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Shielding gases for arc welding and cutting (May 2001)

   
W Lucas
W Lucas

W Lucas

Originally published in Welding & Metal Fabrication, 2001, Vol. 69, No. 4, May, pp 16-18 by DMG World Media UK Ltd, - www.dmgworldmedia.com/

 

 


Lucas, DSc, PhD, CEng, FIM, FWeldI, is Consultant & Technology Manager, Arcs at TWI in the Metallurgy, Corrosion, Arc & Surfacing Group. He is also visiting Professor at Liverpool University.

In recent years, there have been substantial changes in the range of shielding gases available for arc welding and cutting. Equally significant has been the re-branding of gases by some of the major gas supply companies. The range of shielding gases currently available in the UK are listed in Table 1together with their designation in accordance with the requirements of BS EN 439: 1994, Welding consumables - Shielding gases for arc welding and cutting.

Classification of shielding gases

BS EN 439 classifies shielding gases into six main groups according to their chemical properties and reaction behaviour. The groups and the prefix letter are as follow:

The groups, apart from Group S, are then sub-divided with an Identification Number which specifies the components and the compositional ranges. The Identification Number and the components in percent volume are as follows:

R reducing gas mixtures - those mixtures containing hydrogen
I inert gases and mixtures - argon, helium and their mixtures
M mixed gases - argon based gases with additions of oxygen or carbon dioxide or both
C carbon dioxide rich mixtures
F unreactive or reducing gases and mixtures - nitrogen and nitrogen based mixtures
S specials - any gas or mixture not covered in the other groups

Table 2. Classification of shielding gases for arc welding and cutting

The shielding gases in Groups R and M containing helium have a suffix identifying the amount of helium in the mixture:

SymbolComponents in percent volume
GroupIdentification No.OxidisingInertReducingUnreactive
CO 2O 2ArHeH 2N 2
R 1     Balance   > 0 to 15  
2     Balance   > 15 to 35  
I 1     100      
2       100    
3     Balance > 0 to 95    
M1 1 > 0 to 5   Balance   > 0 to 5  
2 > 0 to 5   Balance      
3   > 0 to 3 Balance      
4 > 0 to 5 > 0 to 3 Balance      
M2 1 > 5 to 25   Balance      
2   > 3 to 10 Balance      
3 > 0 to 5 > 3 to 10 Balance      
4 > 5 to 25 > 0 to 8 Balance      
M3 1 > 25 to 50   Balance      
2   > 10 to 15 Balance      
3 > 5 to 50 > 8 to 15 Balance      
C 1 100          
2 Balance > 0 to 30        
F 1           100
2         > 0 to 50 Balance

(1) contains >0 to 33% helium
(2) contains >33 to 66% helium
(3) contains >66 to 95% helium

Applying the classification

The reaction behaviour of the shielding gas will determine its suitability for arc welding and cutting processes. For example, an oxidising gas is normally required to stabilise the arc in MIG/MAG welding but an inert or reducing gas is required for TIG and plasma processes.

Typical applications of the shielding gases are given in Table 3. The Classification Code can be used to differentiate between, for example, slightly oxidising (Group M1), intermediate (Group M2) and more pronounced oxidising gases (Group M3).

Table 3. Typical applications of shielding gases for arc welding and cutting

The Classification Code can be used to identify the shielding gas on the Welding Procedure Approval Record (BS EN 288) but the range of approval is normally restricted to the type of gas (nominal composition) used in the welding procedure test. In approval testing of welders to BS EN 287, the Classification Code is shown on the Manufacturer's Welding Procedure Specification (WPS) but the test will confer approval on the welder to use any similar shielding gas.

GroupIdentification No.RemarksTypical applications
R 1 Reducing TIG plasma arc welding, plasma arc cutting, back shielding
2
I 1 Inert MIG, TIG, plasma arc welding, back shielding
2
3
M1 1 slightly oxidizing

More pronounced oxidation
MAG
2
3
4
M2 1
2
3
4
M3 1
2
3
C 1
2
F 1 Unreactive Plasma arc cutting, back shielding
2 Reducing

Acknowledgements

The author would like to acknowledge the information provided for the table by:

A Williams Air Products Plc
D Yates BOC
R Eden Linde Gas
G Bruton Messer UK Ltd

Table 1. Shielding gases available in the UK 

EN 439
Class
Composition (Volume %)Reaction
behaviour
Air ProductsBOCMesserLindeProcess
ArHeCO 2O 2H 2N 2
Pure gases
I1 >99.998 - - - - - Inert Argon HP Pureshield Argon Argon 4.8 Argon TIG, MIG
I2 - >99.9 - - - - Inert Helium Helium Helium Helium TIG, MIG
C1 - - >99.9 - - - Pronounced oxidising CO 2 CO 2 CO 2 CO 2 MAG
Argon-Helium
13 70 30 - - - - Inert Alumaxx Plus Alushield Light Stellar 30 Heliweld 7 TIG, MIG
13 50 50 - - - - Inert Astec 50 Alushield Universal Stellar 50 Heliweld 5 TIG, MIG
13 30 70 - - - - Inert -     Heliweld 2 TIG, MIG
13 25 75 - - - - Inert Astec 75 (25) Alushield Heavy Stellar 75 - TIG, MIG
Argon-Hydrogen
R1 99 - - - 1 - Reducing       Hygon 1 TIG
R1 98.5 - - - 1.5 - Reducing   Stainshield TIG     TIG
R1 98 - - - 2 - Reducing Inomaxx TIG   Hylar 2 Hygon 2 TIG
R1 95 - - - 5 - Reducing Hytec 5 Specshield 5%
H 2
Hylar 5 Hygon 5 TIG
R1 85 11 - - 4 - Reducing   Specshield 11%He, 4%H 2     TIG
R1 65 - - - 35 - Reducing   Specshield 35% H 2   Hygon 35 TIG, Plasma Cutting
Argon-Helium-Hydrogen
R1(1) 71.9 25 - - 3.1 - Inert       Corgon He 25S TIG, MIG
Argon-Oxygen
M13 99 - - 1 - - Slightly oxidising       Argon S1 MAG
M13 98 - - 2 - - Slightly oxidising Prodarc 2 Specshield 2% O 2 Exellar 2 Argon S2 MAG
M22 95 - - 5 - - Slightly oxidising     Exellar 5   MAG
M22 92 - - 8 - - Slightly oxidising       Argon S8 MAG
Argon-CO 2
M12 98 - 2 - - - Slightly oxidising Inomaxx 2       MAG
M12 97.5 - 2.5 - - - Slightly oxidising   Specshield 2.5% CO 2 Krysal 3 Cronigon 2 MAG
M12 96.5 - 3.5 - - - Slightly oxidising       Cronigon 3 MAG
M21 92 - 8 - - - More oxidising   Specshield 8% CO 2 Krysal 8   MAG
M21 90 - 10 - - - More oxidising   Specshield 10% CO 2     MAG
M21 86 - 14 - - -       Krysal 14   MAG
M21 86 - 20 - - - More oxidising   Specshield 20% CO 2 Krysal 210 Corgon 18 MAG
M21 75 - 25 - - - More oxidising   Specshield 25% CO 2     MAG
Argon-Helium-CO 2
M12(1) 79.5 20 0.5 - - - Slightly oxidising       Heliweld DB1 MAG
M21(1) 68 20 12 - - - Oxidising Ferromax Plus       MAG
M12(2) 63 35 2 - - -       Stellar 6   MAG
M12 (2) 60 38 2 - - - Slightly oxidising Inomaxx Plus Stainshield Heavy   Heliweld 3 MAG
M21(1) 50 25 25 - - - Oxidising       Cronigon He 25C MAG
M12(2) 49.95 50 0.1 - - - Slightly oxidising       Cronigon He 50S MAG
M12 (2) 43 55 2 - - - Slightly oxidising Astec S4 Stainshield Universal   Heliweld 6 MAG
M12 (3) 25 73 2 - - - Slightly oxidising       Heliweld 1 MAG
M12 (3) 23.5 75 1.5 - - - Slightly oxidising Astec S5 (15)       MAG
M14 (3) 13.5 85 1.5 - - - Slightly oxidising   Stainshield Light     MAG
M12 (3) 13 85 2 - - - Slightly oxidising     Stellar 1   MAG
Argon-Helium-O 2
M13(1) 69.97 30 - 0.03 - - Slightly oxidising       Varigon He 30S MIG/TIG
M13(2) 49.97 50 - 0.03 - - Slightly oxidising       Varigon He 50S MIG/TIG
M13(2) 49 50 - 1 - - Slightly oxidising       Brazematic MAG
Argon-CO 2-O 2
M14 93 - 5 2 - - More oxidising Coogar 5 Argoshield Light Krysal 5 Corgon 5 MAG
M24   - 7 2.5 - - More oxidising Ferromax 7       MAG
M24 86 - 12 2 - - More oxidising   Argoshield Universal   Corgon 12 MAG
M24 85 - 13.5 1.5 - -       Krysal SM   MAG
M24 83 - 15 2 - - More oxidising Coogar SG       MAG
M24 82.5 - 15 2.5 - - More oxidising Ferromax 15       MAG
M24 78 - 20 2 - - More oxidising Coogar 20 Argoshield Heavy Krysal 20 Corgon 20 MAG
Argon-Helium-CO 2-H 2
M11(1) 67.95 30 0.1   2   Reducing       Cronigon He 30S MIG
Argon-Helium-CO 2-O 2
M14(3) 25 71 2 2     More oxidising       Heliweld 4 MAG
Argon-N 2
SI1 97.5         2.5 Inert   Specshield 2.5% N 2   Argon DNI TIG
Argon-Helium-N 2
S13 79 20       1 Inert Duplex 1       TIG
S13 77.75 20       2.25 Inert Duplex 2       TIG
S13 67.5 30       2.5 Inert       Heliweld DN1 TIG, MIG

Notes

Identification numbers for gases in Groups R and M containing Helium
(1) Contains >0 to 33% Helium
(2) Contains >33 to 66% Helium
(3) Contains >66 to 95% Helium

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