1ORBITAL TIG WELDING HANDBOOK

INNOVATIVE ORBITAL SOLUTIONS

Orbital T IG weld ing HANDBOOK

INNOVATIVE ORBITAL SOLUTIONS

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2ORBITAL TIG WELDING HANDBOOK

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INT R ODU CT ION

The requirements in terms of quality, standards, monitoring and traceability are forcing industrial companies to increasingly resort to automated processes to manufacture welded joints. The quality of the welds is key within the IS because it is in direct contact with the sensitive fluids circu-lating in it. It is the case for the following industries: agri-food, pharmacy, petrochemical, nuclear, semiconductor.

Among all the welding processes made available to industrial companies, TIG (Tungsten Inert Gas) welding makes it possible to meet the criteria listed above.

In the beginning, this process was not recognized by all industrial enter-prises, but it soon became an effective technique. Indeed, this process is the only one that can put noble materials and exotic alloys together! In addition, the quality of the welds obtained by the TIG process makes it possible to easily switch to an automated TIG process!

Orbital welding technologies are becoming popular thanks to one key element: the automation of TIG welding allows welding for various applications.Today, a number of industries use orbital welding, such as food proces-sing, pharmaceutical, nuclear, aerospace, chemical, petrochemical, semi-conductor, etc...

You’ll find in our handbook all you need to know about orbital TIG welding ! ”

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TIG welding was developed in the forties. At the begin-ning, this process was used to weld corrosion resistant alloys. Welding these kinds of metals, especially alumi-nium and magnesium based alloys, was very difficult in the past. The TIG welding process has been developed at a high rate and allows a weld without oxidation of all metal grades available on the market.

TIG welding is an arc welding process using a non-fusing electrode. An electric arc is created between a non-fusing electrode and the piece to be welded.If a filler material is needed, it would be placed manually in the weld bead (welding rod) or in an automated way (filler wire spool).

When we talk about Tungsten Inert Gas, Tungsten designs the electrode and Inert Gas is the type of plasmagenic gas that will be used. The arc is created between the refractory electrode (- of the power source) and the weld piece (+ of the power source) in a gas stream. Generally speaking, welders use either one gas or a mix of several rare gases.

TIG, WIG or GTAW? These three terminologies relate to the same process: TIG (Tungsten Inert Gas) welding. ”

W h at is T I G weld ing?

The only difference is the language. In German language, you translate Tungsten with Wolfram: Wolfram Inert Gas (WIG). In the United States, they call it Gas Tungsten Arc Welding (GTAW).

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Cooling water supply

Power supply

Argon gas supply

Filler material

Tungsten Electrode

Nozzle

Shielding gas

Gaseous atmosphere

Welding torch

Water backflow

BA

SE

ME

TAL

SO

LIDIFIE

DM

ETA

L

ADVANCING DIRECTION

Weld area

Melted metal Heat-affected zone

Melted area

Root pass

Joining Area

BA

SE

ME

TAL B

AS

E M

ETA

L

> 18 000 Kelvins

14 000 à 18 000 K

1 000 à 10 000 K

TIG ARC The temperature of the welding cone where the electrode is located is higher than 4800°C.

Due to these levels of temperatures, the equipment must be cooled either during prefabrication, or when using open welding heads, or directly in the welding head when you use closed chamber welding heads

TIG welding is an arc welding processusing a non-fusing electrode. ”

The arc is created through the gas that circulates in the gas nozzle placed all around the electrode. Welding can be performed by a direct polarity (the – pole of the power source is connected to the electrode), for most of the metals and alloys - (steel, stainless steel, copper, titanium, nickel…), but not in the case of light aluminum alloys or magnesium. In these cases you will need to weld with alternating polarity (for a limited time the elec-trode is connected with the + pole of the power source). If you weld in a continuous way with alternating polarity (+ pole connected to the power source), the electrode will be damaged as it will melt.

The TIG welding process allows easy transfer from the electricity (the electric arc between the electrode and the weld piece) into heat, wit-hout any contact with the welding piece. These high temperatures create the fusion of the tube, allowing them to be joined together in this way. When using filler metal, the wire is, this will be directly added to the weld puddle under the electrode. TIG welding is a very stable process and can be used in all positions. Automating the process can be achieved very easily.

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ORBITAL TIG WELDING HANDBOOK 5

Advantages-Depending on the final application, TIG welding

process can be used with or without filler wire.-With TIG welding, there is virtually no welding

smoke or residue.-Most metals can be welded with TIG, even in the

case of heterogeneous basic materials: stainless steel, titanium, magnesium, aluminium, copper.

-TIG welding is a stable process, and it can be automatized and applied in all welding positions.

-Defects of welding are extremely rare using TIG orbital welding, and the welds are of a high quality.

D isadvantages- Compared to a MIG/MAG welding equipment,

the productivity of TIG welding might be a little bit smaller

- Again, compared to MIG/MAG welding, the requested energy of TIG welding can be slightly higher.

- TIG welding can require a slightly cleaner environment

- TIG welding equipment represent a higher investment on some occasion compared to other processes.

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TYPE OF POWER

When using TIG process for welding, the most common power that is used is Direct current (DC). Alternating current (AC) is used when welding aluminum.

GASES Shielding gases protect the weld bead and the metal that is transferred through the arc from the ambient air, (which is 21% oxygen, 78% nitrogen, 1% other gases and humidity). The most common shielding gas is Argon. This gas helps with arc striking and is stable. Sometimes different gases are mixed depending on wall thickness, heat required and alloy.

ELECTRODES

In the past, tungsten-thoria electrodes have been frequently used for TIG welding, but the thorium represents a risk in terms of radioactive isotopes. A specific grinding machine is necessary in order to perform a good evacuation of the grinding dust par This can also present health hazards when grinding the tungsten.

Today, welders use mostly cerium or lanthanum based tungsten electrodes in order to avoid any risk of radioactivity .In addition to this, they are equally as effective as tungsten-thoria electrodes.

FILLER WIRENo filler wire is necessary if you want to weld stainless steel

with a thickness of less than 3mm. The TIG welding process does not always require a filler wire. But in some cases a filler metal can be necessary when required on certain exotic alloy and of course heavier wall applications.

Filler wire may be used when:- Certain highly corrosive resistant alloys are being welded- Thicker wall material requires a beveled joint- Different types of alloys are being joined together- If the structure of alloy is modified during the welding

process

A TIG installation includes several main components ”

M ater ials and cons umables

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What kind of industries needs TIG welding?When welding tube, the TIG welding process offers numerous advantages:

A clean process

Compact

Full penetration

A thin weld seam

An important point of this procedure is that the weld seam is very high in quality, for two reasons: the purity of the weld as well as the surface finish. This becomes critical when a specific welding project demands such results for applications in industries such as semi-conductor, pharmaceutical, food & dairy and aerospace.

TIG welding can be used for assembling production lines as well as on site repairs and other field applications.

As you can see, TIG welding is used when a very high quality of weld, with full penetration is required.

TIG welding can be used for assembling production lines, as well as for repairs on site.”

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Orbital welding was developed during the sixties, in order to meet the requirements of the aerospace industry, especially in regards of elements that must have a high degree of integrity, such as hydraulic systems.

Orbital TIG welding can be automated very easily. In fact, the torch is mobile and the piece remains stationary. The process is thus particularly suitable for welding tubes. Orbital welding is well adapted to on site welding appli-cations.For automatic orbital TIG welding on stainless steel pipe systems, repeatability is influenced by several factors. These include the shape of the tungsten, the pressure of the purging gas inside the pipe system, the purity of the purging gas, surface preparation during the cutting, etc. Surface preparation is absolutely essential to obtain a quality weld. The pieces (pipe) being joined must be cut

very straight and cleanliness is essential.This type of weld is used on pure gas manifolds in the semiconductor industry, for pure water (water for injec-tion, for example) in the pharmaceutical industry, in the foodstuffs industry, in the chemical and oil industry and also in the nuclear industry.

Cases of weld failure on these components, in flight and at speeds approaching the speed of sound, resulted in the development of orbital welding.”

W h at is orb italT I G weld ing?

9ORBITAL TIG WELDING HANDBOOK

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Orbital welding is a very stable process, but careful preparation is neces-sary, particularly concerning the grade of the rods used, the quality of the gases used, the quality of the tubes and elements welded, the quality of the tack -welds, as we shall see later, and also the quality of the welding current used. When all these elements are properly controlled, the orbital TIG welding defect ratio is less than 1%.

From the beginning, orbital welding has almost always been combined with a TIG process and a tungsten rod without fusion, except in certain cases where a cold wire has to be used. Very many metals can be welded: the hardest, the most heat resistant and the most corrosion resistant steel, non -alloy or low alloy carbon steel, nickel alloys, titanium, copper, aluminum. The process is executed under control, in a protecting atmosphere. It is extremely clean, generates few particles and doesn’t cause unwanted projections. The process is mainly used for welding stainless steels and it meets the most stringent requirements in terms of both mechanical quality and appearance.

The human -machine interfaces make the process very user friendly, so that orbital welding is made relatively easy and can be attempted by trained operators who may not necessarily be welders.

In most cases, an integral auto-computing system sets the welding parameters, to guide the operator towards an optimum welding result. The parameters precisely control the energy applied to compensate for gravity and the heating of the tube during welding.The main problem with this process is the low execution rate (around 100 mm/mn), and the small deposit when welding with wire.

P

P

PP

Torch rotates

Fix

When all the elements are properly controlled, the orbital TIG welding defect ratio is less than 1%:

- quality of the tube and elements welded,

- careful preparation,- quality of the tack -welds,- quality of the welding

current used-quality of the gases used ”

Setting up an orbital welding system, in terms of both the mechanical system that guides the tungsten around the tube, and the electronics, with the communicating and sophisticated power sources, remains an invest-ment that is between 10 and 30 times greater than for a manual system. However, it is less expensive than a welding robot.

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10ORBITAL TIG WELDING HANDBOOK

AdvantagesHIGH QUALITY WELDS You obtain a much better quality by automated TIG welding compared to manual welding. Welds produced manually are not always of a poor quality, but the number of discarded tubes / defects is higher compared to TIG welding.

TRAINING / COMPETENCES Using an orbital welding equipment is possible without a long and tedious training. You do not need to be an accomplished welder to proceed to orbital welding. Training sessions are typically much shorter and easier compared to those of a specialized welder. This results in a gain in terms of labour costs and in deploying the welding teams.

A HIGHER PRODUCTIVITYAutomated orbital TIG welding provides you with a better productivity compared to manual welding. The welding tasks can be registered and repeated any time it will be necessary. When you make a weld manually, a variety of factors have a direct influence over it, whereas with automated TIG welding, the welds can be repeated by the equipment as often as required in the future.

A WELDING TECHNOLOGY SUITINGCONFINED SPACE ENVIRONMENTS.Orbital welding equipment allows welding in all situations: confined spaces, lack of visibility, high-risk environments. Welding can be performed from a remote location and a special welding camera can be added to the equipment, reducing any risk for the operators.

ORBITAL TIG WELDING ENSURES BETTER MONITORING AND TRACEABILITY OF THE WELDS Orbital welding equipment allows a great recording of each weld. Every welding parameter is registered, the welds can be repeated any time by means of the data acquisition of each weld.

D isadvantagesOrbital TIG welding requires an investment if you want to automatize welding, but the return on investment is achieved quickly by the high quality of the welds that automated welding provides, as well as the increase in productivity.

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functionality equipments of orbital welding

ARC PHENOMENA

A difference in potential is used, between two rods that are very close to each other in a gaseous sub-atmosphere, to release electrons from the CATHODE, which are attracted by the ANODE.The CATHODE (generally the electrode) is connected to the negative pole, while the ANODE is connected to the positive pole (generally earth). The electron transfer causes an impact on the gas atoms (ionisation) which releases other electrons. A current is set up through the arc column or the plasma column forming a gaseous conductor between the job cathode and the job anode. Only 30% of the calorific energy generated by the arc is used for welding, the rest being absorbed by the mass of the piece, by radiation or by convection. It is for this reason that the TIG process is mainly used for quality work, and cannot achieve a productivity level comparable with other welding processes, such as coated rod, MIG-MAG or submerged arc, etc.

Depending on the type of material being welded, the arc may be AC or DC, pulsed or non-pulsed.

Depending on the type of material being welded, the arc may be AC or DC, pulsed or non-pulsed.”

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WIRE, TORCH ROTATION, GAS

The advantage with orbital TIG welding is that every settings can be customized.

Whether it is gas, torch rotation or filler wire, you will be able to adjust all of these settings before the machine welds.

In this way, you will be able to control several gases (of protection and welding), regulate the rotational speed of the torch, manage the start and stop of the wire, ... All this before the welding so that the final weld is of an impeccable quality.

WELDING CURRENT

DC / Direct polarityIn DC, theoretically, direct polarity is used, which means that the rod is connected to the negative polarity and thus emits electrons. In this case, the temperature is higher on the fusion bath than on the rod. The “reasonable” temperature of the rod tip allows it to retain its shape. The welding arc is therefore perfectly stable and the weld bead will be even. Direct polarity is used for carbon steels, alloyed steels and copper or nickel-based alloys. In very specific cases, direct polarity can also be used for welding light alloys under helium protection.

DC / Reverse polarityIn reverse polarity, the rod is connected to the positive pole. In this case, the temperature on the rod is higher than on the fusion bath. The impact of the electrons then tends to heat the rod, which is thus damaged, forcing the operator to reduce the welding current. The rod tip will form a blob and the arc will become unstable and erratic. Thus, DC welding with reverse polarity is only used for very specific applications. However, reverse polarity offers advantages for the coated rod welding process.

The advantage with orbital TIG welding is that everything is configurable”

Reversed polarity

Direct polarity

+

-

+

-

-

+

-

+

Reversed polarity

Direct polarity

+

-

+

-

-

+

-

+

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CONCLUS IONAs you have seen during this short presentation, orbital TIG welding offers many possibilities for applications with high standards and distinctive features, which require high quality welds.

We are aware that this presentation does not go into detail and some points have not been addressed, but don’t you worry! This document was only an introduction on the vast subject of automated TIG and orbital TIG welding!

Stay tuned: we will send you another more complete and precise guide on our Global Process offer and all the parameters you should take into account for an orbital TIG welding.

In the meantime, this guide may have raised some questions, so don’t hesitate to contact us to discuss them.

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