AWS A5.1 Classification

Tensile Strength (N/mm2) Type of Coating

E6010 414 Cellulosic E6011 Cellulosic E6012 Rutile E6013 Rutile E7014 482

Rutile, iron powder

E7015 Basic

E7016 Basic

E7018 Basic, iron powder

E7024 Rutile high recovery

Figure 2 Examples of some of the commonly used AWS A5.1 Electrodes.

Figure 3 Mandatory Classification Designators Designates: an electrode Designates: the tensile strength

(min.) in ksi of the weld metal

Designates: the welding position the type of covering the kind of current Typical electrode to AWS A5.1

General Description EN 499 AWS A5.1 / 5.5 Cellulosic electrodes

(For vertical-down welding ‘Stovepipe welding’ of pipeline girth welds)

E 38 3 C 21 E 42 3 Z C 21 E 46 3 Z C 21 E 42 3 C 25 E 46 4 1Ni C 25 E6010 E7010-G E8010-G E7010-P 1 * E8010-P 1 *

* P = specially designated piping electrodes

Rutile electrodes

(For general purpose fabrication of low strength steels – can be used for all positions except vertical-down)

E 38 2 R 12 E 42 0 R 12

E6013 E6013

Heavy coated rutile electrodes

(Iron-powder electrodes) (For higher productivity welding for

general fabrication of low strength steels – can generally only be used

for downhand or standing fillet welding) E 42 0 RR 13 E 42 0 RR 74 E6013 E7024 Basic electrodes

(For higher strength steels, thicker section steels where there is risk of H cracking; for all applications requiring good fracture toughness)

E 42 2 B 12 H10 E 42 4 B 32 H5 E 46 6 Mn1Ni B 12 H5 E 55 6 Mn1Ni B 32 H5 E 46 5 1Ni B 45 H5* E 55 5 Z 2Ni B 45 H5* E 62 5 Z 2Ni B 45 H5* E7016 E7018 E 7016-G E8018-C1 E8018-G E9018-G E10018-G * Vertical-down low H electrodes

14.6 TIG FILLER WIRES

Filler wires manufactured for TIG welding have compositions very similar to base material compositions. However, they may contain very small additions of elements that will combine with oxygen and nitrogen as a means of scavenging any contaminants from the surface of the base material or from the atmosphere.

For manual TIG, the wires are manufactured to the BS EN 440 and are provided in 1m lengths (typically 1.2, 1.6, and 2.4mm dia.) and for identification have flattened ends on which is stamped the wire designation (in accordance with a particular standard) and, for some grades, a batch number.

TIG consumable identification is stamped at the end of the wire

For making precision root runs for pipe butt welds (particularly for automated TIG welding) consumable inserts can be used that are made from material the same as the base material, or are compatible with it.

For small diameter pipe, the insert may be a ring but for larger diameter pipe an insert of the appropriate diameter is made from shaped strip/wire, examples of which are shown below.

14.6.1

TIG SHIELDING GASES

Pure Argon is the shielding gas that is used for most applications and is the preferred gas for TIG welding of steel and gas flow rates are typically ~ 8 to 12 litres/minute for shielding.

The shielding as not only protects the arc and weld pool but also is the medium required to establish a stable arc by being easy to ionise. A stable arc cannot be established in air and hence the welder would not be able to weld if the shielding gas were not switched on.

Argon with a Helium addition – typically ~30% may be used when a ‘hotter’ arc is needed such as when welding metals with high thermal conductivity, such as copper/copper alloys or thicker section aluminium/aluminium alloys.

There are some circumstances when special shielding gases are beneficial, for example:

Ar + 3 to 5% H for austenitic stainless steels and Cu-Ni alloys Ar + ~3% N for duplex stainless steels

14.6.2

TIG BACK-PURGING

For most materials, the underside of a weld root bead needs to be protected by an inert gas (a back-purge) – typically ~ 6 to 8 litres/minute during welding.

For C steels and low alloy steels with total alloying additions ≤ 2.5% it may not always be necessary to use a back-purge but for higher alloyed steels and most other materials there may be excessive oxidation – and risk of lack of fusion if a back-purge is not used.

14.7 MIG/MAG FILLER WIRES

Solid filler wires manufactured for MIG/MAG generally have chemical compositions that have been formulated for particular base materials and the wires have compositions similar to these base materials. Solid wires for welding steels with active shielding gases are deoxidised with manganese and silicon to avoid porosity. There may also be titanium and aluminium additions. Mild steel filler wires are available with different levels of deoxidants, known as double or triple de-oxidised wires. More highly deoxidised wires are more expensive but are more tolerant of the plate surface condition, e.g. mill scale, surface rust, oil, paint and dust. There may, therefore, be a reduction in the amount of cleaning of the steel before welding.

These deoxidiser additions yield a small amount of 'glassy' slag on the surface of the weld deposit, commonly referred to as silica deposits. These small pockets of slag are easily removed with light brushing; but when galvanising or painting after welding, it is necessary to use shot blasting. During welding, it is common practice to weld over these small islands since they do not represent a thick slag, and they usually spall off during the contraction of the weld bead. However, when multipass welding, the slag level may build up to an unacceptable level causing weld defects and unreliable arc starting.

Steel wires usually have a flash coating of copper to improve current pick-up and to extend the shelf life of the wire. However, the copper coating can sometimes flake off and be drawn into the liner and wire feed mechanism, particularly if there is misalignment in the wire feed system. This may cause clogging and erratic wire feed. Uncoated wires are available as an alternative, although electrical contact may not be

as good as with copper-coated wires, and contact tip operating temperatures may be higher.

Some typical Standards for specification of steel wire consumables are:

EN 440: Welding consumables - Wire electrodes and deposits for gas shielded metal

arc welding of non-alloy and fine grain steels - Classification.

EN 12534: Welding consumables - Wire electrodes, wires, rods and deposits for gas

shielded metal arc welding of high strength steels - Classification.

Wire sizes are typically in the range 0.6 to 2.4mm diameter but the most commonly used sizes are 0.8, 1.0, 1.2 and 1.6mm and provided on layer wound spools for consistent feeding.

Spools should be labelled to show the classification of the wire and its’ diameter.

Flux-cored and metal-cored wires are also used extensively although the process is then referred to as FCAW (Flux Cored Arc Welding) and MCAW (Metal Cored Arc Welding)

14.7.1

MIG/MAG GAS SHIELDING

For non-ferrous metals and their alloys (such as Al, Ni & Cu) an inert shielding gas must be used. This is usually either pure Argon or an Argon rich gas with a Helium addition.

The use of a fully inert gas is the reason why the process is also called MIG welding (Metal Inert Gas) and for precise use of terminology this name should only be used when referring to the welding of non-ferrous metals

The addition of some Helium to Argon gives a more uniform heat concentration within the arc plasma and this affects the shape of the weld bead profile

Argon-Helium mixtures effectively give a ‘hotter’ arc and so they are beneficial for welding thicker base materials those with higher thermal conductivity e.g. Copper or Aluminium.

For welding of steels – all grades, including stainless steels – there needs to be a controlled addition of oxygen or carbon dioxide in order to generate a stable arc and give good droplet wetting. Because these additions react with the molten metal they are referred to as active gases and hence the name MAG welding (Metal Active Gas) is the technical term that is use when referring to the welding of steels.

The percentage of carbon dioxide (CO2) or oxygen depends on the type of steel being welded and the mode of metal transfer being used – as indicated below: -

 100%CO2

and faster welding

this gas promotes globular droplet transfer and gives high levels of spatter and welding fume

for low carbon steel to give deeper penetration (Figure 4)

 Argon + widely used for carbon and some low alloy steels (and 15 to 25%CO2

 Argon + widely used for stainless steels and some low alloy steels FCAW of stainless steels)

1 to 5%O2

Figure 4 The effects of shielding gas composition on weld penetration and profile

Figure 5 Active shielding gas mixtures for MAG welding of carbon, carbon-manganese and low alloy steels