ARC WELDING ELECTRODE

ARC WELDING ELECTRODE

ARC WELDING

ELECTRODE

NAFFAA AL-ANEZI MECHANICAL INSPECTOR

OCTOBER 30,2005

 TYPES OF ELECTRODE COATING

 STORAGE AND DRYING OF

ELECTRODES

TESTING OF ELECTRODES

HISTORY OF ARC WELDING COATED

ELECTRODE

During first stage of work with metal arc welding a bare electrode was in use which was producing brittleness in the welded area and the weld was considerably weak overheating effect on weld metal was noticed as there was no arc stability.

To overcome these difficulties researchers developed a number of electrodes in 1907 that were covered with organic or mineral materials which is known as coating or flux

WHAT IS AN ELECTRODE ?

The electrode may be defined as “it is metal of which the sole purpose to carry the current and sustain the electric arc between its tip and base metal as well as in some cases it melts and supplies filler metal addition in the proposed joint.”

Electrode can be divided into two groups depending upon their functions which are given below

ELECTRODE

CONSUMABLE AND

NON-CONSUMABLE

 The consumable electrodes refers to conduct current from electrode holder to metal and supply filler metal to the joint, like in SMAW

 non-consumable electrodes are only used to work as conductor carrying the current from electrode holder to base metal, like in GMAW

Arc welding electrodes are classified in

groups by American Welding Society (AWS a5.1-91) based upon their type of coating, mechanical properties and performance characteristics as well as weld metal chemistry for our discussion we can categorize the electrode as under

TYPES OF ELECTRODE

ELECTRODES TYPES

ELECTRODE

BASED UPON MATERIALS BASED UPON COATING

BASED UPON MATERIALS

 MILD STEEL ELECTRODES (AWS A5.1)

 LOW ALLOY STEEL ELECTRODES (AWS A5.5)

 STAINLESS STEEL ELECTRODES (AWS A5.4)

 ELECTRODES FOR CAST IRON (AWS A5.15)

 COPPER AND COPPER ALLOY ELECTRODE

MILD STEEL ELECTRODES

AMERICAN WELDING SOCIETY SPECIFICATION

AWS 5.1 DESCRIBES THE REQUIREMENTS FOR

MILD STEEL ELECTRODES AN IDENTIFICATION SYSTEM HAS ADOPTED IN ORDER TO KNOW THE PROPERTIES AND CHEMISTRY OF THE ELECTRODE THE IDENTIFICATION HAS EXPLAINED AS UNDER

EXXXX

“E” DESIGNATES FOR ELECTRODE

 EXXXX FIRST TWO NUMBERS REFER TO

TENSILE STRENGTH OF THE DEPOSITED

WELD METAL

FOR EXAMPLE : E6010

“60” MEANS 60, 000 PSI TENSILE

STRENGTH OF THE DEPOSITED WELD METAL

 EXX X X THIRD NUMBER IS DENOTING THE POSITION IN WHICH THE

ELECTRODE CAN BE USED

EXAMPLE:

MOSTLY SUITABLE FOR V-DOWN

ONLY.

 EXXXX LAST NUMBER REFERS TO CHEMICAL COMPOSITION PRESENT IN THE ELECTRODE COATING FOR EXAMPLE :

 EXXXX The last two numbers together

indicate the type of welding current the

electrode can be used with

For example

EXX10 DC+

EXX11 AC OR DC+ EXX20 AC , DC

+,-EXX12 AC OR DC- EXX24 AC , DC

+,-EXX13 AC , DC+,- EXX27 AC, DC

+,-EXX14 AC , DC+,- EXX28 AC, DC +

EXX15 DC+

EXX16 AC , DC+

EXX18 AC , DC+

LOW ALLOY STEEL ELECTRODE

THESE ELECTRODES ARE DESIGNED FOR THE

WELDING OF LOW-ALLOY STEELS COMMONLY USED

IN STRUCTURES, PIPING, PRESSURE VESSEL.

THEY GIVE WELD DEPOSITS OF STEEL

CONTAINING A SMALL AMOUNT OF ALLOYING

ELEMENTS SUCH AS Mo, Cr, Ni, AND V THESE

ELECTRODES ARE SPECIFIED IN AWS A5.5

SPECIFICATION AND IDENTIFICATION IS SAME AS FOR MILD STEEL ELECTRODES.THE ELECTRODES

HAS A SUFFIX TO REFER AS LOW ALLOY STEEL

CONTENT LIKE

A1 0.5 Mo, B3 1.0% Mo,2.25%Mn , G 0.2% Mo, 0.3%Mn, 0.1% V

STAINLESS STEEL ELECTRODES

STAINLESS STEEL ELECTRODES ARE USED FOR THE WELDING OF CORROSION –

RESISTING AND HEAT- RESISTING STEELS THEY ARE EXPLIANED IN AWS A5.4

“SPECIFICATION FOR CORROSION –

RESISTING Cr AND Cr-Ni STEEL COVERED ELECTRODES”

SOME SS ELECTRODES HAVE GIVEN WITH THEIR MECHANICAL PROPERTIES IN THE

FOLLOWING TABLE.

Mechanical Properties As Per AWS A5.4

AWS

Classificatio

n

Tensile Strength Ksi

BASED UPON COATING

CELLULOS TYPE

THE CELLULOSE IS A ORGANIC MATERIAL WHICH CONTAIN 30 % IN THE ELECTRODE COATING BY WEIGHT IT DECOMPOSES IN THE ARC AND PRODUCE A GAS SHIELD WHICH PROTECTS ARC FROM

AUTMOSPHERIC OXYGEN AND NITROGEN EXX10 IS THE EXAMPLE OF THIS TYPE ELECTRODE COATING GENERALLY THIS COATED ELECTRODE IS SUITABLE FOR ALL POSITION WITH DC +

RUTILE TYPE

RUTILE IS NATURALLY- OCCURING SAND USALLY CONTAIN AROUND 95% OF

USALLY CONTAIN AROUND 95% OF

TITANIUM DIOXIDE THIS TYPE OF

TITANIUM DIOXIDE THIS TYPE OF

ELECTRODE IS GOOD FOR USE WITH AC AND

DC + OR DC - GENERALLY USE FOR VERTICAL AND OVERHEAD POSITIONS AS THE SLAG IS VERY VISCOUS AND QUICKLY FREEZED EXX12 AND EXX13 ARE THE EXAMPLES OF THIS TYPE OF COATING

ACID TYPE

THIS TYPE OF COATING CONTAIN OXIDE AS A MAJOR CONSTITUENT DURING WELDING IT PRODUCE A IRON-MANGANESE OXIDE –SELICA FLUID SLAG WHOSE METALLARGICAL EFFECT IS ACIDIC THIS SLAG SOLIDIFIES LIKE HONEY-

COMBSTRUCTURE AND EASLY DETACHED ELECTRODE HAVING THIS COATING IS GOOD FOR FILLET WELD ONLY

EXX22 IS THE EXAMPLE OF THIS TYPE OF ELECTRODE.

OXIDIZING TYPE

IT CONTAIN MAINLY IRON-OXIDE AND SILICATES WITH OR WITH OUT

MANGANESE OXIDES IT PRODUCE A HEAVY SLAG WHICH HAS OXIDISING PROPERTIES THIS TYPE ELECTRODE IS LIMITED IN USE BECAUSE THE

RESULTANT WELD METAL IS SOFT AND LOW MECHANICAL PROPERTIES

EXX27 ELECTRODES ARE HAVING THIS TYPE OF COATING, GENERALLY USING

BASIC TYPE

THIS TYPE OF COATING CONTAINS CALCIUM

CARBONATES (CaCO3), CALCIUM FLOURIDE (CaF2) , METAL POWDER AND COMPARATIVELY MORE

POWERFUL DEOXIDISERS

THIS RESULTS IN A CHEMICALLY BASIC SLAG, WHICH

IS FAIRLY FLUID.THE SOLIDIFIED SLAG, WHICH IS

HEAVY AND FRIABLE HAS BROWN TO DARK- BROWN COLOR AND GLASSY APPEARANCE

MOISTURES IS REMOVED FROM THE COATING TO

RENDER IT LOW HYDROGEN ELECTRODES THE

ELECTRODES HAVING THIS TYPE OF COATING IS

PREFERRED TO USE FOR MINIMISE THE RISK OF

HYDROGEN-INDUCED CRACKING OR COLD CRACKING

IN THE BASE METAL

EXX15,16,18 OR THE EXAMPLES OF THIS TYPE OF

COATING.

STORAGE AND DRYING OF

ELECTRODE

stored in order to deposit quality welds when electrodes absorb moistures from the

atmosphere, they must be dried in order to

restore the ability to deposit quality welds

Electrode with too much moisture may lead to

characteristics may be affected as well If it is

problems, or if the electrode arc performance may have deteriorated, it may be due to the

 All electrodes must

be dried to the right

can lead to major

weld problems such

as internal porosity,

weld cracking or poor

operating

characteristics

 Low Hydrogen Electrodes

Storing and exposure limits

SMAW electrodes with low hydrogen

coatings, such as E7018 and E8018-C3,

must be kept very dry since hydrogen

induced cracking can easily occur, especially

in steels that are 80,000 psi and higher yield strengths To keep these electrodes dry

during storage, here are some suggestions:

 Purchase these electrodes in hermetically sealed containers, which provide excellent protection against moisture pickup

 Do not open the hermetically sealed

containers until the electrode is needed for use

 When the cans are opened, electrodes that will not be immediately used should be

placed in a OVEN at 250 degrees F to 300

degrees F

(120 – 150 degrees C)

 Electrodes should be supplied to welders in quantities that can be consumed within time limits that are dependent on the electrode type and strength level For example,

standard E7018 electrodes can be safely be exposed to the atmosphere for 4 hours

whereas standard E11018 electrodes are

restricted to only ½ hour

Re-drying Of Low Hydrogen Electrodes

When the electrodes have been exposed to the atmosphere for period of a four hours , the electrode can be re-dried The following re-drying procedure should be used:

 To re-dry, electrodes should be removed from the can, and placed in suitable oven The electrodes should be spread out in the oven so that all electrodes will reach the drying temperature The can of electrodes should not be put in the oven; the cardboard liners can char, and the temperature of the electrodes will not be uniform

REGULATOR

POTABLE OVEN

 When the electrodes are initially placed in

the oven, the temperature should not be

greater than half the re-drying temperature The electrodes should be held at that

temperature for ½ hour before heating the electrode to the final temperature

governed by AWS A5.1 (such as E7018), the final re-drying temperature is typically 500-

800 degrees F(260-430 degrees C) For low alloy electrodes governed by AWS A5.5, the final re-drying temperature should be 700-

800 degrees F (700 – 430 degrees C) The

manufacturer’s recommendations should be

 One hour at the listed final temperature is satisfactory if it is supplied in the dried condition Do not dry electrodes at higher temperatures Also, several hours at a lower temperature is not equivalent to using the specified requirements Moisture becomes chemically bonded (absorbed) to the electrode coating and those chemical bonds must be broken at the proper temperature for the proper length of time

How Many Times Low Hydrogen Electrodes Can Be Re-dried?

 Electrodes may be re-dried only once Electrodes that have become wet or moist shall not be used and shall be discarded.

Standard Tests For Electrodes

THE END

THANKS