use of equipment; or design and build bespoke pipe cladding systems as specific solutions, in response to customer requirements.

pipe cladding column boom of tee piece head for TIG GTAW weld overlay
Weld overlay installation on site. This standard installation includes a Column & Boom, high precision cross slides with brushless motorisation, SPX collector head equipped with a cladding lance. The smart welding station and the cooling unit are installed on a dedicated platform around the column & boom. Two operators are following an internal cladding operation on a valve for Oil & Gas industry.

Pipe cladding using TIGer Technology

Internal pipe cladding has been significantly improved by Polysoude TIGer technology.

internal pipe cladding with triple layer of inconel TIG GTAW weld lance inside TIGer model pipe sample
TIGer torch with its two electrodes generating a single bi-cathode arc; the torch is placed inside a tube where 3 layers of the cladding welding process are shown

The TIGer torch has two electrodes, each supplied with current and positioned to generate a single bi-cathode arc. Low arc pressure, combined with high welding intensity, increases welding speeds and pipe cladding productivity rates. High deposition rates are achieved, with a low dilution rate between the deposited alloy and substrate. Welding parameters can be adjusted, to optimise the thickness of each layer. Smooth layer surfaces and reliable metallurgical bonding are achieved between deposit and substrate.

The Process

Cladding of two main types of components is required:

  • Line pipe – of 6-12 metres (requiring horizontal installations)
  • Elbows, Tees, Flanges, fittings, branch pieces (requiring vertical installations)

Horizontal

Steel pipes up to 12 metres long can be horizontally positioned and rotated around their longitudinal axes. Two bi-cathode torches with attached wire feeding devices are mounted at the end of a welding lance and guided along the inner wall. The weld cycle begins with the ignition of the first torch, the welding cladding lance is retracted at a controlled speed, the positioner rotates the pipe synchronously and a first layer of CRA is deposited inside the pipe. The second torch, mounted further along the welding lance, reaches the first deposited layer and begins cladding a second layer, thus two layers of coating are deposited in a single pass.

Vertical

TIGer technology can be used in vertical installations, for cladding welding shorter pipes of up to 2 metres and more complex fittings and components. One bi-cathode torch is mounted on a column and boom device; the workpiece is fixed to turning gear; fine-positioning and moving in the direction of different axes is carried out using slides.

In both horizontal and vertical installations, the power source controls the synchronised movements of torch and workpiece throughout the weld cycle.

Who we are

Polysoude specialises in the design, development and manufacture of innovative arc welding solutions. The brand is synonymous with world-leading expertise in 3 core sectors: automatic orbital TIG welding systems, automated TIG and plasma welding solutions and TIGer™ weld overlay.
Situated in Nantes since 1961, the company manufactures a variety of power sources and orbital welding equipment, like a wide range of open and closed orbital weld heads.
Nowadays, as a smart factory-oriented company, Polysoude products are all designed to be ready for Industry 4.0.

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