Welding R1

8/13/2019 Welding R1

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WHAT IS WELDING ?


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WELDING Fastening two pieces of metal together by softening with heat and

applying pressure.

Join together by heating, as of metals.

Unite closely or intimately.

Arc welding:

A group of welding processes wherein

coalescence is produced by heating with an

electric arcs or arcs , with or without theapplication of pressure and with or without the use

of filler metal.


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WELDING PROCESSES Arc welding process is the most common use ,

sub divided in to

Shielded metal arc welding ( SMAW ) Stick

Gas tungsten arc welding ( GTAW )

Sub merged arc welding (SAW)

Gas metal arc welding (GMAW)

Selection of process depends:

Thickness and size, location and position of weld,joint design, welding equipment availability,process and operation requirement andproduction cost.


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Plate positions

Flat position :1 GHorizontal position : 2G

Vertical position : 3G

Overhead position : 4G

WELDING POSITIONS


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WELDING POSITIONS

Pipe positions

1G , 2G

Multiple position : 5G

( Welding groove in a

vertical plane )

Multiple position : 6G( Inclined at 45 degrees to

horizontal )


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ELECTRODE CLASSIFICATION

AS per AWS

E XXXX / EXXXXX The prefix "E"designates arc welding

electrodes.

The first two digitsof 4 digit Nos. and first 3digitsof 5 digit Nos. indicate minimumTensile strength.

E-60xx indicates minimum tensile strength60,000 p.s.i.

E-100xxindicates minimum tensilestrength 100,000p.s.i. Etc.


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AS per AWS

E XXXX / E XXXX Second lastdigit indicates the welding

position.

The last digit indicate the welding positiongiving coating type, current & polarity.


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AS per AWS

E XXXXDigit Type of coating Welding current

0 Cellulose sodium DCEP

1 Cellulose potassium AC or DCEP

2 Titanium sodium AC or DCEN 3 Titanium potassium AC or DCEP or DCEN

4 Iron powder titanium AC or DCEP or DCEN

5 Low hydrogen sodium DCEP

6 Low hydrogen potassium AC or DCEP 7 Iron powder iron oxide AC or DCEP or DCEN

8 Iron powder low hydrogen AC or DCEN

E 6020 Iron oxide sodium AC or DCEP or DCEN


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AS per AWS

E XXXX Position :

1 Flat , Horizontal, Vertical , Overhead

2 Flat and Horizontal only.

3 Flat , Horizontal, Vertical down andOverhead

E 7018 H 4 R

H 4 Hydrogen less than 4 ml / 100 gm.

R - Meets requirement of absorbed moisturetest.


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The (EXXXX-'') indicates the approximatealloy in the weld deposits.

A1 - 0.5%Mo

B1 - 0.5%Cr 0.5%Mo

B2 - 1.25%Cr 0.5%Mo

B3 - 2.25%Cr 1%Mo

B4 - 2%Cr 0.5Mo

B5 - 0.5%Cr 1%Mo

B6 0.5 Cr 0.5 Mo

B9

9 Cr 1 Mo

ELECTRODE CLASSIFICATIONAS per AWS E XXXX - XX


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The (EXXXX-'') indicates the approximate alloy

in the weld deposits

C1 2.5%Ni

C2 3.5%Ni

C3 1%Ni 0.35Mo 0.15%Cr

D1& 0.25 - 0.45%Mo, 1.75%Mn

D2

G 1%minMn, 0.5%minNi,

0.3%minCr, 0.2%minMo, 0.1%minV


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Welding flux Basicity Melting point c

Acidic < or = 0.9 1100 1300

Neutral = 0.9 1.2 1300 1500

Basic = 1.2 2.0 > 1500

High basic > 2.0 > 1500

Welding Flux


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SMAW 2 mm thick and heavier.

Electric arc sustained electricdischarge between two poles.

Converts electrical energyin to

heat. Heat produced will be used for

heating and melting of jointedges and the electrode and its

coating. Some portion lost in radiation (

waves ) and convection(Gases).


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SMAW Shorter arcLess arc voltage

increases current resultsincreased weld deposition rate and

welding speed.

Longer arc - Higher arc voltage andlowers current Leads to lower

welding productivity.

Arc is too longheat is lost in air ,spatter increases, weld metal picksup nitrogen results porosity and

reduced toughness. The amount of welding is small- heat

is immediately dissipated in to theparent metal and air- reducesductility- to control low carbon in

the weld metal.


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SMAWAdvantages

Low capitalinvestment.

Easy and economicalto use.

Applied onwide variety of metalsand

jobs.

Disadvantages Careis required for storage and

handling of electrodes.

Protective clothingis required for

welders. Excess current is used alloying

elements in the flux coating will not

be transferred to weld metals.

Removal of slag.


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GTAW

Non- consumable electrode shieldedby an inert gas usually argon.

Advantages

Slag-metal reactionsare absent.

De-slaggingtime will be saved.

Control of heat input of the arc andfiller metal additions are independentof each other making control of puddle( pool of liquid ) easier.


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Uniform penetrationbest

as welded appearance .

Though more costly

,sometimes save overallcost where cleanliness

andsoundnessof welds

are of paramount

importance.

GTAW


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GTAW

Disadvantages. Low depositionrates.

Requires skillon the part of

welder. Progress is costlierwhere

backing , purging is required.

An acute angle of torch willcause contamination of

shielding gas which air resulting

in porous welds.


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SAW

Arc is maintained between

end of bare wire electrode

and the work.

Wire feed speed isautomatically controlled.

Arc length is constant.

Flux provide a protective

blanketover the weld pool.


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SAW Advantages.

Absenceof smoke and arc flash ,hence

minimum need for protective clothing.

High weld metal quality.

Smoothand weld finish with no spatter.

Extremely high deposition rateand

welding speed.

High electrode deposition efficiency.

Welders manipulative skillnot needed ,minimum operator fatigue.


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SAW

Limitations High initial cost.

Limited welding position.

Requirement of specialjigsand fixtures.

Difficulty in welding low

thicknessmetals.

Full penetrationjoint welds

can not be performed from

single side.


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GMAW / MIG The arc and the molten puddle

are protectedfrom

contamination by the

atmosphere with an extremelysupplied shield of inert gas

such or argon or helium.

Later mild steel welded using

CO2as shielding gas.

Since CO2 is not an inert gas

termed as MIG /CO2 or MAG.


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GMAW / MIG

How Metal transfer in CO2welding ?

Spray transfer

The metal dropis detachedand transferred along thearc column in to the weldpool.

Dip transfer

The wire tip touchesweldpool and transfers the fillermetal by direct contact.


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GMAW / MIGAdvantages

Slag metal reactionsareabsent

Time spent in deslaggingissaved.

High speedand mechanizedprocess.

Thin sheetscan be welded inall positionsby dip transfer.

CO2 is expensive ,widelyused for welding mild steel.


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GMAW / MIG

Limitations of CO2 process Only carbon steelscan be

welded.

Consumable must have de-oxidizers.

Dip transfernot suitable for

penetration welds.

Spray transfernot suitable

for positional welds.


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Deposition efficiency

SMAW 59 - 66 %

(As size increases reduction in efficiency) GTAW 82 - 85%

SAW 99 %

GMAW 93 98 %


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WPS : Written document that provides

Direction to the welder making production welds

In accordance with the code requirements.

PQR :

Documents what occurred during welding. Test coupon and its results

Important is essential variables.

What are the parameters to be consideredto prepare WPS ?

( ASME . I X Boiler & Pressure vessel code ,Welding and

Brazing Qualifications )

What is WPS PQR ?


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Parameters to be considered.

1. Joints - QW 402 2. Base metals QW 403

3. Filler metals - QW 404

4. Positions - QW 405

5. Preheat - QW 406

6. PWHT - QW 407

7. Gas - QW 408

7. Elect.Charecter. - QW 409 8. Technique - QW 410

QW 401 - General ( JBF 3P GET)


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HOW TO PROCEED ?

Essential variables

Supplementary variables.

Non essential variables.


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TYPES OF JOINTS IN WELDING

1. Butt Joint

2. T Joint

3. Corner Joint 4. Lap Joint


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FOR SMAW or STIC WELDING

( AS per ASME section IX)

QW 402 : JOINTS

1 .Groove design -Change in type of groove

V groove , U groove , single bevel anddouble bevel etc Non essential.

4 . Backing -

10 . Root spacing -

11 . +/- Retainers -


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QW 403 Base Metals

5 Group Number - Supplementary

6 - T limits impact Supplementary

7 - T / t limits > 8 in . ( 203 mm ) - Essential

8 T Qualified - Essential

9 - t pass > in. (13 mm ) - Essential

11 - P.No. Qualified Essential

13 - P.No.5/9/10 - Essential


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Materials

Grouping P1, P2, . . . . . . . P 53.

EX :

P1 carbon steels P4 1 Chrome , molybdenum

P5 - 2.5 chrome , 1 molybdenum

P8 Stainless steels. P9 Nickel 1.5 to 3.5

P10 Ni, Cr and Mo based.


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QW 404 Filler Metals

4 - F Number - Essential

5 - A Number - Essential

6 - Diameter Non Essential

7 - Diam . > in. ( 6 mm ) - supplementary

Essential

12 AWS class Supplementary Essential

30 - t Essential

33 AWS class Non essential.


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QW 405 - Positions

1 + Position Nonessential

2 Positions Supplementary essential.

3 Vertical welding Nonessential


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QW 406 - Preheat

1 Decrease > 56 c - Essential

2 Preheat maint. - Supplementary

3 Increase > 56 c - Supplementary


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PREHEATING

Reduce shrinkagestress in the weld andbase metal.

To provide slowerrate of cooling.

To prevent excessivehardening.

Allowing more timefor any hydrogenthat is

present to diffuse awayfrom weld to avoidunder bead cracking.

Preheat and inter pass based on ?


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Carbon equivalent for steel

CE = C + Mn / 6 + ( Cr + M0 + V ) / 5 +

( Ni + Cu ) / 15.

CE up to 0.45 - Optional

0.45 to 0.60 - Preheat 95 205 deg. C

Over 0.60 - Preheat 205 372 deg. C


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How to check the preheating temp

on job ? Temperature of the job immediately before

welding begins .

To be measured for a distance at least 75mmon each side of the joint .

Preferably on the opposite facefrom that

which was heated in case of plate.


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QW 407 - PWHT

1 PWHT - Essential

2 PWHT ( T & T range ) Supplementary

4 T limits- Essential( Qualified thickness

is 1.1 times of the production test coupon )


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PWHT Welded joint contains internal stresses

called locked up stresses.

Some times rise to values as high as YSof

the material. This will be expected to relievethe locked

up stresses so called as stress relieving.

Heating to suitable temp

Holdto enoughto reduce residual stresses cooling

slowly enough to minimize thedevelopment of new stresses.


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PWHT

Post weld temperature usually in the range

: 590 to 760 deg .centigrade.

Soaking : 1 hour / inch.

Heating and cooling rate : 100 to 200 deg.

centigrade per hour thickness up to 25 mm

and slower rates for thicker plates.

( Depending upon the code being followed )


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QW 409 Electrical characteristics

1 > Heat input - Supplementary

4 Current or polarity Supple. /

Nonessential

8 I & E range Nonessential


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HEAT INPUT

Voltage x amperage x 60 /Travel speed (in./min) or mm/min


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CURRENT Diameter of rod Current in amperes

( MM ) Min Max Ave

1.6 25 45 40

2.0 34 65 50

2.5 50 90 90

3.2 60 130 115

4.0 100 180 140

5.0 150 250 200

6.0 200 310 280

Straight polarity electrode negative DCEN.

Reverse polarity electrode positive DCEP.


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QW 410 Technique 1 String / weave Nonessential 5 Method cleaning -Nonessential

6 Method back gouge-Nonessential

9 Multi / single pass - supplementary 25 Manual or automatic-Nonessential

26 Peening -Nonessential

String : Like Chain. Weave : Side to side motion of the

electrode.


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What more interesting

to know ?


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WELDING DEFFECTS AND NONDESTRUCTIVE TESTING .


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THANKS

Welding R1

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