Welding Dm

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WELDING

Debasis Mitra

Inspection Department


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Contents

1. Welding

1.1 Definition

1.2 Type of welding processes.

2. Welding processes used in HPL.

2.1 Shielded Metal Arc Welding ( SMAW )2.2 Gas Tungsten Arc Welding ( GTAW )

3. Welding process variables : - Welding Technique.

4. Fillers & Electrodes.

5. Welding Defects


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1. Welding


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Welding is a localized fusion of metalsproduced by heating to suitabletemperatures. Pressure and/or filler mayor may not be used. The filler material has

a melting point approximately the same orbelow that of the base metals.

1.1 Definition :-


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2. Welding processes mainly used in HPL

Shielded Metal Arc Welding ( SMAW )

Gas Tungsten Arc Welding ( GTAW )


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Welding Process Basics : SMAW and GTAW

Advantage and limitation of GTAW & SMAW

SMAW Process variable : Controlling issues

GTAW Process variable : Controlling Issues


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Shielded Metal Arc Welding ( SMAW ) or Stick

welding as commonly known as is an arcwelding process where coalescence is produced by heating the workpiece with an electric arc setup between a flux coated electrode and theworkpiece.

2.1 Shielded Metal Arc Welding ( SMAW )


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SMAW Process


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SMAW Process : Advantages

Uses an electrode rod that is quickly consumed ( highdeposition rate)

Uses equipment that is simple, inexpensive, and highlyportable,

Uses an electrode that provides and regulates its ownflux,

Provides all position flexibility,Is less sensitive to wind or drafts,


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Gas Tungsten Arc Welding process is an arc welding process wherein coalescence is produced by heating the job with an electric arc struck between a tungstenelectrode and the job.

2.2 Gas Tungsten Arc Welding


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GTAW Process


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GTAW Process : Advantages

Produces very high-quality, superior welds,

Is excellent for thin section

Welds can be made with or without filler metal,

Provides precise control of welding variables (i.e. heat),

Heat Flux and deposition rate can be independently controlled

Excellent Root Penetration

Welding yields low distortion,

Leaves no slag or splatter.


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GTAW Process : Limitations

Slow Process . Weld deposition rate is very low .

Needs more set up than SMAW . Complex than SMAW

Needs welder skill better than needed for SMAW

More expensive . Not economical for section thickness > 10mm

Sensitive to Windy / Drafty environment


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3. Welding Process Variables


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Type of Current ( Power Source )

Terminal connection

Size of Electrodes

Amperage

Shielding Gas

Shielding Gas flow


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Welding Process Variables : Welding technique

Arc length

Travel Speed

Travel Angle

Welding Bead / Welding Technique


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Type of Power ( Current )

AC : advantageCheaper Power source

No ARC blow

Better Slag cleaning action

Limitations

Arc instability

Not preferred for Overhead / Vertical position


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Type of Power ( Current )

DC : advantage Mostly used

Smoother arc

Produces uniform weld bead size

Is good for short arc technique

Preferred for Vertical and Over Head welding

Produces good wetting action

Limitations

Arc Blow


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Terminal connection

For GTAW

DCSP ( DC straight polarity ) /

DCEN ( DC Electrode negative )

For SMAW

DCRP ( DC Reverse polarity ) /

DCEP ( DC Electrode Positive )


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Electrode Size : Selection factors

Deposition Rate requirement

Joint design ( Bevel angle / Root opening )

Position ( Flat / Horizontal / Vertical / Overhead)

Pass


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Amperage setting

Higher the amp erage : Higher the depos i t ion rate

But Excess amperage produces defects

Also too low amperage produces defects


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Welding Procedure Specification (WPS)Prepared as per ASME Sec IXContains Essential and Non-Essentialvariables.

Fillers / Electrodes as per ASME Sec IIPart C.


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4. Electrodes and fillers


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Functional difference between

Electrode

E-

Filler

ER-


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Electrode / Filler Specification designation

As per AWS ( American Welding Society ) .

E XXAB

E Electrode ER Filler

XX minimum tensile strength of weld metal in thousands of pounds persq.inch.

A indicates the welding position ( 1-> all , 2-> flat , 3-> horizontal , 4->overhead )

B - Power supply, type of covering, type of arc, penetration characteristics,etc.

Eg; E 6012 60000 psi 1 denotes all positions 2 High rutile sodiumsilicate binder etc.


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5. Welding Defects


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Typical cracks in welding

Solidification crack


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Thank You

Welding Dm

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