Selection of Welding Electrode

Dear Readers,

We often encountered a problem at site is selection of welding electrodes with respect to parent material or Grade of material. These are grades are characterized by improved weldability.

Following guidelines are suggested for achieving satisfactory weld joint properties:Use of low hydrogen basic coated electrode with matching strength.

Welding electrodes of such specification are suitable for welding of high strength low alloy steels, fine grained steels, quenched & tempered steels having UTS upto 600 MPa. The welding type, electrodes etc for different grades are given below:

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Welding Positions

Dear Readers,

In Construction Industry any conversation around welding starts with a discussion on welding position, it is mandatory to qualify the welder. At site welding activity starts with welder qualification. The American Welding Society (AWS) has defined the four basic welding positions. The same positions is followed in construction as well as welding related industries.

The four basic welding positions are: flat, horizontal, vertical, and overhead. An Alpha numeric is used to identify the position. Eg. 4F & 2G First number is used to define the position and alphabetic is used for the weld.

1 = Flat Position

2 = Horizontal Position

3 = Vertical Position

4 = Overhead Position

F = Fillet Weld

G = Groove Weld

1 refers to a flat position, either 1F or 1G

2 refers to a horizontal position, either 2F or 2G

3 is a vertical position, either 3F or 3G

4 is an overhead position, either 4F or 4G

The 1G and 5G horizontal and 2G vertical positions refer to the pipe position.

6G is an inclined position

Flat Position Welding: This type of welding is performed from the upper side of the joint. The face of the weld is approximately horizontal. The common term for this kind of weld is called, 'flat position' but it is also referred to as the 'down hand' position.

Horizontal Position Welding: In horizontal welding, the weld axis is approximately horizontal, but the weld type dictates the complete definition. For a fillet weld, welding is performed on the upper side of an approximately horizontal surface and against an approximately vertical surface. For a groove weld, the face of the weld lies in an approximately vertical plane.

Vertical Position Welding: In vertical position welding, the axis of the weld is approximately vertical. When welding is done on a vertical surface, the molten metal has a tendency to run downward and pile up.

Overhead Position Welding: Overhead welding is performed from the underside of a joint. In overhead welding, the metal deposited tends to drop or sag on the plate, causing the bead to have a high crown.

The welding positions explained above are commonly used by codes and industrial practice when qualifying welders and job execution.

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Weld Joints

Welds are made at the junction of the various pieces that make up the weldment. The junctions of parts, or joints, are defined as the location where two or more members are to be joined. The five basic types of welding joints are listed below.

 

1). Butt Joint (B). A joint between two members lying approximately in the same plane. 

2). Corner Joint (C). A joint between two members located approximately at right angles to each other in the form of an angle. 

3). Edge Joint (E). A joint between the edges of two or more parallel or mainly parallel members. 

4). Lap Joint (L). A joint between two overlapping members. 

5). Tee Joint (T). A joint between two members located approximately at right angles to each other in the form of a T.

In order to produce weldments, it is necessary to combine the joint types with weld types to produce weld joints for joining separate members. Each weld type can not always be combined with each joint type to make a weld joint. Below table shows the welds applicable to the basic joints.

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Classification of Electrode - AWS

Dear Readers,

The American Welding Society’s classification number series for welding electrodes has been adopted by the welding industry. AWS CLASSIFICATION A 5.1 & 5.5 for Covered Carbon Steel & Low alloy steel welding electrodes. The electrode identification system for steel arc welding is set up as follows:

E

7

0

1

8

X

1. Prefix Letter 'E' stands electrode for arc welding.

2. The first two digits indicate tensile strength (the resistance of the material to forces trying to pull it apart) in thousands of pounds per square inch of the deposited metal.

3. The third digit indicates the position of the weld.

            1 is for all positions;

            2 is for flat and horizontal positions only;

            3 is for flat position only.

4. The fourth digit indicates the type of electrode coating and the type of power supply used;

                0. High cellulose sodium DC reverse polarity (+)

                1. High cellulose potassium AC or  DC reverse polarity (+)

                2. High titania sodium AC or DC straight polarity (-)

                3. High titania potassium AC or DC either polarity ( ± )

                4. Iron powder titania AC or DC either polarity ( ± )

                5. Low Hydrogen sodium DC reverse polarity (+)

                6. Low Hydrogen potassium AC or  DC reverse polarity (+)

                7. High iron oxide, iron powder AC /DC (+) / DC (-)

                8. Low Hydrogen potassium ,iron powder AC/DC (+)

5. Suffix Letter 'X' stands for suffixes A1,B1,B2,B3,C1,C2,C3,D1,D2,G,M etc. and designates the chemical composition of the deposited weld metal.

Example illustrated in below picture. Click on Picture to enlarge
 

For Example let us see E7018
 

The number E7018 indicates an arc welding electrode with a minimum stress relieved tensile strength of 70,000 psi; is used in all positions; and Low Hydrogen potassium ,iron powder with AC/DC (+) polarity is required.

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